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+The Project Gutenberg EBook of Territory in Bird Life, by H. Eliot Howard
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: Territory in Bird Life
+
+Author: H. Eliot Howard
+
+Illustrator: G. E. Lodge
+             H. Grönvold
+
+Release Date: April 14, 2010 [EBook #31987]
+
+Language: English
+
+Character set encoding: UTF-8
+
+*** START OF THIS PROJECT GUTENBERG EBOOK TERRITORY IN BIRD LIFE ***
+
+
+
+
+Produced by Chris Curnow, Turgut Dincer, Joseph Cooper and
+the Online Distributed Proofreading Team at
+https://www.pgdp.net
+
+
+
+
+
+
+
+  +-------------------------------------------------------+
+  |  TRANSCRIBER'S NOTE:                                  |
+  |                                                       |
+  |  There are a large number of compound words in        |
+  |  this book including bird names which occur joined,   |
+  |  spaced and hyphenated. No attempt has been made to   |
+  |  correct these discrepancies as these are mostly      |
+  |  alternative spellings of the same word. In the case  |
+  |  of bird names it is difficult to decide as           |
+  |  ornithologists are still debating on this subject.   |
+  +-------------------------------------------------------+
+
+
+  TERRITORY IN BIRD LIFE
+
+
+  [Illustration: A pair of Lesser Spotted Woodpeckers attacking a Great
+     Spotted Woodpecker
+
+  Emery Walker ph.sc.]
+
+
+  TERRITORY IN
+  BIRD LIFE
+
+  BY H. ELIOT HOWARD
+
+
+  WITH ILLUSTRATIONS BY
+  G. E. LODGE AND H. GRÖNVOLD
+
+
+  NEW YORK
+  E. P. DUTTON AND COMPANY
+  1920
+
+
+
+
+PREFACE
+
+
+When studying the Warblers some twenty years ago, I became aware of the
+fact that each male isolates itself at the commencement of the breeding
+season and exercises dominion over a restricted area of ground. Further
+investigation, pursued with a view to ascertaining the relation of this
+particular mode of behaviour to the system of reproduction, led to my
+studying various species, not only those of close affinity, but those
+widely remote in the tree of avian life. The present work is the outcome
+of those investigations. In it I have endeavoured to interpret the
+prospective value of the behaviour, and to trace out the relationships
+in the organic and inorganic world which have determined its survival.
+Much is mere speculation; much with fuller knowledge may be found to be
+wrong. But I venture to hope that a nucleus will remain upon which a
+more complete territorial system may one day be established.
+
+I have to thank Mr. G. E. Lodge and Mr. H. Grönvold for the trouble they
+have taken in executing my wishes; I also want to record my indebtedness
+to the late E. W. Hopewell; and to Professor Lloyd Morgan, F.R.S., I am
+beholden more than I can tell.
+
+
+
+
+  CONTENTS
+
+                                                        PAGE
+  CHAPTER I
+
+  INTRODUCTION                                             1
+
+
+  CHAPTER II
+
+  THE DISPOSITION TO SECURE A TERRITORY                   20
+
+
+  CHAPTER III
+
+  THE DISPOSITION TO DEFEND THE TERRITORY                 73
+
+
+  CHAPTER IV
+
+  THE RELATION OF SONG TO THE TERRITORY                  119
+
+
+  CHAPTER V
+
+  THE RELATION OF THE TERRITORY TO THE SYSTEM
+    OF REPRODUCTION                                      169
+
+
+  CHAPTER VI
+
+  THE WARFARE BETWEEN DIFFERENT SPECIES AND ITS
+    RELATION TO THE TERRITORY                            216
+
+
+  CHAPTER VII
+
+  THE RELATION OF THE TERRITORY TO MIGRATION             259
+
+
+  INDEX                                                  302
+
+
+
+  LIST OF ILLUSTRATIONS
+
+
+                                                             _Face page_
+
+  A pair of Lesser Spotted Woodpeckers attacking a Great
+      Spotted Woodpecker                                  _Frontispiece_
+
+  Territorial flight of the Black-tailed Godwit                       54
+
+  Competition for territory is seldom more severe than
+      among cliff-breeding seabirds, and the efforts of
+      individual Razorbills to secure positions on the
+      crowded ledges lead to desperate struggles                      64
+
+  Male Blackbirds fighting for the possession of territory.
+      The bare skin on the crown of the defeated bird shows
+      the nature of the injuries from which it succumbed              74
+
+  Male Cuckoos fighting before the arrival of a female                82
+
+  Two pairs of Pied Wagtails fighting in defence of their
+      territories                                                     86
+
+  Long-tailed Tit: males fighting for the possession of
+      territory. The feathers have been torn from the crown
+      of the defeated and dying rival                                 96
+
+  A battle between two pairs of Jays                                 106
+
+  The Female Chaffinch shares in the defence of the territory
+      and attacks other females                                      110
+
+  Peregrine Falcon attacking a Raven                                 216
+
+  A battle between a pair of Green Woodpeckers and a
+      Great Spotted Woodpecker for the possession of a hole
+      in an oak-tree                                                 238
+
+  Plans of the Water-meadow showing the Territories
+      occupied by Lapwings in 1915 and 1916          _Between_ 58 and 59
+
+
+SCIENTIFIC NAMES OF BIRDS MENTIONED IN THE TEXT
+
+  Raven                       _Corvus corax._
+
+  Carrion-Crow                _Corvus corone._
+
+  Hooded Crow                 _Corvus cornix._
+
+  Rook                        _Corvus frugilegus._
+
+  Magpie                      _Pica pica._
+
+  Jay                         _Garrulus glandarius rufitergum._
+
+  Chough                      _Pyrrhocorax pyrrhocorax._
+
+  Starling                    _Sturnus vulgaris._
+
+  Greenfinch                  _Chloris chloris._
+
+  Hawfinch                    _Coccothraustes coccothraustes._
+
+  House-Sparrow               _Passer domesticus._
+
+  Chaffinch                   _Fringilla cœlebs._
+
+  Brambling                   _Fringilla montifringilla._
+
+  Linnet                      _Acanthis cannabina._
+
+  Corn-Bunting                _Emberiza calandra._
+
+  Yellow Bunting              _Emberiza citrinella._
+
+  Cirl Bunting                _Emberiza cirlus._
+
+  Reed-Bunting                _Emberiza schœniclus._
+
+  Sky-Lark                    _Alauda arvensis._
+
+  Pied Wagtail                _Motacilla lugubris._
+
+  Tree-Pipit                  _Anthus trivialis._
+
+  Meadow-Pipit                _Anthus pratensis._
+
+  Great Titmouse              _Parus major newtoni._
+
+  Blue Titmouse               _Parus cœruleus obscurus._
+
+  Long-tailed Titmouse        _Ægithalus caudatus roseus._
+
+  Red-backed Shrike           _Lanius collurio._
+
+  Whitethroat                 _Sylvia communis._
+
+  Lesser Whitethroat          _Sylvia curruca._
+
+  Blackcap                    _Sylvia atricapilla._
+
+  Grasshopper-Warbler         _Locustella nœvia._
+
+  Savi's Warbler              _Locustella luscinioides._
+
+  Reed-Warbler                _Acrocephalus scirpaceus._
+
+  Marsh-Warbler               _Acrocephalus palustris._
+
+  Sedge-Warbler               _Acrocephalus schœnobænus._
+
+  Willow-Warbler              _Phylloscopus trochilus._
+
+  Wood-Warbler                _Phylloscopus sibilatrix._
+
+  Chiffchaff                  _Phylloscopus collybita._
+
+  Song-Thrush                 _Turdus musicus clarkii._
+
+  Redwing                     _Turdus iliacus._
+
+  Blackbird                   _Turdus merula._
+
+  Redstart                    _Phœnicurus phœnicurus._
+
+  Redbreast                   _Erithacus rubecula melophilus._
+
+  Nightingale                 _Luscinia megarhyncha._
+
+  Stonechat                   _Saxicola rubicola._
+
+  Whinchat                    _Saxicola rubetra._
+
+  Wheatear                    _Å’nanthe Å“nanthe._
+
+  Hedge-Sparrow               _Accentor modularis._
+
+  Wren                        _Troglodytes troglodytes._
+
+  Spotted Flycatcher          _Muscicapa striata._
+
+  Swallow                     _Hirundo rustica._
+
+  Martin                      _Delichon urbica._
+
+  Sand-Martin                 _Riparia riparia._
+
+  Great Spotted Woodpecker    _Dryobates major anglicus._
+
+  Lesser Spotted Woodpecker   _Dryobates minor._
+
+  Green Woodpecker            _Picus viridis._
+
+  Cuckoo                      _Cuculus canorus._
+
+  Tawny Owl                   _Strix aluco._
+
+  Buzzard                     _Buteo buteo._
+
+  Sparrow-Hawk                _Accipiter nisus._
+
+  Peregrine Falcon            _Falco peregrinus._
+
+  Merlin                      _Falco æsalon._
+
+  Kestrel                     _Falco tinnunculus._
+
+  Shag                        _Phalacrocorax graculus._
+
+  Wild Duck                   _Anas boschas._
+
+  Snipe                       _Gallinago gallinago._
+
+  Dunlin                      _Tringa alpina._
+
+  Ruff                        _Machetes pugnax._
+
+  Redshank                    _Totanus totanus._
+
+  Black-tailed Godwit         _Limosa limosa._
+
+  Curlew                      _Numenius arquata._
+
+  Whimbrel                    _Numenius phæopus._
+
+  American Golden Plover      _Charadrius dominicus._
+
+  Lapwing                     _Vanellus vanellus._
+
+  Oyster-Catcher              _Hæmatopus ostralegus._
+
+  Herring-Gull                _Larus argentatus._
+
+  Kittiwake                   _Rissa tridactyla._
+
+  Razorbill                   _Alca torda._
+
+  Guillemot                   _Uria troille._
+
+  Puffin                      _Fratercula arctica._
+
+  Fulmar                      _Fulmarus glacialis._
+
+  Water-Rail                  _Rallus aquaticus._
+
+  Corn-Crake                  _Crex crex._
+
+  Moor-Hen                    _Gallinula chloropus._
+
+  Coot                        _Fulica atra._
+
+  Wood-Pigeon                 _Columba palumbus._
+
+  Turtle-Dove                 _Streptopelia turtur._
+
+  Partridge                   _Perdix perdix._
+
+  Black Grouse                _Lyrurus tetrix britannicus._
+
+  Red Grouse                  _Lagopus scoticus._
+
+
+
+
+TERRITORY IN BIRD LIFE
+
+
+
+
+CHAPTER I
+
+INTRODUCTION
+
+
+In his _Manual of Psychology_ Dr Stout reminds us that "Human language
+is especially constructed to describe the mental states of human beings,
+and this means that it is especially constructed so as to mislead us
+when we attempt to describe the working of minds that differ in a great
+degree from the human."
+
+The use of the word "territory" in connection with the sexual life of
+birds is open to the danger which we are here asked to guard against,
+and I propose, therefore, before attempting to establish the theory on
+general grounds, to give some explanation of what the word is intended
+to represent and some account of the exact position that representation
+is supposed to occupy in the drama of bird life.
+
+The word is capable of much expansion. There cannot be territories
+without boundaries of some description; there cannot well be boundaries
+without disputes arising as to those boundaries; nor, one would
+imagine, can there be disputes without consciousness as a factor
+entering into the situation; and so on, until by a simple mental
+process we conceive of a state in bird life analogous to that which we
+know to be customary amongst ourselves. Now, although the term "breeding
+territory," when applied to the sexual life of birds, is not altogether
+a happy one, it is difficult to know how otherwise to give expression to
+the facts observed. Let it then be clearly understood that the
+expression "securing a territory" is used to denote a process, or rather
+part of a process, which, in order to insure success to the individual
+in the attainment of reproduction, has been gradually evolved to meet
+the exigencies of diverse circumstances. Regarded thus, we avoid the
+risk of conceiving of the act of securing a territory as a detached
+event in the life of a bird, and avoid, I hope, the risk of a conception
+based upon the meaning of the word when used to describe human as
+opposed to animal procedure.
+
+Success in the attainment of reproduction is rightly considered to be
+the goal towards which many processes in nature are tending. But what is
+meant by success? Is it determined by the actual discharge of the sexual
+function? So many and so wonderful are the contrivances which have
+slowly been evolved to insure this discharge, that it is scarcely
+surprising to find attention focused upon this one aspect of the
+problem. Yet a moment's reflection will show that so limited a
+definition of the term "success" can only be held to apply to certain
+forms of life; for where the young have to be cared for, fostered, and
+protected from molestation for periods of varying lengths, the actual
+discharge of the sexual function marks but one stage in a process which
+can only succeed if all the contributory factors adequately meet the
+essential conditions of the continuance of the species.
+
+Securing a territory is then part of a process which has for its goal
+the successful rearing of offspring. In this process the functioning of
+the primary impulse, the acquirement of a place suitable for breeding
+purposes, the advent of a female, the discharge of the sexual function,
+the construction of the nest, and the rearing of offspring follow one
+another in orderly sequence. But since we know so little of the organic
+changes which determine sexual behaviour, and have no means of
+ascertaining the nature of the impulse which is first aroused, we can
+only deal with the situation from the point at which the internal
+organic changes reflect themselves in the behaviour to a degree which is
+visible to an external observer. That point is reached when large
+numbers of species, forsaking the normal routine of existence to which
+they have been accustomed for some months, suddenly adopt a radical
+change in their mode of behaviour. How is this change made known to us?
+By vast numbers of individuals hurrying from one part of the globe to
+another, from one country to another, and even from mid-ocean to the
+coasts; by detachments travelling from one district to another; by
+isolated individuals deserting this place for that; by all those
+movements, in fact, which the term migration, widely applied, is held to
+denote. Now the impulse which prompts these travelling hosts must be
+similar in kind whether the journey be long or short; and it were
+better, one would think, to regard such movements as a whole than to
+fix the attention on some one particular journey which fills us with
+amazement on account of the magnitude of the distance traversed or the
+nature of the difficulties overcome. For, after all, what does each
+individual seek? There may be some immature birds which, though they
+have not reached the necessary stage of development, happen to fall in
+with others in whom the impulse is strong and are led by them--they know
+not where. But the majority seek neither continent nor country, neither
+district nor locality is their aim, but a place wherein the rearing of
+offspring can be safely accomplished; and the search for this place is
+the earliest visible manifestation in many species of the reawakening of
+the sexual instinct.
+
+The movements of each individual are then directed towards a similar
+goal, namely, the occupation of a definite station; and this involves
+for many species a distinct change in the routine of behaviour to which
+previously they had been accustomed. Observe, for example, one of the
+numerous flocks of Finches that roam about the fields throughout the
+winter. Though it may be composed of large numbers of individuals of
+different kinds, yet the various units form an amicable society actuated
+by one motive--the procuring of food. And since it is to the advantage
+of all that the individual should be subordinated to the welfare of the
+community as a whole there is no dissension, apart from an occasional
+quarrel here and there.
+
+In response, however, to some internal organic change, which occurs
+early in the season, individuality emerges as a factor in the developing
+situation, and one by one the males betake themselves to secluded
+positions, where each one, occupying a limited area, isolates itself
+from companions. Thereafter we no longer find that certain fields are
+tenanted by flocks of greater or less dimensions, while acres of land
+are uninhabited, but we observe that the hedgerows and thickets are
+divided up into so many territories, each one of which contains its
+owner. This procedure, with of course varying detail, is typical of that
+of many species that breed in Western Europe. And since such a radical
+departure from the normal routine of behaviour could scarcely appear
+generation after generation in so many widely divergent forms, and still
+be so uniform in occurrence each returning season, if it were not
+founded upon some congenital basis, it is probable that the journey,
+whether it be the extensive one of the Warbler or the short one of the
+Reed-Bunting, is undertaken in response to some inherited disposition,
+and probable also that the disposition bears some relation to the few
+acres in which the bird ultimately finds a resting place. Whilst for the
+purpose of the theory I shall give expression to this behaviour in terms
+of that theory, and speak of it as a disposition to secure a territory,
+using the word disposition, which has been rendered current in recent
+discussion, for that part of the inherited nature which has been
+organised to subserve a specific biological purpose--strict compliance
+with the rules of psychological analysis requires a simpler definition;
+let us therefore say "disposition to remain in a particular place in a
+particular environment."
+
+But even granting that this disposition forms part of the hereditary
+equipment of the bird, how is the process of reproduction furthered? The
+mere fact of remaining in or about a particular spot cannot render the
+attainment of reproduction any less arduous, and may indeed add to the
+difficulties, for any number of individuals might congregate together
+and mutually affect one another's interests. A second disposition comes,
+however, into functional activity at much the same stage of sexual
+development, and manifests itself in the male's intolerance of other
+individuals. And the two combined open up an avenue through which the
+individual can approach the goal of reproduction. In terms of the theory
+I shall refer to this second disposition as the one which is concerned
+with the defence of the territory.
+
+Broadly speaking, these two dispositions may be regarded as the basis
+upon which the breeding territory is founded. Yet inasmuch as the
+survival value of the dispositions themselves must have depended upon
+the success of the process as a whole, it is manifest that peculiar
+significance must not be attached to just the area occupied, which
+happens to be so susceptible of observation; other contributory factors
+must also receive attention, for the process is but an order of
+relationships in which the various units have each had their share in
+determining the nature and course of subsequent process, so that, as Dr
+Stout says, when they were modified, it was modified.
+
+Now the male inherits a disposition which leads it to remain in a
+restricted area, but the disposition cannot determine the extent of that
+area. How then are the boundaries fixed? That they are sometimes adhered
+to with remarkable precision, that they can only be encroached upon at
+the risk of a conflict--all of this can be observed with little
+difficulty. But if we regard them as so many lines definitely delimiting
+an area of which the bird is cognisant, we place the whole behaviour on
+a different level of mental development, and incidentally alter the
+complexion of the whole process. It would be a mistake, I think, to do
+this. Though conscious intention as a factor may enter the situation,
+there is no necessity for it to do so; there is no necessity, that is to
+say, for the bird to form a mental image of the area to be occupied and
+shape its course accordingly. The same result can be obtained without
+our having recourse to so complex a principle of explanation, and that
+by the law of habit formation. In common with other animals, birds are
+subject to this law in a marked degree. An acquired mode of activity
+becomes by repetition ingrained in the life of the individual, so that
+an action performed to-day is liable to be repeated to-morrow so long as
+it does not prejudice the existence or annul the fertility of the
+individual.
+
+Let us see how this may have operated in determining the limits of the
+area acquired, and for this purpose let us suppose that we are observing
+a male Reed-Bunting recently established in some secluded piece of marsh
+land. Scattered about this particular marsh are a number of small
+willows and young alder trees, each one of which is capable of providing
+plenty of branches suitable for the bird to perch upon, and all are in a
+like favourable position so far as the outlook therefrom is concerned.
+Well, we should expect to find that each respective tree would be made
+use of according to the position in which the bird happened to find
+itself. But what actually do we find--one tree singled out and resorted
+to with ever-increasing certainty until it becomes an important point in
+relation to the occupied area, a headquarters from which the bird
+advertises its presence by song, keeps watch upon the movements of its
+neighbours, and sets out for the purpose of securing food. We then take
+note of its wanderings in the immediate vicinity of the headquarters,
+especially as regards the direction, frequency, and extent of the
+journeys; and we discover not only that these journeys proceed from and
+terminate in the special tree, but that there is a sameness about the
+actual path that is followed. The bird takes a short flight, searches a
+bush here and some rushes there, returns, and after a while repeats the
+performance; we on our part mark the extreme limits reached in each
+direction, and by continued observation discover that these limits are
+seldom exceeded, that definition grows more and more pronounced, and
+that by degrees the movements of the bird are confined within a
+restricted area. In outline, this is what happens in a host of cases. By
+repetition certain performances become stereotyped, certain paths fixed,
+and a routine is thus established which becomes increasingly definite as
+the season advances.
+
+But while it would be quite untrue to say that this routine is never
+departed from, and equally profitless to attempt to find a point beyond
+which the bird will under no circumstances wander, yet there is enough
+definition and more than enough to answer the purpose for which the
+territory has, I believe, been evolved, that is to say the biological
+end of reproduction. Again, however, the process of adjustment is a
+complex one. Habit plays its part in determining the boundaries in a
+rough and ready manner, but the congenital basis, which is to be found
+in the behaviour adapted to a particular environment, is an important
+factor in the situation. For example, if instead of resting content with
+just a bare position sufficient for the purpose of reproduction, the
+Guillemot were to hustle its neighbours from adjoining ledges, the
+Guillemot as a species would probably disappear; or if instead of
+securing an area capable of supplying sufficient food both for itself
+and its young, the Chiffchaff were to confine itself to a single tree,
+and, after the manner of the Guillemot, trust to spasmodic excursions
+into neutral ground for the purpose of obtaining food, the Chiffchaff
+as a species would probably not endure. All such adjustments have,
+however, been brought about by relationships which have gradually become
+interwoven in the tissue of the race.
+
+The intolerance that the male displays towards other individuals,
+usually of the same sex, leads to a vast amount of strife. Nowhere in
+the animal world are conflicts more frequent, more prolonged, and more
+determined than in the sexual life of birds; and though they are
+acknowledged to be an important factor in the life of the individual,
+yet there is much difference of opinion as to the exact position they
+occupy in the drama of bird life. Partly because they frequently happen
+to be in evidence, partly because they are numerically inferior, and
+partly, I suppose, because the competition thus created would be a means
+of maintaining efficiency, the females, by common consent, are supposed
+to supply the condition under which the pugnacious nature of the male is
+rendered susceptible to appropriate stimulation. And so long as the
+evidence seemed to show that battles were confined to the male sex, so
+long were there grounds for hoping that their origin might be traced to
+such competition. But female fights with female, pair with pair, and,
+which is still more remarkable, a pair will attack a single male or a
+single female; moreover, males that reach their destination in advance
+of their prospective mates engage in serious warfare. How then is it
+possible to look upon the individuals of one sex as directly
+responsible for the strife amongst those of the other, or how can the
+female supply the necessary condition? As long as an attempt is made to
+explain it in terms of the female, the fighting will appear to be of a
+confused order; regard it, however, as part of a larger process which
+demands, amongst other essential conditions of the breeding situation,
+the occupation of a definite territory, and order will reign in place of
+confusion.
+
+But even supposing that the male inherits a disposition to acquire a
+suitable area, even supposing that it inherits a disposition which
+results indirectly in the defence of that area, how does it obtain a
+mate? If the female behaved in a like manner, if she, too, were to
+isolate herself and remain in one place definitely, that would only add
+to the difficulties of mutual discovery. We find, however, in the
+migrants, that the males are earlier than the females in reaching the
+breeding grounds, and, in resident species, that they desert the females
+and retire alone to their prospective territories, so that there is a
+difference in the behaviour of the sexes at the very commencement of the
+sexual process. What is the immediate consequence? Since the male
+isolates itself, it follows, if the union of the sexes is to be
+effected, that the discovery of a mate must rest largely with the
+female. This of course reverses the accepted course of procedure. But
+after all, what reason is there to suppose that, the male seeks the
+female, or that a mutual search takes place; what reason to think that
+this part of the process is subject to no control except such as may be
+supplied by the laws of chance?
+
+Now, clearly, much will depend upon the rapidity with which the female
+can discover a male fit to breed; for if the course of reproduction is
+to flow smoothly, there must be neither undue delay nor waste of energy
+incurred in the search--some guidance is therefore necessary, some
+control in her external environment. Here the song, or the mechanically
+produced sound, comes into play, and assists in the attainment of this
+end. Nevertheless if every male were to make use of its powers whether
+it were in occupation of a territory or not, if the wandering individual
+had an equal chance of attracting a mate, then it would be idle to
+attempt to establish any relation between "song" on the one hand, and
+"territory" on the other, and impossible to regard the voice as the
+medium through which an effectual union of the sexes is procured. But
+there is reason to believe that the males utilise their powers of
+producing sound only under certain well-defined conditions. For
+instance, when they are on their way to the breeding grounds, or moving
+from locality to locality in search of isolation, or when they desert
+their territories temporarily, as certain of the residents often do,
+they are generally silent; but when they are in occupation of their
+territories they become vociferous--and this is notoriously the case
+during the early hours of the day, which is the period of maximum
+activity so far as sexual behaviour is concerned. So that just at the
+moment when the sexual impulse of the female is most susceptible to
+stimulation, the males are betraying their positions and are thus a
+guide to her movements. Nevertheless, even though she may have
+discovered a male ready to breed, success is not necessarily assured to
+her; for with multitudes of individuals striving to procreate their
+kind, it would be surprising if there were no clashing of interests, if
+no two females were ever to meet in the same occupied territory.
+Competition of this kind is not uncommon, and the final appeal is to the
+law of battle, just as an appeal to physical strength sometimes decides
+the question of the initial ownership of a territory.
+
+I shall try to make clear the relations of the various parts to the
+whole with the assistance of whatever facts I can command. I shall do so
+not only for the purposes of the theory, but because one so often finds
+the more important features of sexual behaviour regarded as so many
+distinct phenomena requiring separate treatment, whereas they are
+mutually dependent, and follow one another in ordered sequence. I spoke
+of the process as a series of relationships. Some of these relationships
+have already been touched upon; others will become apparent if we
+consider for a moment the purposes for which the territory has been
+evolved. Indirectly its purpose is that of the whole process, the
+rearing of offspring. But inasmuch as a certain measure of success could
+be attained, and that perhaps often, without all the complications
+introduced by the territory, there are manifestly advantages to be
+gained by its inclusion in the scheme. The difficulties which beset the
+path of reproduction are by no means always the same--all manner of
+adjustments have to be made to suit the needs of different species.
+There are direct relationships, such as we have been speaking of, which
+are essential to the every-day working of the process, and others which
+are indirect, though none the less important for they must have
+exercised an influence throughout the ages. These latter are furnished
+by the physical--the inorganic world, by climate, by the supply of the
+particular kind of breeding stations, by the scarcity or abundance of
+the necessary food and by the relative position of the food supply to
+the places suitable for breeding. Why does the Reed-Bunting cling so
+tenaciously to an acre or more of marshy ground, while the Guillemot
+rests content with a few square feet on a particular ledge of rock? The
+answer is the same in both cases--to facilitate reproduction. But why
+should a small bird require so many square yards, whilst a very much
+larger one is satisfied with so small an area? The explanation must be
+sought in the conditions of existence. The Reed-Bunting has no
+difficulty in finding a position suitable for the construction of its
+nest; there are acres of waste land and reedy swamps capable of
+supplying food for large numbers of individuals, and the necessary
+situations for countless nests. But its young, like those of many
+another species, are born in a very helpless state. For all practical
+purposes they are without covering of any description and consequently
+require protection from the elements, warmth from the body of the
+brooding bird, and repeated supplies of nourishment. A threefold burden
+is thus imposed upon the parents: they must find food for themselves,
+they must afford protection to the young by brooding, and they must
+supply them with the necessary food at regular intervals. And their
+ability to do all this that is demanded of them will be severely taxed
+by the brooding which must perforce curtail the time available for the
+collection of food.
+
+Let us then suppose that the Reed-Buntings inhabiting a certain piece of
+marsh are divided into two classes, those which are pugnacious and
+intolerant of the approach of strangers, and those which welcome their
+presence. The nests of the former will be built in isolation, those of
+the latter in close proximity. In due course eggs will be laid and
+incubation performed, and thus far all alike will probably be
+successful. Here, however, a critical point is reached. If the young are
+to be freed from the risk of exposure, the parents must find the
+necessary supply of food rapidly. But manifestly all will not be in a
+like satisfactory position to accomplish this, for whereas the isolated
+pairs will have free access to all the food in the immediate vicinity of
+the nest, those which have built in proximity to one another, meeting
+competition in every direction, will be compelled to roam farther
+afield and waste much valuable time by doing so; and under conditions
+which can well be imagined, even this slight loss of time will be
+sufficient to impede the growth of the delicate offspring, or to lead
+perhaps to still greater disaster. If any one doubts this, let him first
+examine one of the fragile offspring; let him then study the conditions
+under which it is reared, observing the proportion of time it passes in
+sleep and the anxiety of the parent bird to brood; and finally let him
+picture to himself its plight in a wet season if, in order to collect
+the necessary food, the parents were obliged to absent themselves for
+periods of long duration.
+
+Now take the case of the Guillemot. Its young at birth are by no means
+helpless in the sense that the young Reed-Bunting is, and food is
+readily procured. But breeding stations are scarce, for although there
+are many miles of cliff-bound coast, yet not every type of rock
+formation produces the fissures and ledges upon which the bird rests.
+Hence vast stretches of coast-line remain uninhabited, and the birds are
+forced to concentrate at certain points, where year after year they
+assemble in countless numbers from distant parts of the ocean. If, then,
+different individuals were to jostle one another from adjoining
+positions, and each one were to attempt to occupy a ledge in solitary
+State, not only would the successful ones gain no advantage from the
+additional space over which they exercised dominion, but inasmuch as
+many members that were fitted to breed would be precluded from doing
+so, the status of the species as a whole would be seriously affected.
+The amount of space occupied by each individual is therefore a matter of
+urgent importance. A few square feet of rock sufficient for the
+immediate purpose of incubation is all that can be allowed if the
+species is to maintain its position in the struggle for existence.
+
+Our difficulty in estimating the importance of the various factors that
+make for success or failure arises from our inability to see more than a
+small part of the scene as it slowly unfolds itself. The peculiar
+circumstances under which these cliff-breeding forms dwell does,
+however, enable us to picture, on the one hand, the precarious situation
+of an individual that was incapable of winning or holding a position at
+the accustomed breeding station, and, on the other, the plight of the
+species as a whole if each one exercised authority over too large an
+area. With the majority of species it is difficult to do this. So many
+square miles of suitable breeding ground are inhabited by so few
+Reed-Buntings that, even supposing certain members were to establish an
+ascendency over too wide an area, it would be impossible to discover by
+actual observation whether the race as a whole were being adversely
+affected. Competition doubtless varies at different periods and in
+different districts according to the numerical standing of the species
+in a given locality and according to the numerical standing of others
+that require similar conditions of existence; at times it may even be
+absent, just as at any moment it may become acute. These examples show
+how profoundly the evolution of the breeding territory may have been
+influenced by relationships in the inorganic world, and they give some
+idea of the intricate nature of the problem with which we have to deal.
+
+I mentioned that the first visible manifestation of the revival of the
+sexual instinct was to be found in the movements undertaken by the males
+at the commencement of the breeding season. Such movements are
+characterised by a definiteness of purpose, whether they involve a
+protracted journey of some hundreds of miles or merely embrace a parish
+or so in extent, and that purpose is the acquirement of a territory
+suitable for rearing offspring. They are thus directly related to the
+territory, and the question arises as to whether their origin may not be
+traced to such relatedness. So long as we fix our attention solely upon
+the magnitude of the distance traversed the suggestion may seem a
+fanciful one. Nevertheless, if the battles between males of the same
+species _are_ directly related to the occupation of a position suitable
+for breeding purposes, if those which occur between males of closely
+related forms _can_ be traced to a similar source, if the females take
+their share in the defence of the ground that is occupied, if, in short,
+the competition is as severe as I believe it to be, and is wholly
+responsible for the strife which is prevalent at the commencement of the
+breeding season--then such competition must have introduced profound
+modifications in the distribution of species; it must have even
+influenced the question of the survival of certain forms and the
+elimination of others; and since the powers of locomotion of a bird are
+so highly developed it must have led to an extension of breeding range,
+limited only by unfavourable conditions of existence.
+
+
+
+
+CHAPTER II
+
+THE DISPOSITION TO SECURE A TERRITORY
+
+
+Those who have studied bird life throughout the year are aware that the
+distribution of individuals changes with the changing seasons. During
+autumn and winter, food is not so plentiful and can only be found in
+certain places, and so, partly by force of circumstances and partly on
+account of the gregarious instinct which then comes into functional
+activity, different individuals are drawn together and form flocks of
+greater or less dimensions, which come and go according to the
+prevailing climatic conditions. But with the advent of spring a change
+comes over the scene: flocks disperse, family parties break up, summer
+migrants begin to arrive, and the hedgerows and plantations are suddenly
+quickened into life. The silence of the winter is broken by an outburst
+of song from the throats of many different species, and individuals
+appear in their old haunts and vie with one another in advertising their
+presence by the aid of whatever vocal powers they happen to possess--the
+Woodpecker utters its monotonous call from the accustomed oak; the
+Missel-Thrush, perched upon the topmost branches of the elm,
+persistently repeats its few wild notes; and the Swallow returns to the
+barn.
+
+All of this we observe each season, and our thoughts probably travel to
+the delicate piece of architecture in the undergrowth, or to the hole
+excavated with such skill in the tree trunk; to the beautifully shaped
+eggs; to the parent birds carrying out their work with devoted zeal--in
+fact, to the whole series of events which complete the sexual life of
+the individual; and the attachment of a particular bird to a particular
+spot is readily accounted for in terms of one or other of the emotions
+which centre round the human home.
+
+But if this behaviour is to be understood aright; if, that is to say,
+the exact position it occupies in the drama of bird life is to be
+properly determined, and its biological significance estimated at its
+true value, it is above all things necessary to refrain from appealing
+to any one of the emotions which we are accustomed to associate with
+ourselves, unless our ground for doing so is more than ordinarily
+secure. I shall try to show that, in the case of many species, the male
+inherits a disposition to secure a territory; or, inasmuch as the word
+"secure" carries with it too much prospective meaning, a disposition to
+remain in a particular place when the appropriate time arrives.
+
+If the part which the breeding territory plays in the sexual life of
+birds is the important one I believe it to be, it follows that the
+necessary physiological condition must arise at an early stage in the
+cycle of events which follow one another in ordered sequence and make
+towards the goal of reproduction, and that the behaviour to which it
+leads must be one of the earliest visible manifestations of the seasonal
+development of the sexual instinct. When does this seasonal development
+occur? For how long does the instinct lie dormant? In some species there
+is evidence of this first step in the process of reproduction early in
+February; there is reason to believe that in others the latter part of
+January is the period of revival; and the possibility must not be
+overlooked of still earlier awakenings, marked with little definiteness,
+though nevertheless of sufficient strength to call into functional
+activity the primary impulse in the sexual cycle. Here, then, we meet
+with a difficulty so far as direct observation is concerned, for the
+duration of the period of dormancy and the precise date of revival vary
+in different species; and, if accurate information is to be obtained,
+the study of the series of events which culminate in the attainment of
+reproduction ought certainly to begin the moment behaviour is
+influenced by the internal changes, whatever they may be, which are
+responsible for the awakening of the sexual instinct.
+
+In considering how this difficulty might be met, the importance of
+migratory species as a channel of information was gradually borne in
+upon me; for it seemed that the definiteness with which the initial
+stage in the sexual process was marked off, as a result of the incidence
+of migration, would go far towards removing much of the obscurity which
+appeared to surround the earlier stages of the breeding problem in the
+case of resident species. Recent observation has shown that I
+exaggerated this difficulty, and that it is generally possible to
+determine with reasonable accuracy the approximate date at which the
+internal changes begin to exert an influence on the behaviour of
+resident species also. Nevertheless, the specialised behaviour of the
+migrants furnished a clue, and pointed out the direction which further
+inquiry ought to take.
+
+Those who are accustomed to notice the arrival of the migrants are aware
+that the woods, thickets, and marshes do not suddenly become occupied by
+large numbers of individuals, but that the process of "filling up" is a
+gradual one. An individual appears here, another there; then after a
+pause there is a further addition, and so on with increasing volume
+until the tide reaches its maximum, then activity wanes, and the slowly
+decreasing number of fresh arrivals passes unnoticed in the wealth of
+new life that everywhere forces itself upon our attention. If now,
+instead of surveying the migrants as a whole, our attention be directed
+to one species only, this gradual arrival of single individuals in their
+accustomed haunts will become even more apparent; and if the
+investigation be pursued still further and these single individuals
+observed more closely, it will be found that in nearly every case they
+belong to the male sex. Males therefore arrive before females. This does
+not mean, however, that the respective times of arrival of the males and
+females belonging to any one species are definitely divided, for males
+continue to arrive even after some of the females have reached their
+destination; and thus a certain amount of overlapping occurs. A truer
+definition of the order of migration would be as follows:--Some males
+arrive before others, and some females arrive before others, but on the
+average males arrive before females. This fact has long been known.
+Gätke refers to it in his _Birds of Heligoland_. "Here in Heligoland,"
+he says, "the forerunners of the spring migration are invariably old
+males; a week or two later, solitary old females make their appearance;
+and after several weeks, both sexes occur mixed, _i.e._, females and
+younger males; while finally only young birds of the previous year are
+met with." Newton alludes to it as follows:--"It has been ascertained by
+repeated observation that in the spring movement of most species of the
+northern hemisphere, the cock birds are always in the van of the
+advancing army, and that they appear some days, or perhaps weeks, before
+the hens"; and Dr Eagle Clarke, in his _Studies in Bird Migration_,
+makes the following statement:--"Another characteristic of the spring
+is that the males, the more ardent suitors, of most species, travel in
+advance of the females, and arrive at their meeting quarters some days,
+it is said in some cases even weeks, before their consorts." Some
+interesting details were given in _British Birds_[1] in regard to the
+sex of the migrants that were killed by striking the lantern at the
+Tuskar Rock, Co. Wexford, on the 30th April 1914. In all, there were
+twenty-four Whitethroats, nine Willow-Warblers, eight Sedge-Warblers,
+and six Wheatears; and on dissection it was found that twenty
+Whitethroats, seven Willow-Warblers, eight Sedge-Warblers, and one
+Wheatear were males.
+
+What a curious departure this seems from the usual custom in the animal
+world! Here we have the spectacle afforded us of the males, in whom
+presumably the sexual instinct has awakened, deserting the females just
+at the moment when we might reasonably expect their impulse to accompany
+them would be strongest; and this because of their inherited disposition
+to reach the breeding grounds. If, in order to attain to reproduction,
+the male depended primarily upon securing a female--whether by winning
+or fighting matters not at the moment--if her possession constituted the
+sole difference in his external environment between success and failure,
+then surely one would suppose that an advantage must rest with those
+individuals which, instead of rushing forward and inflicting upon
+themselves a life of temporary isolation, remained with the females and
+increased their opportunities for developing that mutual appreciation
+which, by some, is held to be a necessary prelude to the completion of
+the sexual act, and to which close companionship would tend to impart a
+stimulus.
+
+In thus speaking, however, we assume that the revival of the sexual
+instinct in the migratory male is coincident in time with its return to
+the breeding quarters; and we do so because the act of migrating is
+believed to be the first step in the breeding process. But it is well to
+bear in mind just how much of this assumption is based upon fact, and
+how much is due to questionable inference. All that can be definitely
+asserted is this, that appropriate dissection reveals in most of the
+migrants, upon arrival at their destination, unquestionable evidence of
+seasonal increase in the size of the sexual organs. Beyond this there is
+nothing to go upon. Yet if the term "sexual instinct" is held to
+comprise the whole series of complex relationships which are manifest to
+us in numerous and specialised modes of behaviour, which ultimately lead
+to reproduction, and which have gradually become interwoven in the
+tissue of the race, there can be little doubt that the assumption is a
+reasonable one. To some, the term may recall the fierce conflicts which
+are characteristic of the season; to others, emotional response; to not
+a few, perhaps, the actual discharge of the sexual function--all of
+these, it is true, are different aspects of the one instinct; but at the
+same time each one marks a stage in the process, and the different
+stages follow one another in ordered sequence. However, we are not
+concerned at the moment with the term in its wider application; we wish
+to know the precise stage at which the disposition to mate influences
+the behaviour of the male. Is the female to him, from the moment the
+seasonal change in his sexual organs takes place, a goal that at all
+costs must be attained? Or is it only when the cycle of events which
+leads up to reproduction is nearing completion that she looms upon his
+horizon? One would like to be in a position to answer these questions,
+but there is nothing in the way of experimental evidence to go upon; and
+if I say that there is reason to believe that, in the earlier stages,
+the female is but a shadow in the external environment of the male, it
+must be taken merely as an expression of opinion, though based in some
+measure upon a general observation of the behaviour of various species.
+
+Before attempting to explain the difference in the times of arrival of
+the male and female migrant, let us examine the behaviour of some
+resident species at a corresponding period. My investigations have been
+made principally amongst the smaller species--the Finches and the
+Buntings--which often pass the winter in or near the localities wherein
+they brought up offspring or were reared. It is true that they wander
+from one field to another according to the abundance or scarcity of
+food; it is also true that, if the weather is of a type which precludes
+the possibility of finding the necessary food, these wanderings may
+become extensive or even develop into partial migrations. But under the
+normal climatic conditions which prevail in many parts of Britain, these
+smaller resident species seem to find all that they require without
+travelling any great distance from their breeding haunts. Flocks
+composed of Yellow Buntings, Cirl Buntings, Corn-Buntings, Chaffinches,
+Greenfinches, etc., can be observed round the farmsteads or upon arable
+land; small flocks of Reed-Buntings take up their abode on pieces of
+waste land and remain there until the supply of food is exhausted,
+deserting their feeding ground only towards evening when they retire to
+the nearest reed-bed to pass the night; flocks of Hawfinches visit the
+same holly-trees day after day so long as there is an abundance of
+berries on the ground beneath; and so on.
+
+I have mentioned the Reed-Bunting; let us take it as our first example
+and try to follow its movements when the influence exerted by the
+internal secretions begins to be reflected on the course of its
+behaviour. First, it will be necessary to discover the exact localities
+in any given district to which the species habitually returns for the
+purpose of procreation; otherwise the earlier symptoms of any
+disposition to secure a territory may quite possibly be overlooked in
+the search for its breeding haunts.
+
+In open weather Reed-Buntings pass the winter either singly, in twos or
+threes, or in small flocks, on bare arable ground, upon seed fields, or
+in the vicinity of water-courses; but in the breeding season they
+resort to marshy ground where the _Juncus communis_ grows in abundance,
+to the dense masses of the common reed (_Arundo phragmites_), and such
+like places. During the winter, the male's routine of existence is of a
+somewhat monotonous order, limited to the necessary search for food
+during the few short hours of daylight and enforced inactivity during
+the longer hours of darkness. But towards the middle of February a
+distinct change manifests itself in the bird's behaviour. Observe what
+then happens. When they leave the reed-bed in the morning, instead of
+flying with their companions to the accustomed feeding grounds, the
+males isolate themselves and scatter in different directions. The
+purpose of their behaviour is not, however, to find fresh feeding
+grounds, nor even to search for food as they have been wont to do, but
+rather to discover stations suitable for the purpose of breeding; and,
+having done so, each male behaves in a like manner--it selects some
+willow, alder, or prominent reed, and, perching thereon, leads a quiet
+life, singing or preening its feathers. Now if the movements of one
+particular male are kept in view, it will be noticed that only part of
+its time is spent in its territory. At intervals it disappears. I do not
+mean that one merely loses sight of it, but that it actually deserts its
+territory. As if seized with a sudden impulse it rises into the air and
+flies away, often for a considerable distance and often in the same
+direction, and is absent for a period which may vary in length from a
+few minutes to an hour or even more. But these periodical desertions
+become progressively less and less frequent in occurrence until the
+whole of its life is spent in the few acres in which it has established
+itself.
+
+The behaviour of the Yellow Bunting is similar. In any roadside hedge
+two or more males can generally be found within a short distance of one
+another, and in such a place their movements can be closely and
+conveniently followed. Under normal conditions the ordinary winter
+routine continues until early in February; but the male then deserts the
+flock, seeks a position of its own, and becomes isolated from its
+companions. Now the position which it selects does not, as a rule,
+embrace a very large area--a few acres perhaps at the most. But there is
+always some one point which is singled out and resorted to with marked
+frequency--a tree, a bush, a gate-post, a railing, anything in fact
+which can form a convenient perch, and eventually it becomes a central
+part of the bird's environment. Here it spends the greater part of its
+time, here it utters its song persistently, and here it keeps watch upon
+intruders. The process of establishment is nevertheless a gradual one.
+The male does not appear in its few acres suddenly and remain there
+permanently as does the migrant; at first it may not even roost in the
+prospective territory. The course of procedure is somewhat as
+follows:--At dawn it arrives and for a while utters its song, preens its
+feathers, or searches for food; then it vanishes, rising into the air
+and flying in one fixed direction as far as the eye can follow, until it
+becomes a speck upon the horizon and is ultimately lost to view. During
+these excursions it rejoins the small composite flocks which still
+frequent the fields and farm buildings. For a time the hedgerow is
+deserted and the bird remains with its companions. But one does not have
+to wait long for the return; it reappears as suddenly as it vanished,
+flying straight back to the few acres which constitute its territory,
+back even to the same gate-post or railing, where it again sings. This
+simple routine may be repeated quite a number of times during the first
+two hours or so of daylight, with, of course, a certain amount of
+variation; on one occasion the bird may be away for a few minutes only,
+on another for perhaps half an hour, whilst sometimes it will fly for a
+few hundred yards, hesitate, and then return--all of which shows clearly
+enough that these few acres possess some peculiar significance and are
+capable of exercising a powerful influence upon the course of its
+behaviour. And so the disposition in relation to the territory becomes
+dominant in the life of the bird.
+
+Or take the case of the Chaffinch. In winter large or small flocks can
+be found in many varied situations. But in the latter part of February,
+or the early days of March, these flocks begin to disperse. At daylight
+males can then be observed in all kinds of situations, either calling
+loudly, uttering their spring note, or exercising their vocal powers to
+the full; and it will be found that, in the majority of instances, these
+males are solitary individuals, that they pass the early hours of the
+morning alone, and that their normal routine of calling, singing, or
+searching for food, is only interrupted by quarrels with their
+neighbours. The same locality is visited regularly--not only the same
+acre or so of ground, but even the same elm or oak, has, as its daily
+occupant, the same cock Chaffinch. And temporary desertions from the
+territory occur also, much like those referred to in the life of the
+Bunting, but perhaps not so frequently. One has grown so accustomed
+during the dark days of winter to the sociable side of Chaffinch
+behaviour--to the large flocks searching for food, to the endless stream
+of individuals returning in the evening to roost in the holly-trees, to
+the absence of song--that this radical departure from the normal routine
+comes as something of a surprise; for the days are still short, the
+temperature is still low, the nesting season is still many weeks ahead,
+and yet for part of the day, and for just that part when the promptings
+of hunger must be strongest, the male, instead of joining the flock,
+isolates itself and expends a good deal of energy in insuring that its
+isolation shall be complete. And in place of the silence we hear from
+all directions the cheerful song uttered with such marked persistency
+that it almost seems as if the bird itself must be aware that by doing
+so it was advertising the fact of its occupation of a territory. This is
+surely a remarkable change, and the females in the meantime continue
+their winter routine.
+
+One other example. The monotonous call of the Greenfinch is probably
+familiar to all. In winter these birds accompany other Finches and form
+with them flocks of varying sizes, but in the spring the flocks
+disperse, and the Greenfinch, in common with other units of the flock,
+alters its mode of life. But whereas the Chaffinch or the Bunting begins
+to acquire its territory in February, the Greenfinch only does so in
+April. When the organic changes do at length begin to make themselves
+felt, the male seeks a position of its own, and having found one remains
+there, uttering its characteristic call. But owing probably to the fact
+that it is much later than the aforementioned species in acquiring a
+territory, temporary desertions are not so much in evidence. The species
+is so very plentiful, and the bird is so prone to nest in gardens and
+shrubberies surrounding human habitations, that this seasonal change in
+its routine of existence cannot fail to be noticed. One can hear its
+call in every direction, one can watch the same individual in the same
+tree; and it is the male that is thus seen and heard, the female appears
+later. Thus the behaviour falls into line with that of the Bunting or
+the Chaffinch.
+
+The behaviour of these resident species throws some light upon the early
+arrival of the males which we are endeavouring to explain in the case of
+the migrants. Let us see how their actions compare. The male resident
+deserts the female early in the year and establishes itself in a
+definite position, where it advertises its presence by song; the male
+migrant travels from a great distance, arrives later, and also
+establishes itself in a definite position, where it, too, advertises its
+presence by song. The male resident passes only the earlier part of the
+day in its territory at the commencement of the period of occupation;
+the male migrant remains there continuously from the moment it arrives.
+The male resident deserts its territory at intervals, even in the
+morning; the male migrant betrays no inclination to do so. Thus there is
+a very close correspondence between the behaviour of the two, and what
+difference there is--slight after all--cannot be said to affect the main
+biological end of securing territory. One is apt to think of the problem
+of migration in terms of the species instead of in terms of the
+individual. One pictures a vast army of birds travelling each spring
+over many miles of sea and land, and finally establishing themselves in
+different quarters of the globe; and so it comes about, I suppose, that
+a country or some well-defined but extensive area is regarded as the
+destination, the ultimate goal, of the wanderers. But the resident male
+has a journey to perform, short though it may be; it, too, has a
+destination to reach, neither a country nor a locality, but a place
+wherein the rearing of offspring can be safely accomplished, and it,
+too, arrives in that place in advance of the female.
+
+With these facts at our disposal, we will endeavour to find an
+explanation. It is unlikely that specialised behaviour would occur in
+generation after generation under such widely divergent conditions,
+and, moreover, expose the birds to risk of special dangers, if it were
+but an hereditary peculiarity to which no meaning could be attached.
+Hence the appearance of the males in their breeding haunts ahead of the
+females becomes a fact of some importance, and suggests that the
+extensive journey in the one case, and the short journey in the other,
+may both have a similar biological end to serve.
+
+Darwin evidently attached importance to this difference between the
+males and the females in their times of arrival. In the _Descent of Man_
+he referred to it as follows: "Those males which annually first migrated
+in any country, or which in spring were first ready to breed, or were
+the most eager, would leave the largest number of offspring; and these
+would tend to inherit similar instincts and constitutions. It must be
+borne in mind that it would have been impossible to change very
+materially the time of sexual maturity in the females without at the
+same time interfering with the period of the production of the young--a
+period which must be determined by the season of the year." Newton
+suggested the following explanation[2]: "It is not difficult to
+imagine that, in the course of a journey prolonged through some 50° or
+60° of latitude, the stronger individuals should outstrip the weaker by
+a very perceptible distance, and it can hardly be doubted that in most
+species the males are stouter, as they are bigger than the females."
+Granting that the males are the stronger, how can this account for
+their outstripping the females by a week, ten days, or even a fortnight,
+in a journey of perhaps 1500 miles? To expect the birds to accomplish
+such a distance in seven days is surely not estimating their
+capabilities too highly, and any slight inequality in the power of
+flight or endurance could give the males an advantage of a few hours
+only. But this explanation, based upon inequalities in the power of
+flight and endurance on the one hand, and the magnitude of the distance
+traversed on the other, cannot afford a solution of the behaviour of the
+resident males, and is less likely, therefore, to be a true solution of
+that of the migrants.
+
+There is another theory, simple enough in its way, which will probably
+occur to many. It is based on the assumption that the males reach sexual
+maturity before the females; and it is contended that the functioning of
+the instincts which contribute towards the biological end of
+reproduction depend upon the organic changes which the term "sexual
+maturity" is held to embrace, and that, inasmuch as the migratory
+instinct belongs to the group of such instincts, the males must be the
+first to leave their winter quarters.
+
+What is meant by the "migratory instinct"? To speak of it as one of the
+instincts concerned in reproduction is not enough. Reproduction involves
+the actual discharge of the sexual function, which involves the
+females; but the first visible manifestation of organic change in the
+male is its desertion of the females. Yet this is the behaviour which is
+referred to as the "migratory instinct," and which comes into play,
+according to this theory, because the bird has reached sexual maturity.
+Manifestly we must have some clear understanding as to what these terms
+represent. That organic changes determine the functioning of certain
+definite instincts at certain specified times there can be no doubt;
+that these changes may occur at a somewhat earlier date in the male than
+in the female is more than probable, but that this explains the
+behaviour in question I do not believe. One wants to know why the
+changes should occur earlier in the male, what disposition it is which
+first comes into functional activity, and to what such disposition is
+related.
+
+It may, however, be urged that, after all, this apparent eagerness to
+reach the breeding grounds is but a modification of hereditary procedure
+under the guiding hand of experience. What more likely result would
+follow from the enjoyment associated with previous success in the
+attainment of reproduction than a craving to repeat the experience? What
+stronger incentive to a hurried return could be imagined? It must be
+admitted that there are certain facts which might be used in support of
+an appeal to experience as a reasonable explanation. For example, the
+first males to arrive often display that richness of colouring which is
+generally supposed to indicate a fuller maturity. Gätke even speaks of
+the "most handsome old birds being invariably the first to hasten back
+to their old homes." But if experience is a factor, if some dim
+recollection of the past is held to explain the hurried departure of the
+male migrant, one wants to know with what such recollection is
+associated. Is it associated with the former female, or with the former
+breeding place, or with both? I take it that any recollection, no matter
+how vague, must be primarily associated with the particular place
+wherein reproduction had previously been accomplished; and I grant that
+if the first individuals to appear were invariably the older and
+experienced birds, their early return might be explained on the basis of
+such an association. But if there is reason to believe that a proportion
+are young birds on the verge of carrying out their instinctive routine
+for the first time, then we cannot appeal to past experience in
+explanation of their behaviour.
+
+The age of a bird is difficult to determine. Experience leads me to
+believe that some of the males that arrive before the females are birds
+born the previous season; one finds, for instance, individuals with
+plumage of a duller hue, which denotes immaturity, amongst the first
+batch of arrivals. But though plumage may sometimes be a satisfactory
+guide, yet to rely upon it alone, or upon a more perfect development of
+feather, is to exceed the limits of safety. How, then, can we ascertain
+whether all the males that arrive before the females have had some
+previous experience of reproduction? Well, we take a particular locality
+and note the migrants that visit it year after year, and we find that
+the respective numbers of the different species are subject to wide
+annual fluctuations. Not every species lends itself to an inquiry of
+this kind: some are always plentiful and fluctuation is consequently
+difficult to discern; others are scarce and variation is easily
+determined. Those which are of local distribution but conspicuous by
+their plumage, or easily traced by the beauty or the peculiarity of
+their song, afford the more suitable subjects for investigation. For
+example, the Grasshopper-Warbler, Marsh-Warbler, Nightingale, Corncrake,
+Red-backed Shrike, or Whinchat have each some distinctive peculiarity
+which makes them conspicuous, and each one is subject to marked
+fluctuation in numbers. The small plantation or wooded bank may hold a
+Nightingale one year, but we miss its song there the next; the osier bed
+or gorse-covered common which vibrates with the trill of the
+Grasshopper-Warbler one April is deserted the following season; the
+plantation which is occupied by a host of common migrants this summer
+may be enlivened next year by the song of the rarer Marsh-Warbler also;
+and so on. The fluctuation is considerable: we observe desertion on the
+one hand, appropriation on the other, and yet males appear before
+females whether the particular plantation, osier bed, or swamp had been
+inhabited or not the previous season. This fact is not without
+significance. It shows that similar conditions prevail both amongst the
+males that appropriate breeding grounds new to them, and amongst those
+that return to some well-established haunt; and on the assumption that
+the earlier arrivals are experienced males, the same birds evidently do
+not return to the same place year after year. Granting, then, that the
+males which appropriate new breeding-grounds are young birds, how can
+their earlier arrival be explained in terms of past experience; and
+granting that they are old, and therefore experienced, how can it be
+explained in terms of association?
+
+Again, it may be urged that if there is some biological end to be
+furthered by this hurried return, and if recollection of past experience
+is a means towards that end, such recollection need not necessarily be
+associated with a definite place, but only in a vague way with the whole
+series of events leading up to reproduction--in which series the
+migratory journey may even have acquired meaning. Whether there be any
+recollection of a previous journey or of a nest with young, I do not
+know. But the young bird is capable of performing its journey, of
+building its nest, and of rearing its young antecedent to
+experience--racial preparation has fitted it thus far; why then exclude
+the other event in the series, the earlier departure of the male, from
+hereditary equipment? If the journey were a casual affair without any
+goal attaching to it, if the males upon arrival wandered about in search
+of a mate, there would be some ground for thinking that a vague
+recollection of the whole former experience was sufficient to explain
+the hurried return; but since the pleasurable effect of association,
+founded upon previous experience of a definite place, cannot well be
+established, and since it is so difficult to study the objective aspect
+of the behaviour in question without coming to the conclusion that the
+journey is related to the appropriation of a place suitable for the
+rearing of offspring, one is tempted to ask whether the hurried return
+may not also be so related.
+
+Now the males of some of the migratory species, especially of those
+which are accustomed to return to their breeding haunts early in the
+season, are called upon to face greater dangers and have a greater
+strain imposed upon their strength by starting forth upon their journey
+ten days or a fortnight before their prospective mates. The blizzards
+which so often sweep across the northern parts of Europe in the latter
+half of March, destroying in their course the all too scanty supply of
+insect life, may take toll of their numbers; or the westerly gales,
+which are not infrequent at that period, may meet them in mid-ocean and
+add to the perils of their journey; or the temperature of the previous
+weeks may have been sufficiently low to arrest the development of insect
+life--and yet males are annually exposed to these risks in hurrying to
+their breeding grounds. For what purpose? The answer will largely depend
+upon the way in which we regard those few acres wherein a resting place
+is ultimately found. For myself, I believe that they are of importance,
+inasmuch as the securing of a place suitable for the rearing of
+offspring is a primary condition of success in the attainment of
+reproduction; and if this be so, it is evident that the interests of
+the race will be better served by the males making good this first step
+before the females are ready to pair, otherwise they might oscillate
+between two modes of behaviour, created by the premature functioning of
+conflicting impulses.
+
+The different steps in the process seem to follow one another in ordered
+sequence. The male inherits a disposition--which for us, of course, has
+prospective meaning--to seek the appropriate breeding ground and there
+to establish itself; and as early a functioning of this disposition as
+possible, consonant with the conditions of existence in the external
+environment, may have been evolved for the following reasons--firstly,
+the earlier individuals will meet with less interference wherever they
+may settle, every locality will be open to them, every acre free, their
+only need being that particular environment for which racial preparation
+has fitted them. In the second place, being already established when
+other males appear upon the scene, and advertising their presence by
+song, they will be less liable to molestation; thirdly, in those cases
+in which a long journey is undertaken, they will have ample time to
+recover from the fatigue, and, if attacked by later arrivals, will thus
+be in a better position to defend their territories; and lastly, a
+greater uniformity in their distribution will be insured before the
+females begin their search.
+
+There is, besides, another good reason for thinking that the earlier
+males will have an advantage. We will assume--and from the abundant
+evidence supplied by the marking of birds, it is quite a reasonable
+assumption--that there is a tendency, generally speaking, for
+individuals to return to the neighbourhood of their birthplace, or to
+the place in which they had previously reared their offspring. Now the
+earlier arrivals will have no difficulty in securing territories; those
+that come later may have to search more diligently, still they will gain
+all that they require so long as any available space remains. Then comes
+the point when all suitable ground is occupied, and yet there are males
+to be provided for. What will be the position of these males? Urged by
+their inherited nature, they will leave the district and possibly
+continue their search into those adjoining, only, however, to add to the
+difficulties of the males there similarly situated; and even allowing
+that they are at length successful in establishing themselves, what are
+their prospects of securing mates? Since the earlier females will not
+extend their wanderings farther than is absolutely necessary, but will
+pair whenever the opportunity for doing so arises, it is to the later
+females, forced onwards by competition, that the late males must look
+for mates; so that when at length pairing does take place, much valuable
+time will have been lost.
+
+The disadvantages which the late arrivals have to face are therefore
+great, and it is probable that the percentage which attain to
+reproduction will on the average be somewhat lower than the percentage
+in the case of the earlier arrivals. The district in which my
+observations have been made lies well within the limits of the breeding
+range of most of our common species, and it is not surprising that I
+should have met with little evidence of failure to breed as a result of
+failure to secure territory. Some interesting information was supplied
+to me, however, by the late Robert Service. He found, in certain seasons
+in Dumfriesshire, flocks of from ten to fifty unmated Sedge-Warblers,
+which, from the time of their arrival in May until the middle of July,
+haunted reed-filled spaces along stagnant streams. These flocks appeared
+to him to be composed of loosely-attached individuals of a migrant flock
+that had failed to find things congenial enough to entice them to
+disperse. But may they not have been composed of males that had failed
+to secure territories, or of females that had failed to discover males
+in possession of territories, or of both?
+
+
+We have seen that, in the case of many species, each male establishes
+itself in a particular place at the commencement of the breeding season,
+even though this may mean a partial or perhaps a complete severance from
+former companions. We must now discuss this fact in greater detail
+because it is opposed to the views often held regarding the sexual
+behaviour of birds, and is manifestly of importance when considering
+the theory of breeding territory.
+
+First, however, there is a point which requires some explanation. I
+speak of the _same_ male being in the _same_ place. How can I prove its
+identity? In the first place it is highly improbable that a bird which
+roams about within the same small area of ground, makes regular use of a
+certain tree and a certain branch of that tree, and observes a similar
+routine day after day, can be other than the same individual. But, apart
+from this general consideration, are there any means by which
+individuals of the same species can be identified? Well, there is
+variation in the plumage. Supposing we take a dozen cock Chaffinches and
+examine them carefully, we shall find slight differences in pattern and
+in colour--more grey here or a duller red there, as the case may be--and
+though these differences may not be sufficient to enable us to pick out
+a bird at a distance, they are nevertheless conspicuous when it is close
+at hand. Then again there is variation in the song; and the more highly
+developed the vocal powers the greater scope there is for variation. But
+even the phrases of a simple song can be split up and recombined in
+different ways. If one were asked casually whether the different phrases
+of the Reed-Bunting's song always followed one another in the same
+sequence, the answer would probably be that they certainly did so,
+whereas the bird is capable of combining the few notes it possesses in a
+surprising number of different ways. And lastly, there are differences
+in just the particular way in which specific behaviour, founded upon a
+congenital basis, is adapted by each individual to its own special
+environment. Racial preparation determines behaviour as a whole, but the
+individual is allowed some latitude in the execution of details which
+are in themselves of small moment--the selection of a particular tree as
+a headquarters and a particular branch upon that tree, the direction of
+the distant excursion, and the direction of the limited wanderings
+within the small area surrounding the headquarters which in the course
+of time determine the extent of the territory, are matters for each
+individual to decide when the occasion for doing so arises. Moreover
+instances of abnormal coloration or abnormal song are not rare, and they
+are valuable since they place the identity of the individual beyond
+dispute. I can recall the case of a Willow-Warbler whose song was unlike
+that of its own or any other species, and of a Redbreast whose voice
+puzzled me not a little. I can recollect also a male Yellow Bunting
+whose foot was injured or deformed. Of this bird's behaviour I kept a
+record for two months or so; and inasmuch as it inhabited a roadside
+hedge, and was of fearless disposition, the deformed foot could plainly
+be seen whenever it settled upon the road to search for food.
+Identification is not, therefore, a difficulty. There is always some
+small difference in colour or in song, or some well-defined routine
+which makes recognition possible.
+
+Owing to their great powers of locomotion, birds have generally been
+regarded as wanderers more or less; anything in the nature of a fixed
+abode, apart from the actual nest, having been accounted foreign to
+their mode of life; and even the locality immediately surrounding the
+nest has not been apprehended as possessing any meaning for the owner of
+that nest. No doubt the supply of food determines their movements for a
+considerable part of the year; they seek it where they can find it, here
+to-day, there to-morrow--in fact few species fail to move their quarters
+at one season or another, so that there is much truth in the notion that
+birds are wanderers. Yet to suppose that every individual one sees or
+hears--every Lapwing on the meadow, or Nightingale in the withy bed--is
+in that particular spot just because it happens to alight there as it
+roams from place to place, is to take a view which the observed facts do
+not support. For as soon as the question of reproduction dominates the
+situation, a new condition arises, and the habits formed during the
+previous months are reversed, and the males, avoiding one another, or
+even becoming actively hostile, prefer a life of seclusion to their
+former gregariousness--all of which occurs just at the moment when we
+might reasonably expect them to exhibit an increased liveliness and
+restlessness as a result of their endeavour to secure mates; and so
+universal is the change that it might almost be described as an
+accompaniment of the sexual life of birds generally.
+
+That the Raven and certain birds of prey exert an influence over the
+particular area which they inhabit has long been known, and it has been
+recognised more especially in the case of the Peregrine Falcon,
+possibly because the bird lives in a wild and attractive country, and,
+forcing itself under the notice of naturalists, has thus had a larger
+share of attention devoted to its habits. Moreover, when a species is
+represented by comparatively few individuals, and each pair occupies a
+comparatively large tract of country, it is a simple matter to trace the
+movements and analyse the behaviour of the birds. There is a rocky
+headland in the north-west of Co. Donegal comprising some seven miles or
+so of cliffs, where three pairs of Falcons and two pairs of Ravens have
+nested for many years. Each year the different pairs have been more or
+less successful in rearing their young; each year the young can be seen
+accompanying their parents up to the time when the sexual instinct
+arises; and yet the actual number of pairs is on the whole remarkably
+constant, and there is no perceptible increase. It seems as if the
+numbers of three and two respectively were the maximum the headland
+could maintain. But this is no exceptional case; it represents fairly
+the conditions which obtain as a rule amongst those species, granting,
+of course, a certain amount of variation in the size of each territory
+determined by the exigencies of diverse circumstances.
+
+If we take a given district, and devote our attention to the smaller
+migrants that visit Western Europe each returning spring for the purpose
+of procreation, we shall find that the movements of the males are
+subject to a very definite routine. This, however, is not true of every
+male; some may be wending their way to breeding grounds at a distance;
+others may be seeking the particular environment to which they may be
+adapted; others again, having found their old haunts destroyed, may
+consequently be seeking new.
+
+Of all this there is evidence. Small parties of Chiffchaffs pass through
+a district on their way to other breeding grounds, flitting from hedge
+to hedge as they move in a definite direction with apparently a definite
+purpose; Reed-Warblers settle in a garden or plantation, eminently
+unsuited to their requirements, and disappear; Wood-Warblers arrive in
+some old haunt, and finding it no longer suitable for their purpose,
+seek new ground. So that plenty of individuals are always to be found,
+which, for the time being at least, are wanderers.
+
+In the district which I have in mind, the wandering males form only a
+small part of the incoming bird population. The majority of individuals
+that fall under observation are those that have made this particular
+district their destination; and in doing so, they may possibly have been
+guided by their experience as owners or inmates of former nests, for it
+cannot be doubted that a return to the neighbourhood of the birthplace
+would lead to a more uniform distribution and therefore be advantageous,
+and the tendency to do so might consequently have become interwoven in
+the tissue of the race. How, then, do they behave? A certain amount of
+movement, an interchanging of positions, even though restricted to an
+area defined, let us say, by experience, might be expected under the
+circumstances--that, however, is not what we find; we observe the
+available situations plotted out into so many territories, each one of
+which is occupied by a male who passes the whole of his time therein.
+Take whatever species we will--Whitethroat, Whinchat, Willow-Warbler,
+Red-backed Shrike, it matters not which, for there is no essential
+difference in the general course of procedure--this condition will be
+found to prevail. Generally speaking, the behaviour in relation to the
+territory can be studied more conveniently where a number of individuals
+of the same species have established themselves in proximity to one
+another. Such species as the Chiffchaff, Willow-Warbler, or Wood-Warbler
+are often sufficiently common to allow of three or more of their
+respective males being kept in view at the same time; and the
+disposition to occupy a definite position can be readily observed. The
+Reed-Warbler is a suitable subject for an investigation of this kind;
+for since it is restricted by its habits to localities wherein the
+common reed (_Arundo phragmites_) grows in abundance, and since such
+localities are none too plentiful and often limited in extent, the area
+occupied by each individual is necessarily small--if it were not so the
+species would become extinct. Hence it is a simple matter to study the
+routine of the different individuals and to mark the extent of their
+wanderings.
+
+In this way the males of all the Warblers that breed commonly in Great
+Britain establish themselves, each one in its respective station at the
+respective breeding ground; so, too, do those of many other
+migrants--for example, the Whinchat, Wheatear, Tree-Pipit, and Red-backed
+Shrike. All of these, it is true, are common species--numbers of
+individuals can often be found in close proximity--and therefore it may
+be argued that they keep to one position more from pressure of
+population than from any inherited disposition working towards that end.
+But the rarer species behave similarly. Districts frequented by the
+Marsh-Warbler and offering plenty of situations of the type required by
+the bird are often inhabited by a few members only, and yet the
+disposition to remain in a definite position is just as marked.
+
+You will say, however, that these smaller migrants have no exceptional
+powers of flight; that they have besides just completed a long and
+arduous journey; and you will ask why they should be expected to wander,
+whether it is not more reasonable to expect that, in order to overcome
+their fatigue, they should remain where they settle. The Cuckoo is a
+wanderer in the wider sense of the term, and is gifted with considerable
+powers of flight. Upon arrival the male flies briskly from field to
+field, showing but little signs of weariness; yet we have only to follow
+its movements for a few days in succession to assure ourselves that the
+bird is no longer a wanderer; for just as the Warbler or the Chat moves
+only within a definitely delimited area, so the male Cuckoo, strange as
+it may seem, restricts itself to a particular tract of land. The area
+over which it wanders is often considerable and consequently it is not
+possible to keep the bird always in view, but inasmuch as the variation
+in the voices of different individuals is quite appreciable,
+identification is really a simple matter. If we cannot keep the bird in
+sight, we can trace its movements by sound and mark the extent of its
+wanderings, which by repetition become more and more defined, until a
+belt of trees here, or an orchard there, mark a rough and rarely passed
+boundary line.
+
+Let us take another example from the larger migrants--the Black-tailed
+Godwit, a bird common enough in the Dutch marshes but no longer breeding
+in this country. On suitable stretches of marsh land, numbers will be
+found in proximity one to another after the manner of the Lapwing, each
+male occupying a definite space of ground wherein it passes the time
+preening, searching for food, or in sleep--though at the same time
+keeping a strict watch over its territory. Now the preference shown for
+a particular piece of ground, and the determination with which it is
+resorted to, is the more remarkable when we take into consideration the
+specific emotional behaviour arising from the seasonal sexual condition.
+This behaviour is expressed in a peculiar flight. The bird rises high in
+the air, circles round with slowly beating wings above the marsh, and
+utters a call which, as far as my experience goes, is characteristic of
+the performance. The air is often full of individuals circling thus
+even beyond the confines of the marsh, for a male does not limit its
+flight to a space immediately above its territory; but nevertheless
+careful observation will show how unerringly each one returns to its own
+position on the breeding ground, no matter how extensive the aerial
+excursion may have been. And so, when the males of the smaller migrants
+confine their movements to an acre of ground at the completion of their
+long journey, they are acting no more under the influence of fatigue
+than the Cuckoo, which keeps within certain bounds yet flies about
+briskly, or the Godwit which, though holding to its few square yards on
+the ground, executes most tiring and extensive flights above the marsh.
+
+Of all the migrants, however, the behaviour of the Ruff is perhaps the
+most strange, and though it has long been known that these birds have
+their special meeting places where they perform antics and engage in
+serious strife, yet it is only within recent years that the primary
+purpose of these gatherings has been ascertained--that purpose being the
+actual discharge of the sexual function. Mr. Edmund Selous has carried
+out some exhaustive investigations into their activities at the meeting
+places, and he makes it clear that each bird has its allotted position.
+He says, for example, that "It begins to look as though different birds
+had little seraglios of their own in different parts of the ground,"
+that "each Ruff has certainly a place of its own," or again that "this
+Ruff indeed, which I think must be a tender-foot, does not seem to have
+a place of its own like the others." Nevertheless it is only at the
+meeting places that they have their special positions; there is no
+evidence to show that each one has a special territory, wherein it seeks
+its food, as the Warbler has, and therefore some may think that we are
+here confronted with behaviour of a different order. But we must bear in
+mind that the process has been adjusted to meet the requirements of
+different species: the size of the territory, the period of its daily
+occupation, the purpose which it serves--these all depend upon manifold
+relationships and do not affect the principle. Why it has been
+differentiated in different circumstances we shall have occasion to
+discuss later; for the moment it is enough that at the end of its
+migratory journey each Ruff occupies one position on the meeting ground.
+
+[Illustration: Territorial flight of the Black-tailed Godwit
+
+Emery Walker ph.sc.]
+
+Now birds that are paired for life, whose food-supply is not affected by
+alternations of climate, have no occasion to desert the locality wherein
+they have reared their offspring, and so their movements, being subject
+to a routine which would tend to become increasingly definite, must in
+the course of time and according to the law of habit formation become
+organised into the behaviour we observe. Is it necessary, therefore, to
+seek an explanation of their tendency to remain in one place in anything
+so complex as an inherited disposition? Again, since we have to confess
+to so very much ignorance on so many points connected with the whole
+phenomenon of migration, may there not be some condition, hitherto
+shrouded in mystery, which might place so different a complexion on the
+corresponding aspect of migrant behaviour as to rid us, in their case
+also, of the necessity of appealing to an inherited disposition? Such
+questions are justifiable. And if the life-histories of other species
+gave no further support to our interpretation, if, in short, the
+evidence were to break down at this point, then we should be forced to
+seek some other explanation more in keeping with the general body of
+facts.
+
+But far from placing any obstacle in the way of an interpretation in
+terms of inherited disposition, the behaviour of many of those residents
+which are not paired for life gives us even surer ground for that
+belief. Moreover in their case the initial stages in the process are
+more accessible to observation. I will endeavour to explain why. In the
+process of reproduction the environment has its part to play--whether in
+the manner here suggested, or indirectly through the question of
+food-supply, matters not at the moment. Now, migratory species are more
+highly specialised than resident species as regards food, and are
+affected more by variations of temperature, so that they can live for
+only a part of the year in the countries which they visit for the
+purpose of procreation. Hence the organic changes, which set the whole
+process in motion, must be coincident in time with the growth of
+appropriate conditions in the environment; for if it were not so, if the
+internal organic changes were to develop prematurely, the bird would
+undertake its journey only to find an insufficiency of food upon its
+arrival, and this would scarcely contribute towards survival. Definite
+limitations have therefore been imposed upon the period of organic
+change. But in the case of many resident species the conditions are
+somewhat different, for they remain in the same locality throughout the
+year, and a gradual unfolding of the reproductive process cannot
+therefore have a similarly harmful effect. Thus it comes about that the
+behaviour of the migrant, when it arrives at the breeding ground and
+first falls under observation, represents a stage in the process which,
+in the case of the resident, is only reached by slow degrees; and by
+closely observing the behaviour as it is presented to us in the life of
+the resident male, we not only gain a better insight into the changes in
+operation, but can actually witness the breaking down of the winter
+routine, stereotyped through repetition, by the new disposition as it
+arises.
+
+The first visible manifestations, even though they may be characterised
+by a certain amount of vagueness, are therefore of great importance if
+the behaviour is to be interpreted aright; and in order to insure that
+none of these earlier symptoms shall be missed, it is necessary to begin
+the daily record of the bird's movements at an early date in the season.
+As a rule the second week in February is sufficiently early for the
+purpose, but the date varies according to the prevailing climatic
+conditions. Even in species widely remote there is great similarity of
+procedure, and the behaviour of the Buntings is typical of that of many.
+With the rise of the appropriate organic state the male resorts at
+daybreak to a suitable environment, occupies a definite position, and
+singling out some tree or prominent bush, which will serve as a
+headquarters, advertises its presence there by song. At first the bird
+restricts its visits, which though frequent in occurrence are of short
+duration, for the most part to the early hours of the morning; it
+disappears as suddenly as it appeared, and one can trace its flight to
+the feeding grounds--a homestead or perhaps some newly sown field. But
+by degrees the impulse to seek the society of the flock grows less and
+less pronounced, the visits to the territory are more and more
+prolonged, and the occupation of it then becomes the outstanding feature
+of the bird's existence. This in outline is the course of procedure as
+it appears to an external observer.
+
+But although much can be learnt from the lives of these smaller species,
+there is no gain-saying the fact that a great deal of patient
+observation is required, and the process is apt to become tedious. There
+are others, however, which are more readily observed, whilst their
+life-histories afford just as clear an insight into the effect produced
+by the new disposition upon the developing situation; and among these
+the Lapwing takes a prominent position, because it is plentiful and
+inhabits open ground where it is easily kept in view.
+
+There is a water meadow with which I am familiar, where large numbers
+resort annually for the purpose of procreation. Here they begin to
+arrive towards the end of February, and at first collect in a small
+flock at one end of the meadow. A male, here and there, can then be seen
+to break away from the flock, and to establish itself in a definite
+position upon the unoccupied portion of the ground, where it remains
+isolated from its companions. Others do likewise until the greater part
+of the meadow is divided into territories. Six of these territories I
+kept under observation for approximately two months in the year 1915.
+The occupant of the one marked No. 6 upon the 1915 plan was a lame bird,
+a fortunate occurrence as it enabled me to follow its movements with
+some accuracy; and though it maintained its position for some weeks, it
+ultimately disappeared, as a result, I believe, of the persistent
+attacks of neighbouring males. The behaviour of the males during the
+first fortnight or so after they broke away from the flock was
+interesting. Though they retired to their territories and remained in
+them for the greater part of their time, yet it was only by degrees that
+they finally severed their connection with the flock, for so long as a
+nucleus of a flock remained, so long were they liable to desert their
+territories temporarily and to rejoin their companions.
+
+[Illustration: Emery Walker Ltd. sc.
+
+Plan of the water meadow showing the territories occupied by Lapwings in
+the year 1915.]
+
+[Illustration: Emery Walker Ltd. sc.
+
+Plan of the water meadow showing the territories occupied by Lapwings in
+the year 1916.
+
+_Between pages 58 and 59._]
+
+Lapwings, as is well known, collect in flocks during the winter months,
+and these flocks, which sometimes reach vast proportions, are to be
+found on tidal estuaries, water meadows, arable land, and such like
+places, according to the prevailing climatic conditions. This flocking
+may contribute towards survival, and may therefore be the result of
+congenital dispositions which have been determined on biological
+grounds. On the other hand, since food at that season is only to be
+obtained in a limited number of situations, the birds may be simply
+drawn together by accident. In the former case the behaviour would be
+instinctive, in the latter, though accidental at first, recurrent
+repetition would tend to make it habitual; but in either case the
+impulse to accompany the flock must be a powerful one, for on the one
+hand it would depend upon inherited, and on the other hand upon
+acquired, connections in the nervous system. Now observe that soon
+after the flock arrived in the meadow, single males detached themselves;
+there was no hesitation, they just retired from their companions and
+settled in their respective territories. They were not expelled, for if
+their leaving had been compulsory much commotion would have preceded
+their departure, and their return would certainly not have been
+welcomed. A reference to the plan will make the position clearer; the
+neutral zone inhabited by the flock is there shown as situated in one
+corner of the meadow, the territories that fell under observation are
+plotted out as far as possible to scale, and the more important zones of
+conflict are also marked.
+
+The males spent part of their time in their respective territories and
+part with the flock, so long as it remained in existence. When a male
+was in its territory it avoided companions and was openly hostile to
+intruders; when it was with the flock it wandered about with companions
+in search of food. The contrast between the two modes of behaviour was
+very marked, and it was evident that the gregarious instinct was
+gradually yielding its position of importance to the new factor--the
+territory. If there had been no flock, if a few solitary individuals had
+appeared here and there and had established themselves in different
+parts of the meadow, one would have had no definite evidence of the
+strength of the impulse in the male to seek a position of its own, one
+could only have argued from the general fact of males flocking in the
+winter and isolating themselves in spring that something more than
+accident was required to explain so radical a change. But since the
+birds returned in a flock to the ground upon which they intended to
+breed, and since the flock occupied temporarily part of the ground
+whilst the partitioning of the remainder was still proceeding, it was
+possible to gauge the strength of the impulse, which was forcing the
+males to isolate themselves in particular areas of ground, by comparing
+it with the impulse to accompany the flock--and the measure of its
+intensity was the rapidity with which the latter impulse yielded its
+position of importance.
+
+Like the Lapwing, the Coot and Moor-Hen are easily kept under
+observation, and since many individuals often breed in proximity, more
+than one can be watched at the same moment; moreover the area occupied
+by each male generally embraces an open piece of water as well as part
+of the fringe of reeds, so that the movements of the bird can be
+followed without much difficulty. Under favourable conditions
+manifestations of the developing situation become visible at a
+comparatively early date in the season--the middle or the latter part of
+February--and these manifestations resemble those of other species. But
+the Moor-Hen passes summer and winter alike in the same situation, and
+being therefore in a position to respond at once to internal
+stimulation, however vague, the change from the one state to the other
+is gradual. This, however, is a matter of detail; the main consideration
+lies in the fact that the impulse to retire to a definite position, to
+avoid companions, and to live in seclusion, is strongly marked, and
+produces a type of behaviour similar on the whole to that of the
+Lapwing. First of all there is the appropriation of a certain position,
+the limits of which are fixed according to the law of habit formation,
+and according to the pressure exerted by neighbouring individuals; then
+there is the neutral ground over which the birds wander amicably in
+search of food; and finally there is the contrast between the pugnacity
+of the male whilst in its territory, and its comparative friendliness
+when upon neutral ground.
+
+Evidence of similar behaviour is to be found in the life of the Black
+Grouse, a bird which has always excited the curiosity of naturalists on
+account of the special meeting places to which both sexes resort in the
+spring. Mr. Edmund Selous watched these birds in Scandinavia, where he
+kept a daily record at one of the meeting places. In various passages he
+refers to the appropriation of particular positions by particular males,
+and concludes thus: "It would seem from this that, like the Ruffs, each
+male Blackcock has its particular domain on the assembly ground, though
+the size of this is in proportion to the much greater space of the
+whole. On the other mornings, too, the same birds, as I now make no
+doubt they are, have flown down into approximately the same areas."
+
+The cliff-breeding species--Guillemots, Razorbills, and Puffins--are
+difficult to investigate because individuals vary so little, and the
+sexes resemble one another so closely; yet, despite these difficulties,
+we can gain some idea of the general purport of their activities. But
+when the ledges are crowded and the air is filled with countless
+multitudes, how is it possible to keep a single bird in view for a
+sufficient length of time to understand its routine? The difficulty is
+not an insuperable one. The flights, undertaken seemingly for no
+particular purpose, are often of short duration and are completed before
+the strain of observation becomes too great; moreover an individual
+sometimes possesses a special mark or characteristic which serves to
+make it conspicuous. For example, there is a well-marked variety of the
+Common Guillemot, the Ringed or Bridled Guillemot of science,
+distinguished by an unusual development of white round the eye and along
+the furrow behind it. One such individual I was fortunate in discovering
+upon a crowded cliff, and, as in the case of the Lapwing with the broken
+leg or the Yellow Bunting with the injured foot, the identity of the
+bird was beyond dispute, and one could observe that it appropriated to
+itself a particular position upon a particular ledge.
+
+Guillemots and Razorbills return at intervals to the breeding stations
+early in the season, and these visits are repeated with growing
+frequency until the birds are finally established. I have witnessed
+these periodic returns during March in the south of England, and during
+April in the north-west of Ireland, and I am informed that in the latter
+district such visits may occur as early as February. Gätke, who had
+ample opportunity of observing the birds in Heligoland, puts their
+return at an even earlier date. "They visit their breeding places," he
+says, "in flocks of thousands at the New Year, often even as early as
+December, as though they wanted to make sure of their former haunts
+being well preserved and ready for their reception." Such visits,
+however, are irregular in occurrence; the birds arrive, and, after
+spending a short time upon the ledges, disappear. And since there is not
+the same evidence in their coming and going of that method which we
+observe in the periodical returns of the Bunting or the Finch, it may be
+thought that needless importance is being attached to an episode in
+their lives which is quite intelligible in terms of a feeble response
+determined by a dawning organic change. While it may be quite
+intelligible in such terms it is not thereby explained; for every
+response must have as its antecedent an inherited connection in the
+nervous system determined on biological grounds. Besides, these early
+periodic returns conform in general to the type of behaviour displayed
+by other species, the males of which return to their breeding grounds
+many weeks before the real business of reproduction begins. Are we then
+justified in regarding them as accidents of the developing situation?
+Are we not rather bound to admit that they have some definite biological
+end to serve?
+
+[Illustration: Competition for territory is seldom more severe than
+amongst cliff-breeding sea birds, and the efforts of individual
+Razorbills to secure positions on the crowded ledges lead to desperate
+struggles.
+
+Emery Walker ph.sc.]
+
+These examples show that the males of many species reverse their mode of
+life at the commencement of the breeding season and proceed to isolate
+themselves, each one in a definitely delimited area.
+
+
+There are three ways in which we may attempt to interpret this
+particular mode of male behaviour. We may regard it as an accidental
+circumstance, nowise influencing the course of subsequent procedure; or,
+appealing to the law of habit formation, we may regard it as an
+individual acquirement; or again, we may invest it with a deeper
+significance and seek its origin in some specific congenital disposition
+determined on purely biological grounds.
+
+Which of these three shall we choose? The first by itself requires but
+little consideration; for though it might explain the initial visit, it
+cannot account for the persistency with which the plot of ground is
+afterwards resorted to. Supposing, however, that we combine the first
+and the second; supposing, that is to say, we assume, for the purpose of
+argument, that the initial visit is fortuitous, and that constancy is
+supplied by habit formation--would that be a satisfactory
+interpretation? It is a simple one, inasmuch as it only requires that a
+male shall alight by chance in a particular place for a few mornings in
+succession in order that the process may be set in motion. Now an
+essential condition of habit formation is recurrent repetition; given
+this repetition and, it is true, any mode of activity is liable to
+become firmly established. But how can we explain the repetition? Even
+if we are justified in assuming that the initial visit is purely an
+accidental occurrence, we cannot presume too far upon the laws of chance
+and assume that the repetition, at first, is also fortuitous.
+
+So that we come back to the congenital basis, the last of our three
+propositions. And it will, I think, be admitted that the facts give us
+some grounds for believing that the securing of the territory has its
+root in the inherited constitution of the bird. In comparing the
+behaviour of the migratory male with that of the resident, attention was
+drawn to the manner in which the occupation of a territory was effected:
+the former bird, it may be remembered, established itself without delay,
+whereas the latter did so only by degrees, and the difference was
+attributed to the incidence of migration which required a closer
+correspondence between organic process and external environment. But the
+significance for us just now lies in the fact that the definiteness,
+which accompanies the initial behaviour of the migratory male in
+relation to the territory, cannot have been acquired by repetition; for
+this reason, that when the male occupies its space of ground at the end
+of its long and arduous journey, it does so without preparation or
+experiment, even without hesitation, as if aware that it was making good
+the first step in the process of reproduction. No doubt, if it happened
+to be an individual that had already experienced the enjoyment of
+reproduction, it might be aware of the immediate results to be achieved
+and act accordingly. But among the hosts of migrants that one observes,
+there must be many males which have not previously mated; and yet, upon
+arrival, they all behave in a similarly definite manner--so that
+experience cannot well be the primary factor in the situation. If, then,
+the essential condition of habit formation is absent and experience is
+eliminated, there is nothing left but racial preparation to fall back
+upon.
+
+Nevertheless, it is true that many resident males seem to pass through
+a period of indecision before they establish themselves permanently in
+their respective territories; they come and go, their visits grow more
+and more prolonged, and only after the lapse of some considerable time
+does the process of establishment attain that degree of completeness
+which is represented in the initial behaviour of the migratory male.
+Their whole procedure seems therefore to bear the stamp of individual
+acquirement; and, if it stood alone, we might be content to construe it
+thus, but the example of the migratory male necessitates our looking
+elsewhere for the real meaning of the indecision.
+
+Let me first of all give some instances of the persistence with which a
+male remains in one spot, and this despite the fact that it has no mate.
+
+A Reed-Bunting occupied a central territory in a strip of marshy ground
+inhabited annually by four or five males of this species. Throughout
+April, May, and until the 19th June, it clung to its small plot of
+ground, tolerated no intrusion, and sang incessantly.
+
+Two Whitethroats arrived at much the same time--the 30th April
+approximately--and occupied the corner of a small plantation; the one
+obtained a mate the day following its arrival, the other remained
+unpaired for a fortnight.
+
+A Reed-Warbler established itself amongst some willows and alders
+adjoining a reed-bed and made its headquarters in a small willow bush.
+Not more than fifteen yards away, on the edge of the main portion of the
+reeds, another male was established and was paired on the 22nd May. Each
+morning the single male behaved in much the same way, singing
+continuously whilst perched upon the bush. And so the days passed by
+until it seemed improbable that it would ever secure a mate, but one
+appeared on the 20th June, and a nest was built forthwith.
+
+Now it is difficult to believe that a chance visit, even though repeated
+for a few mornings in succession, could have accounted for the
+Reed-Bunting remaining so persistently in the marsh, or the Whitethroat
+in one corner of the osier bed, or the Reed-Warbler in that one
+particular willow. Not only so, but if a habit of such evident strength
+can be acquired so readily, we have a right to ask why it should only be
+acquired in the spring--why not at every season? Considerations such as
+these lead to the belief that there must be some congenital basis to
+account for such persistent endeavour; the more so since it is difficult
+not to be impressed with the conative aspect of the male's behaviour. To
+a stranger, unacquainted with its previous history, the bird might
+appear to be leading a life of hesitation, whereas, if carefully
+watched, its whole attitude will be found to betray symptoms of a
+striving towards some end; and the frequent departure and return, which
+might be pointed to as the material from which a definite mode of
+procedure would be likely to emerge, is in reality behaviour of a
+determinate sort.
+
+My interpretation, then, of the apparent indecision in the behaviour of
+the resident male is this. During the winter most species live in
+societies, together they seek their food and together they retire in the
+evening to the accustomed roosting places; and the association of
+different individuals confers mutual benefits upon the associates. The
+movements of these societies are dominated by the question of food; all
+else is subservient, and the supply of the necessary sustenance may,
+under certain conditions, become a difficulty which can only be met by
+energy and resource. After the long night the sensation of hunger is
+strong, and the birds, on awakening, fly to the accustomed feeding
+grounds, returning again in the evening to the selected spot, and by
+frequent repetition a routine becomes established. Thus the behaviour of
+each individual is determined not only by the powerful gregarious
+impulse but also by the habits formed in connection therewith during
+many weeks in succession. Now with the rise of the appropriate organic
+state, the disposition to seek the breeding ground and there to
+establish itself becomes dominant in the male. But the process is a
+gradual one. There is no need, as happens amongst the migrants, for the
+period of organic change to conform rigidly to the growth of any
+particular condition in the environment, and hence for a time the bird
+oscillates between two modes of behaviour--between that one organised by
+frequent repetition and that one determined by the functioning of this
+new disposition.
+
+To look at the matter broadly, it is scarcely likely that so definite a
+mode of behaviour would recur with such regularity, generation after
+generation, in the individuals belonging to so many widely divergent
+forms, if it had no root in the inborn constitution of the bird. But the
+law of habit formation has its part to play also. By itself it is
+inadequate; yet it probably does assist very materially in adding still
+greater definition, and it probably is responsible in a large measure
+for determining the limits of the territory according to the conditions
+of existence of the species--thus the Falcon seeks its prey over wide
+tracts of land, and, by hunting over certain ground repeatedly,
+establishes a routine, which broadly fixes the area occupied; the
+Woodpecker cannot find food upon every tree, and every forest does not
+contain the necessary trees, and therefore the bird regulates its flight
+according to the position of the trees; and the Warbler, finding food
+close at hand, does not need to travel far, and the area it occupies is
+consequently small.
+
+So that the most likely solution of the problem will be found in a
+combination of our second and third propositions; that is to say, in an
+initial responsive behaviour provided for in the inherited constitution
+of the nervous system, and in a definiteness acquired by repetition and
+determined by relationships in the external environment.
+
+
+
+
+CHAPTER III
+
+THE DISPOSITION TO DEFEND THE TERRITORY
+
+
+In the previous chapter I endeavoured to show that each male establishes
+a territory at the commencement of the breeding season, and there
+isolates itself from members of its own sex. And further I gave my
+reasons for believing that this particular mode of behaviour is
+determined by the inherited nature of the bird, and that we are
+justified in speaking of it as "a disposition to secure a territory"
+because we can perceive its prospective value. But the act of
+establishment is only one step towards "securing." By itself it can
+achieve nothing; for any number of different individuals might fix upon
+the same situation, and if there were nothing in the inherited
+constitution of the bird to prevent this happening, where would be the
+security, or how could any benefit accrue to the species?
+
+In withdrawing from its companions in the spring, the male is breaking
+with the past, and this action marks a definite change in its routine of
+existence. But the change does not end in attempted isolation; it is
+carried farther and extends to the innermost life and affects what,
+humanly speaking, we should term its emotional nature, so that the bird
+becomes openly hostile towards other males with whom previously it had
+lived on amicable terms.
+
+The seasonal organic condition is responsible for the functioning of the
+disposition which results in this intolerance, just as it is for the
+functioning of the disposition which leads to the establishment of the
+territory; and the effect of these two dispositions is that a space of
+ground is not only occupied but made secure from intrusion. The process
+is a simple one. There is no reason to believe, there is no necessity to
+believe, that any part of the procedure is conditioned by anticipatory
+meaning; the behaviour is "instinctive" in Professor Lloyd Morgan's
+definition of the word, since it is of a "specific congenital type,
+dependent upon purely biological conditions, nowise guided by conscious
+experience though affording data for the life of consciousness."
+
+That the males of many animals are apt to become quarrelsome during the
+mating period is notorious. Darwin collected a number of facts, many of
+which related to birds, showing the nature and extent of the strife when
+the sexual instinct dominated the situation. And pondering over these
+facts, he deduced therefrom a "law of battle," which, he believed, bore
+a direct relation to the possession of a female. And it must be admitted
+that he had excellent ground for his conclusion in the fact not only
+that the conflicts occur mainly during the pairing season, but that
+the female is often a spectator and seems even to pair with the victor.
+I accepted it, therefore, as the most reasonable interpretation of the
+facts. But, as time passed by, incidents of a conflicting character led
+me to think that after all there might be another solution of the
+problem. And when it was no longer possible to doubt that there was a
+widespread tendency to establish territories, it at once became manifest
+that the battles might have an important part to play in the whole
+scheme. But how was this to be proved? What sort of evidence could show
+whether the proximate end for which the males were fighting had
+reference to the female or to the territory? Clearly nothing but a
+complete record of the whole series of events leading up to reproduction
+could supply the necessary data upon which a decision might rest. In the
+present chapter I shall give, in the first place, the reasons which lead
+me to think that the origin of the fighting cannot be traced to the
+female; afterwards, the evidence which seems to show that it must be
+sought in the territory; and finally, I shall make a suggestion as to
+the part the female may play in the whole scheme.
+
+[Illustration: Male Blackbirds fighting for the possession of territory.
+The bare skin on the crown of the defeated bird shows the nature of the
+injuries from which it succumbed.
+
+Emery Walker ph.sc.]
+
+The facts upon which the "law of battle" was founded were ample to
+establish the truth of its main doctrine. But the evidence upon which
+the interpretation of the battles was based was somewhat superficial. It
+was based mainly upon the general observation that one or more females
+could frequently be observed to accompany the combatants; and if this
+were the sole condition under which the fighting occurred, one must
+admit that this view would have much to recommend it. But it is not
+merely a question of males disputing in the presence of a female; for
+males fight when no female is present, pair attacks pair, or a male may
+even attack a female--in fact there is a complexity of strife which is
+bewildering.
+
+In attributing the rivalry to the presence of the female, it is assumed
+that males are in a preponderance, and that consequently two or more are
+always ready to compete for a mate. Her presence is presumably the
+condition under which his pugnacious nature is rendered susceptible to
+its appropriate stimulus, the stimulus being, of course, supplied by the
+opponent. There would be nothing against this interpretation if it were
+in accord with the facts; but it can, I think, be shown that the males
+are just as pugnacious and the conflicts just as severe even when the
+question of securing a mate is definitely excluded; and I shall now give
+the evidence which has led me to this conclusion.
+
+In the previous chapter we had occasion to refer to the difference in
+the times of arrival of the male and female migrants, and we came to the
+conclusion, it may be remembered, that this was a fact of some
+importance, because it gave us a clue to the meaning of much that was
+otherwise obscure in their behaviour. But it is also of importance in
+connection with the particular aspect of the problem which we now have
+in view, for if it can be shown that males, when they first reach their
+breeding grounds, are even then intolerant of one another's presence, if
+their actions and attitudes betray similar symptoms of quasi-conation,
+if disputes are rife and the struggles of a kind to preclude all doubt
+as to their reality, then it is manifest that in such cases their
+intolerance cannot be due to the presence of the female.
+
+Here, however, I must refer to a view which is held by some
+psychologists, namely, that amongst the higher animals, even on the
+occasion of the first performance of an instinctive act, there is some
+vague awareness of the proximate end to be attained. Discussing the
+nature of instincts, Dr M'Dougall[3] says, "Nor does our definition
+insist, as some do, that the instinctive action is performed without
+awareness of the end towards which it tends, for this, too, is not
+essential; it may be, and in the case of the lower animals no doubt
+often is, so performed, as also by the very young child, but in the case
+of the higher animals some prevision of the immediate end, however
+vague, probably accompanies an instinctive action that has often been
+repeated." A similar view seems to be held by Dr Stout.[4] "As I have
+already shown," he says, "animals in their instinctive actions do
+actually behave from the outset as if they were continuously interested
+in the development of what is for them one and the same situation or
+course of events; they actually behave as if they were continuously
+attentive, looking forward beyond the immediately present experience in
+preparation for what is to come. They apparently watch, wait, search,
+are on the alert. They also behave exactly as if they appreciated a
+difference between relative success and failure, trying again when a
+certain perceptible result is not attained and varying their procedure
+in so far as it has been unsuccessful. All these characters are found in
+the first nest-building of birds as well as in the second; they are
+found also in courses of conduct which occur only once in the lifetime
+of the animal." Both these writers would, I imagine, contend that, even
+when a female is absent, the idea of the female, as the end in view
+throughout, is present; and they would argue that the fact of her
+absence during the fighting in no way disposes of the belief that she is
+the condition under which the pugnacious instinct of the male is
+rendered susceptible to stimulation. What reason is there to think that
+this interpretation is applicable to the case under consideration? When
+a female is present, we observe that the males are pugnacious, and, when
+she is absent, that they still continue to be hostile--that is to say,
+they behave _as if_ she were present. Now, as far as I can ascertain,
+the "_as if_" is the only ground there is for supposing that the female
+is represented in imaginal form--there is no evidence of the fact, if
+fact it be. On the contrary, the behaviour of the male affords some
+fairly conclusive evidence that no such image is the primary factor in
+exciting the instinctive reaction. For if it be the actual presence of
+the female, or, in the absence of such, a mental image, that renders the
+pugnacious nature of the male responsive; provided the usual stimulus
+were present, the instinct ought surely to respond, not only under one
+particular circumstance, but under all circumstances. Yet, as we shall
+presently see, a male is by no means consistently intolerant of other
+males. It may be sociable at one moment or pugnacious at another, but
+the pugnacity is always peculiar to a certain occasion--the occupation
+of a territory. What shall we say then--that a mental image is a
+situational item only when the territory is occupied? It may be so; it
+may be that the fact of occupation gives rise to the mental image which,
+in its turn, renders the fighting instinct explosive, which again
+renders the possession of the territory secure. That such an
+interpretation is possible we must all admit. But if it were true,
+though it would not affect the main consideration, namely, whether the
+fighting has reference to the possession of a particular female, or to
+the protection of the territory, it would make further discussion as to
+which of these is the condition of the fighting unprofitable, for each
+would have its part to play in the process, the territory remaining,
+however, the principal factor in the situation.
+
+Now the difference in the times of arrival of the male and female
+migrant varies in different species from a few days to a fortnight or
+even more. It is most marked in those that return to their breeding
+grounds early in the season, and the greater the margin of difference
+the greater scope is there for observation. In my records for the past
+twelve years, there are frequent references to these initial male
+contests in the life of the Willow-Warbler and of the Chiffchaff; and in
+the district which I have in mind, these two species arrive early in the
+season, the males preceding the females by a week or even as much as a
+fortnight. Suppose, then, that two Chiffchaffs establish themselves in
+adjoining territories; or suppose that a male settles in a territory
+already occupied; what is the result? Well, scenes of hostility soon
+become apparent; as the birds approach one another they become more and
+more restive, their song ceases, they no longer search for food in the
+usual methodical manner, but instead their movements are hurried and
+their call-notes are uttered rapidly--all of which betrays a heightened
+emotional tone. Then the climax is reached, there is a momentary
+fluttering of tiny wings, a clicking of bills, and for the time being
+that may be all. But unless one or other of the combatants retires, this
+scene may be repeated many times in the course of a few hours, and
+repeated with varying degrees of severity. Yet the fighting, even in the
+most extreme form, when the birds locked together fall slowly to the
+ground, is seldom of an impressive kind, and one has to bear in mind the
+capabilities of the actors, remembering that the most severe struggle
+might readily be interpreted as a game if it were not for certain
+symptoms which reveal its inner nature.
+
+The males of many other migrants can frequently be observed to fight
+when there was every reason to believe that females had still to arrive.
+The Blackcap is notoriously pugnacious, but not more so than the
+Marsh-Warbler or the Whinchat. Here in Worcestershire, the _Arundo
+phragmites_ grows mainly on certain sheets of water which are
+comparatively few and far between, and the Reed-Warbler is consequently
+restricted to isolated and more or less confined areas. The males arrive
+early in May before the new growth of reeds has attained any
+considerable height, and each one has its own position in the reed-bed,
+sings there, and throughout the whole period of reproduction actively
+resists intrusion on the part of other males. I have kept watch upon a
+small area of reeds daily from the date of the first arrival; each
+individual was known to me, and as the growing reeds were only a few
+inches in height, a female could scarcely have escaped detection. Yet
+time and again disputes arose, and males pursued and pecked one
+another, striving to attain that isolation for which racial preparation
+had fitted them.
+
+But on account of their violence, or their novelty, or because the
+absence of a female was beyond question, some battles stand out in one's
+memory more prominently than others. An instance of this was a struggle
+between two Whitethroats which happened in the latter part of April and
+lasted for three successive days. The scene of its occurrence was more
+or less the same on each occasion, and the area over which the birds
+wandered was comparatively small. The fighting was characterised by
+persistent effort and was of a most determined kind, and so engrossed
+did the assailants become that they even fluttered to the ground at my
+feet. No trace of a female was to be seen at any time during these three
+days, nor, during the pauses in the conflict, was the emotional
+behaviour of a kind which led me to suppose that a female was anywhere
+in the vicinity. And, if she had been near, she must have made her
+presence known, for the belief that she is a timid creature, skulking on
+such occasions in the undergrowth, is by no means borne out by
+experience.
+
+Even more impressive was a battle between two male Cuckoos. It occurred
+high up in the air above the tops of some tall elm-trees which roughly
+marked the boundary line between their respective areas, and the actions
+of the birds were plainly visible. At the moment of actual collision
+the opponents were generally in a vertical position, and wings, feet,
+and beaks were made use of in turn; one could plainly see them strike at
+one another with their feet, and one could observe the open bill which
+generally denotes exhaustion, but may of course have been due to anger,
+or used as a means of producing terror. Yet no female appeared in the
+locality until six days after the occurrence of this struggle--and
+she certainly is not easily overlooked, for her note is unmistakable
+even when the behaviour of the male does not betray her arrival.
+
+[Illustration: Male Cuckoos fighting before the arrival of a female
+
+Emery Walker ph.sc.]
+
+That the actual presence of the respective females exercised any
+influence on the course of these struggles is more than doubtful. Not
+only did one fail to detect them, but one's failure to do so was
+confirmed by the knowledge that they had not yet arrived in those
+particular localities. Hence the fact of the male preceding the female
+is a valuable aid to the interpretation of subsequent behaviour; and one
+appreciates it the more after having experienced the difficulty of
+deciding whether she is present during the conflicts between resident
+males, for no matter how carefully we may observe the conditions which
+lead up to, and which accompany, such conflicts, or how closely we may
+scrutinise the surrounding trees, undergrowth, or ground, there always
+remains the possibility that she may, after all, have been overlooked.
+But this must not be taken to imply that in such cases direct
+observation alone can lead to no serviceable result, or that the
+evidence gained therefrom is worthless. Far from it. Failure to detect a
+female is so very common an occurrence that, even if we lacked the
+corroborative evidence supplied in the life of the migratory male, it
+would still be unreasonable to suppose that it were solely due to
+mistaken observation. We mark her absence during the conflicts between
+the respective males of many common species--the Finches, Buntings, and
+Thrushes that occupy their territories early in the season when the
+hedgerows and trees are still bare; but more frequently amongst those
+that inhabit open ground, because the movements of the birds are there
+more accessible to observation. For instance, half a dozen or more
+Lapwings can be kept in view at the same time, and as they stand at dawn
+in solitary state, keeping watch upon their respective territories, they
+are conspicuous objects on the short, frosted grass; no stranger can
+enter the arena without the observer being aware of it, no commotion can
+occur but one detects it, no movement however small need be missed. And
+so they fight, in a manner which leaves no doubt as to the reality of
+the struggle, when their prospective mates are absent not only from the
+particular territories in which the conflicts take place, but absent too
+from those adjoining.
+
+If the fact that males fight before they are paired and in the absence
+of a female could be placed beyond all question, it would no longer be
+possible to regard her possession as the end for which they are
+contending, and consequently there would be no need to produce further
+evidence. But the examples which I have given refer, of course, to only
+a few migrants and a few residents--and moreover it must be admitted
+that a female _is_ often conspicuous during the battles--so that by
+themselves they must be regarded, and rightly so, as inconclusive. We
+must therefore pass on to consider evidence of a somewhat different
+character.
+
+I spoke of the complexity of the strife. By this I mean that it is not
+merely a matter of disputes between adjoining males, but that it is a
+far more comprehensive business involving both sexes. Thus female fights
+with female and pair with pair, or a male will attack a female, or,
+again, a pair will combine against a single male or a single female. And
+from all this complexity of strife we gain much valuable evidence in
+regard to the question immediately before us. For when one pair attacks
+another, or males that are definitely paired fight with one another, or
+an unpaired male attacks either sex of a neighbouring pair
+indiscriminately, there is surely little ground for supposing that the
+possession of a mate is the reason of it all.
+
+The battles between pairs of the same species are by no means uncommon.
+Observe, for example, the central pair of three pairs of Reed-Buntings
+occupying adjoining territories, and keep a daily record of the routine
+of activity practised by both sexes during the early hours of the
+morning; then, at the close of the season, summarise all the fighting
+under different headings, and it will be found that the number of
+occasions upon which the central pair attacked, or was attacked by,
+neighbouring pairs will form a considerable portion of the whole.
+
+Or watch the Moor-Hen, and for the purpose choose some sheet of water
+large enough to accommodate three or more pairs, and so situated that
+the birds can always be kept in view. Early in February the pool will be
+haunted by numbers of individuals of both sexes, all swimming about
+together, and, if the pool is surrounded by arable land, wandering over
+that land subject to no territorial restrictions, apparently free to
+seek food where they will. But as time goes by, their number gradually
+decreases until a few pairs only remain, and these will occupy definite
+areas. If careful watch is then kept and the relations of the pairs
+closely studied, there will be no difficulty in observing the particular
+kind of warfare to which I am alluding, and it will be noticed that the
+encounters are of a particularly violent description. Thus two pairs
+approach one another, and, when they meet, throw themselves upon their
+backs, each bird striking at its adversary with its feet or seizing hold
+of it with its beak; and though, in the commotion that ensues, it is
+almost impossible to determine what exactly is happening, there is
+reason to believe that the sexes attack one another indiscriminately.
+
+A struggle between two pairs of Pied Wagtails is worth mentioning. It
+impressed itself upon my memory because of the unusual vigour with which
+it was conducted. The battle lasted for fifteen minutes or more, and
+the four birds, collecting together, pursued and attacked one
+another--at one moment in the air, at another upon the roof of a house
+where they would alight and flutter about on the slates, uttering their
+call-note without ceasing--until finally they disappeared from view,
+still, however, continuing the struggle.
+
+[Illustration: Two pairs of Pied Wagtails fighting in defence of their
+territories.
+
+Emery Walker ph.sc.]
+
+Such is the nature of the warfare which prevails between neighbouring
+pairs, and which can be observed in the life of many other species--the
+Chaffinch, Stonechat, Blackbird, Partridge, Jay, to mention but a few.
+
+The conflicts between males that are definitely paired are of such
+common occurrence that it is scarcely necessary to mention specific
+instances. But the occasions on which a male attacks either sex of a
+neighbouring pair indiscriminately, or on which a pair combine to attack
+a female, are less frequent.
+
+Now if it be true that males fight for no other purpose than to gain
+possession of a mate, what meaning are we to attach to the battles
+between the pairs, or what explanation are we to give of the fact that
+paired males are so frequently hostile? Those who hold this view will
+probably argue thus: "The presence of the female is the condition under
+which the pugnacious instinct of the male is rendered susceptible to
+appropriate stimulation, and the stimulus is supplied by a rival male;
+we admit that all the fighting which occurs after pairing has taken
+place has nothing to do strictly speaking with gaining a mate, but,
+inasmuch as the fact of possession is always liable to be
+challenged--and no male can differentiate between a paired and an
+unpaired intruder--we contend that it would add to the security of
+possession if the pugnacious instinct remained susceptible to
+stimulation so long as there were any possibility of challenge from an
+unpaired male; and we think that the waste of energy involved in the
+struggles between paired birds, and which we grant is purposeless, would
+be more than balanced by the added security." This is a possible
+explanation and requires consideration. It cannot account for all the
+diverse ways in which the sexes are mixed up in the fighting--it cannot,
+for instance, explain the fact that an unpaired male will attack either
+sex of an adjoining pair indiscriminately--but nevertheless it appears
+at first sight to be a reasonable explanation of some of them. We must
+remember, however, that fighting continues throughout the whole period
+of reproduction. Even after the discharge of the sexual function has
+ceased, and the female is engaged in incubation or in tending her young,
+the male is still intolerant of intruders; and it is difficult to
+believe that, at so late a stage in the process, a female could be any
+attraction sexually to an unpaired male. But apart from any theoretical
+objection, there remains the fact--namely that there is no evidence
+that a male, after having once paired, is liable to be robbed of its
+mate. And in support of this fact I have only to state that I have met
+with no single instance of failure to obtain and hold a mate when once a
+territory had been secured. Bearing in mind then that both sexes
+participate in the fighting, and that individuals of the opposite sex
+frequently attack one another; that all such conflicts are characterised
+by persistent effort, and that they are not limited to just the
+particular period when the sexual instinct is dominant but continue
+throughout the breeding season; bearing in mind that in at least one
+form of this promiscuous warfare the influence of the female can be
+definitely excluded, and that, in the remaining forms, the evidence
+which is required to link them up with the biological end of securing
+mates is lacking--can it be denied that the complexity of the strife
+makes against the view that the possession of a female is the proximate
+end for which the males are fighting?
+
+We started with the most simple aspect of the whole problem, the
+fighting of two males in the presence of one female--the aspect upon
+which attention has usually been fixed. And if it remained at that, if
+observation failed to disclose any further development in the situation,
+then there would be no need to probe the matter deeper, there would be
+no reason to doubt the assertion that the quarrel had direct reference
+to the female. But assuredly no one can ponder over the diversity of
+battle and still believe that the possession of a mate furnishes an
+adequate solution of the mystery. Clearly such an hypothesis cannot
+cover all the known facts; there are conflicts between separate pairs,
+and there are conflicts between males when females are known to be
+absent and when their mates are even engaged in the work of
+incubation--these cannot be due to an impulse in a member of one sex to
+gain or keep possession of one of the other sex. So that taking all
+these facts into consideration, we are justified, I think, in hesitating
+to accept this view, and must look elsewhere for the real condition
+under which the pugnacious nature of the male is rendered susceptible to
+appropriate stimulation.
+
+
+What then is the meaning of all this warfare? The process of
+reproduction is a complex one, built up of a number of different parts
+forming one inter-related whole; it is not merely a question of
+"battle," or of "territory," or of "song," or of "emotional
+manifestation," but of all these together. The fighting is thus one link
+in a chain of events whose end is the attainment of reproduction; it is
+a relationship in an inter-related process, and to speak of it as being
+even directly related to the territory is scarcely sufficient, for it is
+intimately associated with the disposition which is manifested in the
+isolation of the male from its companions, and forms therewith an
+_imperium in imperio_ from which our concept of breeding territory is
+taken. But let me say at once that it is no easy matter to prove this,
+for since so many modes of behaviour, which can be interpreted as
+lending support to this view, are likewise interpretable on the view
+that the presence of a female is a necessary condition of the fighting,
+it is difficult to find just the sort of evidence that is required.
+Nevertheless, after hearing the whole of the evidence and at the same
+time keeping in mind the conclusion which we have already reached, I
+venture to think that the close relationship between the warfare on the
+one hand and the territory on the other will be fully admitted.
+
+Formerly I deemed the spring rivalry to be the result of accidental
+encounters, and I believed that an issue to a struggle was only reached
+when one of the combatants succumbed or disappeared from the locality, a
+view which neither recognised method nor admitted control. Recent
+experience has shown, however, that I was wrong, and that there is a
+very definite control over and above that which is supplied by the
+physical capabilities of the birds.
+
+Let us take some common species, the Willow-Warbler being our first
+example; and, having found three adjoining territories occupied by
+unpaired males, let us study the conflicts at each stage in the sexual
+life of the three individuals, observing them before females have
+arrived upon the scene, again when one or two of the three males have
+secured mates, and yet again when all three have paired. Now we shall
+find that the conditions which lead up to and which terminate the
+conflicts are remarkably alike at each of these periods. A male
+intrudes, and the intrusion evokes an immediate display of irritation on
+the part of the owner of the territory, who, rapidly uttering its song
+and jerking its wings, begins hostilities. Flying towards the intruder,
+it attacks viciously, and there follows much fluttering of wings and
+snapping or clicking of bills. At one moment the birds are in the
+tree-tops, at another in the air, and sometimes even on the ground, and
+fighting thus they gradually approach and pass beyond the limits of the
+territory. Whereupon a change comes over the scene; the male whose
+territory was intruded upon and who all along had displayed such
+animosity, betrays no further interest in the conflict--it ceases to
+attack, searches around for food, or sings, and slowly makes its way
+back towards the centre of the territory.
+
+Scenes of this kind are of almost daily occurrence wherever a species is
+so common, or the environment to which it is adapted so limited in
+extent, that males are obliged to occupy adjacent ground. The Moor-Hen
+abounds on all suitable sheets of water, and it is a bird that can be
+conveniently studied because, as a rule, there is nothing, except the
+rushes that fringe the pool, to hinder us from obtaining a panoramic
+view of the whole proceedings, and moreover the area occupied by each
+individual is comparatively small. Towards the middle of February,
+symptoms of sexual organic change make themselves apparent, and the pool
+is then no longer the resort of a peaceable community; quarrels become
+frequent, and as different portions of the surface of the water are
+gradually appropriated, so the fighting becomes more incessant and more
+severe. Each individual has its own particular territory, embracing a
+piece of open water as well as a part of the rush-covered fringe, within
+which it moves and lives. But in the early part of the season, when the
+territories are still in process of being established, and definiteness
+has still to be acquired, trespassing is of frequent occurrence, and the
+conflicts are often conspicuous for their severity.
+
+Now these conflicts are not confined to unpaired individuals, nor to one
+sex, nor to one member of a pair--every individual that has settled upon
+the pool for the purpose of breeding will at one time or another be
+involved in a struggle with its neighbour. If then we single out certain
+pairs and day by day observe their actions and their attitude towards
+intruders, we shall notice that, instead of their routine of existence
+consisting, as a casual acquaintance with the pool and its inmates might
+lead us to believe, of an endless series of meaningless disputes, the
+behaviour of each individual is directed towards a similar goal--the
+increasing of the security of its possession; and further, if we pay
+particular attention to the circumstances which lead up to the quarrels
+and the circumstances under which such quarrels come to an end, we shall
+find, when we have accumulated a sufficient body of observations, that
+the disputes always originate in trespass, and that hostilities always
+cease when the trespasser returns again to its own territory. By careful
+observation it is possible to make oneself acquainted with the
+boundaries--I know not what other term to use--which separate this
+territory from that; and it is the conduct of the birds on or near these
+boundaries to which attention must be drawn. A bird may be feeding
+quietly in one corner of its territory when an intruder enters. Becoming
+aware of what is happening it ceases to search for food, and approaching
+the intruder, at first swimming slowly but gradually increasing its
+pace, it finally rises and attacks with wings and beak, and drives its
+rival back again beyond the boundary. Thereupon its attitude undergoes a
+remarkable change; ceasing to attack, but remaining standing for a few
+moments as if still keeping guard, it betrays no further interest in the
+bird with which a few seconds previously it was fighting furiously. On
+one occasion I watched a trespasser settle upon a conspicuous clump of
+rushes situated near the boundary. The owner, who was at the moment some
+distance away, approached in the usual manner, and, having driven off
+the trespasser, returned immediately to the clump, where it remained
+erect and motionless.
+
+A feature which marks all the fighting, and which we cannot afford to
+disregard, is the conative aspect of the behaviour of the owner of the
+territory. The bird attacks with apparent deliberation _as if_ it were
+striving to attain some definite end. I recollect an incident which was
+interesting from this point of view. A pair of Reed-Buntings were
+disturbed by a Weasel which had approached their nest containing young.
+Both birds betrayed symptoms of excitement; as the Weasel threaded its
+way amongst the rushes, so they fluttered from clump to clump or clung
+to the stems, uttering a note which is peculiar to times of distress,
+and followed it thus until finally it disappeared in a hedge. The
+rapidly uttered note and the excitement of the birds caused some
+commotion, and the male from an adjoining territory approached the
+scene. Now one would have expected that the presence of this bird, and
+possibly its aid in driving away a common enemy, would have been
+welcomed; one would have thought that all else would have been
+subservient to the common danger, and that so real a menace to the
+offspring would have evoked an impulse in the parent powerful enough to
+dominate the situation and subordinate all the activities of the bird to
+the attainment of its end. But what happened? Three times during this
+incident, the male, whose young were in danger, abandoned the pursuit of
+the Weasel and pursued the intruder. It was not merely that he objected
+to the presence of this neighbouring male in a passive way, nor even
+that he had a momentary skirmish with it, but that he determinedly drove
+the intruder beyond the boundary and only then returned to harass the
+Weasel.
+
+Thus it seems clear that the proximate end to which the fighting is
+directed is not necessarily the defeat of the intruder, but its removal
+from a certain position. And inasmuch as this result will be obtained
+whether the retreat is brought about by fear of an opponent or by
+physical exhaustion, it is manifest that too much significance need not
+be attached to the amount of injury inflicted. It is necessary to bear
+this in mind, because it is held by some, who have carefully observed
+the actions of various species, that overmuch importance is attached to
+the conflicts, that in a large number of instances they are mere
+"bickerings" and lead to nothing, and that they are now only "formal,"
+which means, I suppose, that they are vestigial--fragments of warfare
+that determined the survival of the species in bygone ages. But if the
+conclusion at which we have just arrived be correct, if we can recognise
+a single aim passing through the whole of the warfare--and that one the
+removal of an intruder from a certain position, then we need no longer
+concern ourselves as to the degree of severity of the battles--we see it
+all in true perspective. Neither exhaustion nor physical inability are
+the sole factors which determine the nature and extent of the fighting;
+there is a more important factor still--position. According, that is to
+say, to the position which a bird occupies whilst fighting is in
+progress, so its pugnacious nature gains or loses susceptibility, and it
+is this gain or loss of susceptibility which I refer to when I speak of
+the fighting as being controlled.
+
+What we have then to consider is the relation of "susceptibility" to
+"position." We can explain the relationship in two ways. We can say that
+the part of the nature of the male which leads to the occupation of a
+territory, and is partly hereditary and partly acquired, is stronger
+than the part which leads the bird to fight, and which is conditioned by
+the presence of a female, and that consequently when the male passes the
+boundary, the impulse to return asserts itself and the conflict ceases;
+or we can say that the occupation of a territory is the condition under
+which the pugnacious instinct is rendered susceptible to stimulation,
+that the stimulus is supplied by the intruder, and that when the male
+passes outside the accustomed area its instinct is no longer so
+susceptible and it therefore retires from the conflict.
+
+[Illustration: Long-tailed Tit Males fighting for possession of
+territory. The feathers have been torn from the crown of the defeated
+and dying rival.
+
+Emery Walker ph.sc.]
+
+Of these explanations, the first is not altogether satisfactory. It
+requires the presence of a female and, as we have seen, a female is by
+no means always present. Then it attributes to the one side of the
+inherited nature an influence which is not borne out by the facts, for
+in the ordinary routine of existence, without the incentive of battle,
+every individual is liable to wander occasionally beyond its boundary
+and to intrude temporarily upon its neighbours; and this it could
+scarcely do, providing its nature to remain within the territory were
+powerful enough to dominate its movements and curtail its activities
+even during the excitement of an encounter. But there is nothing
+inherently improbable in the alternative hypothesis, nor anything that
+is at all inconsistent with the behaviour as observed; on the contrary,
+if it is admitted, the facts become connected together and exhibit a
+meaning which they otherwise would not have possessed.
+
+So much for the controlling influence of "position," which alone seems
+to me sufficient ground for believing that the fighting has reference to
+the territory. But it is not the whole of the evidence.
+
+Now if it were possible to demonstrate by actual observation that those
+males which had not established territories were not pugnacious, we
+should have something in the nature of proof of the correctness of this
+view. Demonstrative evidence of this kind is, however, unattainable. Yet
+we can come very near to obtaining it by reason of a peculiar feature
+which marks the process of acquiring territory--the neutral ground. The
+Lapwing will serve as an illustration. In the previous chapter I
+referred to the small flocks that appeared in the accustomed water
+meadow early in February, and I described how they settled day after day
+in that meadow, but only in a limited part of it, where they passed
+their time in rest, in preening their feathers, or in running this way
+and that lazily searching for food; and how, at length, the flock
+dwindled by reason of individuals breaking away in order to secure
+positions on the remaining part of the meadow. Here the neutral ground
+is adjacent to the territories, and, while still occupied by the flock,
+is resorted to by the males that had deserted that flock in order to
+establish those territories.
+
+Suppose now that we have the whole meadow in view from some point of
+vantage. In front of us are the territories, in the distance the neutral
+ground; and in each territory there is a solitary male, while on the
+neutral ground a number of individuals of both sexes are assembled, and
+move about freely one amongst another. So that the scene presented to
+view is somewhat as follows: a flat meadow, at one end of which, and at
+fairly regular intervals, a few solitary individuals are dotted about,
+each one keeping at a distance from its neighbours; while at the other
+end a number of individuals are collected together in a comparatively
+small space, apparently deriving some satisfaction from their close
+association. That surely is a very remarkable contrast. But let us
+continue our investigation, first fixing our attention upon the solitary
+individuals; one is standing preening its feathers, another is squatting
+upon the ground, a third runs a few yards in this direction then a few
+yards in that, stimulated apparently by the sight of food, and so on.
+Moreover, each one keeps strictly to a well-defined area and makes no
+attempt to associate with its fellows. One of the males, however, whilst
+roaming backwards and forwards approaches the limit of its territory,
+and this brings the neighbouring bird, whose boundary is threatened,
+rapidly to the spot. In an upright position both stand face to face, and
+the battle then begins; with their wings they attempt to beat one
+another about the body, with their beaks they aim blows at the head, and
+in the mêlée wings and legs seem to be inextricably mixed; whilst at
+intervals, driven backwards by the force of the collision, they are
+compelled to separate, only, however, to return to the charge--and the
+sound of beating wings and the feathers that float in the air are tokens
+of earnestness. Such scenes are of frequent occurrence; but the
+conflicts vary in intensity, and the circumstances under which they
+occur vary too, and females come and go without leaving any clue as to
+their ultimate intentions.
+
+Turning now to the flock one is impressed with the friendship that seems
+to exist between the various members. There are, it is true, occasional
+displays of pugnacity which never seem to develop into anything very
+serious; for instance, one bird will fly at another, and a momentary
+scuffle is followed by a short pursuit but nothing more--nothing, that
+is to say, in the least comparable with the battle previously described.
+Of what is the flock composed? Of members of both sexes. There is no
+difficulty in assuring oneself that this is so. But is it entirely
+composed of individuals in whom development has not reached a stage
+adequate for the functioning of the primary dispositions? No, not
+entirely; for it will be observed that its number is a fluctuating one,
+that birds come and go, and, if a close watch is kept upon the different
+individuals as they leave, it will be noticed that some at least are
+inmates of the territories at the opposite end of the meadow--the
+solitary members whose behaviour we were recently watching. This fact is
+an important one. We were impressed, it may be remembered, with the
+contrast between the general behaviour of the birds at the opposite
+ends of the meadow. But now it appears as if the contrast were not
+between this individual and that, but between the behaviour of the same
+one under different circumstances. The male, that is to say, which,
+while in its territory, tolerates the approach of no other male, flies
+to the flock and is there welcomed by the very individuals with whom a
+short time previously it had been engaged in serious conflict.
+
+But if the conditions are reversed and the flock happens to settle in an
+occupied territory, the attitude of the owner towards the flock is very
+different. In the year 1916 an incident of this kind occurred in the
+meadow to which reference has already been made. The weather had been
+exceptionally severe--very cold easterly and north-easterly winds,
+frost, and frequent falls of snow had affected the behaviour of the
+Lapwings, and seemed to have checked the normal development of their
+sexual routine. The males would attempt to establish themselves, and
+then, when the temperature fell and the ground was covered with snow,
+would collect again in flocks and follow their winter routine. It was on
+the 9th March, during one of the spells of milder weather, that the
+flock on the neutral ground was disturbed and settled mainly in the
+territory marked No. 3 on the 1916 plan, but partly on that marked No.
+2. The owners thereupon began to attack the different members of the
+invading flock. Fixing attention upon a particular bird whilst ignoring
+the remainder, the No. 3 male drove it away, and then after a pause
+drove another away, and so on until by degrees all the invaders were
+banished, and the No. 2 male did likewise. The interest of this incident
+lies, however, in the behaviour of the different individuals of which
+the flock was composed; when attacked they made no real show of
+resistance, but accepted the situation and left. The will to fight was
+clearly lacking, yet their presence was a source of annoyance to the
+owners of the territories. A short time previously a female had
+accompanied one of the males and was at that time somewhere in the
+vicinity, but beyond this there was no evidence to show that either of
+them were paired, and even if the presence of the female were the reason
+of the pugnacity of the one, it could not well account for that of the
+other.
+
+The neutral ground does not always happen to be so close at hand as in
+the case of the meadow referred to. Sometimes the birds will resort to a
+particular field, attracted probably by a plentiful supply of food, and
+here they collect and behave as they do during the winter, running this
+way and that as the fancy takes them, meeting together by accident at
+one moment, parting at another, according to the direction in which they
+happen to wander. Of animosity there is little sign; the season might be
+the middle of winter instead of the middle of March for all the
+indication there is of sexual development, and yet one knows that they
+will behave differently when they leave this ground, as presently they
+will, and return to their territories in the surrounding neighbourhood,
+and that there each one will fight if necessary to preserve its acre
+from intrusion.
+
+It would seem, then, from this that the fighting must bear some relation
+to the particular area of ground in which it occurs; and unless it can
+be shown that there is some other factor in the external environment of
+the male, that is the direction in which we must look for the condition
+under which the instinct is rendered susceptible. One's thoughts turn,
+of course, to the female, but she too passes backwards and forwards
+between the territories and the neutral ground, and if her presence were
+really a _conditio sine qua non_ of the strife, one would like to know
+why, when she leaves those territories and joins the flock and the males
+do likewise, similar conflicts should not prevail there also.
+
+Other species have their neutral ground, but the environment seldom
+affords such facilities for observation as does that of the Lapwing.
+Even though the Moor-Hens, who are so conspicuously intolerant upon the
+pool, _do_ feed together amicably upon the meadows adjoining; and the
+Chaffinch that is so pugnacious in the morning, _does_ seek out the
+flock later in the day; yet their conditions of existence prevent our
+obtaining a panoramic view of the whole proceeding, and we have to study
+each scene separately before discovering that the relationship between
+intolerance and the territory on the one hand, and friendship and the
+neutral ground on the other, is just as strong a feature as it is in the
+behaviour of the Lapwing.
+
+I shall now give a brief account of the conduct of a male Reed-Bunting
+which by persistent effort established itself late in the season, and I
+shall do so because its behaviour tends to confirm much that has been
+said in the preceding pages.
+
+Early in March three male Reed-Buntings occupied a small water meadow
+overgrown with the common rush, and by the third week all of them were
+paired. On the 30th March two of the males were unusually pugnacious,
+and on the following day fighting continued and at times was very
+severe. Now I knew that the occupants of the ground in which the
+fighting was taking place were paired, and not doubting that the
+combatants were the owners of two territories marked for convenience
+sake Nos. 1 and 2, I was at a loss to understand the meaning of so
+determined and persistent a struggle. My attention, however, was
+presently drawn to a third bird, which also joined in the conflict and
+made the whole situation still more perplexing. This bird, as it soon
+became clear, was none other than the owner of No. 2 territory, and the
+one that I had previously regarded as such was a new arrival. On the
+following day, the 1st April, fighting continued, and in my record for
+that day there is a note to the effect that "No. 2 female seems to be of
+no interest to No. 5 male (the new arrival); its purpose seems to be to
+drive away intruders." On the 2nd April and subsequent days, this bird
+attacked every other male that approached, and not only maintained its
+position but ultimately succeeded in securing a mate. Here then we have
+two territories occupied by two males, both of which had obtained a
+mate. The relation of these two birds was normal, a month's routine had
+defined their boundaries, and conflicts were less frequent than
+formerly. But upon this comparatively peaceful scene a strange male
+intrudes. Observe the manner of the intrusion. The stranger does not
+wander about first in this direction and then in that, but acts _as if_
+it had some definite end in view, and establishing itself in a small
+alder bush which it uses as a base or headquarters, it gradually extends
+its dominion, gains the mastery over the surrounding ground, part of
+which belonged to No. 1 male and part to No. 2, and finally drives a
+wedge, so to speak, between the two territories.
+
+How is its behaviour to be explained, and why did its presence cause
+such commotion? No one could have watched the gradual unfolding of this
+incident day by day and not have been impressed by the persistent
+endeavour with which this male maintained its position in one small part
+of the meadow. This is the first and most important consideration. Then
+there is the attitude, also significant, which it adopted towards the
+females; for I take it that, apart from the question of territory, the
+explanation of its intrusion must be sought in the necessity for
+securing a mate--that it was attracted by the presence of the females,
+and that the proximate end of its behaviour was the possession of one of
+them. But if there is one thing that emerges from the facts more clearly
+than another it is that the course of its behaviour was in no way
+influenced by the presence or absence of either of the females. My
+reasons for saying so are the following: in the first place, it made no
+attempt to pursue or to thrust its attention upon either one or the
+other of them; secondly, it even went so far as to attack and drive them
+away when they approached too closely; and in the third place, when an
+unpaired female did at length appear, it adopted a different attitude
+and forthwith paired. And bearing in mind that these two females had
+already been with their respective mates for some considerable time, and
+that there was reason to believe that coition had actually taken place,
+is it likely that any counter-attraction would have proved successful in
+tempting either of them away from its mate, or probable, if they were
+the sole attraction, that the intruding male would have been so
+persistent in remaining? How very much simpler it is to fit the pieces
+together, if for the time being we ignore the female and fix our
+attention upon the territory. Each item of behaviour then falls into its
+proper place, and the fighting which seemed so perplexing and
+meaningless becomes a factor of prime importance. First of all the male
+arrives; then it establishes itself in a small alder bush and advertises
+its presence by song; next, by persistent effort in attacking the
+neighbouring males, it frees a piece of ground from their dominion; and
+finally, in proper sequence, a female arrives, pairing takes place, and
+reproduction is secured.
+
+[Illustration: A battle between two pairs of Jays
+
+Emery Walker ph.sc.]
+
+How then does the whole matter stand? If it were males only that engaged
+in serious conflict, and if they fought only in the presence of a
+female, the problem would resolve itself into one simply of obtaining
+mates. But the warfare extends in a variety of directions, it is not
+confined to one sex, nor to unpaired individuals, nor need the opponents
+necessarily be of the same sex; it involves both sexes alike singly or
+combined. Now the view that the biological end of battle is, in its
+primary aspect, related to the female, cannot, as we have seen, apply to
+the conflicts between different pairs, and only by much stretching of
+the imagination can it be held responsible for the hostility that males
+frequently display towards females or _vice versa_. It is valid only for
+a certain form of warfare. But that form represents, you will say, a
+large proportion of the whole, which is true; and so long as we ignore
+the remainder, we might rest content in the belief that we had solved
+the major part of the problem. But can we ignore the remainder? Can we
+say that the conflicts between paired males, for example, are simply
+offshoots of the pugnacious disposition, and have no part to play in the
+process of reproduction? They recur with marked persistency season after
+season and generation after generation; they are to be found in species
+widely remote; they are frequent in occurrence; and no one who had
+observed them and noted the vigour with which they are conducted, could,
+I think, conclude that they were meaningless--and be satisfied. They
+must somehow be explained. So that if anyone thinks fit to maintain that
+possession of a mate is an adequate explanation of part of the
+hostilities, it is clearly impossible to regard all the fighting as a
+manifestation of one principle directed towards a common biological end.
+
+But wherever we extend our researches, we find that the facts give
+precision to the view that the occupation of a territory is the
+condition under which the pugnacious instinct is rendered susceptible to
+stimulation. The Lapwing, when in its territory, displays hostility
+towards other males of its own species, but when upon neutral ground,
+treats them with indifference; the Chiffchaff pursues its rival up to
+the boundary and is then apparently satisfied that its object has been
+achieved; the cock Chaffinch in March permits no other male to intrude
+upon its acre or so of ground during the early hours of the morning, but
+for the rest of the day it joins the flock and is sociable; the
+Herring-Gull resents the approach of strangers so long as it occupies
+its few square feet of cliff, but welcomes companions whilst it is
+following the plough--all of which points to a relation between the
+territory and the fighting. And this view has at least one merit--it
+accounts for all the fighting no matter what degree of severity may be
+reached or in what way the sexes may be involved. The complexity of the
+strife presents no obstacle; for if the biological end of the fighting
+is to render the territory, which has already been established, secure
+from intrusion, each sex will have its allotted part to play at the
+allotted time: thus the battles between the males before females appear
+on the scene will decide the initial question of ownership; those
+between the females will give an advantage to the more virile members
+and insure an even distribution of mates for the successful males; the
+constant struggles between paired males will roughly maintain the
+boundaries and prevent such encroachment as might hamper the supply of
+food for the young; and the co-operation of male and female in defence
+of the territory will be an additional safeguard. Each form of battle
+will contribute some share towards the main biological function of
+reproduction.
+
+
+Hitherto we have dealt principally with the male. We have referred, it
+is true, to the fact that the female co-operates with her mate in order
+to drive away intruders, but beyond this, we have made no attempt to
+trace what part, if any, she plays in the whole scheme. We must do so
+now.
+
+The various steps by which the territory is not only established but
+made secure from invasion, imply an inherited nature nicely balanced in
+many directions--first of all the male must be so attuned as to be ready
+to search for a territory at the right moment; then it must be capable
+of selecting a suitable environment; and, having established itself, it
+must be prepared to defend its area from a rival, and to resist
+encroachment by its neighbours--and if it failed in any one of these
+respects, it would run the risk of failure in the attainment of
+reproduction. Each individual has therefore to pass, so to speak,
+through a number of sieves--the meshes of which are none too
+wide--before it can have a reasonable prospect of success. This being
+so, we ask, in the first place, whether the female, too, may not have an
+eliminating test to pass; and in the second place, whether she may not
+also assist in furthering the biological end of securing the territory.
+
+Now the answer to the first of these questions will be found to be in
+the affirmative. Just as, in the securing of a territory, the ultimate
+appeal is to the physical strength of the male, so, in the course of her
+search for a mate, the female may be called upon to challenge, or may be
+challenged by a rival, and the issue is decided by force. My attention
+was first drawn to this fact by a struggle between two female
+Whitethroats, which I have described elsewhere. The scene of its
+occurrence was the corner of a small osier bed occupied by one male, and
+the females that took part in it had only recently arrived, but the
+male, an unpaired bird, had been in possession of its territory for some
+days. The sequel to this struggle, which was protracted and severe, was
+the disappearance of both females, the male being left without a mate
+for a further ten days.
+
+[Illustration: Emery Walker ph.sc.
+
+The female Chaffinch shares in the defence of the territory and attacks
+other females.]
+
+Numerous instances have since come under my notice. Hen Chaffinches
+become so absorbed that they fall to the ground and there continue the
+struggle. Seizing hold of one another by the feathers of the head, they
+roll from side to side, and then, without relaxing their grip, lie
+exhausted--the quickened heart-beat, altered respiration, tightly
+compressed feathers and partially expanded wings betraying the intensity
+of the conflict.
+
+As the breeding season approaches, hen Blackbirds grow more pugnacious.
+Individuals that early in the year have frequented the same spot daily
+and have even shown every sign of friendship, become openly hostile. For
+two years in succession I had an opportunity of observing females under
+such conditions, and of studying the gradual change in their
+relationship. Each morning at break of day and for some hours afterwards
+they could be seen in the same place, one following the other as they
+searched for food first in this direction and then in that, as if they
+derived some special pleasure from the fact of their companionship. Then
+a change began to manifest itself. Indications of animosity became
+apparent; one would run towards the other in a threatening attitude and,
+in a half-hearted manner, peck at it; and gradually the hostility grew,
+until the tentative pecking developed into a scuffle and the scuffle
+into a conflict.
+
+Much fighting also occurs between the females of the Reed-Bunting, and
+likewise between those of the Moor-Hen, and because these two species
+are not only common but inhabit respectively open stretches of marshy
+ground or large sheets of water, the fighting can be readily observed.
+
+Why do the females fight before they are definitely paired? To obtain
+mates? This certainly seems to be the obvious explanation because any
+question of securing territory can be excluded; yet if it be true that
+their sex is numerically inferior, it is difficult to understand the
+necessity for such strenuous competition. But what is the condition
+under which the pugnacious instinct of the female is rendered
+susceptible to stimulation? It cannot be merely the presence of a male
+ready to breed, for then there would be endless commotion amongst the
+flocks of Chaffinches or of Lapwings which in March are composed of both
+sexes, including even males that have secured territories. There must be
+some other circumstance; and, judging by experience, it is to be found
+in the territory--a male, that is to say, in occupation of one, is the
+condition under which the inherited nature of the female is allowed free
+play. We must bear in mind, however, that the competition between the
+males is very severe, that large numbers probably fail to pass even this
+preliminary test, and that only a proportion are in a position to offer
+to the female the condition under which her process can successfully run
+its course; so that the presumption is--though it is incapable of
+demonstration--that there is a competition for such males each recurring
+season, and that, on the average, the weaker females fail to procreate
+their kind.
+
+But apart from any direct assistance she may give in driving away
+intruders, does she in any way help to further the biological end of
+reproduction? This is a difficult question to answer, and the suggestion
+I have to make can only apply in those cases in which the territory is
+occupied throughout the breeding season. Much of the fighting between
+the males occurs in her presence, and it must be admitted--though it is
+difficult to speak with any degree of certainty--that such fighting,
+taken as a whole, bears the stamp of exceptional determination. Let us
+then grant that the excitement of a male does, under these
+circumstances, reach a higher level of intensity, and let us see how
+this will add to the security of the territory. The fact that the male
+has established itself and obtained a mate is not alone sufficient to
+accomplish the end for which the territory has been evolved. During the
+period between the initial discharge of the sexual function and the time
+when incubation draws to a close, much may happen to prejudice the
+future of the offspring; there is always the possibility of invasion by
+an individual whose development is backward or which has been
+unsuccessful in making good the first step, and, as we saw in the case
+of the Reed-Bunting, a portion of the ground won may be lost; there is
+always the danger of gradual encroachment by neighbouring owners; and
+there is even a possibility that a pair may be so persistently harassed
+by more virile neighbours as to forsake the locality permanently. If
+then a male is to attain a full measure of success it must be capable
+of keeping its boundaries intact up to the time when the young are able
+to fend for themselves, and consequently it is important that its
+intolerant nature should remain susceptible to stimulation throughout
+the greater part of the season.
+
+Does the presence of a female serve to promote this end? Now we know
+very little of the influence exerted by one sex upon the other.
+Professor Lloyd Morgan has suggested that the male raises the emotional
+tone of the female, a suggestion which seems to me in accordance with
+the facts. There is reason to believe, however, that the converse is
+also true--namely that the excitement of the male reaches a higher level
+of intensity when a female is present. Granting then that his emotional
+tone is raised, how will this affect the question? So great is the
+difference of opinion as to the part that the emotions play in
+furthering the life of the individual that one hesitates to accept any
+particular one. But it seems to be generally admitted that emotion adds
+to the efficacy of behaviour, and this is the view of Professor Lloyd
+Morgan. "Whatever may be the exact psychological nature of the emotions,
+it may be regarded," he says, "as certain that they introduce into the
+conscious situation elements which contribute not a little to the energy
+of behaviour. They are important conditions to vigorous and sustained
+conation." Therefore, if it be true that the female raises the emotional
+tone of the male, the result will be an increased flow of energy into
+all the specific modes of behaviour connected with reproduction, amongst
+which those directly concerned in the securing and defence of the
+territory will receive their share; so that instead of a progressive
+weakening of just those elements in the situation which make for
+success, the level of their efficiency will be maintained as a result of
+such reinforcement. But the female becomes intolerant of her own sex
+when she has discovered a male ready to breed, and, later, assists her
+mate in resisting intrusion; and by raising her emotional tone, he may
+be the means of furthering more strenuous behaviour on her part. Each
+member of the pair would in this way contribute towards the energy of
+behaviour of its mate, and hence add indirectly to the security of the
+territory.
+
+It may be well to illustrate the foregoing remarks. Suppose that there
+is a small piece of woodland barely sufficient to hold three pairs of
+Willow-Warblers, and suppose that the male and female in the middle
+territory did not respond to one another's influence quite as readily as
+the adjoining males and females, what would be the result? The emotional
+tone of the central pair would stand at a lower level of intensity; and,
+since their congenital dispositions would lack the necessary
+reinforcement, the birds would tend to become less and less punctilious
+in keeping their boundaries intact, whereas the adjoining pairs, always
+on the alert and meeting with little opposition, would encroach more and
+more and gradually extend their dominion. And so, by the time the young
+were hatched, the parents would be in occupation of an area too limited
+in extent to insure the necessarily rapid supply of food, and would be
+compelled to intrude upon the adjoining ground. But knowing how routine
+becomes ingrained in the life of the individual, knowing that for weeks
+this pair had submitted to their neighbours, can we believe that they
+would be capable of asserting their authority and that the young would
+be properly cared for? Or suppose that different pairs of Kittiwake
+Gulls on the crowded ledges, or different pairs of Puffins in the
+crowded burrows, varied in like manner, would they all have equal
+chances of rearing their offspring? The struggle for reproduction is
+nowhere more severe than amongst the cliff-breeding sea birds; it is not
+for nothing that one sees Kittiwake Gulls, locked together, fall into
+the water hundreds of feet below and struggle to the point of
+exhaustion, or, as has been reported, to the point of death; it is not
+for nothing that Puffins fight with such desperation. And surely success
+will be attained by that pair whose emotional tone stands high and whose
+impulse to fight is therefore strong, rather than to the ill-assorted
+couple.
+
+
+The argument, then, is briefly this. In the spring, a marked change
+takes place in the character of the males of very many species; instead
+of being gregarious they either avoid one another and become hostile,
+or, if their conditions of existence require that they shall still live
+together, they become irritable and pugnacious. This change is made
+known to us by the battles of varying degrees of severity which are such
+a feature of bird life in the spring; and since a female can commonly be
+observed to accompany the combatants, the possession of a mate appears
+at first sight to be the proximate end for which the males are
+contending. But when the circumstances which lead up to the quarrels are
+investigated closely, the problem becomes more difficult; for it is not
+merely a question of males fighting in the presence of a female, as is
+generally supposed to be the case, but on the contrary there is a
+complexity of strife which is bewildering--males attack females or _vice
+versa_; female fights with female; or a pair combine to drive away
+another pair, or even a solitary individual no matter of which sex. This
+complexity of strife makes against the view that the possession of a
+mate is the reason of the fighting. But an even stronger objection is to
+be found in the fact that males are hostile when no female is
+present--and hence we must seek elsewhere for the true explanation.
+
+Now if the behaviour of a male be closely observed, it will be found
+that its pugnacious instinct gains or loses susceptibility according to
+the position which it happens to occupy--when its ground is trespassed
+upon, the impulse to fight is strong; but when it crosses the boundary
+it seems to lose all interest in the intruder. Moreover, in some
+species, the male rejoins the flock at intervals during the early part
+of the season and for a time leads a double existence, passing backwards
+and forwards between its territory and the neutral ground. Its behaviour
+under these circumstances affords some valuable evidence, for the bird
+displays little if any hostility when accompanying the flock, yet when
+it returns to the ground over which it exercises dominion, no male can
+approach without being attacked. The conclusion, therefore, seems to be
+inevitable, namely that the actual occupation of a territory is the
+condition under which the pugnacious nature of the male is rendered
+susceptible to appropriate stimulation.
+
+
+
+
+CHAPTER IV
+
+THE RELATION OF SONG TO THE TERRITORY
+
+
+If we listen to the voices of the Waders as, in search of food, they
+follow the slowly ebbing tide, we shall notice that each species has a
+number of different cries, some of which are uttered frequently and
+others only occasionally. Not only so, but if we study the circumstances
+under which they are uttered, we shall in time learn to associate
+certain specific notes with certain definite situations.
+
+The Curlew, when surprised, utters a cry with which most of us, I
+suppose, are familiar; but when with lowered head it drives away another
+individual from the feeding ground, it gives expression to its feelings
+by a low, raucous sound, which again is different from its cry when a
+Common Gull steals the _arenicola_ that has been drawn out of the mud
+with such labour.
+
+Thus we come to speak of "alarm notes," "notes of anger," "warning
+notes"--naming each according to the situations which normally accompany
+their utterance. And so, all species, or at least a large majority of
+them, have, in greater or lesser variety, cries and calls which are
+peculiar to certain seasons and certain situations; and since on many
+occasions we have indisputable evidence of the utility of the sound
+produced--as when, upon the alarm being given by one individual, the
+flock of Lapwing rises, or when, in response to a particular note of the
+parent, the nestling Blackcap ceases to call--so are we bound to infer
+that all the cries are, in one way or another, serviceable in furthering
+the life of the individual.
+
+But besides these call-notes, birds produce special sounds during the
+season of reproduction--some by instrument, others by voice, others
+again by the aid of mechanical device. And not only is this the case,
+but many accompany their songs with peculiar flights, such as soaring to
+a great height, or circling, or floating in the air upon outstretched
+wings. These special sounds and special flights are those with which I
+now propose to deal, including under the heading "song" all sounds
+whether harsh or monotonous or beautiful, and whether vocally or
+otherwise produced; and I shall endeavour to show not only that they are
+related to the "territory," but that they contribute not a little to the
+successful attainment of reproduction.
+
+The vocal productions are infinite in variety and combination. At the
+one extreme we have songs composed of a single note repeated slowly or
+rapidly as the case may be, whilst at the other we have the complex
+productions of the Warblers; and between these two extremes, notes and
+phrases are combined and recombined in ways innumerable. And just as
+there is a rich variety of combination, so there is a very wide
+variation in the purity and character of the notes--some are harsh,
+others melodious, some flute-like, others more of a whistle, and others
+again such as can only be likened to the notes of a stringed instrument.
+Hence in variety of phrase combination added to variety in the character
+of the note, there is a possibility of infinite modes of expression.
+
+If, in the latter part of May, we take up a position at dawn in some
+osier bed, we listen to songs which have reached a high degree of
+specialisation, songs, moreover, which appeal to us on account of their
+beauty; if, on the other hand, we climb down the face of the sea cliff,
+we hear an entirely different class of songs--harsh, guttural, weird,
+monotonous sounds, which, appeal to us though they may, lack the music
+of the voices in the osier bed. And just as, in the osier bed, we can
+recognise each species by its voice, so we can distinguish the "cackle"
+of the Fulmar, the "croak" of the Guillemot, or the "grunt" of the Shag.
+In the osier bed, however, there is considerable variation in the song
+of different individuals of the same species, so much so that we can
+recognise this one from that; whereas on the cliff we cannot distinguish
+between the voices of different individuals. And the more highly
+developed the song, the greater the range of variation appears to be;
+but notwithstanding this--notwithstanding the fact that the pitch may
+differ, the phrase combination may differ, and the timbre may
+differ--the song remains nevertheless specific. So that the two
+principal features of "song," broadly speaking, are "diversity" and
+"specific character."
+
+In contrast with the call-notes, the majority of which can be heard at
+all times of the year, the song is restricted as a rule to one season,
+and that one the season of reproduction. It is true, of course, that
+some birds sing during the autumn, and, if the climatic conditions are
+favourable, in the winter also, just as others betray, in the autumn,
+symptoms of emotional manifestation peculiar to the spring; but just as
+the manifestation of the latter is feeble and vestigial, so, too, does
+the song of the former lack the vigour and persistency which is
+characteristic of the spring. Again, in contrast with the call-notes,
+which are common alike to both sexes, song is confined to one sex--a
+peculiar property of the males.
+
+Now all, I think, will agree that it must serve some biological
+purpose--this at least seems to be the conclusion to be drawn from the
+two outstanding features of "diversity" and "specific character"; and
+since the voices of different individuals of the same species vary, it
+has been suggested that, by creating a more effective pairing situation,
+it is serviceable in furthering the life of the individual. I do not
+propose at the moment to enquire whether this doctrine be true, but
+rather to direct attention to other ways in which the song may be
+useful.
+
+Is the instinct susceptible to stimulation under all conditions during
+the season of reproduction, or only under some well-defined condition?
+This is the question to which we will first direct inquiry.
+
+Song in its full development belongs, as we have seen, to the season of
+reproduction; it is heard at the dawn of the seasonal sexual process,
+and is the most conspicuous outward manifestation of the internal
+organic changes which ultimately lead to reproduction. These changes
+would appear, at first sight, to be the primary condition which renders
+the instinct susceptible to appropriate stimulation. But while this is
+true up to a point, in so far, that is to say, as organic changes are a
+necessary antecedent of all behaviour connected with the attainment of
+reproduction, closer acquaintance with the circumstances under which the
+instinct is allowed full play leads to the belief that they are not
+alone sufficient to account for the facts as observed. In order to
+arrive at a decision we must seek out the specific factors in the
+external environment with which "song" is definitely related.
+
+Some birds cross whole continents on their way to the breeding grounds,
+others travel many miles, others again find suitable accommodation in a
+neighbouring parish--nearly all have a journey to perform, it may be
+short or it may be long. The flocks of Finches gradually decrease and we
+observe the males scattering in different directions in search of
+territories; we watch the summer migrants on their way--small parties
+halting for a few hours in the hedgerows and then continuing their
+journey, single individuals alighting on trees and bushes and resting
+there for a few minutes, and the constant passage of flocks of various
+dimensions at various altitudes; and we see Fieldfares, Redwings, and
+Bramblings slowly making their way from the south and the west to their
+homes in the far north. Occasionally we hear their song, not the
+emotional outburst customary at this season, but, except in isolated
+cases, a weak and tentative performance. Gätke speaks of the absence of
+song on the Island of Heligoland, and refers to the Whitethroat as one
+of the few migrants that enliven that desolate rock with their melody.
+On the other hand, many migrants that rest temporarily on the Isle of
+May sing vigorously.[5] But on the whole there is, I think, no question
+that the male whilst travelling to its breeding grounds, and, even after
+its arrival, whilst in search of a territory, sings but little--and that
+little lacks the persistency characteristic of the period of sexual
+activity. Yet, when a suitable territory is eventually secured, the
+nature of the bird seems to change; for, instead of being silent and
+retiring, as if aware of some end not fully attained, it not only makes
+itself conspicuous but advertises its presence by a song uttered with
+such perseverance as to suggest that that end is at length attained.
+Hence, in a general way, the instinct of song seems to be related to the
+establishment of a territory.
+
+Now the subsequent course of behaviour tends to confirm this view. We
+have already had occasion to refer to the fact that the males of some
+species desert their territories temporarily and join together on ground
+which is regarded by the birds that associate there as neutral, and that
+they do so not merely for the purpose of securing food but because they
+derive some special pleasure from the act of association, and we shall
+find that the altered behaviour of the male when it leaves its territory
+to seek food or to join the flock is an important point for us just now.
+
+Buntings desert their territories temporarily and collect in flocks on
+the newly sown fields of grain. Some of the males are single, others are
+paired, and accompanied, it may be, by their mates; they wander over the
+ground in search of food, uttering their call-notes from time to time,
+or, settling upon the hedges and trees surrounding the field, rest there
+and preen their feathers. But even though a male may be surrounded by
+other males, even though it may occupy a position where it is
+conspicuous to all around, even though, that is to say, it is
+apparently in contact with just those stimulating circumstances which
+will evoke a response when it returns to its territory, yet it makes no
+attempt to sing.
+
+Lapwings, when they resort to the neutral ground, run this way and that
+in full enjoyment of one another's companionship, behaving as they do
+when they flock in autumn and winter. Specific emotional manifestation
+is, however, absent, and their actions seem to be in nowise affected by
+the powerful impulse which only a few minutes previously determined
+their conduct, for of the characteristic flight with its accompanying
+cry there is no sign.
+
+Early in the season Turtle Doves often collect from the surrounding
+country at certain spots where their favourite food is abundant. The
+croak of this Dove--its true song--is a familiar sound during the
+summer, but in addition the bird has a sexual note characteristic of the
+race. I watched a flock of upwards of one hundred on some derelict
+ground approximately eight acres in extent. Here, in May, the birds were
+attracted by the seeds of _Stellaria media_ which was growing in
+profusion. After 5 A.M. there was continuous traffic between this piece
+of ground and the surrounding neighbourhood, a constant arrival and
+departure of single individuals or pairs; and, as they fed, the sexual
+note could be heard in all directions. Now some of the males occupied
+territories close at hand, and one could watch their passage to and
+fro; yet in no single instance did I hear the true song uttered on the
+feeding ground, although the moment a male returned to its territory its
+monotonous croak could be heard, uttered moreover with that persistence
+which is so marked a feature of all song or of the sounds that
+correspond to it.
+
+Thus it will be seen that, even after the internal organic changes have
+taken place, the instinct of song is not susceptible to stimulation at
+all times and under all circumstances, but only at certain specified
+times and under special circumstances which can be observed to
+correspond with the occupation of the territory.
+
+In many species each male singles out within its territory some
+prominent position to which it resorts with growing frequency. This
+position is an important feature of the territory, and exercises a
+dominating influence on the life of the bird. I have referred to it as
+the "headquarters," and it may be a solitary tree or bush, an
+outstanding mound or mole hillock, a gatepost or a railing--anything in
+fact that supplies a convenient resting place so long as it fulfils one
+condition, namely that the bird when it is there is conspicuous. It need
+not, however, be a tree or a mound or indeed anything upon which the
+bird can perch, for there is reason to think that the soaring flight
+undertaken at this season by so many males, since it is generally
+accompanied by the specific sexual sound, answers the same purpose as
+the topmost branch of a tree.
+
+Now there is nothing in the external environment to which the song is
+more definitely related than to the "headquarters"--this at least is the
+conclusion to be drawn from the behaviour, and I will indicate the sort
+of evidence upon which such conclusion is based. There is, first of all,
+the persistency with which the male resorts to the same tree, even to
+the same branch, and, as it seems, solely for the purpose of
+advertisement. We know by experience the approximate routine of the
+male's behaviour; we know where to seek it, where to hear it, and when
+once we have discovered its headquarters, we know that there it will
+sing day after day for weeks or it may be for months together--perhaps
+the most striking feature of its behaviour at this season. Next, we find
+that other trees, though made use of, are not made use of to a similar
+extent for the purpose of song. The area occupied varies much according
+to the nature of the environment; it is sometimes extensive, and seldom
+less than half an acre or so in extent; but in most instances it
+contains plenty of trees and bushes which could, one would imagine,
+serve the purpose of a "headquarters" just as well as the particular one
+selected, and yet the bird, when there, betrays no inclination to sing
+at all comparable with that which can be observed when it occupies its
+accustomed perch. Further evidence is afforded in the behaviour of those
+species that make temporary excursions from their territories. The male,
+on its return, flies as a rule direct to its special tree and sings.
+Sometimes, however, it settles upon the ground, not unfrequently
+accompanied by the female, and while there remains silent; but presently
+rising from the ground and deserting its mate, it flies to the
+headquarters and sings. Again, nearly every male at one time or another
+in the course of the season is aroused to action by the intrusion of a
+rival. The emotional tone of the owner of the territory is then raised,
+and the intruder is pursued and attacked; but this alone is not
+sufficient, it seems as if the chain of instinctive activities, when
+once aroused by appropriate stimulation, must pursue its course to the
+end--and the end in such a case is only reached and complete
+satisfaction only gained when the bird has not merely returned to his
+"headquarters" but has given vocal expression to his emotion. Finally,
+we must bear in mind these two facts, that the "headquarters" is
+occupied solely by the male--it forms no part of the life of the
+female--and that it is the male only that sings.
+
+Many such subtle incidents of behaviour as the foregoing can be
+perceived but not readily described, and trifling though they may seem
+to be in themselves, yet in the aggregate they yield full assurance of a
+close relationship.
+
+The distant song of a male, or the presence of an intruding male, have
+also stimulating effects, though in somewhat different ways. The former
+evokes the normal reply, that is to say the bird, if silent, is liable
+to utter a corresponding reply; the latter arouses hostility into which
+is infused much feeling tone, the bird sings hurriedly while in pursuit
+of its rival, and, which is more remarkable still, even in the midst of
+an encounter. Both the normal reply and the emotional song must be
+similar in origin--different aspects of the same situation--and both are
+clearly related to the other male.
+
+The arrival of a female may also be followed by an emotional outburst
+which can be heard at intervals for some days; on the other hand, the
+song may continue as before or, for a time, entirely cease.
+
+To take the emotional outburst first. This would appear to be
+susceptible of explanation on the hypothesis that the voice contributes
+to a more effective pairing situation; an hypothesis which admittedly,
+at first sight, gains some support from the fact that a second or a
+third male is frequently present. But, in truth, the presence of a
+second male makes the situation, so far as the relationship between the
+song and the female is concerned, all the more perplexing; for, as we
+have already seen, the instinct of pugnacity, when aroused by the
+appearance of an intruder, is also liable to be accompanied by a
+similarly extravagant song. On each occasion the vocal effort is infused
+with much feeling tone, and it would be impossible to point to any one
+feature which is peculiar to only one occasion. The question therefore
+arises as to whether the emotional outburst which we are attributing to
+the arrival of a female may not after all be due to the presence of an
+intruding male. It may be so. But although I can recall no single
+instance in which the presence of an intruder could be definitely
+excluded, yet I should hesitate to base upon this any broad
+generalisation.
+
+When the normal course of the song is not interrupted by the arrival of
+a female, when, that is to say, the male still pursues the routine to
+which he has all along been accustomed, and still sings at stated
+intervals in stated places with a voice that betrays no heightened
+emotional tone, even though the song may convey some meaning to the
+delicate perceptual powers of the female, we have nothing to lay hold
+upon which can be construed as an indication of direct relationship
+between the song and the presence of the female.
+
+The partial or complete suspension of the song after pairing has taken
+place is the most interesting, as it is the most noticeable, feature.
+Not that it is by any means universal--if it were so, some of the
+difficulties that beset the path of interpretation would be removed, but
+it is sufficiently widespread to demand explanation. In nearly every
+case it is, however, only temporary, the period during which the male is
+silent varying from a few days to a few weeks. The male
+Grasshopper-Warbler, when it first reaches us, sings persistently, but
+when it is joined by a female a change becomes apparent; instead of the
+incessant trill, there are spasmodic outbursts of short duration, and in
+the course of a few days the bird lapses into a silence which may be
+broken for a short while at dawn, or late in the evening, but is often
+complete. More striking still is the change in the case of the
+Marsh-Warbler, and the sudden deterioration, or even suspension, of
+strains so beautiful and so varied, at a moment, too, when it might
+least be expected, at once arrests the attention. The Reed-Warbler that
+had its headquarters in a willow sang vigorously from the middle of May
+until a female arrived on the 20th June, when its voice was hushed,
+except for occasional outbursts which lacked force and were of short
+duration. When the Wood-Warbler secures a territory it repeats its
+sibilant trill with unwearying zeal, yet no sooner does a mate appear
+than its emotion is manifested in other directions. The Reed-Bunting is
+vociferous during February and March; but when a female arrives, periods
+of silence are frequent and the instinct of the bird becomes
+progressively less susceptible to stimulation. After the manner of the
+race the male makes temporary excursions from its territory accompanied
+by his mate, and it is noteworthy that when he returns and she is absent
+he sings, but that the moment she joins him, or even comes into sight,
+he is silent. In fact, in greater or less degree, a change is noticeable
+in the song of many resident and migratory species under similar
+circumstances, a deterioration so marked that we learn by experience to
+regard it as a certain indication of the arrival of a mate.
+
+Thus it becomes clear that there are certain specific factors in the
+external environment with which the instinct can be definitely related,
+and in the order of their importance they are (1) the territory as a
+whole; (2) the headquarters; (3) an intruding male; (4) the female.
+
+To what extent are these relationships interrelated? Are they all
+mutually dependent upon one another, or is there one which conditions
+the remainder?
+
+In the first place it is evident that if a male were not to establish a
+territory, no opportunity would be afforded for making use of any
+special post or for acquiring a habit in relation to it, and so without
+further consideration we may say that the connection between the song
+and the headquarters, whatever it may be, is primarily dependent upon
+the establishment of a territory.
+
+Next, we have the fact that the distant voice, or still more so the
+presence, of another male has an exciting influence and evokes a
+corresponding reply. Here we have a direct relationship, and one which
+at first sight appears to be exclusive of cross-correlation. But is it
+really so; does no circumstance arise under which even the proximity of
+a rival fails to evoke response? The reply is not doubtful. Such a
+circumstance _does_ arise--when a male for one reason or another passes
+outside the limits of its accustomed area. This aspect of behaviour has
+already been fully discussed in connection with the question of
+hostility, and everyone, I imagine, must by now be pretty well familiar
+with the facts. However, it does not often happen that we are given
+such an aid to interpretation as is vouchsafed to us in the altered
+behaviour of the male when it joins the flock, and if, as I believe,
+song and hostility are intimately associated, forming part of an
+inter-related whole which, for biological interpretation, has, as its
+end, the attainment of reproduction, it is not surprising that
+circumstances which lead to the modification of the one should likewise
+affect the other; I offer no apology, therefore, for adverting to this
+aspect of behaviour once again.
+
+Now a male may leave its territory for three reasons--to pursue an
+intruder, to join the flock on neutral ground, or to find the necessary
+means of subsistence on other feeding grounds. On each of these
+occasions it hears the song of, and is in close contact with, other
+males; and if the relationship of which we are speaking be really
+exclusive of cross-correlation, its instinct ought to respond with the
+customary freedom. But what happens? A male pursues its rival, betraying
+much emotion and singing extravagantly, until the boundary is passed,
+when emotion subsides and it is silent; or, it flies to the flock on
+neutral ground, and, although surrounded by the very males that a short
+time previously evoked response, is there unresponsive; or again, it
+goes in search of food and collects with other males bent on a similar
+errand, and in presence of what we know would be an exciting influence
+under other circumstances, it nevertheless remains silent. Hence the
+relationship between the song and a male rival seems, as in the case of
+the headquarters, to depend in the first instance upon the occupation
+of a territory.
+
+So that the relationship between the song and the territory as a whole
+is clearly of a different order from that which obtains between the song
+and the headquarters, or the song and a male rival; for the first, as
+far as can be judged by observation, is exclusive of, whilst the second
+and the third involve, cross-correlation. How are these facts to be
+explained? We have already seen that it belongs to the nature of the
+male during the season of reproduction to establish itself in a definite
+place, and this action is just as much a part of its hereditary nature
+as the building of the nest is of that of the female, and it is just as
+necessary for the successful attainment of reproduction. What exactly
+the stimulus is to this mode of behaviour we do not know; we can go no
+further back than the internal organic changes which are known to occur
+and which we assume, not without some reason, are responsible for its
+initiation. Granting, then, that there is this congenital disposition,
+what relation does it bear to the song? Without a doubt the song is
+likewise founded upon a congenital basis; it is truly instinctive, and
+as such requires appropriate stimulation; furthermore the male sings
+only when in occupation of its territory. Having regard to these two
+facts we might say that the territory is the stimulus to the song. But
+this can scarcely be a true interpretation, for inasmuch as the stimulus
+would be relatively constant, a relatively constant response ought to
+follow, and even a slight acquaintance with the daily round of
+behaviour will furnish plenty of evidence to the contrary, seeing that
+the song, though persistent, is never continuous--in fact there are long
+periods of silence during the daytime, and only in the morning and the
+evening does the male become really vociferous. What then is the
+stimulus? Through awareness of something in the environment the male
+responds to stimulation, and the only reply we can give is that the
+headquarters, or a distant song, or the proximity of another male--with
+all of which, as we have seen, the instinct is definitely related--are
+the specific factors which normally evoke response--and experience
+teaches us that the periods of quiescence are just those when life is at
+its lowest ebb and these stimulating factors less in evidence. Bearing
+this in mind, bearing in mind the fact that when a male joins the flock
+or crosses the boundary its instinct ceases to respond, bearing in mind,
+that is to say, that there is evidence of relationship between these
+specific factors and the song only when the territory is actually
+occupied, the conclusion seems inevitable that we have here the
+determining condition which renders the instinct susceptible to
+appropriate stimulation.
+
+There remains the female. I place her last in order of importance, not
+because I regard her influence as of small consequence, but because the
+evidence is of a varied and complex kind, so much so that it is
+difficult to ascertain by observation just how far she is a situational
+item. It will be remembered that the only direct evidence we had of such
+influence was a deterioration or, in some instances, a complete
+cessation of vocal manifestation. Clearly then we are confronted with a
+relationship of a different kind from that which we have been
+discussing; for not only is anything in the nature of stimulation
+absent, but, and this is a remarkable fact, the other items in the
+environment which formerly evoked response no longer do so in quite the
+same way. Is there any awareness on the part of the male of the relation
+between his voice and the mate that is to be, or is it merely that as
+the sexual situation increases in complexity some inhibiting influence
+comes into play? These are questions which lead up to difficult
+problems. But it is no part of my task to discuss the psychological
+aspect of the behaviour; my purpose is merely to show that the situation
+on the arrival of a female undergoes marked modification, that the
+instinct of the male is then less susceptible to stimulation, and that
+the factors in the external environment which formerly elicited response
+become relatively neutral.
+
+Hence the appearance of the female on the scene marks the opening of a
+new stage in the life-history of the male, and, to judge by the course
+of events, it would seem as if the song with its network of
+relationships had now served its main biological purpose.
+
+And now, what is the purpose, and what the origin, of song? Is it, as
+some naturalists have conceived, a means of raising the emotional tone
+of the female, of creating a more effective pairing situation, and so
+of removing a barrier to the successful discharge of the sexual
+function; or, is the emphasis here too much upon the emotional, too
+little upon the strictly utilitarian, aspect? All, I think, will agree
+that it must serve some biological purpose, and the position we have so
+far reached is that the determining condition of its manifestation is
+not merely the establishment, but the actual occupation of a territory,
+and that there are no factors in the external environment which can
+evoke response in the absence of such condition. This being so, the
+further questions arise as to whether it contributes towards the
+attainment of the end for which the whole territorial system has been
+built up, and what precisely is the way in which it does so.
+
+Everyone knows that in the spring the shyest of birds no longer practise
+the art of concealment. The Curlew soars to a great height, and upon
+outstretched wings hovers in the air whilst uttering its plaintive wail;
+the cock Grouse, as if dissatisfied with its "crowing," springs into the
+air and becomes a conspicuous object of the moor; the wary Redshank,
+poised on flickering wings, forgets its mournful alarm cry, and finds
+again its melodious song; and even the secretive Grasshopper-Warbler
+crawls out of the midst of the thicket in order to "reel," just as, for
+a similar reason, Savi's Warbler climbs to the top of a tall reed. In
+fact the males of most species, when they are finally established on the
+breeding grounds, make themselves as conspicuous as possible by sight
+and by sound. And since the sounds produced by no two species are
+exactly alike, the females are able to recognise their prospective
+mates, and the males that are still in search of ground have ample
+warning if that upon which they are treading is already occupied. So
+that you see, from the remarkable development of the vocal powers in the
+male, there follow two important results--"recognition" and "warning."
+
+We here turn from song as the expression of an instinctive disposition,
+and the question of what calls forth this expression, to the impression
+produced by the song on the hearer.
+
+Most birds have a call-note or a number of call-notes, which, generally
+speaking, are specifically distinct. But to the human ear they are not
+always so, perhaps because our power of hearing is less sensitive than
+that of a bird, and unable to appreciate delicate differences of tone.
+Be this as it may, however, the fact remains that we often find it
+difficult, and in not a few cases impossible, to recognise a bird merely
+by its call. The plaintive notes of the Willow-Warbler and of the
+Chiffchaff are to our ears very closely akin, so, too, are those of the
+Marsh-Warbler and of the Reed-Warbler, and there is a great resemblance
+between the hissing sound produced by the two Whitethroats. In Co.
+Donegal I have been deceived by the spring-call of the Chaffinch which,
+owing possibly to the humidity of the atmosphere, is, there, almost
+indistinguishable from the corresponding note of the Greenfinch. The
+Yellow Bunting and the Cirl Bunting frequently make use of a similar
+note, so do the Curlew and the Whimbrel. In fact, numberless instances
+could be quoted in which notes appear to us identical, and, as a rule,
+the more closely related the species, the more difficult it becomes to
+distinguish the sounds--alike in plumage, alike in behaviour, alike in
+emotional manifestation, it would be surprising if they were not alike
+in voice. But the moment we pass from the call-notes to a consideration
+of the songs we are faced with a very remarkable fact, for not only are
+these readily distinguished, but in many cases they bear no resemblance
+in any single characteristic. What could be more unlike than the songs
+of the Willow-Warbler and of the Chiffchaff, of the Marsh-Warbler and
+the Reed-Warbler, or of the Yellow Bunting and the Cirl Bunting?
+
+Now when different individuals collect in flocks at certain seasons,
+they assist one another in finding food, and afford mutual protection by
+giving timely warning of the approach of a common enemy, and the
+gregarious instinct is thus of great advantage to the species; but no
+matter how powerful the impulse to flock might be, if there were no
+adequate means of communication, the different units would frequently
+fail to discover their neighbours. Here the specific cries and calls
+come into play, enabling them as they move about in search of food, or
+change their feeding grounds, or whilst they are on migration, to keep
+constantly in touch with one another; and hence one purpose that these
+call-notes serve is that of recognition. Moreover, they convey their
+meaning to individuals of other species and are acted upon, and are thus
+in every sense socially serviceable; but on the other hand, whilst
+there is much evidence to show that the song is of great individual
+value, there is none to show that it is in any like manner of direct
+advantage to the community.
+
+If, then, there is in the call-notes an adequate means of communication
+and of recognition, why do I suggest that the song has also been evolved
+primarily for the purpose of recognition?
+
+What, first of all, are the conditions in the life behaviour during the
+season of reproduction that make the intervention of the voice a
+consideration of such importance? The general result of our
+investigation might be summed up thus: we found that the male inherits a
+disposition to secure a territory, that at the proper season this
+disposition comes into functional activity and leads to its
+establishment in a definite place, and that it cannot search for a mate
+because its freedom of action in this respect is forbidden by law; that
+the female inherits no such disposition, that she is free to move from
+place to place, free to satisfy her predominant inclination, and to seek
+a mate where she wills; and, since the appropriate organic condition
+which leads to pairing must coincide with appropriate conditions in the
+environment, that the union of the sexes must be accomplished without
+undue delay. Furthermore we found that a territory is essential if the
+offspring are to be successfully reared; that, since the available
+breeding ground is limited, competition for it is severe, and that the
+male is precluded from leaving the ground which he has selected, and is
+obliged, in order to secure a mate, to make himself conspicuous. That
+was our general result. Now there are two ways by which the male can
+make himself conspicuous--by occupying such a position that he can be
+readily seen, or by producing some special sound which will be audible
+to the female and direct her to the spot. The former, by itself, is
+insufficient; in the dim light of the early dawn, when life is at its
+highest, and mating proceeds apace, what aid would it be for a male to
+perch on the topmost branch of a tree, how slender a guide in the depth
+of the forest? But whether in the twilight or in the dark, in the
+thicket or the jungle, on the mountain or on the moor, the voice can
+always be heard--and the voice is the principal medium through which the
+sexes are brought into contact.
+
+Well now, we come back to the question, why, if all species have a
+serviceable recognition call, that call should not be sufficient for the
+purpose, just as, without a doubt, it is adequate for all purposes at
+other seasons? The answer is, I think, clear. The recognition call is
+not confined to one sex, nor only to breeding birds; it is the common
+property of all the individuals of the species, and if the female were
+to rely upon it as a guide she might at one moment pursue another
+female, at another a non-breeding male; she might even be guided to a
+paired female or to a paired male, and time would be wasted and much
+confusion arise. So that no matter how much a male might advertise
+himself by cries and calls which were common alike to all the
+individuals of the species, it would not assist the biological end which
+we have in view. Something else is therefore required to meet the
+peculiar circumstances, some special sound bearing a definite meaning by
+which the female can recognise, amongst the host of individuals of no
+consequence to her, just those particular males in a position to breed
+and ready to receive mates. Hence the vocal powers, the power of
+producing sounds instrumentally, and the power of flight, have been
+organised to subserve the biological end of "recognition."
+
+And this view is strengthened, it seems to me, by the erratic behaviour
+of certain species, more particularly by one remarkable case, the case
+of the Cuckoo. The male, after having established himself, utters his
+call persistently from the day of arrival until approximately the middle
+of June; but, in contrast with the large majority of species, the female
+has a characteristic call which she, too, utters at frequent intervals.
+The female is polyandrous and has a sphere of influence embracing the
+territories of a number of males; she wanders from place to place, is
+often silent, and not unfrequently is engaged in dealing with her egg or
+in searching for a nest in which to deposit it, and therefore she is not
+always in touch with a male, still less with any particular one. Now
+there is much evidence to show that the discharge of the sexual function
+amongst birds is subject to control, and that this control operates
+through the female--through her physiological state becoming
+susceptible to stimulation only at certain periods. So that we have
+these considerations, that the female is polyandrous, that she has a
+territory distinct from that of the male, and that her sexual impulse is
+periodical; and the further consideration that the impulse, since it is
+periodical, is of limited duration and must receive immediate
+satisfaction. Such being the circumstances of the case, would the voice
+of the male serve to insure the union of the sexes at the appropriate
+moment? Well, the fact that she is polyandrous implies that every male
+in her sphere of influence is not always capable of satisfying her
+sexual instinct. Is, then, the male's call an indication of his
+readiness to yield to stimulation? Without a doubt it is an index of the
+general physiological state which generates the sexual impulse, without
+a doubt it denotes a general preparedness to breed, but there is no
+evidence to show that it denotes the degree of ardour of the male at any
+particular moment, and much that proves the contrary. So that only by
+the female producing some special sound which will attract the males
+that are eager and bring them rapidly to the spot where she happens to
+be, only thus is it possible to insure the consummation of the sexual
+act. This, it seems to me, is the purpose of the peculiar call of the
+female--a call which, so far as biological interpretation is concerned,
+is just as much a song as the melody of the Marsh-Warbler--and its
+interest for us just now lies in this, that here we have a special case
+in which the sexes have separate territories, the female is polyandrous,
+and the voice of the male is not sufficient by itself to bring to pass
+the union of the sexes; and in which, consequently, if the purpose of
+song be that of recognition, we should expect to find, as we do find,
+that the female had a distinct and penetrating call.
+
+We now come to the question of "warning," by no means the least
+important purpose of song. I pointed out that one of the chief
+differences between the call-notes and the song was that the former were
+socially serviceable, whereas the latter was only serviceable to certain
+individuals; and in making this statement, I had in mind the direct
+benefits to the community which proceeded from an appreciation of sounds
+having a mutually beneficial meaning, not the indirect, though none the
+less beneficial, consequences to the species as a whole. Biologically
+considered, song, if it acts as a warning and thereby leads in one way
+or another to more complete success in the rearing of offspring, may be
+spoken of as socially serviceable; but it is legitimate to draw a
+distinction between the prospective value of remote relationships which
+we can foresee, and the mutual assistance which the individuals of a
+community derive from their close association.
+
+If there were always sufficient breeding ground to support the offspring
+of all the individuals of each species, if the individuals were always
+so distributed that there was no possibility of overcrowding in any
+particular area, and if the conditions of existence of different
+species were so widely divergent that the presence of this one in no way
+affected the interests of that, no opportunity would be afforded for the
+development of so complex a system as is involved in the "territory" and
+all that appertains to it. But the available breeding ground is by no
+means unlimited. The supply of food, which is a determining factor in
+the environment, is always fluctuating according to the climate and
+according to the changes in the earth's surface; and so the distribution
+of the bird population in any given area, though it may be suitably
+adjusted for one year or even for a period of years, is bound in the
+course of time to require readjustment. Now there cannot be readjustment
+without competition, nor competition without combat. But the appeal to
+physical force is only a means to an end, and, since no male can endure
+incessant warfare and the perpetual strain of always being on the alert,
+without experiencing such physical exhaustion as might affect his power
+of reproduction, its direct effect upon the combatants cannot be
+otherwise than harmful--in fact it is a necessary evil which for the
+good of the species must be kept strictly within bounds. Bearing in
+mind, then, these two facts, namely that the distribution of the males
+is never stable and that overmuch fighting may defeat the end in view,
+we can appreciate the importance of any factor which will lead to a more
+uniform distribution and at the same time insure security by peaceable
+means.
+
+The proximate end of the male's behaviour is isolation--how is it to be
+obtained? If, after having occupied a territory, the bird were to remain
+silent, it would run the risk of being approached by rivals; if, on the
+other hand, it were merely to utter the recognition call of the species,
+it would but attract them. In neither case would the end in view be
+furthered, and isolation would solely depend upon alertness and the
+capacity to eject intruders. Supposing, however, that the song, just as
+it serves to attract the females, serves to repel other males, a new
+element is introduced deserving of recognition; for those males that had
+established themselves would not only be spared the necessity of many a
+conflict, but they would be spared also the necessity of constant
+watchfulness, and so, being free to pursue their normal routine--to seek
+food, to rest, and, if migrants, to recover from the fatigue of the
+journey, they would be better fitted to withstand the strain of
+reproduction; and those that were still seeking isolation in an
+appropriate environment, instead of settling first here and then there
+only to find themselves forestalled, would avoid and pass by positions
+that were occupied, establishing themselves without loss of time in
+those that were vacant. Without the aid of something beyond mere
+physical encounter to regulate dispersal, it is difficult to imagine how
+in the short time at disposal anything approaching uniformity of
+distribution could be obtained. Hence, both in the direction of limiting
+combat, of insuring accommodation for the maximum number of pairs in the
+minimum area, and of conserving energy, the song, by conveying a
+warning, plays an important part in the whole scheme.
+
+And if this be so, if the song repels instead of attracting, it follows
+that the more distinct the sounds, the less likelihood will there be of
+confusion; for supposing that different species were to develop similar
+songs, whole areas might be left without their complement of pairs just
+because this male mistook the voice of that, and avoided it when there
+was no necessity for doing so. So that just as from the point of view of
+"recognition" each female must be able to distinguish the voice of its
+own kind, so likewise the warning can only be adequate providing that
+the sounds are specifically distinct. A point, however, arises here in
+regard to closely related forms. Some species require similar food and
+live under similar conditions of existence; they meet in competition and
+fight with one another; and, if they did not do so, the food-supply of a
+given area would be inadequate to support the offspring of all the pairs
+inhabiting that area. Generally speaking, the more closely related the
+forms happen to be, the more severe the competition tends to become; and
+it may be argued that in such cases a similar song would contribute to
+more effective distribution and in some measure provide against the
+necessity of physical encounter; that, in fact, it would stand in like
+relation to the success of all the individuals concerned, as does the
+song to the individuals of the same species. But we must bear in mind
+that the primary purpose of song is to direct the females to those males
+that are in a position to breed; and to risk the possibility of prompt
+recognition in order that the males of closely related species should
+fight the less, would be to sacrifice that which is indispensable for a
+more remote and less important advantage.
+
+What meaning does the song convey to a male that is unestablished? Does
+the bird recognise that it is forestalled; does it foresee and fear the
+possibility of a conflict, and conclude that the attempt to settle is
+not worth while? I do not imagine that it thinks about it at all. How
+then does the warning warn? We will endeavour to answer this question,
+but, in order to do so, we must review the stages by which a territory
+is secured.
+
+We take as our starting point the internal organic changes which are
+known to occur. These changes are correlated with other changes,
+manifested by a conspicuous alteration in behaviour--to wit, the
+disappearance of sociability and its replacement by isolation. Having
+found a station which meets the requirements of its racial
+characteristics, the male establishes itself for a season, becomes
+vociferous, displays hostility towards others of its kind, and in due
+course is discovered by a female. The whole is thus an inter-related
+whole, a chain of activities which follow one another in ordered
+sequence. Now we have seen that it is neither pugnacious nor vociferous
+until the territory is actually occupied; we have seen that the fact of
+occupation is the condition under which the instincts of pugnacity and
+of song are rendered susceptible to appropriate stimulation; we have
+discussed the nature of the stimulus in each case, and we wish to know
+the sort of meaning that the song conveys to an individual which is
+still in the preliminary stage of seeking a station. In sequential order
+we have the following: (1) internal organic changes which lead to
+isolation, (2) the appropriate environment which gives rise to an
+impulse to remain in it, (3) the occupation of a territory which is the
+condition under which the instincts are rendered susceptible to
+stimulation, (4) the various stimuli. Each is dependent upon that which
+precedes it, and no part can be subtracted without failure of the
+biological end in view, neither can the different stages be combined in
+different order. So that, in considering the significance of song to an
+unestablished male, we are dealing with the situation at a point at
+which all the latent activities have not been fully felt, for all that
+so far has occurred is the change from sociability to isolation
+determined by internal organic changes. The bird has not established a
+territory because it has not come into contact with the appropriate
+environment, and it is not pugnacious because the condition which
+renders its instinct susceptible is absent; and so, as it wanders from
+place to place and hears the voices of males here or males there, it
+merely behaves in accordance with that part of its nature which
+predominates just at that particular moment--the impulse to avoid them.
+
+But given the appropriate environment, given, that is to say, just that
+combination of circumstances which might bring into functional activity
+all the latent instincts of the intruder, and no matter how vociferous
+the occupant of a territory might be, it would not be preserved from
+molestation. The advantage of the song, biologically considered, is then
+this, that it will often prove just sufficient to preclude males in
+search of isolation from coming into contact with the environmental
+conditions adequate to supply the stimulus to their latent activities
+and to convert them into rivals.
+
+If this interpretation be correct, if we are right in attributing the
+withdrawal solely to the fact that the first stage only in the
+relational series has been reached, it follows that the effect of song
+upon males that have reached subsequent stages in that series must be of
+a very different kind. We have dealt with the male when in the
+preliminary stage of seeking isolation, we must deal with it now when
+eventually it occupies a territory. How does it behave when it hears, as
+it is bound to do, the voices of rivals in its neighbourhood? You may
+remember that some allusion was made to the fact that an outburst of
+song from one individual was followed, not unfrequently, by a similar
+outburst on the part of other individuals in the immediate locality. For
+example, silence may reign in the reed-bed except for an occasional note
+of the Reed-Warbler or Sedge-Warbler. Suddenly, however, a dispute
+arises between two individuals, accompanied by a violent outburst of
+song, and forthwith other males in the vicinity begin to sing excitedly
+and continue doing so for some minutes in a strangely vigorous manner,
+the tumult of voices affording a striking contrast to the previous
+silence. Spasmodic outbursts of this kind, stimulated by an isolated
+utterance, are by no means uncommon. But not only does song stimulate
+song; under certain conditions it has the still more remarkable effect
+of arousing hostility. The boundary that separates two adjoining
+territories is by no means a definite line, but rather a fluid area
+wandered over by this owner at one moment, by that at another. Now so
+long as the bird is silent while in this area, the probability is that
+it will escape detection and remain unmolested; let it however sing--it
+often does so--and it will not merely be approached but attacked, and
+consequently this area is the scene of much strife. The point to be
+noticed here is that the song brings about no withdrawal; it elicits a
+response, attracts instead of repelling, and, in short, arouses the
+impulse that is always predominant in the nature of the male when
+eventually it occupies a territory--the impulse of self-assertiveness.
+Therefore it seems clear that the different stages in the process of
+reproduction mark the appearance of different conditions, each of which
+renders some new impulse susceptible to stimulation, and that the
+significance of song depends upon the stage which happens to have been
+reached. Hence when we speak of song acting as a "warning," we do not
+mean that it arouses any sensation of fear; it is but a stimulus to
+that part of the inherited nature of the hearer which predominates at
+the moment.
+
+Are we then justified in the use of such terms as "warning,"
+"significance," or even "meaning," when it is but a matter of stimulus
+and response? In what does the impulse to avoid other males consist?
+There is no reason to suppose that there is any sensation of fear in the
+first stage, and the course of behaviour demonstrates that there is none
+in the later stages. But it is difficult to conceive of an impulse which
+has, as its end, the isolation of the individual from members of its own
+sex and kind, without some feeling-tone, the reverse of pleasurable,
+entering into the situation; just as it is difficult to believe that the
+female experiences no pleasurable sensation when she hears the voice of
+the male that directs her search. So that the song may be actually
+repellent in the one case and attractive in the other; and it is none
+the less repellent when, as in the later stages, it attracts a
+neighbouring male, for the attraction is then of a different order,
+determined by the presence of the condition which renders the pugnacious
+nature susceptible and leads to attack. In a sense, therefore, we can
+speak of "meaning"--though not perhaps of "significance"--and of
+"warning," when we refer to the prospective value of the behaviour.
+
+So much for the purpose of "song"; there still remains the more
+difficult question--the question of origin. Let me make clear what I
+mean by origin. As we have already seen, there is infinite diversity in
+the sexual voice of different species; some are harsh and others
+monotonous, and some strike the imagination by their novelty whilst
+others are melodious; and to the naturalist each, in its particular way
+and in a particular degree, probably makes some appeal according to the
+associations that it arouses. But just why a Marsh-Warbler is gifted
+with a voice that is so beautiful and varied, whilst the
+Grasshopper-Warbler must perforce remain content with a monotonous
+trill; just why the tail feathers of the Snipe have developed into an
+instrument, whilst the Pied Woodpecker has developed muscles which
+enable it to make use of a decayed branch as an instrument--we know no
+more than we do of the nature of the forces which lead the Reed-Warbler
+to weave its nest to reeds, or the caterpillar of the Elephant Hawk Moth
+to assume so peculiar an attitude when disturbed. When therefore I speak
+of the origin, I do not refer to the mode of origin of variation; I take
+for granted that variations somehow arise, and I seek to ascertain
+whether there is anything in the phenomena which we have explored which
+might reasonably be held to determine the survival of this one in
+preference to that.
+
+When we reflect upon the problem of song and consider the numerous and
+diverse forms in which it is manifested, we are apt to draw a
+comparison between the sounds we hear and those produced by musical
+instruments, and hence to conclude that each bird is gifted with a
+special instrument in virtue of which it produces its characteristic
+melody. But there is a very remarkable phenomenon connected with the
+singing of birds which shows that this is really not the case--I mean
+the phenomenon of imitation. There are plenty of good imitators amongst
+our native species, and the power of imitation is not the exclusive
+property of those which have reached a high degree of vocal development,
+nor, for the matter of that, of song-birds at all. Even the Jay, than
+which few birds have a more raucous voice, that "hoots" like the
+Wood-Owl, or copies the sounds produced by the tail feathers of the
+Snipe, will occasionally imitate the most melodious strains of some
+other species; and the Red-backed Shrike, whose sexual call is
+principally a few harsh notes rapidly repeated, bursts at times into
+perfect imitations of the song of the Swallow, Linnet, or Chaffinch.
+Nevertheless it is amongst such typical songsters as the Warblers that
+we find the greatest volume of imitation, and no limit seems to be
+placed upon their capacity. The Marsh-Warbler can utter the call of the
+Green Woodpecker, or sing as the Nightingale does, with as much facility
+as it sings its own song; and the Blackcap is well-nigh as proficient in
+copying the cries and melodies of surrounding species--and so, if it
+were necessary, we might proceed to add to the list.
+
+These examples demonstrate that different songs are not represented by
+a corresponding number of different physiological contrivances; for if
+the difference were really attributable to some structural peculiarity,
+then the range of sounds embraced in the call-notes and the sexual call
+of any given species, must be the measure of the capacity of its
+instrument; and no matter how great its power of imitation may be, it
+follows that it will only be capable of copying those sounds which fall
+within that range. There is plenty of evidence to show that the power of
+imitation is almost unlimited, at all events that it is not confined
+within such narrow limits as are here demanded. Hence it seems clear
+that the diversity of song is not to be sought in structure, but in some
+innate capacity to play one tune in preference to another; and if this
+be so, and if out of the same instrument, which has been primarily
+evolved to further the biological end of intercommunication, all manner
+of diverse sounds can be made to proceed, the problem of the origin of
+song is to that extent simplified.
+
+We must next inquire into the nature of song, and endeavour to ascertain
+whether all the individuals of a species are alike proficient, or,
+failing this, whether there is any quality which can be observed to be
+constant under all conditions. I watch the Reed-Buntings in a marsh and
+find that there are three males occupying adjoining territories. Two of
+them are fully mature and their plumage is bright: that is to say the
+crown is black, the collar and breast are white, the flanks are dull
+white spotted with black, and the mantle is reddish-brown. The third is
+immature: the crown, instead of being black, is suffused with brown; the
+collar, instead of being white, is mottled with brown; and the flanks
+are more heavily streaked with brown. These three birds take up their
+positions in February, and, as is their wont, sing incessantly each day
+at daybreak. The song of the first two is normal, including the usual
+number of phrases which flow in no definite sequence, but are combined
+and recombined in different order, and the tone is pure; that of the
+third, the immature bird, is, however, very different; for just as in
+comparison its plumage is dull, so the phrases of its song are limited
+and reiterated with great monotony, the tone is impure, and the whole
+performance is dull and to our ears unmusical. I watch them from
+February to June, and observe the order in which they are mated--first a
+mature male; next, after a short interval, the immature male; and
+finally, after a still longer interval, the remaining bird gets a mate.
+As the season advances, still keeping watch on the development of the
+plumage and of the voice of the immature male, I observe that no very
+definite change takes place--that the colours remain dull, that there is
+a conspicuous absence in the song of certain phrases, and that the notes
+lack purity of tone.
+
+If now, instead of Reed-Buntings in a marsh, I watch Yellow Buntings on
+a furze-covered common, I find that, establishing themselves early in
+February, they sing persistently, and in a few weeks are paired. But
+what arrests my attention more particularly is the quality of the song;
+for although the voice is unmistakably the voice of the Yellow Bunting,
+yet it is incomplete and lacks the variety of phrases and musical
+notation which we customarily associate with the bird. Nevertheless, as
+the season advances, there is a progressive development in both these
+directions, and by the end of March or the beginning of April the song
+possesses all those qualities which appeal to us so forcibly.
+
+There is one other fact to which attention must be drawn--the variation
+in the song of the same species in different districts. As an
+illustration let us take the case of the Chaffinch. In Worcestershire
+the bird sings what I imagine to be a normal song--the notes are clear
+and the phrases are distinct and combined in numerous ways. With the
+notes fresh in mind I leave them and go to the west of Donegal, where I
+am at once conscious of a difference; not a subtle difference that
+perplexes the mind and is difficult to trace, but a change so remarkable
+that one is conscious of a passing doubt as to whether after all the
+voice is the voice of the Chaffinch; the song is pitched in a lower key,
+certain phrases are absent, the notes lack tone and are sometimes even
+harsh, and the bird seems wholly incapable of reaching the higher notes
+to which I am accustomed.
+
+Now the immature Reed-Bunting, though to our ears its song is but a poor
+representation of that of the adult, gains a mate; the Yellow Bunting
+pairs, and the discharge of the sexual function may even have taken
+place before its voice attains what we judge to be its full development;
+and there are no grounds for supposing that the Donegal Chaffinch, with
+its less musical notes, has on that account any the less chance of
+procreating its kind--facts which demonstrate that the biological value
+of song is neither to be sought in the purity of tone, nor in the
+variety and combination of phrases, nor, indeed, in any of those
+qualities by which the human voice gains or loses merit, and which leave
+us with no alternative but to dismiss from our minds all æsthetic
+considerations in the attempt to estimate its true significance.
+
+What, then, determines its value? Are there any qualities which, whether
+the bird is mature or immature, whether it is untrained or has acquired
+fuller expression by practice, whether it inhabits this district or
+that, are alike constant? Well, no matter how great the variation, no
+matter how much this voice falls below or exceeds the standard, judged
+from the human standpoint, attained by that, even we, with our duller
+perception, have no difficulty in recognising the species to which the
+owner of the voice belongs; in other words, the song is always specific,
+and this is the most noticeable, as it is the most remarkable,
+characteristic.
+
+There is still, however, another quality to which I would draw
+attention--that of loudness. The sounds produced are on the whole alike
+penetrative, and the individuals of any given district, even though the
+climate by affecting their vocal muscles may have modified the character
+of the song, are at no disadvantage in this respect; neither are the
+females on the same account the less likely to hear the undeveloped
+voice of the immature male.
+
+We have then the following considerations: firstly, there is the
+widespread and remarkable phenomenon of imitation, from which we can
+infer that the diversity of song is not due to structural differences
+but must be sought in some innate capacity to play one tune in
+preference to another; secondly, not all the individuals of the same
+species play a similar tune--we find that there is in certain directions
+a noticeable variation which nevertheless does not seem to affect the
+question of success or failure in the attainment of reproduction; in the
+third place, in contrast with this variation, we can observe a striking
+uniformity in two important particulars, namely in the specific
+character and penetrative power of the song--qualities which we know are
+essential for the purposes of "recognition" and "warning"; and finally,
+from the general course of our investigation, we can infer that if a
+male had no certain means of advertising its position, the territory
+would not be brought into useful relation in its life. Have we here
+sufficient ground on which to construct a theory of origin; in other
+words, has the evolution of song been incidental to, and contributory
+to, the evolution of the territory?
+
+We have all along spoken of the song and of the call-notes as if they
+were manifestations of separate emotional states having their respective
+and well-defined spheres of usefulness; and while, speaking generally,
+this is a true statement of the case, there is much evidence to show
+that the relationship between them is nevertheless very close. There
+are, for example, quite a number of cases in which a particular
+call-note is uttered with unusual energy during sexual emotion, and is
+attached to the song, of which it may be said to form a part; but a
+still closer connection can be traced in many simple melodies which are
+merely compositions of social and family calls repeated many times in
+succession, and even in some of the more complex productions there will
+be found indications of a similar construction. And since this is so,
+since moreover, in the seasonal vocal development of such a bird as the
+Yellow Bunting, we can observe the gradual elaboration from simple to
+complex--from the repetition of single notes to phrases and from phrases
+to the complete melody--we have every reason to suppose that it is along
+these lines that the evolution of the voice has proceeded.
+
+In all probability there was a time when vocal expression was limited
+to primitive social and family cries which would be called into play
+with special force during times of excitement, more particularly during
+the sexual season which is the period of maximum emotional excitement.
+But the excitement would express itself in all the congenital modes of
+behaviour peculiar to the season, and thus the repetition of these cries
+would become associated with combat, with extravagant feats of flight,
+and with other forms of motor response. Now the more emotional
+individuals would be the more pugnacious, and all the more likely
+therefore to secure territory and so to procreate their kind; and, being
+of an excitable disposition, they would at the same time be the more
+vociferous. Hence variations of the hereditary tendency to vocal
+expression, even though in themselves they were not of survival value,
+would be fostered and preserved, so long as they were not harmful, in
+virtue of their association with pugnacity. But if, instead of being
+neutral, they helped to further the biological end of combat, the
+relationship between the voice and pugnacity would be of a mutually
+beneficial kind; and those individuals in which variation in both
+directions happened to coincide, would have a better chance of success
+in the attainment of reproduction.
+
+A territorial system, closely corresponding to that which we have
+discussed, forms part of the life behaviour of certain mammals, and of
+its existence much lower in the scale of life evidence is not wanting;
+from which we can infer that it is not of recent origin, but that the
+conditions in the external environment demanded such a system at a
+remote period of avian development. Now even in its incipient stages the
+system must have involved a separation of the sexes, and howsoever
+slight the degree of separation may have been in comparison with that
+which can be observed to-day, inasmuch as the power of locomotion was
+then less highly developed, mating could only have proceeded
+satisfactorily providing that males fit to breed had some adequate means
+of disclosing their positions. Thus there is reason to think that from
+the very commencement of the process variations of emotional disposition
+expressed through the voice would have been of survival value.
+
+But expressed in what direction, in loudness and persistency of
+utterance, these are the qualities which, I imagine, would have been
+more likely to have facilitated the search of the female? Yet if she
+were uncertain as to the owner of the voice, neither loudness nor
+persistent repetition would avail much; and as species multiplied and
+the competition for the means of living became increasingly severe, so
+the necessity of a territory would have become intensified, and so, too,
+with the extension of range, would the separation of the sexes have been
+an ever-widening one; and as with their multiplication, irregularities
+and delays in mating, arising from the similarity of the calls, would
+have increased in frequency, so a distinctive call, which would have
+tended to minimise these risks, would have come to possess biological
+value.
+
+Here we have a theory of origin, but origin of what? Of certain
+characteristics of song--nothing more; and therefore to suppose that it
+furnishes a complete explanation, which satisfies all the requirements
+of scientific logic, of so wonderful an intonation as that, for example,
+of the Marsh-Warbler, or that no other relationships, except that of the
+territory, enter into the total emotional complex, simplifying here or
+elaborating there to meet the exigencies of diverse circumstances--to
+suppose this would be foolish. That there are many relationships which
+even to-day are leading to modifications in important particulars, but
+which at the present time are beyond our cognisance, of this there can
+be no doubt.
+
+There is one process by which song may have attained a fuller
+development, and which would account in some measure for the
+elaboration, inexplicable merely in terms of "recognition." It is this:
+the effect of the sexual call upon the female cannot well be neutral, it
+must be either pleasurable or the reverse--it must, that is to say, be
+accompanied by some suggestiveness, and by suggestion I mean the
+arousing of some emotion akin to that of the male; and if there are
+degrees of suggestiveness, which well there may be, some males will mate
+sooner than others and some will remain mateless--this is the theory of
+sexual selection. The question to be decided here is whether the
+biological emphasis is on loudness, or specific distinctness, or pitch,
+or modulation, or the manner in which the phrases are combined--that is,
+on some qualities in preference to others--or whether the emphasis is on
+the whole. We have already seen, and it is well known, that there is
+much variation in the voices of different individuals of the same
+species, and thus the first condition of the theory is fulfilled. Now
+the conditions which lead to variation are threefold--immaturity,
+seasonal sexual development, and isolation. Of the three, the variation
+in the case of the immature bird is the most instructive; the tone is
+not so pure, the combination of phrases is incomplete, and elaboration
+is imperfect, and yet, notwithstanding all these imperfections, we can
+observe that the bird pairs as readily as does the adult. But even if we
+lacked this demonstrative evidence, we should still be justified in
+assuming that such must be the case, for we know from experience in the
+preservation of game, where there is no surer way of reducing the stock
+than by leaving too high a percentage of old cocks, that for the young
+bird to be at any disadvantage in competition with the adult is
+detrimental, if not disastrous, to the species. So that while there is
+plenty of evidence of variation in those particular qualities which
+appeal to our æsthetic faculties, there is at the same time evidence
+which demonstrates that such variations exercise no influence on the
+course of mating; and inasmuch as it is difficult to conceive of any
+voice departing more from the normal type in these particular qualities
+than the immature does from the adult, if there be degrees of
+suggestive influence, we must seek it in some other direction. There
+remain the two other characteristics which we found to be constant under
+all circumstances, namely, loudness and specific distinctness; and if,
+in addition to serving the purpose of disclosing the positions of the
+males, they serve to evoke some emotion in the female, which helps to
+further the biological end of mating, so much the more reason is there
+for their survival.
+
+There can be no question that this ingenious and attractive theory, if
+it were true in its special application to song, would immensely
+simplify interpretation, and moreover that preferential mating would
+contribute not a little to the success of the whole territorial system.
+No one can deny the strength of the argument: that the sexual instinct,
+like all other instincts, must require a stimulus of an appropriate
+kind; that the effect of the sexual call upon the female cannot be
+neutral; and hence the probability that stimulation varies too; no one,
+I say, can question the strength of this evidence, and, one might add,
+of the evidence derived from the analogy of the human voice. But when we
+have said this, we have said all; and our acceptance of the hypothesis,
+so far as song is concerned, must remain provisional so long as the
+evidence remains but secondary evidence.
+
+
+
+
+CHAPTER V
+
+THE RELATION OF THE TERRITORY TO THE SYSTEM OF REPRODUCTION
+
+
+In the first two chapters I tried to show that the inherited nature of
+the male leads it to remain in a definite place at a definite season and
+to become intolerant of the approach of members of its own sex, and that
+a result is thus attained which the word "territory" in some measure
+describes. But the use of this word is nevertheless open to criticism,
+for it denotes a human end upon which the highest faculties have been
+brought to bear, and consequently we have to be on our guard lest our
+conception of the "territory" should tend to soar upwards into regions
+which require a level of mental development not attained by the bird. It
+is necessary to bear this in mind now we have come to consider the
+meaning of the territory, or rather the position that it occupies in the
+whole scheme of reproduction.
+
+Relationship to a territory within the interrelated whole of a bird's
+life serves more than one purpose, and not always the same purpose in
+the case of every species. We have only to glance at the life-histories
+of divergent forms to see that the territory has been gradually adjusted
+to suit their respective needs--limited in size here, expanded there, to
+meet new conditions as they arose. Now some may think that the theory
+would be more likely to be true if the territory had but one purpose to
+fulfil, and that one the same for every species; and they may see
+nothing but weakness in the multiplication of ways in which I shall
+suggest it may be serviceable. But such an objection, if it were raised,
+would arise from a mistaken conception, a conception which, instead of
+starting with a relationship and working up to the "territory," sees in
+the "territory" something of the bird's own selection and thence works
+back to its origin. Holding the view that it is nothing but a term in a
+complex relationship which has gradually become interwoven in the
+history of the individual, I see no reason why the fact of its serving a
+double or a treble purpose should not be a stronger argument for its
+survival. I now propose to examine the various ways in which the
+territory may have been of use in furthering the life of the individual,
+and the circumstances in the inorganic world which have helped to
+determine its survival.
+
+The purpose that it serves depends largely upon the conditions in the
+external environment--the climate, the supply of food, the supply of
+breeding-stations, and the presence of enemies. Hence its purpose varies
+with varying conditions of existence. But before we proceed to examine
+the particular ways in which it has been modified to suit the needs of
+particular classes of species, and the reason for such modifications, we
+must inquire whether there is not some way in which it has been
+serviceable alike to every species, or at least to a large majority of
+them.
+
+Success in the attainment of reproduction depends upon the successful
+discharge of the sexual function; and the discharge of the sexual
+function depends primarily upon an individual of one sex coming into
+contact with one of the opposite sex at the appropriate season and when
+its appropriate organic condition arises. Now the power of locomotion is
+so highly developed in birds that it may seem unreasonable to suppose
+that males and females would have any difficulty in meeting when their
+inherited nature required that they should do so, still less reasonable
+to suggest that this power might even act as a hindrance to successful
+mating. Nevertheless, if we try to picture to ourselves the conditions
+which would obtain if the movements of both sexes were in no wise
+controlled, and mating were solely dependent upon fortuitous gatherings,
+we shall come, I fancy, to no other conclusion than that much loss of
+valuable time and needless waste of energy would often be incurred in
+the search, and that many an individual would fail to breed just because
+its wanderings took it into districts in which, at the time, there
+happened to be too many of this sex or too few of that. And as the power
+of locomotion increased and the distribution of the sexes became more
+and more irregular, so the opportunity would be afforded for the
+development of any variation which would have tended to facilitate the
+process of pairing, and by so doing have conferred upon the individuals
+possessing it, some slight advantage over their fellows.
+
+What would have been the most likely direction for variation to have
+taken? Any restriction upon the freedom of movement of both sexes would
+only have added to the difficulties of mating; but if restriction had
+been imposed upon one sex, whilst the other had been left free to
+wander, some order would have been introduced into the process. That the
+territory serves to restrict the movements of the males and to
+distribute them uniformly throughout all suitable localities, there can
+be no question; and since the instinctive behaviour in relation to it is
+timed to appear at a very early stage in the seasonal sexual process,
+the males are in a position to receive mates before the impulse to mate
+begins to assert itself in the female.
+
+We will take the Ruff as an example. According to Mr. Edmund Selous,
+pairing, in this species, is promiscuous--the Ruffs are polygamous, the
+Reeves polyandrous. Suppose, then, that upon this island of some few
+miles in circumference, whereon his investigations were made, the
+movements of neither Ruff nor Reeve were subject to control, that the
+birds wandered in all directions, and that the union of the sexes were
+fortuitous, would the result have been satisfactory? We must remember
+that the Reeve requires more than one Ruff to satisfy her sexual
+instinct; we must also bear in mind the possibility that the functioning
+of her instinct may be subject to some periodicity, and we ask whether,
+under these circumstances, accidental gatherings would meet all the
+requirements of the situation. Now, manifestly, she must be in a
+position to find males when her appropriate organic condition arises.
+But in the absence of any system in the distribution of the sexes, how
+could delay be avoided, or how could a uniform discharge of the sexual
+function be assured? There is, however, a system. In the first place,
+there are the assembly grounds to which the birds repair season after
+season; and then, on the assembly grounds, there are the territories,
+represented, as Mr. Selous tells us, by depressions where the grass by
+long use has been worn away, and each depression is owned by one
+particular Ruff. The assembly grounds have the effect of splitting up
+and scattering the birds, and the number of Ruffs at any one particular
+meeting place is limited by the territories; with the result that Ruffs
+fit to breed are evenly distributed and always to be found in certain
+definite places, and the Reeves know by experience where to find them.
+
+The advantage of this territorial system is therefore apparent. Instead
+of this district being overcrowded and that one deserted; instead of
+there being too many of one sex here and too few of the other sex there;
+instead of a high percentage of individuals failing to procreate their
+kind, just because circumstances over which they have no control prevent
+their discovering one another at the appropriate time--each sex has its
+allotted part to play, each district has its allotted number of
+inhabitants, and the waste of energy and the loss of time incurred in
+the process of mating is reduced to a minimum.
+
+Let us return again to the question of fortuitous mating, and consider
+the position of a male and female that have discovered one another by
+accident and have paired; what will be the subsequent course of their
+behaviour? We are assuming, of course, that a territory forms no part of
+their life-history. If the discharge of the sexual function takes place
+immediately and the ovaries of the female are in an advanced state of
+seasonal development, the construction of the nest will proceed without
+delay--and the nest will answer the same purpose as the territory in so
+far as it serves to restrict the movements of the birds and tends to
+make them remain in, or return to, its vicinity; but if not, there will
+be an interval during which both sexes will continue to wander as
+before, guided only by the scarcity or abundance of food. In the first
+case, there will be the attraction of the nest to prevent any untimely
+separation; in the second, there will be nothing in the external
+environment to induce them to remain in any particular spot. Now if we
+turn to any common species and observe the sequence of events in the
+life of different pairs, we shall find that pairing is seldom followed
+by an immediate attempt to build; that an interval of inactivity is the
+rule rather than the exception, and that this interval varies in
+different species, in different individuals, and in different seasons.
+Our imaginary male and female will therefore be faced with considerable
+difficulty; for with nothing in the external environment to attract them
+and with no restriction imposed upon the direction or extent of their
+flight, their union will continue to be, as it began by being,
+fortuitous. Next, let us consider their position were a disposition to
+establish a territory to form part of the inherited nature of the male.
+Each one will then be free to seek food when and where it wills and to
+associate with other individuals without the risk of permanent
+separation from its mate; and, no matter how long an interval may elapse
+between mating and nest-building, each one will be in a position to find
+the other when the appropriate moment for doing so arrives. Hence, while
+preserving freedom of movement for each individual, the territory will
+render their future, as a pair, secure.
+
+No doubt the course of behaviour, as we observe it to-day in the lives
+of many species, is the outcome of, rather than the condition which has
+led to, the evolution of the territory. Thus, in many cases, we find
+that early mating is the rule rather than the exception; we find that
+the sexes frequently separate to seek their food, and fly away
+temporarily in different directions; and, under exceptional climatic
+conditions, we find that they even revert to their winter routine and
+form flocks; only, however, to return to their territories, as pairs,
+under more congenial conditions. Yellow Buntings, for example, pair
+comparatively early in the season--some in the latter part of February,
+others in March, and others again in April; and some build their nests
+in April, others in May. There is a gorse-covered common which I have in
+mind, a favourite breeding resort of this species. Between this common
+and the surrounding country, the birds constantly pass to and fro. If
+you watch a particular male you will observe that it sings for a while
+in its territory, that it then rises in the air and disappears from
+view, and finally that it returns to the tree, bush, or mound which
+constitutes its headquarters, where it again sings. Meanwhile the
+female, with which there is every reason to believe that this male has
+paired, behaves similarly; she, too, flies to the surrounding country
+and in time returns with equal certainty. Sometimes male and female
+accompany one another--that is, they leave simultaneously and likewise
+return; at other times, though they depart together, the male returns
+alone; or the male may disappear in one direction whilst the female does
+so in another--and, on the whole, there is a sameness in the direction
+of flight taken by the same pairs on different occasions. An interval of
+nearly two months may thus elapse between mating and nest-building,
+during which the sexes are not only often apart but often separated by a
+considerable distance.
+
+What does this species gain by the individuals belonging to it mating so
+early in the season? If the appropriate condition which leads the
+females to seek males were to arise in each individual at a late date,
+the first stage in the process--mating--would not be completed before
+the second--the discharge of the sexual function--were due to begin.
+Thus, instead of having ample time, the females would have but a short
+period in which to discover males; and this in some cases might lead to
+delay, in others to failure, and in others again to needlessly severe
+competition, entailing physical exhaustion at a critical moment in
+their lives. Hence those females in which the appropriate organic
+condition developed early in the season would not only be more likely to
+find males, but would be in a position to rear more broods than those in
+which it developed late; and they would have a better chance of leaving
+offspring, which, in their turn, would reproduce the peculiarities of
+their parents. Moreover, within certain limitations, the more these
+successful females varied in the date of their development, the less
+severe would be the competition, and the more uniformly successful would
+the mating of all the individuals in a given district tend to become.
+But all of this renders an interval of sexual inactivity unavoidable; an
+interval which must constitute a danger unless there were something in
+the external environment to prevent the male and female from drifting
+apart. Inasmuch, then, as the occupation of a territory serves to remove
+all possibility of permanent separation, I suggest that its evolution
+has afforded the condition under which this beneficial procedure has
+developed--free to mate when they will, free to seek food where they
+will, free to pursue their normal routine of existence, and to meet all
+exigencies as they arise in their ordinary daily life--whilst free to do
+this, their future, as a pair, is nevertheless secure.
+
+Thus far we have considered the territory in its relation to the
+discharge of the sexual function. In many of the lower forms of life,
+the success or the failure of reproduction, so far as the individual is
+concerned, may be said to end with the completion of the sexual act--the
+female has but to deposit her eggs in a suitable environment and then
+her work is done, because in due course and under normal conditions of
+temperature the young hatch out, and from the first are able to fend for
+themselves. And so, when we come to consider the question of
+reproduction in the higher forms of life, we are apt to focus attention
+too much upon the sexual function and too little upon the contributory
+factors, the failure of any one of which would mean failure of the
+whole. For a bird, success in the attainment of reproduction does not
+merely imply the successful discharge of the sexual function; much more
+is demanded; it must find somewhere to build its nest and to lay its
+eggs, it must shield its young from extremes of temperature and protect
+them from enemies, and it must be in a position to supply them with food
+at regular intervals. And, consequently, every situation is not equally
+favourable for rearing young; there must be a plentiful supply of food
+of the right kind in the immediate vicinity of the nest, and it must be
+in greatest abundance just at the moment when it is most urgently
+needed--that is to say, during the first few weeks after the birth of
+the young. Success, therefore, depends upon manifold relationships which
+centre in the station, and these relationships vary in intensity with
+the conditions of existence.
+
+First, then, let us examine the problem from the point of view of the
+food-supply. There are many species whose success in rearing offspring
+is largely dependent upon the rapidity with which they can obtain food;
+and it makes but little difference which species we choose out of
+many--Finch, Bunting, Warbler, or Chat. I shall choose the Buntings, as
+their life-history in broad outline conforms to the general type, and,
+moreover, their behaviour is fresh in my mind. The young are born in a
+very helpless state; they are without covering--fragile organisms,
+ill-fitted, one would think, to withstand extremes of temperature, and
+wholly incapable of protecting themselves from enemies of any
+description. For the first three days after they are hatched the female
+spends much of her time in brooding them, and, when she is thus
+occupied, the male sometimes brings food to her, which she proceeds to
+distribute or swallows. But all the young cannot be fed, neither are
+they ready to be fed, at the same moment; and the parents have besides
+to find food for themselves, and the nest has to be cleaned--all of
+which necessitates the young being exposed to the elements at frequent
+intervals. Now it is impossible to observe the instinctive routine of
+the parents, when the young need attention, without being impressed with
+the conative aspect of their behaviour. Why, we ask, are the movements
+of the female so brisk; why does she seek food and clean the nest so
+hurriedly; why, if her instinctive routine is interrupted, do her
+actions and her attitude betray such bewilderment? I take it that the
+only answer we can give to these questions is that the part of her
+inherited nature which predominates just at this particular time is to
+brood. But why is brooding of such importance? Partly to maintain the
+young at the proper temperature, and thereby to induce sleep--and sleep
+for offspring newly hatched is as important as food--and partly to
+protect them from the risk of exposure to extremes of temperature. This
+latter danger is no imaginary one. Examine a young bird that has
+recently left the egg; observe its nakedness; and consider what it has
+to withstand--a temperature that may rise to 70° F. or may fall to 40°
+F., the tropical rain of a thunderstorm or the persistent drizzle of
+many hours' duration, the scorching effect of a summer sun or the
+chilling effect of a cold north-easterly wind, and, constantly, the
+sudden change of temperature each time that the parent leaves the nest.
+One marvels that it ever does survive; one marvels at the evolution of a
+constitution sufficiently elastic to withstand such changes. But,
+however much the constitution may give us cause to wonder, it is clear
+that much depends upon the parents. A slight inefficiency of the
+instinctive response which the presence of the young evokes, a little
+slowness in searching for food or sluggishness in returning to the nest,
+might lead to exposure and prove fatal. And, however much is demanded of
+the parents, it is clear that much also depends upon the relationships
+in the external environment; for no matter how sensitive or how well
+attuned the instinctive response of the parent may be, it will avail but
+little in the presence of unfavourable conditions in the environment.
+
+Everything turns upon the question of the effect of exposure. And in
+order to ascertain how far extremes of temperature are injurious, I
+removed the nests of various species containing newly hatched young,
+and, placing them in surroundings that afforded the customary amount of
+protection from the elements, I made a note of the temperature and the
+atmospheric conditions and then observed the condition of the young at
+frequent intervals. Details of these experiments will be found at the
+end of the chapter.
+
+The experiments with the Blackbirds and the Whitethroats gave the most
+interesting results. Both broods of each species were respectively of
+much the same age, yet one brood of Blackbirds survived for five, and
+the other only for two and a half hours, and one brood of Whitethroats
+lived for twelve hours whilst the other succumbed in a little over an
+hour. This difference is rather remarkable; and it seems clear that the
+power of resistance of the young diminishes rapidly when the temperature
+falls below 52° F. It must be borne in mind, however, that the
+conditions under which the experiments were made were, on the whole,
+favourable--the weather was dry, the temperature was not unusually low,
+nor was the wind exceptionally strong or cold; and even in those cases
+in which the young succumbed so rapidly, the atmospheric conditions
+could by no means be regarded as abnormal.
+
+What, then, would happen in an unusually wet or cold breeding season?
+For how long would the young then survive? In the spring and early
+summer of the year 1916, I was fortunate in observing the effect of
+exposure under natural but inclement conditions. I happened to be
+watching the Yellow Buntings on Hartlebury Common--200 acres of Upper
+Soft Red Sandstone, profusely overgrown with cross-leaved heath (_Erica
+tetralix_), ling (_Calluna vulgaris_), and furze (_Ulex_)--in one corner
+of which eight males had established adjoining territories covering some
+fifteen acres of ground. The males obtained mates towards the end of
+March or at the beginning of April; nests were built in the middle of
+May, and the successful pairs hatched out their young in June. On the
+10th June the weather became exceptionally cold, and during the next ten
+days the temperature fell at times to 40° F. during the daytime. Slight
+frosts were registered at night in the district, and the young bracken,
+which covered the Common in places, had the appearance of having been
+scorched and eventually withered away. At the coldest period of this
+cold spell the young were hatched in two of the nests--in the first one
+on the 10th June, and in the second a day or so later; and on the
+morning of the 10th June, having found a suitable position near the
+first nest, I began to watch the movements of the parents, with the
+intention of keeping some record of their behaviour each day so long as
+the young needed attention. An hour passed without their appearing, and
+on examining the young I found that they were cold, feeble, and
+unresponsive, but the female presently arrived and went to the nest.
+Later in the day the young were lively and responded freely when the
+nest was approached, but nevertheless I was impressed with the length of
+time during which the parents were absent; for, judging by the
+experience of previous experiment, there seemed to be every likelihood
+of their losing their offspring in such abnormally cold weather, unless
+they brooded them more persistently. On the 11th June at 5.50 A.M.
+neither parent was to be seen and the young could scarcely be made to
+respond; but shortly afterwards both male and female appeared, and,
+after remaining a few minutes, again disappeared without even
+approaching the nest. At 6.45 A.M. no attempt had been made to brood and
+the young were then so feeble that they were scarcely able to open their
+mouths, and at 6 P.M. one was still alive but the remaining three were
+dead. Yet the parents returned and the female went to the nest; and,
+from a distance of a few feet, I watched her brooding the living and the
+dead. At 5.45 A.M. the following day the remaining young bird had
+succumbed, the temperature then being 49° F.
+
+At the second nest, I was unable to watch the behaviour of the parents
+so closely. On the 15th June the nest contained three young from three
+to four days old, and during the morning of that and the succeeding day
+nothing unusual occurred, with the exception that the period of exposure
+seemed, as in the former case, to be too long. On the 17th June at 3.10
+A.M. the young had collapsed and were stiff, but the parents were in
+their territory and anxious apparently to attend to their brood. At 9.15
+A.M. only two of the young were left in the nest, and though I searched
+amongst the undergrowth and in the gorse bush in which the nest was
+placed, no trace of the third bird was to be found. Of the two remaining
+young, one was alive and responsive but the other was dead, and though
+the female attended assiduously to the sole surviving offspring, yet it
+too had succumbed by the following morning.
+
+In a third territory, there was a nest containing four eggs. These eggs
+were due to hatch at much the same time as those in the two nests just
+referred to, but they failed to do so, and an examination showed that
+they contained well developed but dead chicks.
+
+To what can the death of the young and of the chicks in the eggs be
+attributed? Not to any failure in the instinctive response of the
+females, for they fed their young, they brooded them, they even brooded
+the dead as well as the living, and probably did all that racial
+preparation had fitted them to do. Yet the fact that the young in the
+second nest were lifeless and exposed at 3 A.M. seems to betoken absence
+on the part of the parents during the night, and may be interpreted as a
+failure of the parental instinctive response. Let us return for a moment
+to the experiments. These showed, it will be remembered, that a rise or
+fall in the temperature of but a few degrees was sufficient to make an
+astonishing difference in the length of time that the young were able to
+survive without their parents; that when the temperature reached 58° F.
+the bodies of the young retained their warmth, and that under such
+conditions even a night's exposure had little, if any, effect; so that
+even supposing that the parents were absent during the night, the death
+of the young cannot be said to have been due to a failure of the
+parental instinct, because under normal conditions--and under such has
+their instinctive routine been evolved--their absence would not have
+prejudiced the existence of the offspring. I attribute the collapse of
+the young solely to the exceptional cold that prevailed at just the most
+critical time, and I base this conclusion partly on the experience
+gained from experiment, but mainly on their condition observed at
+different intervals; for during exposure they collapsed rapidly, their
+flesh became cold and their movements sluggish, their response grew
+weak, and gradually they became more and more feeble until they could
+scarcely close their bills after the mandibles had been forced asunder.
+Yet, even after having reached so acute a stage of collapse, the warmth
+from the body of the brooding bird was sufficient to restore them
+temporarily; once more they would become lively and responsive, only,
+however, to revert to the previous condition soon after the parent had
+again abandoned them. Doubtless their power of resistance grew less and
+less during each successive period of exposure.
+
+If the nestling Bunting is to be freed from the risk of exposure, it is
+evident that there must be, in the vicinity of the nest, an adequate
+supply of food upon which the parents can draw liberally. Hence those
+pairs that exercise dominion over the few acres surrounding the nest,
+and are thus able to obtain food rapidly, will stand a better chance of
+rearing their offspring than others which have no certain supply to draw
+upon--and this, I believe, is one of the biological ends for which the
+territory has been evolved. But it must not be supposed that each pair
+finds, or even attempts to find, the whole of the food within its
+territory, or that it is necessary for the theory that it should do so;
+all that is required is that such overcrowding as might lead to
+prolonged absence on the part of the parents and inordinate exposure of
+the young shall be avoided. So that the problem has to be considered not
+merely from the point of view of the individual, but from the larger
+point of view of all the pairs inhabiting a given area.
+
+Now there were eight pairs of Yellow Buntings occupying the one corner
+of Hartlebury Common, and their territories in the aggregate covered
+some fifteen acres. The birds obtained part of their food-supply amongst
+the gorse and in some young scattered oak-trees, and part in an
+adjoining coppice and on the surrounding arable land. But they were not
+the sole occupants of this corner of the Common; other insectivorous
+species had territories there also--amongst which were Whitethroats,
+Grasshopper-Warblers, Willow-Warblers, Whinchats, Stonechats,
+Meadow-Pipits, Tree-Pipits, and Skylarks. Suppose then that there had
+been sixteen pairs of Yellow Buntings instead of eight; that there had
+been other pairs, which assuredly there were, inhabiting the locality;
+that they had also resorted, which assuredly they did, to the coppice
+and arable ground for the purpose of securing food; and that their
+numbers had also been increased in a similar ratio--would a supply of
+food for all have been forthcoming with the necessary regularity and
+promptitude? Well, the parents might have had to travel a little
+farther; but even if they had been compelled to do so, their absence
+would only have been prolonged by so many minutes the more, and under
+normal conditions what harmful result to the offspring could possibly
+have followed? The question for us, however, is not what might have
+occurred under normal conditions, but whether the life behaviour is so
+adjusted as to meet the exigencies of diverse, and in this case of
+abnormal, circumstances. Now the capacity of the young to resist
+exposure diminishes very rapidly when the temperature falls below the
+normal--the danger zone seems to be reached at approximately 52° F., and
+the length of time during which they survive then becomes astonishingly
+short--and moreover the fall in the temperature would tend to decrease
+the supply of insect life upon which they depend, so that if the size of
+the territories had been reduced by one half, and the parents in
+consequence had been compelled to seek their food at a greater distance,
+can it be doubted that the cumulative effect of even a few minutes of
+additional exposure would have been detrimental, if not disastrous, to
+the offspring?
+
+We speak, however, of the parents extending their journeys a little
+farther in this direction or a little farther in that, as though they
+could do so with impunity except in so far as it affected themselves, or
+their offspring, or the other Yellow Buntings inhabiting that particular
+area. But, most certainly, any extension would have meant so much
+encroachment upon the available means of support of other members of the
+species inhabiting adjoining areas, whose young in turn would have been
+liable to have been affected; and, with even greater certainty, the
+Whitethroats, the Stonechats, the Tree-Pipits, and the Willow-Warblers
+that had also established themselves in that one corner of the Common
+would have been hard pressed to find sufficient food with sufficient
+rapidity.
+
+Let me give another illustration of a somewhat different kind. Lapwings,
+as we saw in the previous chapters, establish territories and guard them
+from intrusion with scrupulous care. The young are able to leave the
+nest soon after they are hatched, and consequently the parents are not
+necessarily obliged to bring food _to_ them--they can, if they so
+choose, lead them _to_ the food. Whether each pair limits its search for
+food to its territory, I do not know. But even supposing that all
+ownership of territory were to lapse directly the young were hatched,
+that the boundaries were to cease to exist, and that the birds were free
+to wander at will without fear of molestation, the end for which the
+territory had been evolved would none the less have been obtained; for
+inasmuch as the parents are accompanied by their young, it matters not
+in what part of the meadow they seek their food; all that matters is
+that the number of families shall not exceed the available supply of
+food. So far, then, as the Lapwing is concerned, the territory fulfils
+its purpose when once it limits the number of males, since, by doing so,
+it limits the number of families and prevents undue pressure upon the
+means of support.
+
+Nevertheless, there are many birds that seem to rely entirely upon the
+territory to supply them with all that is necessary. Each Warbler seeks
+its food within the precincts of its own particular domain, and, except
+in occasional instances, neither resorts to neutral ground nor makes
+excursions into the locality immediately surrounding the territory, as
+does the Bunting. Probably it would be disastrous if it attempted to do
+so, for since its young at birth are so delicate and so susceptible to
+changes of temperature, it cannot afford to be absent from them for
+long. Of the two experiments made with young Whitethroats, one was made
+under favourable and the other under unfavourable conditions. In this
+latter case the temperature was 50° F., and the young, it may be
+remembered, only survived for a little over one hour. Now exposure at
+that temperature is evidently dangerous, but it would be still more
+dangerous if the weather were wet instead of dry, and the temperature
+46° F. instead of 50° F.; and it is, I imagine, on this account that the
+impulse to brood is so strongly implanted in the female. No sooner, it
+seems, does she depart than she returns with a small quantity of food
+which she hurriedly distributes and immediately settles down to brood;
+and if forcibly prevented from returning, her attitude betrays symptoms
+of what, humanly speaking, we should term great distress. If, then, the
+conditions in the external environment were such as would make it
+difficult for the female to obtain food rapidly, what advantage would
+she derive from so strongly developed an impulse? Might it not be a
+disadvantage? Might it not mean that she would abandon the search too
+readily and be content to return with an insufficient supply, and might
+not that be as injurious to the young as prolonged exposure? Manifestly
+the impulse to brood could only have developed strength in so far as it
+fitted in with all the other factors that make for survival; and the
+principal factor in the external environment seems to be the territory.
+How could the young have been freed from the risk of exposure if the
+impulse to brood had not been so strongly implanted in the parent? How
+could the impulse to brood have been free to develop if a supply of food
+had not been first insured? How could the supply of food have been
+insured if numbers of the same species had been allowed to breed in
+close proximity?
+
+From the foregoing facts it is clear that the young of many species are
+at birth susceptible to cold and unable to withstand prolonged exposure.
+The parents must therefore be in a position to obtain food rapidly, and
+consequently it is important that there should be an ample supply in the
+vicinity of the nest. This end the territory certainly serves to
+promote; it roughly insures that the bird population of a given area is
+in proportion to the available means of subsistence, and it thus reduces
+the risk of prolonged exposure to which the young are always liable.
+
+
+This leads on to a consideration of those cases in which the question of
+securing food is subordinate to the question of securing a station
+suitable for reproduction.
+
+I take the Guillemot as an example. In principle its behaviour is
+similar to that of the Bunting; the male repairs to a definite place,
+isolates itself, and becomes pugnacious. But the Guillemot is generally
+surrounded by other Guillemots, and the birds are often so densely
+packed along the ledges that there is scarcely standing room, so it
+seems, for all of them. Nevertheless the isolation of the individual is,
+in a sense, just as complete as that of the individual Bunting, for each
+one is just as vigilant in resisting intrusion upon its few square feet
+as the Bunting is in guarding its many square yards, so that the
+evidence seems to show that that part of the inherited nature which is
+the basis of the territory is much the same in both species. What we
+have then to consider is, What is the biological value to the Guillemot
+of an inherited nature which, for the Bunting, has utility in relation
+to the supply of food for the young? Up to a point, the act of securing
+a territory has like value for each respective species, whether the area
+occupied be large or small--that is to say, it enables the one sex to
+discover the other with reasonable promptitude.
+
+For the greater part of the year, Guillemots live at sea; singly, in
+twos or threes, or in small parties, they move upon the face of the
+waters, extending their wanderings far away from land, out into the
+broad ocean, where for weeks together they face the gales and heavy seas
+of the Atlantic. But in due course and in response to internal organic
+changes, they return, like the Warbler, to their breeding grounds--rocky
+headlands or islands appropriately situated and affording the
+appropriate rock formation. During all these months of wandering, the
+majority seem to ignore the land, to pass away from it altogether, and
+to spread themselves over the surface of the ocean regardless of
+mainland or island. Some useful observations, which throw some light on
+the distance that Guillemots are accustomed to wander from land, were
+made by Lieut. B. R. Stewart during a number of voyages between various
+ports in Great Britain and Ireland and ports in North America,
+principally New York and Quebec. Thus, on the 24th March, large numbers
+were seen in lat. 55° N., long. 24° W., five hundred miles approximately
+from land, though on the following day--four hundred miles off Tory
+Island--they were not so plentiful. Again, on the 1st October, in lat.
+53° N., long. 27° W., seven hundred miles or so from land, one bird was
+seen, whilst on the following day, in lat. 52° N., long. 21° W., a
+single individual was washed on board by the heavy seas and seemed
+little the worse for the adventure. Within two hundred miles of the west
+coast of Ireland, he found them plentiful on various occasions. From
+this it is clear that the circumstances under which the bird lives for
+many months in succession must impose a considerable strain upon its
+constitution; and how it is able to withstand the buffeting of wind and
+water, to secure its food, and to endure, is a mystery. It is important,
+therefore, that the young bird should be properly nourished and
+protected from anything that might harm its constitution, and important,
+too, that the parents should be freed from any undue strain during the
+course of reproduction.
+
+The conditions which the breeding station has to fulfil are threefold:
+in the first place, it must be in proximity to the food-supply;
+secondly, it must provide the necessary shelter for the egg and for the
+helpless offspring; and, in the third place, it must be so situated that
+the young can reach the water in safety. We will examine these
+conditions one by one.
+
+The proximity to the food-supply is a consideration of some importance.
+The life of the Guillemot during the winter is a strenuous one; we know
+that large numbers succumb in stormy weather, and we can infer that
+slight constitutional defects might make all the difference between
+failure and success; and, therefore, the less severely the constitution
+of the parent is taxed during reproduction, and the more securely the
+constitution of the offspring is built up, the greater prospect will
+both have of resisting the hardships of the winter successfully. Much,
+then, will depend upon the distance the parents have to travel in order
+to obtain food. The farther the breeding station is removed from the
+feeding ground the greater the physical strain which will be imposed
+upon the birds, and the greater the chance will there be of the
+offspring being improperly nourished. Now the food consists of small
+fish, largely of sand-eels, which are secured in deep water, and the
+abundance of which varies, possibly according to the nature of the
+currents. Hence cliffs which are situated away from the water, or from
+which the water recedes at low tide, or which are surrounded by an area
+of shallow water, and are thus not in proximity to the feeding ground,
+even though they may fulfil the second and third condition, will not
+answer the requirements of a breeding station.
+
+Of no less importance is the type of rock-formation. Not every formation
+affords the necessary ledges upon which the egg can be deposited with
+safety--the face of the cliff may be too smooth, or too jagged, or the
+shelves may run at too acute an angle. Many of the large assemblages of
+Guillemots in the British Islands are found where the rock is quartzite,
+mica-schist, limestone, or chalk. The reason of this is that such rocks
+are weathered along the planes of stratification, of jointing, of
+cleavage, or of foliation--the strata being probably of unequal
+durability--with the result that innumerable shelves, ledges, and
+caverns, which are taken advantage of by the birds, form a network over
+the face of the cliff. But only those ledges can be made use of which
+are placed at a considerable height above the water, because, when the
+cliff faces the open sea, the lower ones are liable to be washed in
+stormy weather by the incoming swell and thus become untenable. There is
+a small cove in the midst of the most precipitous part of the breeding
+station at Horn Head, wherein the shingly shore shelves rapidly to the
+Atlantic and faces to the west. Here, towards the end of July, young
+Kittiwake Gulls can sometimes be found washed up on the beach--some
+living, but in every stage of exhaustion, others dead, and in every
+stage of decomposition; here is the young bird, recently caught by the
+swell and thrown upon the shore, lying side by side with the remains of
+others that had previously succumbed to starvation--on every side
+evidence of the devastation wrought by the Atlantic. May not some of
+this destruction have been brought about by the nests having been placed
+upon the lower ledges within reach of an exceptionally heavy sea? Hence
+much depends upon the nature of the rock-formation, and many a mighty
+precipice, even though it may fulfil the first and third condition, is
+nevertheless valueless as a breeding station.
+
+Finally, the young bird must occupy a ledge from which it can reach the
+water in safety. There is much difference of opinion as to the manner in
+which it leaves the ledge, but all agree that it does so before it is
+capable of sustained flight. If, then, the face of the cliffs were made
+up of a series of broken precipices, or if the rocks at the base
+projected out into the water, or if detached rocks abounded in the
+waters beneath, the mortality amongst the chicks would no doubt be
+considerable.
+
+The coast-line of Co. Donegal will illustrate the foregoing remarks. On
+the southern and western side of the Slieve League promontory there is
+no real Guillemot station; only on the northern side--the quartzite in
+the vicinity of Tormore--are the birds to be found in large numbers.
+Northwards from here, a wild and rugged coast is passed over before
+other stations are reached--at the eastern end of Tory Island and on
+Horn Head; and beyond this, to the east, there are none, not even on the
+old rocks that form the promontory of Inishowen. Why, we ask, do
+countless numbers crowd the ledges of Horn Head, whilst they are absent
+from the precipices of Slieve League; why, too, are they absent from
+the granite cliffs of Owey? The reason is not far to seek. Either the
+face of the cliff is made up of a series of broken precipices, or the
+face of the precipices is too smooth, or the otherwise suitable ledges
+are situated too near the water, or the water recedes from the base of
+the cliff at low tide. Many miles of rock-bound coast are thus useless
+for the purpose of reproduction.
+
+Now when we bear in mind how large an expanse of coast is formed of
+blown sand or of rocks of low altitude, and how many miles of cliff fail
+to supply the three essential conditions that we have been considering,
+we can see that suitable breeding stations must be limited both in
+number and extent. From a wide expanse of ocean hosts of individuals are
+therefore obliged to converge at certain definite points; and hence,
+each recurring season, there must arise a competition for positions at
+the station, just as there is competition between individual Buntings
+for positions in the marsh. And the ability to obtain a position upon a
+suitable ledge involves, in the first place, an impulse to search for
+it; in the second place, an impulse to dwell in it; and in the third
+place, an impulse to resist intrusion upon it. It would be useless for
+an individual to be pugnacious if it had no fixed abode; equally useless
+for it to establish itself on a particular ledge if it had no power to
+defend it--all of which implies an inherited nature similar to that of
+the Bunting. But the proximate end to which the competition is directed
+is not alike in the case of both species. In the case of the Guillemot
+it has reference solely to the piece of rock whereon the egg is laid; in
+the case of the Bunting to a piece of ground capable of furnishing an
+adequate supply of food for the young; and the reason for the difference
+is this, that there is always an abundance of food in the water beneath
+the cliff, but breeding stations are scarce, whereas there is always an
+abundance of situations in the marsh in which the Bunting can place its
+nest, but the supply of food varies and at times can only be obtained
+with difficulty.
+
+If then the Guillemot were to behave after the manner of the Bunting and
+assign to itself a portion of the face of the cliff, or if it were only
+to occupy a few ledges, or an even lesser area--a single ledge--what
+would be the result? That it would attain to reproduction is beyond
+question; that the egg would be safely deposited there can be no manner
+of doubt; neither is there any reason to suppose that the offspring
+would not be successfully reared. But, indirectly, its behaviour would
+affect the Guillemot race. For if it be true, as the crowded ledges
+certainly seem to show, that there is a dearth of suitable breeding
+ground, no greater calamity could befall the species than that some
+members should exercise dominion over too large an area of the habitable
+part of the cliff and thus prevent others from breeding. Under such
+conditions the race could not endure, since in this, as in every case,
+its survival must depend upon a close correspondence between the
+behaviour of the individual and the circumstances in the external
+environment.
+
+Scarcity of suitable cliffs is the principal reason of the ledges being
+so closely packed with Guillemots, just as it accounts for this part of
+the precipice being crowded with Kittiwake Gulls, that part with
+Herring-Gulls, and that part again with Razorbills and Puffins. Yet each
+individual preserves its few square feet of rock or soil from
+molestation, and the area each one occupies varies according to the
+conditions of existence of the species. Thus the Herring-Gull occupies a
+comparatively small area, although one many times larger than that of
+the Guillemot. It requires more space than the latter, owing to the fact
+that it not only builds a nest but rears four instead of a single
+offspring, and it can be allowed this, because, since its young remain
+in the nest until they are capable of sustained flight, it can make use
+of many miles of cliff from which the tide recedes at the base, or which
+have, at their base, rocks jutting out into the sea; but manifestly it
+cannot be allowed so much space as the Bunting.
+
+Martins build in close proximity to one another, owing probably to
+shortage of accommodation, and, in their case, the nests have to be so
+situated as to be sheltered from the wet. If water drips upon them for
+any length of time, the mud, of which they are composed, crumbles and
+large pieces fall away, with the result that the eggs or the young are
+precipitated to the ground. Consequently, not every house or
+perpendicular cliff will answer the purpose of a breeding station. A few
+pairs build their nests beneath the eaves close against the walls of my
+house, and year after year the result is much the same; after every
+downfall of rain, the water collects into rivulets, trickles down over
+the eaves, is absorbed by the mud and destroys the nests. Thereupon, the
+birds set to work and rebuild; but again the nest is destroyed, and
+again they rebuild, and so on throughout the summer, and only on rare
+occasions do they succeed in rearing offspring at the proper season.
+Similar conditions must prevail in many situations; but, clearly, the
+more binding and plastic the building material, the longer the nest will
+withstand the action of the dripping water and the greater chance will
+there be of the young being reared in safety. Observe, therefore, how
+far-reaching an effect so small a detail as the nature of the mud can
+have upon the status of the species in any given locality. Where the
+conditions are favourable, there the birds must congregate to breed,
+and, like the Guillemot, if each individual exercised dominion over too
+large an area, the species as a whole would suffer.
+
+In all these examples, the fact of different individuals being in such
+close proximity may afford some protection from enemies both as regards
+the egg and the offspring, and in so far as there is a mutual advantage
+such assemblages may be spoken of as communities. A community, however,
+in the true sense of the word, is a collection of individuals brought
+together, not primarily as a result of shortage of breeding ground, but
+in consequence of advantages of communal ownership over individual
+ownership. A rookery is an example of a true community. Neither shortage
+of nesting accommodation nor scarcity of food can account for Rooks
+assembling together to breed; for if the different pairs which go to
+make up the rookery were to scatter throughout the surrounding
+neighbourhood, they would, as a rule, find plenty of trees in which to
+build their nests, and plenty of food.
+
+How, then, can the theory apply to a species that breeds under such
+conditions? What part can the territory play in furthering the life of
+the individual when large numbers of nests are built closely together in
+the same tree? There is much evidence to show that mutual protection is
+a necessary condition of the Rook's existence; many cases are on record
+of rookeries being destroyed by Carrion-Crows, Hooded Crows, and Ravens.
+For instance, Mr. Ward Fowler records a case in which a pair of Crows
+attacked a small rookery, ransacked the nests, and destroyed the eggs,
+with the result that not a single pair of Rooks was left in the
+settlement. Each Rook must therefore secure a position within the
+precincts of the community if it is to have a chance of success in the
+attainment of reproduction. But every locality cannot supply sufficient
+trees of the right kind, appropriately situated and in suitable relation
+to the food supply, in which numbers of nests can be built in close
+proximity; so that if more than one community were to attempt to
+establish itself in a limited area, the supply of food or the supply of
+trees might become a pressing problem. Each community must therefore be
+prepared to defend its own interests, and each must be regarded as one
+unit and the area occupied as one territory within which are included a
+number of lesser territories. The individual may fail to establish
+itself within a community, but, even if it succeeds, the community may
+fail to establish the rights of communal ownership; hence it has to face
+a twofold possibility of failure, and if it lacked the inherited nature
+which leads the Guillemot to secure a position upon the ledge, or the
+Bunting to obtain a position in the marsh, the chances are that it would
+fail in the attainment of reproduction.
+
+The question now arises as to how it comes about that the area occupied
+by each individual conforms in broad outline to that which has proved
+beneficial for the welfare of the species as a whole. We shall find that
+up to a point the answer is a simple one. No one could study the
+behaviour of animals without observing the important part that habit
+plays in the life of the individual; an action performed to-day is
+liable to be repeated to-morrow and the following day until it becomes
+ingrained in the life of the individual. This must not be taken to mean,
+however, that a particular action has to be performed for many days in
+succession before it becomes definitely fixed; if only it is repeated a
+number of times, even within the space of a few hours, it will acquire
+sufficient strength for its continuance; but continued repetition gives
+increased fixity, and, as time goes by, it becomes increasingly
+difficult for the creature to make a change unless the character of the
+situation necessitates readjustment.
+
+For example, when the organic condition which leads to nest-building
+becomes active, the bird tentatively collects some of the necessary
+material in its bill, flies round with it, and then drops it. After a
+while it collects some more, and this time leaves it perhaps in a bush.
+Later on it makes another attempt, and, meeting with a situation which
+calls forth the appropriate response, it thereupon lays the foundation
+of the structure. We will assume that the nest is placed in the midst of
+a tangled bush. Well, the bird lays the first strands of the foundation
+and then goes in search of more material. The next time it approaches
+the nest from the opposite side of the bush, and presently it finds yet
+a third entrance. But each entrance is not made use of in turn: one is
+employed more frequently than the other two, and in the course of time
+becomes the sole highway to and from the nest. Suppose now that, when
+the young are hatched, I cut away the foliage from the bush on the
+opposite side from that on which the bird customarily enters, and by so
+doing leave the nest exposed, what is the result? The female arrives
+with food, threads her way through the bush, and, when beside the nest,
+pauses as if aware that some change had taken place, and then flies away
+through the new opening. In a short time she returns, flits from twig to
+twig on the outskirts of the bush, and comes upon the new opening--there
+she hesitates. But though the nest is in full view and within a few
+inches of her perch, and though the young stretch out their necks, yet
+so strong is the former habit that she is compelled to return to the
+opposite side and approach the nest by the usual circuitous route before
+she distributes the food amongst her offspring.
+
+Let us see how far this law of habit formation may have been effective
+in defining the extent of the area occupied. When a male Warbler arrives
+at its destination in the spring it seeks out a suitable environment,
+and, having found a place unoccupied by any other male, settles in it
+and remains there--its behaviour up to this point being determined by
+racial preparation. After the fatigue of the journey its movements are
+at first sluggish; hunger, however, asserts itself and a search is made
+for food; wandering away from the position in which it first settled and
+which acts as a headquarters, it hunts through certain trees here or
+certain bushes there and returns, and presently it wanders away again,
+perhaps in another direction, but, as before, works its way back again
+to the headquarters. The journeys thus radiate outwards from the
+headquarters, and according to the success with which the bird meets,
+so, probably, it happens that some trees are searched more often than
+others and certain directions are taken more frequently than others, and
+by constant repetition a routine is established which limits the
+direction and scope of its wanderings.
+
+But in the case of the Guillemot the conditions of existence are
+reversed: food can be had in abundance but suitable breeding stations
+are scarce. The few square feet of ledge correspond to the tree or clump
+of bushes which acts as a headquarters for the Warbler, and the
+occupation of them is determined, as it is in the case of the Warbler,
+by racial preparation. Since, however, the ledge is only made use of for
+the immediate purpose of incubation and is in no way affected by
+questions relating to food, there is no occasion for the bird to wander
+along the ledge nor to encroach upon those adjoining. Hunger stimulates
+the Warbler to search the surrounding trees, and so to extend its area;
+but hunger takes the Guillemot down to the water, and hence the area
+which it primarily occupied remains unmodified.
+
+To sum up: the territory is useful in various ways, but not necessarily
+in the same way for every species. Reproduction would always have
+remained fortuitous, and the number of individuals that attained to it
+would seldom have reached the possible maximum unless some provision had
+been included in its system for insuring that the males and females
+could meet at the proper moment and afterwards remain in touch with one
+another, and that the number of pairs inhabiting a given area did not
+exceed the available means of support. I have tried to show that the
+inclusion of a disposition to secure a territory tends to remove these
+difficulties. In the first place, the disposition which leads to its
+occupation comes into functional activity (in the male) early in the
+season; and so, by the time that the appropriate pairing condition
+arises in the females, the process of acquiring territories is well
+advanced, and the males being regularly distributed, each in its
+respective position, are readily found by their prospective mates. The
+behaviour of each sex is thus adjusted to further the end of mutual
+discovery. Next, after mating has taken place, the position occupied by
+the male acts as a headquarters to which the birds can always repair,
+and becomes a bond of union which is serviceable in that it prevents any
+possibility of their drifting apart. And in the third place, the males
+become pugnacious and in this way secure for themselves areas which vary
+in size according to the conditions of existence of the species, so that
+there is no possibility of too many congregating in this locality, and
+all the less likelihood of too few finding their way to that; and hence,
+on the average, different pairs are distributed throughout all suitable
+localities. Furthermore, owing to the fact of their having a
+headquarters, the male and female are allowed a freedom of movement
+which otherwise they would only possess when the construction of the
+nest had actually begun; they can seek their food independently, and,
+even though paired, they can if necessary continue their winter routine
+without risk of separation. This means that the organic condition which
+leads to pairing, is free to develop in the female earlier than would be
+the case if there were nothing in the external environment to attract
+the pair to a particular spot; and the longer the period over which the
+process of pairing can be spread, the greater chance will females have
+of discovering mates, the less severe will the competition tend to
+become, and, consequently, the smaller the percentage of individuals
+that fail to obtain suitable partners.
+
+In these ways the territory has been serviceable alike to a number of
+species. But much as the questions of mutual discovery and regular
+distribution may have influenced the course of its development, there
+can, I think, be little doubt that, on the one hand, the supply of the
+necessary accommodation for rearing offspring, and on the other, the
+necessity for an adequate supply of food in close proximity to the nest,
+have been the main determining factors, and have led to a wide
+divergence in its function. At the one extreme the function is to insure
+a plentiful supply of food for the young; at the other, to insure a
+station suitable for rearing offspring. I took the Bunting and the
+Guillemot as types of the two extremes. The young of the former species
+are born in a very helpless state. They are susceptible to cold and
+unable to withstand prolonged exposure, and therefore it is essential
+that there should be an ample supply of food, upon which the parents can
+draw liberally, in the vicinity of the nest. But the nest is placed in a
+variety of situations, and accommodation in this respect may be said to
+be unlimited. The young of the latter species are not so susceptible to
+exposure, and moreover there is always an abundance of food in the
+waters beneath the cliff; but ledges of rock, upon which the egg can be
+securely deposited and the young successfully reared, are limited both
+in number and extent. The position then is as follows: there are
+situations in plenty in which hosts of Buntings can build their nests
+but the supply of food is a difficulty, and if the respective areas of
+different individuals were insufficient to supply them with the
+necessary food with the necessary rapidity, they would run the risk of
+losing their offspring and the species would not endure; on the other
+hand, cliffs upon which the Guillemot can rear its young are limited,
+but the supply of food presents no difficulty, and consequently the
+smaller the area over which each individual exercises dominion, the
+greater the number that will attain to reproduction and the greater
+prospect the species will have of survival. The emphasis in the one case
+lies on the fact that the area occupied must be sufficiently large; on
+the other, on its being just sufficient and no more to accommodate the
+egg. Hence the difference in the function at the opposite extremes is
+brought about, not by modifications of the instinctive behaviour which
+leads to the establishment and defence of the territory, but solely by
+modifications in the size of the area occupied, in accordance with the
+conditions prevailing in the external environment. No doubt, if we had
+the life-histories of a sufficient number of species worked out, we
+should find that the gradations were complete from the one extreme to
+the other. We are justified in thinking that this must be so because in
+many directions we can not only observe differences in the size of the
+area occupied, but can recognise a close correspondence between those
+differences and the conditions of life of the species. Thus the
+Herring-Gull occupies a comparatively small area, though one which is
+many times larger than that of the Guillemot. It requires more space
+because it not only builds a nest but rears four instead of a single
+offspring, and it can be allowed more space because the young remain in
+the nest until they are capable of sustained flight, and consequently it
+can make use of many miles of cliff from which the tide recedes at the
+base, and which on this account are denied to the Guillemot, but
+manifestly it cannot be allowed so much space as the Bunting, for then
+comparatively few individuals would attain to reproduction.
+
+Again, the Reed-Warbler inhabits swamps overgrown with the common reed,
+and in such places insect life is abundant just at the time when the
+young are hatched. But these swamps cover a comparatively small acreage
+in the breeding range of the bird, and if each pair were to attempt to
+establish dominion over an area equal, let us say, to that of the
+Willow-Warbler, the species would have but a poor chance in the struggle
+for existence. So that, in a case of this description, the supply of
+food and the comparative scarcity of breeding stations have been factors
+of like importance in the evolution of the territory.
+
+Finally we were led to inquire as to how it comes about that the extent
+of the area occupied by each individual is adapted to the circumstances
+in which the individual finds itself; and we came to the conclusion that
+the movements of the bird, subsequent to the initial act of establishing
+itself in a position, are regulated and defined by the law of habit
+formation. For example, the Warbler, in response to its inherited
+nature, takes up a position in an appropriate situation. It then
+proceeds to search for food; it makes short journeys first in this
+direction and then in that; it repeats these journeys, and gradually
+forms a habit which compels it to remain within more or less
+well-defined boundaries. But the actual distance that it traverses on
+the occasion of its first attempt must be determined by the relative
+abundance or scarcity of the particular kind of insect life which it
+requires. So that, although habit defines and in some measure helps to
+determine the boundaries of the territory, it is clear that in the last
+resort they must depend upon the nature of the conditions in the
+external environment.
+
+We have, then, the congenital basis which leads to the occupation of a
+position, and to the enmity shown by the owner of the position towards
+other individuals; and this congenital basis is found alike in many
+widely divergent forms, living under equally widely divergent
+conditions; we have acquired accommodation; and we have relationships in
+the organic and inorganic world--and the outcome of it all is a system
+of behaviour which we, who can perceive the end to which such behaviour
+is tending, are justified in speaking of as "a disposition to secure a
+territory." In the development of this system a primary value must be
+ascribed to the conditions in the external environment, for they
+determine the direction of the variations of instinctive procedure and
+of acquired habit which work towards the same goal--that of adjustment
+to the conditions of life.
+
+
+
+
+NOTE
+
+
+The following are the experiments referred to on page 181:--
+
+
+On the 14th May 1915, a nest of Blackbirds approximately four days old
+was removed at 6.45 A.M. The temperature was considerably below the
+normal, and snow lay on all the high ground in the neighbourhood. In a
+short time the birds collapsed, and at 9.15 A.M. were dead. On the 29th
+May, at 6 A.M., a second nest was removed, containing young of
+approximately the same age, and although the conditions were more
+normal, the temperature being 50° F., the birds collapsed at 8 A.M., and
+an hour later one of the brood showed little signs of life. The wind,
+however, then changed to the west, and the temperature rose one degree,
+with the result that they were still living at 11 A.M. A further
+experiment was made with Song-Thrushes on the 5th June. The wind was in
+the south and the temperature 63° F. The young, approximately four days
+old, were removed at 7.25 A.M., but as they showed no signs of collapse
+at 1 P.M. I replaced the nest in the original site.
+
+
+On the 30th May, a nest of Whitethroats three days old was removed at
+7.15 A.M. The wind was northerly and the weather fine, but the
+temperature low--50° F. At 8.15 A.M. the birds showed no sign of life. A
+second experiment with this species was made on the 10th June under more
+favourable circumstances, for although the sky was overcast and the wind
+northerly, the temperature was 59° F. In this case the young survived
+from 6.55 A.M. to 7 P.M.
+
+
+On the 27th May 1915, a nest of Hedge-Sparrows hatched the previous day
+was removed at 7 A.M. The temperature was below the normal, being 49° F.
+At 8 A.M. the young were cold and in a state of collapse, but they
+survived nevertheless until 3.20 P.M.
+
+
+On the 7th June 1915, a nest of young Skylarks three days old was
+removed at 7.15 A.M. The temperature was 62° F., and the birds survived
+until 4 A.M. the next day.
+
+
+On the 6th June 1916, a nest of Linnets just hatched was removed at 6.47
+A.M. The temperature was 51° F. At 7.50 A.M. the birds were cold and in
+a state of collapse, and only survived until 8.50 A.M.
+
+
+
+
+CHAPTER VI
+
+THE WARFARE BETWEEN DIFFERENT SPECIES AND ITS RELATION TO THE TERRITORY
+
+
+We have now considered the various ways in which the territory is useful
+in furthering the life of the individual. We have seen that, in some
+cases, there is competition for stations where the egg or eggs can be
+deposited and incubated in safety; that, in others, there is competition
+for stations capable of furnishing an adequate supply of food for the
+young; and that the establishment of "territories" not only renders the
+attainment of reproduction for the individual secure, but serves so to
+regulate the distribution of pairs that the maximum number can be
+accommodated in the minimum area. This being so, the question arises as
+to whether competition for territory is strictly limited to individuals
+of the same species, or whether it may not occur also between different
+kinds of birds, providing always that similar conditions of existence
+are required. First of all I shall relate a number of facts which will
+serve to show the nature and extent of the warfare, and I shall then
+give the reasons which lead me to believe that the fighting not only
+bears some relation to the "territory," but that it is an important
+factor in contributing to the attainment of that which for biological
+interpretation is the end for which the whole territorial system has
+been evolved.
+
+Those who have studied wild life on one of the rocky headlands, which
+are so numerous round our coasts, will probably be familiar with the
+rivalry that exists between the Raven and certain birds of prey. Where
+the Raven finds shelter for its nest, there, too, the Peregrine has its
+eyrie--and so it happens that these two species are continually at war.
+Now the warfare occurs not only during the season of reproduction but
+continues throughout the greater part of the year, and can even be
+observed in the late summer or early autumn--the period when we should
+expect to find the instinct least susceptible to appropriate
+stimulation. But it is of a more determined kind early in the spring,
+and it is then that we often witness those remarkable exhibitions of
+flight, the skill of which excites our admiration. The Falcon rises
+above the Raven, stoops at it, and when it seems no longer possible for
+a collision to be avoided, or, one would imagine, for the Raven to
+escape destruction, the Raven skilfully turns upon its back and
+momentarily faces its opponent, and the Falcon with equal skill changes
+its course, passing upwards and away. The attack, however, is soon
+repeated, and though no collision may actually take place, yet the fact
+that the Raven, when it turns to face its adversary, is obliged to drop
+the stick which it carries, is not only an indication of the character
+of the struggle, but it shows that a definite end is gained--that the
+efforts of the Raven to build in that particular locality are hampered.
+But the Falcon is not the only enemy that the Raven has to face;
+Buzzards are just as intolerant of the presence of Ravens in their
+neighbourhood as the Ravens are of them, and consequently there is
+incessant quarrelling wherever the same locality is inhabited. As a
+rule, the fighting occurs whilst the birds are on the wing; the Buzzard
+rises to a considerable height, and, closing its wings, stoops at the
+Raven below, and when within a short distance of its adversary, swerves
+upwards and gains a position from which it can again attack. The
+Buzzard, however, is by no means always the aggressor; I have watched
+one so persistently harassed by a Raven that at length it left the rock
+upon which it was resting and disappeared from view, still followed by
+its rival. Thus it seems as if they were evenly matched, and, when they
+occupy the same locality, it is interesting to notice how the initiative
+passes from the one to the other according to the position occupied by
+the birds in their respective territories.
+
+[Illustration: Peregrine Falcon attacking a Raven
+
+Emery Walker ph.sc.]
+
+That there is constant warfare between the Green Woodpecker and the
+Starling is well known, the purpose of the Starling being to gain
+possession of the hole which the Woodpecker with much skill has drilled
+for itself. As far as my experience goes, the Starling is always the
+aggressor, and there is only too good reason to fear that, in the course
+of time, the Green Woodpecker will disappear as a result of the greater
+fertility and tenacity of its enemy. The Martin suffers a similar kind
+of persecution from the House-Sparrow, and here again there is reason to
+believe that the greater virility of the Sparrow will hasten the
+extinction of its rival. In cases of this description the purpose of the
+fighting is clear, and one can understand why such divergent species
+should be hostile to one another; yet others, equally remote in the
+scale of nature, are hostile when no such ostensible reason can be
+assigned for their hostility. Few birds are more pugnacious than the
+Moor-Hen, and the determined manner in which different individuals fight
+with one another is notorious. But the intolerance it displays towards
+other species is no less remarkable, and its pugnacious instinct seems
+to be peculiarly susceptible to stimulation by different individuals
+belonging to widely divergent forms. At one moment a Lapwing may be
+attacked, at another a Thrush or a Starling, harmless strangers that
+have approached the pool to drink; even a Water-Rail, as it threads its
+way through the rushes, may fail to escape detection; and, which is
+still more curious, a covey of Partridges will evoke response if they
+approach the pool too closely.
+
+Here is a curious instance of apparent waste of energy. A pair of
+Magpies built their nest in an ilex tree. Early one morning there was a
+commotion in the tree, much flapping of wings and a medley of sounds
+which told of large birds engaged in a struggle--the Magpies were
+attacking a pair of Wood-Pigeons. There was no question as to the
+genuineness of the struggle, nor any doubt as to the proximate end for
+which the Magpies were striving, for their efforts continued so long as
+the Wood-Pigeons remained in the tree, and only ceased when they had
+succeeded in driving them away.
+
+Turning next to species which are less distantly related, we find that
+instances of intolerance are more numerous and that a wider range of
+species is involved. The hostility that the Lapwing displays towards the
+Snipe calls for special remark. It often happens that the marshes or
+water meadows, that are such favourite haunts of the Lapwing, are also
+resorted to by Snipe for the purpose of securing food, or it may be even
+for the purpose of reproduction. In such places both species are often
+abundant; the meadow is divided up into Lapwings' territories, and early
+in the season the Snipe wander over it in small parties, singly, or in
+pairs. Now, if it were only on isolated occasions that the Lapwing paid
+heed to the Snipe, one would not perhaps attach any peculiar
+significance to the fact; but the pugnacious instinct of the bird
+responds to the presence of this intruder almost as freely as it does to
+that of another Lapwing. Again and again, day after day, the Snipe are
+attacked and driven off in a manner which would be fittingly described
+as persistent persecution, for the Snipe has neither the physical
+capacity nor apparently any instinctive tendency to retaliate. Thus a
+Lapwing may come suddenly upon a small party of Snipe hidden from view
+in a dyke where they are probing the ground for food; the Snipe
+immediately rise and fly away and there is momentary confusion as the
+Lapwing darts first at this one, then at that; or, espying a Snipe at
+rest at the opposite end of its territory, it will first of all run
+rapidly towards it, and then fly after it, as, with twisting flight, it
+darts hither and thither a few feet above the ground; or again, it will
+attack and rapidly pursue solitary individuals as they skim across its
+territory and attempt to settle. Is this intolerance merely an exuberant
+expression of an instinct which is serviceable in another direction? The
+behaviour of the Lapwing scarcely justifies such a conclusion, for all
+its actions denote a striving towards some end which we can describe,
+and it seems to gain satisfaction only when the ejection of the intruder
+has been accomplished.
+
+Many of the Warblers display irritation when approached by other birds
+which we should scarcely expect would arouse their hostility. The
+Hedge-Sparrow, for example, is frequently regarded with suspicion, and
+it is by no means unusual to see it attacked by so small a bird as the
+Chiffchaff. The Wood-Warbler is also pugnacious, and will even attack a
+pair of Chaffinches. Between the Tit family and some of the smaller
+Warblers there are constant exhibitions of hostility; even the Great Tit
+is liable to be driven away, but the Blue Tit is especially marked out
+for persecution, though doubtless it is well able to hold its own.
+
+The following incident will show how real is the antagonism between
+these two families. A Chiffchaff occupied the corner of a small osier
+bed, and was particularly aggressive towards other closely-related forms
+in its immediate neighbourhood. On two mornings in succession ten Blue
+Tits invaded its ground, passing from end to end of it as they wended
+their way from tree to tree in search of food. Their presence evoked the
+usual hostile response, yet, withal, aroused the fear of the Chiffchaff,
+which, at times, appeared to be swayed by conflicting impulses. Now, in
+attempting to interpret the nature of the instinct which was evoked, one
+has to be guided, in a case of this description, by the similarity of
+the response to that which can be observed on other occasions and in
+other situations when the intention of the bird is clear. And on this
+occasion the Chiffchaff betrayed all the symptoms which normally precede
+an attack; it spread its tail, quivered its wings, uttered its
+high-pitched note rapidly, hopped from twig to twig, or flew restlessly
+from tree to tree, and seemed to be prevented from attacking only by the
+number of its opponents. This, indeed, was shown by its subsequent
+behaviour, for whenever a Tit became temporarily detached from its
+companions it hesitated no longer but forthwith attacked.
+
+There are other species which are no less aggressive than the
+Warblers--the Chats for example. The Stonechat regards with suspicion
+almost any bird of its own size, and will even pursue a Tree-Pipit if it
+approaches too closely. The same is true of the Whinchat, and one would
+scarcely expect to find this bird attacking Buntings as it sometimes
+does. A Whinchat that occupied some marshy ground was constantly at war
+with a pair of Reed-Buntings; their territories were adjacent and in
+some measure overlapped, and the Whinchat drove away either sex
+indiscriminately, and was not only always the aggressor but seemed to
+be master of the situation.
+
+Coming now to kindred forms, those, that is to say, which belong to the
+same family, we find that, both in intensity and extent, the warfare far
+exceeds anything that we have thus far considered. So frequent, indeed,
+are acts of intolerance, and so readily awakened into activity is the
+pugnacious nature of the bird, that the fighting will almost bear
+comparison in volume with that which occurs between individuals of the
+same species. Between the Thrush and the Blackbird there are incessant
+quarrels early in the year, and the initiative seems to pass from one
+to the other according to the circumstances in which they are placed. If
+the territory of a Thrush is invaded the Thrush is the aggressor, and,
+conversely, if that of the Blackbird is threatened, the Blackbird
+becomes the aggressor; and so, when the territories of the two birds are
+adjacent or overlap, as frequently they do, there is constant friction,
+resulting in quarrels which attract attention on account of the
+noisiness of the birds.
+
+All the Warblers are exceedingly pugnacious, the fighting being
+especially severe between those that are very closely related. The
+Blackcap and the Garden-Warbler are constant rivals, and the scenes
+which can be witnessed when the two meet in competition are interesting
+from many points of view. The birds not only pursue and fight with one
+another, but their emotional behaviour reaches a high level of
+intensity--excitable outbursts of song are indulged in, tails are
+outspread, wings are slowly flapped, and feathers raised--in fact the
+attitudes assumed are similar in all respects to those which occur
+during the contests which are so frequent between the respective
+individuals of each species; and it would be difficult to point to any
+one item of behaviour which is not also manifest at one time or another
+during the battles between these rivals, and still more difficult to
+trace any difference in the intensity of the excitement. And if we are
+satisfied that the fighting in the one case is purposive, so, too, must
+we regard it as having some biological purpose to serve in the other.
+But the Garden-Warbler is not the only bird that acts as a stimulus to
+the instinct of the Blackcap; Whitethroats are often attacked, and the
+Chiffchaff is a source of irritation. Even when a male Blackcap is
+engaged in incubation, it will leave its nest on the approach of a
+Chiffchaff, and, having driven away the intruder, proceed to sing
+excitedly. At other times both male and female will combine to attack
+this small intruder.
+
+But this does not mean that the Chiffchaff suffers persecution; it is
+itself most aggressive, as is shown by the fact that it will join in the
+Blackcap quarrels and attack the combatants indiscriminately. Its
+behaviour, however, requires further consideration, especially as
+regards its relations with its nearest of kin--the Willow-Warbler; for
+here we have a mutual intolerance which is somewhat remarkable, and
+evidence of it can be found wherever the birds occupy the same ground.
+Now it can be observed that the hostility is not limited merely to
+occasional acts of intolerance, but that there is organised warfare
+lasting, it may be, for many days in succession, and that the actions of
+the birds bear the stamp of a persistent striving towards some end. On
+one occasion the Willow-Warbler may be the aggressor, on another the
+Chiffchaff, and at times it is difficult to say which of the two is
+responsible for the quarrel. In size and in strength they are equal, and
+the "will to fight" is as strong in the one as in the other, so that it
+is seldom, if ever, possible to point to this one as the victor and that
+one as the vanquished. Success or failure probably depends more upon the
+cumulative effect of many combats entailing physical exhaustion, than
+upon the issue of any one particular battle; and whilst observation
+might quite well fail to distinguish any resultant change in the
+relative positions of the birds, or any harmful effect upon their
+constitutions, yet the area occupied by this one might be sufficiently
+curtailed to prejudice the welfare of the young, or the vitality of that
+one might be seriously impaired--and we should be none the wiser.
+
+Neither the Marsh-Warbler nor the Reed-Warbler will tolerate strangers
+within the small space of ground over which they exercise dominion. Of
+the two, the Marsh-Warbler is perhaps the more pugnacious, and will
+attack any other Warbler that approaches too closely; Whitethroats are
+often pursued and driven away, and less frequently, Garden-Warblers. In
+one case, a male occupied the same ground as a Sedge-Warbler, and there
+was a constant feud between them; a willow-tree formed its headquarters,
+and this same tree seemed to be the headquarters of the Sedge-Warbler,
+so that they often met and whenever they did so they quarrelled. As a
+rule the Marsh-Warbler was the aggressor and had the mastery over its
+opponent, and when it attacked, it uttered a peculiar harsh scolding
+note, raised the feathers on its back, spread out its wings, and
+betrayed the usual symptoms of emotional excitement.
+
+On the other hand, the Sedge-Warbler is most aggressive towards other
+kindred species, and when a male happens to occupy the same ground as a
+Reed-Warbler, there are frequent battles between them and incessant
+commotion; they fly at one another and meet in the air with an audible
+clicking of bills, or pursue one another amongst the reeds, each one
+uttering its characteristic scolding note.
+
+The Tits, as a family, are notoriously pugnacious. I have seen a pair of
+Blue Tits attack a single Long-tailed Tit with great determination, and
+not only did they pursue it, but, flying at it, struck it with
+considerable force.
+
+In giving an account of the domestic economy of the Carrion-Crow, Mr.
+Edmund Selous refers to the hostility between this bird and the Magpie.
+"About a week ago," he says,[6] "I saw a Crow busily engaged in chasing
+away several Magpies, not only from three or four tall slender trees
+close together, in one of which it had its nest, but also from various
+other trees, not far off, round about. In this the Crow had a good deal
+of trouble, as the Magpies were always returning. After a time it was
+joined by another crow, which however did not take so active a part in
+the drama, nor did I see either of the two actually go to the nest,
+though I could only explain their action by supposing it was their own.
+This morning I saw the same thing reversed, for a pair of Magpies, with
+an undoubted nest, kept attacking a Crow that insisted on settling in
+one of a row of trees--also tall and slender--in which it was placed.
+Both were equally persevering--the Crow, though often chased away,
+always returning, and settling generally in the last tree of the row,
+where he would be left alone sometimes for a minute or two, but before
+long one of the Magpies flew at him, and put him to flight. The Crow
+defended itself, but not, it would seem, very successfully, and in the
+last attack upon him, made, with great spirit, in the air, a large black
+feather floated to the ground, which I made no doubt was his. Yet this
+did not drive him from the trees, and it was only on my approaching
+nearer that he finally left them. Thus we see that both species look
+upon the approach of the other to within a moderate distance of their
+nest as an intrusion."
+
+That the Rook suffers persecution from the Carrion-Crow is a
+well-established fact, and there is reason to believe that it has
+another dangerous enemy in the Hooded Crow. According to the late
+Mr. Ussher, Choughs will attack both Hooded Crows and Ravens. "I once
+saw," he says, "two Choughs energetically attacking a pair of Ravens;
+they shot up into the air and darted down on the latter, whose heavy
+flight made them helpless against their agile tormentors."
+
+Birds of prey are often hostile to one another. The Merlin is
+exceptionally pugnacious, and its boldness in attacking intruders is
+well known. When, for example, a Kestrel approaches its territory, it
+leaves the tree, bush, or rock upon which it was resting, utters its
+characteristic cry, and soars rapidly upwards; then, rising to a
+considerable height, it swoops down upon the Kestrel, and by
+alternately stooping at and chasing its opponent, drives it away from
+the immediate neighbourhood.
+
+What we have, then, to consider is, Do these battles between different
+species contribute towards the attainment of the end for which the whole
+territorial system has been evolved?
+
+Let us take the individual and see whether we can establish any relation
+between the hostility it displays towards members of other species and
+its general disposition to secure a territory. We must remember that a
+male can have no knowledge of the prospective value of its behaviour,
+nor is it likely that it has any ulterior purpose in ejecting other
+males, beyond the pleasure it derives from satisfying its impulse to do
+so. The proximate end of its behaviour is to attack, nothing more, and
+this, of course, it can only do just in so far as the intruder evokes
+the appropriate instinct.
+
+Now the arguments we shall employ will, on the whole, be similar to
+those which we made use of in the second chapter, wherein we attempted
+to ascertain the conditions under which a male becomes intolerant of
+other males of its own species, and examined more especially the claims
+of the "territory" as opposed to those of the "female." But here we
+start on firmer ground, because the one factor which introduced an
+element of uncertainty--the female--can be definitely excluded; at least
+it seems so to me, for granting even that her presence is the condition
+under which the pugnacious nature of the male is rendered susceptible to
+stimulation, it is difficult to see why a male of a different species
+should supply that stimulus, or what biological purpose could be served
+by its doing so.
+
+When dealing with the attitude of a male towards others of its kind, we
+attached considerable significance to the fact that its pugnacious
+nature gained or lost susceptibility according to the position which it
+happened to occupy. We found, it will be remembered, that the same bird
+that was pugnacious in its own territory took no further interest in its
+opponent when the boundary was passed; and, moreover, that if it
+happened to wander into an adjoining one, it made no real effort to
+defend itself when attacked, but returned forthwith to its own
+headquarters. It remains to be shown whether the rivalry between
+different kinds of birds is similarly related to the position which the
+opponents happen to occupy at the time.
+
+First, then, there is the general consideration, namely, that the enmity
+occurs for the most part just at the time when the territories are in
+process of being established. During autumn and winter, many birds of
+more or less close affinity assemble together in flocks, wherever the
+supply of food is abundant, and are then not only sociable, but, so
+there is reason to believe, are mutually helpful both in discovering the
+necessary means of subsistence which are often none too plentiful, and
+in affording protection from enemies, which, on the contrary, are often
+numerous. That the different units of which these flocks are composed
+should live on amicable terms is therefore as necessary for the welfare
+of the whole community at this particular season as that the different
+individuals of the same species should do so. But just as the sociable
+relations, which obtain between these individuals throughout the winter,
+undergo a marked change at the commencement of the breeding season, so,
+too, do different species, which habitually associate together, suddenly
+become hostile to one another. This change is coincident in time with
+the rise of the organic condition which leads to the establishment of
+territories; and the hostility continues, though in diminishing degree,
+throughout the breeding season, and dies away the following autumn.
+
+For example, different Warblers resort to the elders (_Sambucus nigra_)
+in September, and there pass much time feeding on the fruit which is
+then ripe and often abundant. In the same bush there may be Blackcaps,
+Garden-Warblers, Whitethroats, and Lesser Whitethroats, some preening
+their feathers, others searching for the berries, others again, with
+feathers relaxed, making feeble attempts to sing. Occasionally there may
+be a scuffle, perhaps between a Blackcap and a Lesser Whitethroat, or
+between a Garden-Warbler and a Blackcap, but it is of short duration and
+lacks vigour. Apart, however, from such temporary disturbances, there is
+no real rupture in their relations, and certainly nothing to lead one to
+suppose that the bickerings are determined by the functioning of any
+specific instinct. Yet only a few months previously some of them were
+constantly at war, and their quarrels betrayed symptoms of great
+persistence; and if we remember how the observed behaviour of the birds
+suggests the fact that they were striving to attain something definite,
+we shall understand the nature and extent of the change, and shall, I
+fancy, be in a better position to estimate its biological worth at its
+true value.
+
+We can find many similar examples--flocks are to be found on arable
+ground, on the water meadows, and on the mud-flats; here different kinds
+of Thrushes feed on the berries of the yew, there different kinds of
+Tits travel together in parties; hosts of Finches collect in the hollies
+to pass the night and Buntings roost together in the gorse; and, in
+fact, in whatever direction we choose to look in the autumn and winter,
+we find various birds assembled together and living on amicable terms.
+All of this changes in the spring, and the relationship undergoes a
+gradual but noticeable alteration; so much so that whereas the
+outstanding feature of bird life in the winter is sociability, that of
+the spring is hostility.
+
+So much, then, for the seasonal change of relationship; let us now turn
+to particular cases and attempt to trace the condition which accompanies
+such change.
+
+Many migrants in the spring seem to follow the course of the Severn
+during their journey northwards through Worcestershire; and where the
+river bends to the north-west at Lincombe Lock, there they leave it, or,
+rather, continue in a north-easterly direction which takes them across
+the southern end of Hartlebury Common. As I have already mentioned, this
+Common is overgrown with gorse, heather, and ling, and scattered here
+and there are a number of dwarf oak-trees and small elder-bushes. The
+situation is therefore an ideal one for the smaller migrants to rest for
+a brief time, and, from the point of view of the observer, very suitable
+because it is open and the movements of the birds can be traced for some
+distance. Turtle Doves pass over at a great height, or skim across a few
+feet above the gorse; Redstarts settle for a few minutes and then
+disappear; Tree-Pipits, Whinchats, and Willow-Warblers pass from tree to
+tree or flit from bush to bush--and all in a north-easterly direction.
+They do not sing, they are restless, and, judging by their behaviour,
+they are anxious to conceal their presence, not to make it known. Yet we
+know that when they reach their destination, as presently they will, all
+this will change; that each of them will employ every means at its
+disposal to make itself conspicuous; and that each, as far as it is
+able, will resist intrusion on the part of other species.
+
+Now the southern end of the Common is always inhabited by individuals
+belonging to one of these species, or to others of close affinity; so
+that wherever these travellers settle whilst passing across it, the
+chances are that they will find the ground occupied--and their behaviour
+under such circumstances is no less interesting than the behaviour of
+the bird upon whose ground they are trespassing. We will take the case
+of the Whinchat. It arrives from the south-west, and, flying from bush
+to bush, works its way in a north-easterly direction. In doing so it
+intrudes upon the territory of a Stonechat; and the Stonechat, becoming
+excited, flies towards it, and it retires for a short distance in the
+direction from whence it came. Here again it is followed and attacked
+and again moves on, and then, flying in a circle as if to avoid the
+territory which blocked the path, resumes its former line of flight,
+though still followed by the Stonechat, which after continuing the
+pursuit for perhaps a quarter of a mile, suddenly turns in the air and
+returns to its headquarters.
+
+It is difficult to put oneself in the place of the Stonechat or of the
+Whinchat. But even after making due allowance for the danger inseparable
+from any attempt to do so, there remains the unquestionable fact that
+whereas the impulse to attack was strong in the one, the impulse to
+defend itself was wholly lacking in the other. Yet a Whinchat, when it
+has established itself, is most pugnacious; it not only attacks every
+bird of a similar size that approaches its position, but its behaviour
+under such circumstances bears the impress of unusual determination; and
+if we were to take a male and place it in the position of the Stonechat,
+we should find that its nature would change, that the presence of the
+Stonechat would evoke a hostile response, and, conversely, that the
+instinct of the Stonechat would not be susceptible to stimulation. Hence
+it is clear that the nature of a bird when on migration is not quite the
+same as it is when its destination is reached; that the positions
+occupied from time to time during the journey carry no meaning, or,
+rather, are not brought into relation with its life in quite the same
+way as is the position which it finally occupies; and further, it is
+clear that the interest it displays in other species undergoes a
+somewhat remarkable transformation when at length its destination is
+reached.
+
+This altered nature of the migrant is a fact of some importance in
+relation to our present subject, but it does not stand alone--the same
+characteristic is observable in other phases of bird life. Some of the
+residents, the Buntings and the Finches for example, occupy their
+breeding ground very early in the year, and it often happens that the
+situations which they select are not capable of supplying them with food
+so early in the season, though at a later date food will be there in
+abundance; so that they are compelled to resort to the surrounding
+neighbourhood, and since, even there, the available supply is sometimes
+scarce or, if plentiful, limited to certain areas, they are constrained
+from time to time to join together again in flocks. Thus, for part of
+the year, they may be said to lead a double existence; for just as the
+Whinchat, that is sociable on migration, betrays a changed nature when
+it reaches its destination, so too does the nature of these residents
+change from hour to hour according to whether they are seeking food or
+occupying the breeding ground.
+
+In the newly-sown fields of grain the birds frequently find a supply of
+food. Here Yellow Buntings, Greenfinches, and Chaffinches collect from
+the surrounding neighbourhood. The majority are somewhere in possession
+of territories, and not a few are paired. Between the territories and
+the feeding ground a highway is formed by individuals passing to and
+fro. Sometimes both members of the pair leave together in order to seek
+food, at other times they separate and the male may be in his territory
+whilst the female is with the flock. Apart from occasional
+manifestations of sexual emotion on the part of a male, there is nothing
+to disturb the harmony of the flock nor anything in the behaviour of the
+birds which would lead one to suspect that, when they return, their
+nature will change and that they will be no longer sociable; and, which
+is still more remarkable, no matter how great the provocation which an
+individual, when in company with the flock, may be called upon to
+endure, its customary hostile response will fail to be elicited. An
+incident which happened in the spring of 1917 will serve to make this
+clear. A flock of some thirty Yellow Buntings, Greenfinches, and
+Chaffinches were feeding in one corner of a field which had recently
+been sown with barley. As they sought their food they wandered outwards
+into the middle of the field, and in so doing, passed across the
+territory of a Skylark. Whereupon the Skylark became excited, uttered
+its call-note rapidly, and rising a few feet from the ground, attacked
+those members of the flock that were nearest, which happened to be the
+Yellow Buntings; and so determined were its onslaughts that the Yellow
+Buntings were forced to retire. The Skylark showed no discrimination as
+to sex, but attacked both males and females, and within a few minutes
+succeeded in driving away at least two pairs. One would have expected
+that the Yellow Buntings would have made some show of resistance; one
+would have thought that the fact of being violently attacked would have
+supplied a stimulus sufficiently strong to evoke a corresponding hostile
+response: yet there was no mistaking the lack of interest that they
+displayed in the contest--they made no effort to retaliate but seemed to
+accept the situation as unalterable and left.
+
+So far we have examined only those cases in which the pugnacious
+instinct was stimulated in one of the adversaries, and in which
+consequently the fighting seldom reached any high degree of severity. We
+must now consider some others in which each of the opponents acts as a
+stimulus to the pugnacious instinct of the other. It is here, of course,
+that we find the most violently contested battles, and it is here, too,
+that the purpose of the fighting seems clear. The persecution which the
+Green Woodpecker suffers from the Starling is well known. The purpose of
+the Starling's behaviour is clear, namely the possession of the hole
+occupied by the Woodpecker. Bird for bird, the Woodpecker is more than
+the equal of the Starling, but persistent endeavour ultimately wins the
+day. The Starlings perch close beside the hole, and, whenever the
+Woodpecker shows itself, attack with determination; and not only do they
+do so but they are assisted, so there is reason to believe, by other
+individuals or pairs in the attainment of their end, so that no matter
+how stoutly the Woodpecker defends itself, in time it is almost certain
+to be deprived of its ownership.
+
+In like manner different kinds of Woodpeckers contend with one another
+for the possession of a hole, and here the opponents are more equally
+matched. I have seen a pair of Lesser Spotted Woodpeckers endeavouring
+to drive away a Great Spotted Woodpecker. The excitement of all three
+birds was exceptional. Each of the Lesser Spotted Woodpeckers kept
+swooping in turn at their rival, sometimes in the air and sometimes when
+it was settled on the topmost branches of a dead tree, and the sounds
+produced reminded one of the piping of a flock of Oyster-Catchers in
+flight.
+
+A battle between a pair of Green Woodpeckers and a Great Spotted
+Woodpecker is worth mentioning. It occurred on the 24th of April.
+Passing through the middle of a wood, I noticed a Great Spotted
+Woodpecker fly out of a hole in an oak-tree. Shortly afterwards, a pair
+of Green Woodpeckers settled near the hole and then flew to some
+oak-trees close at hand, where they were joined by their rival and signs
+of hostility were soon apparent. Presently the Great Spotted Woodpecker
+returned to the hole and entered. Both of the Green Woodpeckers then
+flew into the tree; and one of them, settling upon the trunk, climbed
+up to the level of the hole and, when it became aware of the Great
+Spotted Woodpecker within, extended its wings fully and proceeded to
+peck viciously at its opponent. Whereupon there was a scuffle at the
+mouth of the hole and the Great Spotted Woodpecker hurriedly left. After
+this, all was quiet and the Green Woodpecker eventually descended and
+entered the hole. The Great Spotted Woodpecker, however, returned again,
+but, after fluttering around the hole, disappeared, leaving the Green
+Woodpeckers in possession.
+
+In this varied field of hostile behaviour which we have explored, one
+feature stands out prominently, namely, that the interest which a bird
+displays in other species varies not only at different seasons but even
+from hour to hour. I have used the word "nature" as equivalent to
+"interest," and I have spoken of the bird's nature changing or altering
+according to the circumstances in which it was placed. But its nature is
+its inborn constitution, and its constitution cannot change from day to
+day, still less from hour to hour. So that, in a sense, and having
+regard to strict scientific accuracy, it is misleading in this
+particular connotation to say that the bird's nature changes.
+
+[Illustration: H. Gronvold dcl. Emery Walker ph.sc.
+
+A battle between a pair of Green Woodpeckers and a pair of Great
+Spotted Woodpeckers for the possession of a hole in an oak tree.]
+
+What then does happen? The instinct of pugnacity must form just as much
+a part of the hereditary make-up of the migrant, when on migration, as
+when finally it reaches its destination; still more must it form part of
+the constitution of the Bunting when it leaves its headquarters
+temporarily and joins the flock. And, if it is there, the question
+arises as to why it does not respond. Now every instinct requires for
+its response a stimulus of an appropriate kind, and, therefore, a
+reasonable view to take would be that the necessary stimulus was
+lacking. But this is a view which we cannot uphold, because on all these
+occasions an opposing male was present--and, so far as it is possible to
+judge by observation, that is the stimulus which in the main evokes a
+hostile response. We must therefore look elsewhere than in its
+direction for a reason which will adequately explain the behaviour.
+
+Though it be true that every instinct requires for its functioning a
+stimulus of an appropriate kind, yet it is also true that the condition
+which will render it responsive must be present. What we have then to
+consider is whether the phenomena which we have explored give us any
+clue as to the particular nature of that condition. In the first place,
+we have the general fact that the hostility is not confined to a few
+species belonging to a few families, but that it is of wide
+application--birds of prey, Warblers, Woodpeckers, all supply us with
+evidence which serves to show, in greater or less degree, its nature and
+extent. Next, we found that the hostility was peculiar to a certain
+season--and that one the season of reproduction. And if the question
+were asked: What condition would then be most likely to render the
+instinct susceptible, the answer that would most certainly be given
+would be--the presence of a female. And in reply to a further question
+as to the particular nature of the stimulus to which the instinct would
+respond, we should be told--the presence of another male of the same
+species. Now the possible influence of the female on the course of the
+male's behaviour was the subject of inquiry in the second chapter,
+wherein we endeavoured to explain the hostility between males of the
+same species, and we came to the conclusion that it was not alone
+sufficient to account for the facts disclosed. Still less likely,
+therefore, is it that her presence can bear any direct relation to the
+hostility between different species, the more so since the biological
+end of securing a mate is definitely excluded. And we have something in
+the nature of proof of the correctness of this view in the fact that she
+accompanies her mate when he joins the flock, and that there his
+instinct is not susceptible to stimulation. We then proceeded to examine
+certain cases in which all the indications pointed to the fact that the
+"will to fight" was present in only one of the opponents; and we
+attached considerable importance to this circumstance, because we knew
+from experience that the same bird which seemed to lack courage, could
+at other times and in other situations be most aggressive. If then we
+ask what condition was present on the one occasion that was absent on
+the other, we have no difficulty in finding a reply--on every occasion
+on which the opponents appeared to be unevenly matched, one was in
+occupation of a territory and the other was not. And if we inquire
+further as to which of the two was the aggressor, the answer is again
+clear, namely, the bird that occupied a territory. Finally we considered
+some particular instances in which the "will to fight" was present alike
+in both opponents, and in which the battles were protracted and severe.
+
+But the fact that a bird has established a territory is not in itself
+sufficient to render its hostile nature susceptible; it must be actually
+in occupation if a response is to be elicited. We reach this conclusion
+step by step: the behaviour of the migrant, that lacks the "will to
+fight" when on migration but is pugnacious when it has secured a
+territory, shows it; the behaviour of the resident, which temporarily
+joins the flock and is there sociable, shows it; and it is shown also by
+the determination with which both opponents fight when the question of
+ownership of a station is in dispute. And of all the facts we have
+reviewed, this is perhaps the most important in relation to our present
+subject, for it demonstrates that the change from sociability to
+hostility is not merely an incident of the sexual season, not merely an
+indirect result of the functioning of the general disposition which
+leads to the establishment of a territory, but that it is intimately
+associated with the whole process, and that the particular part of the
+bird's nature which is concerned is so nicely balanced that it will
+respond under one condition and one only.
+
+Thus we are led to the only conclusion which seems consistent with the
+facts, namely that there is a relationship between the "territory" and
+the hostility.
+
+
+If we are satisfied that all this warfare is not merely an expression of
+an instinct which is serviceable in another direction, what part does it
+play in the whole scheme of reproduction?
+
+The young of many birds are delicate at birth and unable to withstand
+exposure to cold, and in the previous chapter we came to the conclusion
+that the territory was serviceable in that it provided an adequate
+supply of food in the vicinity of the nest, and thus obviated the
+necessity of the parents being absent from them for long. But manifestly
+no matter how active a male may be in driving away members of its own
+sex and kind, it will neither make its position secure, nor insure a
+supply of food for its young, so long as any number of individuals of
+different kinds are allowed to establish themselves in the same space of
+ground. On the one hand, then, we have the fact that there is constant
+strife between males of close affinity, whilst on the other, we know
+that many species require like conditions of existence and are bound to
+assemble wherever these conditions are suitable; and we can infer that
+the territory would fail to serve its purpose if no restriction were
+imposed upon the measure of such assemblies.
+
+The question then arises: Does all this warfare contribute towards the
+attainment of reproduction? Not far from my house there is a small water
+meadow, three acres in extent, which for some years has been derelict
+and is now overgrown with the common rush (_Juncus communis_) and small
+alder trees. For three successive seasons I watched the bird life of
+this meadow, and more especially the Reed-Buntings whose behaviour I was
+studying at the time. In every respect the meadow was suitable for this
+bird; there was an abundance of food and numberless situations in which
+nests could be placed. Each year all the pairs were successful in
+rearing one, if not two broods, yet the number of pairs never exceeded
+five--the first year there were three; the second year five; and the
+third year four. In addition to the four pairs of Reed-Buntings, there
+were in the spring of 1915, six pairs of Whitethroats, one pair of
+Lesser Whitethroats, four pairs of Willow-Warblers, one pair of
+Sedge-Warblers, two pairs of Grasshopper-Warblers, one pair of
+Chiffchaffs, three pairs of Hedge-Sparrows, two pairs of Tree-Pipits,
+one pair of Skylarks, one pair of Whinchats, one pair of Flycatchers,
+two pairs of Song-Thrushes, one pair of Blackbirds, one pair of
+Redstarts, three pairs of Chaffinches, and one pair of Wrens--in all,
+thirty-five pairs, whose young were mainly dependent for their living
+upon the insect life of that meadow and the ground immediately
+surrounding it. If we allow three young to each pair--and this would
+take no account of second broods--we arrive at the following result,
+namely, that one hundred and five young and seventy adults had to be
+supplied with food from that locality, which would mean, if the search
+for food were strictly limited to that meadow, that 83 square yards
+would be allotted to each individual.
+
+Suppose now that the four male Reed-Buntings had each admitted one other
+male, and that they had secured mates, what would have been the effect
+upon the whole community? The four additional pairs with their young
+would have represented twenty individuals, which would have represented
+a decrease of 8.5 square yards in the space allotted to each individual.
+The pressure of the bird population upon the means of support would then
+have been materially increased; and not only the Buntings, but the
+Warblers, Pipits, and all the rest would have suffered. But the result
+would have been the same if, instead of the four additional male
+Reed-Buntings, four males of other kinds had been allowed to enter the
+marsh, and we can multiply the number four until we arrive at a point
+when the means of subsistence would no longer have been adequate for the
+adults, still less for the young. If, then, there were nothing to
+prevent this happening, many of the birds in that marsh would have no
+chance of rearing their young successfully. Hence, if the territory is
+adequately to serve the purpose for which we believe it has been
+evolved, some provision must have been included in the system to meet
+the difficulty.
+
+There are three ways by which this may have been
+accomplished--indirectly, by increasing the size of the area occupied by
+each individual, and thereby reducing the relative number of each
+species; or directly, by rendering the fighting instinct of the bird
+susceptible to stimulation by individuals of other species; or,
+possibly, by a combination of the two. There were four pairs of
+Reed-Buntings in the marsh, and their territories covered the whole of
+it. But inasmuch as other insectivorous birds were established there
+also, and found sufficient food to maintain both themselves and their
+families, it is clear that the area these Reed-Buntings occupied was in
+excess of that which they would have required if they had been the sole
+inhabitants. And such often appears to be the case. Many a Warbler
+allocates to itself a space of ground more than sufficient to supply it
+with all that it needs; so, too, does the Finch, or the Pipit, or the
+Falcon--if we take no account of kindred species. Thus there is reason
+to believe that, by limiting the number of individuals in a given
+locality, this apparently wasteful expanse of territory is serviceable
+in that it provides against the pressure of the bird population upon the
+available means of support becoming too great. But though a reduction in
+the numerical standing of the different species would certainly follow
+from any increase in the area occupied by the respective individuals,
+and with even greater certainty would place them in a more secure
+position as regards their supply of food, yet, when we remember how
+large a number are dependent upon a supply of insect life for their
+young, we can understand that it would not alone be a sufficient
+safeguard against the dangers attendant upon overcrowding. It is here, I
+believe, that we shall find the true explanation of the hostility; it
+roughly insures that the number of pairs in any given area does not
+exceed the available means of support, and indeed it is difficult to
+imagine how such uniformity of distribution as would free the young from
+the risk of exposure could be obtained without some such control.
+
+Some birds, however, have no difficulty in finding the necessary food
+for their young, yet have great difficulty in finding a station where
+they can rear their young in safety; and the area each one occupies has
+been reduced to the smallest proportions in order that the maximum
+number can be accommodated. Here, any increase in the size of the
+territory would inevitably lead to the extinction of the race, so that
+nothing stands between failure and success except the ability of the
+bird to defend its territory. If we study the bird population at one of
+the breeding stations on the coast, we find, generally speaking, that
+each kind of bird inhabits a particular portion of the cliff; on the
+lower ledges are the Guillemots and Kittiwake Gulls; higher up are
+Razorbills and Fulmars, and at the top, where the cliff is broken and
+the face of the rock covered with turf and soil, the Puffin finds
+shelter for its egg. At the same time there is much overlapping; the
+kind of ledge that suits a Razorbill is equally suitable for a Guillemot
+or a Fulmar, and so, no matter how successful the Razorbill may be in
+establishing a territory and preventing intrusion upon it by other
+Razorbills, it will be all to no purpose if it allows itself to be
+jostled out of its position by a Fulmar. Hence, inasmuch as breeding
+stations are limited and competition for territory so severe, only those
+forms in which the fighting instinct responds freely to a wide range of
+stimuli will be in a position to maintain a footing upon the cliff.
+
+In trying to estimate the importance of the hostility in its relation to
+the territory, we must bear in mind that competition varies in different
+seasons and in different localities. The surface of the land is
+constantly undergoing modification, partly owing to human and partly to
+physical agency--forests are cleared; marshes are drained; the face of
+the sea-cliffs is altered by the erosion of the waves; here the coast
+may be locally elevated, there locally depressed; and so forth. Many of
+these changes are slow and imperceptible, many can be observed in our
+own lifetime. The timber is felled and the undergrowth cleared in some
+wood, and the following spring we notice a change in the character of
+the bird population. Migrants which formerly found in it no suitable
+accommodation now begin to appear, and as the seasons pass by and the
+undergrowth affords more and more shelter for the nests and an
+increasing supply of insect life, so their numbers increase until the
+wood becomes an important breeding station, resonant with the song of
+many individuals. But slowly the growth increases; the bushes pass into
+saplings and the saplings into trees, and the undergrowth then
+disappears just as surely as do the migrants which can no longer find
+there the conditions which they require.
+
+Or, as an illustration of the effect produced by natural agency, let me
+describe a change which has taken place in a corner of Co. Donegal. The
+promontory of Horn Head is bounded on the west by extensive sand-hills,
+100 ft. or more in height. On the southern side it is divided from the
+mainland by a channel, which narrows down to 100 yards or so in width
+where it fringes the sand-hills, and then widens out again, covering an
+area of approximately 270 acres. As far as is known in the memory of
+man, this area has always been tidal. But in recent years a change has
+taken place, and the blown sand has silted up the channel, with the
+result that this tidal area has been transformed into a brackish lake.
+What has brought about the change is not easy to determine. There is
+evidence, however, of a slow alteration of the level of the shore-line;
+for in the midst of the sand-hills, situated 150 yards or so from the
+present sea-margin, and running parallel with it, there is an
+accumulation of pebbles some 3 feet high by 4 feet deep. This raised
+beach is now separated from the Atlantic by sand-drifts of considerable
+height, and consequently there are some grounds for believing that
+secular elevation is taking place, which, if it be the case, will
+account for the change in progress. Now the effect on the bird
+population can be seen even now, and will doubtless become more apparent
+as the years pass by. Sand-Martins used to find plenty of places to
+breed amongst the sand-drifts, and moreover do so still. But their
+nesting sites are constantly changing and disappearing, and the
+breeding-place of one colony, that was situated in the bank of a stream
+twelve years ago, is now buried 10 feet or more below the surface of the
+sand. The area that was once tidal, but is now a brackish lake, is fed
+by mountain streams, and as the fresh water predominates, so in course
+of time will it become fringed with vegetation; and instead of the
+flocks of Curlew, Dunlin, and other waders that, at low water, resorted
+there to feed, Coots will fight with one another for the possession of
+territories, and the Wild Duck will teach her young to seek their food.
+
+In whatever direction we turn, we find that many breeding grounds are
+subject to incessant change. Ancient haunts disappear, new ones come
+into being, a change which makes life impossible for this bird, as
+likely as not benefits that one, and so on. There is no stability. Hence
+in any given district each recurring season there must needs be a large
+number of individuals which are obliged to seek new stations, and if
+there were no control over their distribution, if each one were free to
+establish itself wherever it chanced to alight, this locality might be
+overcrowded and that one deserted; and, bearing in mind how many species
+there are that require similar conditions of existence, we can infer
+that the successful attainment of reproduction would become impossible
+for many of those individuals so long as each species was indifferent
+to the presence of the others. On the other hand, if there were no
+control over the range of the intolerance, the smaller bird would have
+no chance in competition with the larger, and it is doubtful whether the
+larger would gain an advantage commensurate with the energy it would
+expend in ridding its area of the smaller. I have described battles in
+which the opponents were only distantly related; for instance, the
+Moor-Hen will attack almost any bird--Partridge, Lapwing, or
+Starling--that approaches its territory even temporarily. Nevertheless
+the antagonism between kindred forms is more prevalent, and, as a rule,
+characterised by more persistent effort; and thus it seems as if the
+susceptibility of the fighting instinct has its limitations, the degree
+of the responsiveness being dependent upon the affinity of the
+opponents.
+
+Suppose now that we take an area inhabited by a number of different
+species requiring like conditions of existence, divide it into three
+sections, and imagine that in one they were all sociable, that in
+another they were all hostile, and that in a third those which were
+closely related were intolerant of one another. Let us suppose further
+that each one of them was represented by the full number of individuals
+that the law of territory would allow. In the first section an
+individual would establish itself, and, becoming intolerant of its own
+kind, would exercise dominion over an area roughly sufficient, providing
+conditions were normal, to insure an adequate supply of food for its
+young. But it would take no account of other species, and since any
+number might occupy the same ground, the fact of its having established
+a territory would not alone suffice to render its supply of food
+secure. Success in the attainment of reproduction would then become
+largely a matter of chance, depending upon the number of individuals
+that happened to settle in this place or in that. In the second section
+there would be perpetual warfare; for whereas the appropriate organic
+condition which leads to pairing arises in different species at
+different times, fresh claimants to occupied ground would constantly be
+appearing, and the efforts of the inhabitants to preserve their
+boundaries intact would have to be maintained throughout the whole
+period of reproduction; and while the stronger or more persistent forms
+would be more likely to breed, they would do so at the expense of their
+young, to which they would be unable to devote proper attention, and
+with an expenditure of energy that would reflect itself upon the future
+of the race. But the conditions of life in the third section would be
+such as would be more likely to yield good results. The relations of the
+different members of the community would be more evenly balanced, for a
+male would only be called upon to compete with those of its own size and
+strength. Thus, on the one hand, accommodation would be so divided as to
+secure the breeding of the maximum number of individuals with the
+minimum of expenditure of energy, whilst on the other, any undue
+pressure upon the available means of subsistence would be prevented.
+
+There can be no question that in the latter section a higher percentage
+of individuals would succeed in rearing offspring. And so, by reason of
+the fighting instinct being more susceptible or less susceptible
+according to the affinity of the opponents, a control is established
+which, while preventing unnecessary extension of warfare, allows for
+sufficient extension to render the biological end secure.
+
+
+These, then, are the facts--this the conclusion which can be drawn from
+them. It may, however, be said of these facts, as it has been said, with
+even less justification, of the battles between individuals of the same
+species, that they do not afford evidence of genuine hostility. No doubt
+there are many naturalists who could supplement these facts with others
+in which the conflicts resulted in bodily injury, or terminated fatally,
+or at least were of a more determined kind. But I have already drawn
+attention to the fact that, so long as a definite result is attained,
+the severity of the struggle and the amount of injury inflicted are
+matters of small moment. Let us, however, run over the substance of the
+argument, and then briefly refer again to this point of view.
+
+After enumerating instances of hostility, sufficient in number, so it
+seemed, to constitute reasonable ground for the belief that they had a
+part to play in the life-history of the individual, the two questions we
+set ourselves to examine in this chapter were: Is there any circumstance
+in the life behaviour of the individual with which the hostility can be
+definitely related; and, will the hostility lead to the securing of a
+greater measure of success in the attainment of reproduction?
+
+Many different species assemble together in winter and roam from place
+to place in search of food. But in spring their behaviour undergoes a
+remarkable transformation; they avoid one another and become
+quarrelsome, so much so that whereas the outstanding feature of the
+winter is sociability, that of the spring is hostility. With this
+general fact before us, we proceeded to investigate this change of
+behaviour still further. First of all we took the case of a migrant,
+and, comparing its behaviour, as it journeyed, with that when finally it
+reached its destination, we found that the bird which was notoriously
+pugnacious when in occupation of a territory betrayed no interest in
+other species as it travelled to the accustomed breeding ground. Not
+only so, but even though it was attacked, we found that its pugnacious
+instinct still failed to respond. Here, however, it may be contended,
+and with reasonable justification, that in the interval which elapses
+before the ultimate destination is reached, some change in the organic
+condition of the bird may occur which will account for its altered
+behaviour; or, it may be urged, with no less justification, that whereas
+on migration the bird is unpaired, when the destination is reached it is
+probably in possession of a mate and is therefore quarrelsome. Now, at
+the most, the interval can only be a matter of a few days, and it is
+unlikely that organic changes sufficient to bring about so important an
+alteration of behaviour could occur in so short a time, still less
+likely that they could be timed to come into functional activity just at
+the moment when the bird reaches its breeding ground. And with regard to
+the suggestion that the change can be accounted for by the presence of a
+mate, we shall do well to remember not only that males as a rule precede
+the females by some days, but that a male may even remain in its
+territory, mateless, for some weeks, and yet display hostility.
+
+Nevertheless the case of the migrant did not, by itself, afford
+sufficient evidence upon which to base any conclusion. We therefore
+inquired into the behaviour of some of the residents at a corresponding
+period. The Bunting served as an illustration. Early in the season it
+establishes a territory, and because food is then scarce it is forced to
+seek it elsewhere than on the small plot of ground which it has
+acquired; and so it makes its way to some spot where the supply is
+abundant, and there, meeting with other species bent on a similar
+errand, forms with them a flock. Part of its time is then spent in the
+territory and part on the feeding ground, and between these two points a
+highway is formed by the bird passing constantly to and fro. But the
+attention which it pays to other species is very different on these two
+occasions--when in the territory it is intolerant of strangers, but when
+it accompanies the flock it displays no interest in their movements.
+From hour to hour its nature seems to change. But, as we saw, the inborn
+constitution of the bird cannot change, and therefore we came to the
+conclusion that an explanation of the altered behaviour was to be found
+in the fact that the pugnacious instinct is only rendered susceptible
+under a certain condition. So that all the evidence tended to confirm
+the impression which we had gained from the course of events in the life
+of the migrant, namely, that the hostility bears a direct relation to
+the occupation of a territory.
+
+Finally we were led to inquire whether the hostility was serviceable in
+promoting the welfare of the individuals. We saw that many different
+species require similar conditions of existence, that ancient breeding
+haunts disappear and that new ones come into being, and that in the
+ordinary course of events such species must often assemble in the same
+area for the purpose of reproduction. So that even though a male might
+be successful in protecting its ground from intruders of its own kind,
+yet it might still fail to rear offspring, just because it happened to
+choose a position in which other kindred forms had gathered. Hence if
+the territory is adequately to serve its purpose, some control over the
+local distribution of species is of paramount importance. Nevertheless,
+if all the different forms that require similar conditions of existence
+were intolerant of one another in a like degree, the smaller bird would
+have no chance in competition with the larger. This, however, is not
+the case. Some, as we saw, arouse little or no animosity in others, in
+fact the more closely related the rivals, the more responsive their
+pugnacious nature seems to become.
+
+To return now to the view that the fighting is not really serious, but,
+on the contrary, that it is either vestigial and has no longer any part
+to play in furthering the life of the individual, or that it is a
+by-product of the seasonal sexual condition to which no meaning can be
+attached. First, there is the relationship with the territory, and this,
+it seems to me, is a fact of some importance; for if the fighting were
+merely an exuberant manifestation of sexual emotion, one would expect to
+find it occurring under all conditions, and not merely under one
+particular condition in the life of the bird. The hostility is too
+widespread, however, and too uniform in occurrence for us to suppose
+that it has no root in the inherited constitution of the bird; and if it
+served some useful purpose in the past, the instinct might still
+persist, so long as it were not harmful. Thus the view that the
+behaviour is vestigial is not perhaps unreasonable. But manifestly it
+makes no difference whether it be vestigial or a by-product of sexual
+emotion, whether the battle be fierce or so trivial as to appear to us
+to be more in the nature of "play," so long as some change in the
+relative prospects of the opponents is the result.
+
+For us, then, the main consideration lies in the question: Is the
+behaviour serviceable now in furthering the life of the individual?
+Whether the evidence which we have examined affords sufficient ground
+for the belief that the hostility is genuine and has a part to play in
+the whole scheme of reproduction, each must judge for himself.
+
+
+
+
+CHAPTER VII
+
+THE RELATION OF THE TERRITORY TO MIGRATION
+
+
+Coincident in time with the growth of appropriate conditions in the
+environment, organic changes take place rendering certain instincts
+susceptible to stimulation; and the stimulus being applied, the Warbler
+leaves the country wherein it had passed the winter and finds its way
+back, with apparently little difficulty, to the district in which it was
+reared or had previously reared offspring. What is the nature of these
+changes and of the impulse which is first brought into functional
+activity; whence comes the stimulus; and what directs the bird on its
+journey--these are all different aspects of one great problem, the
+problem of migration. I do not propose to discuss all these various
+aspects, for indeed I have no suggestions to offer which are in the
+least likely to be helpful, but I seek rather to ascertain whether the
+phenomena which we have explored bear any relation to the problem as a
+whole; whether, that is to say, the competition for territory and all
+that appertains to it can have supplied the conditions under which, in
+the process of time, this complex and definite mode of behaviour has
+evolved.
+
+We are sometimes told that we must seek the origin of migration in the
+physical changes that have occurred in the ancient history of the
+earth--in glacial conditions which gradually forced birds to the south,
+or in the "stability of the water and mobility of the land" which
+brought about a gradual separation of the feeding area from the breeding
+area--and which continued for a sufficient length of time to lead to the
+formation of an instinct, and that the instinct persists because it is
+serviceable in promoting the welfare of the race. But when we consider
+the lapse of time, and the changes that must have occurred in the
+character of the bird population--the appearance of new forms and the
+disappearance of the old, the ebb and flow of a given species in a given
+area--and bear in mind that, notwithstanding this, the migratory
+instinct, if not stronger, is assuredly no less strong, and the volume
+of migration, if not greater, is assuredly no less; in short, that the
+whole phenomenon is progressive rather than retrogressive, we shall find
+the view that the instinct owes its origin to conditions which no longer
+exist, receives but little encouragement.
+
+I doubt not that, throughout the ages, geological changes have been an
+important factor in directing or limiting the scope of migration, and
+moreover are so still; just as climatic changes and the relative
+abundance or scarcity of enemies have influenced the course of its
+evolution. These are all contributory factors operating in the external
+environment. But there are, besides, internal factors which form part of
+the inherited constitution of the bird, and, being passed on from
+generation to generation, afford the conditions under which migration is
+constantly being renewed. It is, I believe, in this field of organic
+change and relationship that the conditions of origin must be sought.
+
+Just as the moth in passing from the rudimentary to the perfect
+condition runs through a series of changes, each one of which is marked
+by a typical behaviour response adjusted to meet some particular
+circumstance in the external environment, so the annual history of a
+bird displays an ordered routine, each phase of which can be observed to
+correspond with one of the successive changes in the environment. In
+almost every direction, we find that this routine is characterised, in
+broad outline, by great uniformity; so much so that, providing we know
+the history of one species, we can forecast with no small degree of
+certainty the general course of behaviour of other members of the
+family. But only the _general_ course. There is endless variation in
+just the particular way in which the behaviour is adapted to meet the
+needs of particular species--the major details may be said to be
+specific, the minor details varietal.
+
+Now it is that part of the behaviour routine which has reference to the
+relationship between one bird and another upon which, for the time
+being, I wish to dwell; for the interest that A displays in B is by no
+means always the same--it changes according to the season, and this
+change can be observed to be uniform throughout a wide range of species.
+
+In winter, in whatsoever direction we turn, we observe not only that
+different individuals but that different species also collect together
+in flocks. And since food at that season is not always easy to obtain,
+and, moreover, is only to be found in certain situations, which are
+limited both in number and extent, it would seem that such assemblages
+are in the main determined by accident. No doubt the abundance or the
+scarcity of food does determine the movements of birds, and hence to
+that extent may be held to account for the flocks. But we shall but
+deceive ourselves if we think that it is the sole or even the principal
+reason, or that the situation is in no wise affected by internal
+factors. The behaviour of the individual in relation to the flock bears
+ample testimony to the presence of a gregarious impulse which derives
+satisfaction from the fact of close association.
+
+As an illustration, let us take a bird whose movements are easily
+watched, and in whose hereditary constitution the impulse to which I
+allude seems to be strongly implanted--the Curlew. When the breeding
+season is over, Curlew leave the mountain and the moor and return to
+the coast or tidal estuaries for the remainder of the year. Here, at low
+water, they find an abundant supply of food--crustaceans amongst the
+sea-weed upon the rocks, and lobworms (_Arenicola piscatorum_) in the
+mud as the tide advances or recedes. But when the tide is full, they
+retire to those parts of the shore that remain uncovered--to isolated
+rocks, or to sand-dunes, or it may even be to pasture-land in the
+neighbourhood. During this period of repose large numbers of individuals
+gather together on a comparatively small space of ground. They are not
+constrained to do so by any shortage of accommodation, nor by any
+question relative to food, nor, for the matter of that, by any
+circumstance in the external environment; they are brought together
+solely, this at least is the impression that one gains, by some
+inherited impulse working towards that end. And their subsequent course
+of behaviour tends to confirm that impression. For if we watch the
+gathering together of the different units of which the flock is
+composed, and study more particularly the emotional manifestation which
+accompanies their arrival and departure, we shall find that the coming
+of a companion arouses some emotion which is expressed by a vocal
+outburst that sweeps through the flock.
+
+Now each call, and the Curlew has a great variety, is not only peculiar,
+generally speaking, to certain occasions, but is accompanied by a
+specific type of behaviour, whence we can infer in broad outline the
+type of emotion which is aroused. Thus we come to recognise fear, anger,
+or sexual emotion, by just the particular sound which is emitted. But
+even if we are going too far in referring particular calls to particular
+emotions, we can, without a doubt, divide them into two broad
+categories--those which are pleasurable and those which are the reverse.
+And we need have no hesitation in placing the particular call to which I
+allude in the first of these two categories, not only on account of the
+nature of the sound produced, but because the activities which are
+aroused are not such as normally accompany irritation. This is well seen
+if the behaviour of different individuals be closely observed. After
+resting on one leg for some time, first one and then another is seized
+with cramp, and running a few yards in an ungainly way, bumps up against
+its companions as if it had not full control over its movements. Its
+behaviour produces irritation which is expressed by a vocal outburst,
+and followed by actions the meaning of which is clear. Moreover, the
+call is taken up by other individuals and sweeps over part of the flock
+as does the greeting. But the nature of the cry is entirely different
+from that which greets the arrival of a companion--humanly speaking it
+is a passionate and impatient utterance, the height of displeasure. The
+arrival, then, acts as a stimulus to something in the inherited
+constitution which is expressed in, and presumably is satisfied by, this
+vocal outburst; and, since the bird that arrives joins also in the
+chorus, there is reason to think that the impulse which determines its
+movements is similar to that which is temporarily aroused in the flock.
+
+Apart, however, from the evidence derived from the affective aspect of
+the operation of the instinct, the general course of behaviour lends
+support to the view that the assemblies are determined by internal
+factors, and are not merely the outcome of circumstances in the external
+environment. Observe, for example, the manner in which the flock is
+built up. Single individuals are content to rest alone so long as no
+assembly is in sight, but they are drawn towards their companions
+directly the opportunity arises, just as surely as the smaller
+aggregation is drawn towards the flock; and so, as the flock increases,
+it gradually absorbs all the lesser flocks and smaller parties, for the
+greater the flock the greater the attraction seems to be; and different
+individuals appear to gain some satisfaction from being in close bodily
+contact with one another.
+
+When the Curlew flies to that part of the mud-flat which is first
+exposed by the receding tide, and there associates with others, it does
+not then do so because it has any interest in its fellows, nor because
+they serve as an attraction, but because it is constrained by hunger--in
+other words, the association is determined by accident. But when, during
+periods of repose, it sees a flock, flies to it, and takes up a position
+in the midst of it, it does so not because suitable accommodation is
+lacking--not therefore because of external constraint--but because it
+derives some pleasure from satisfying something in its organic complex.
+We speak of this behaviour and of the emotion which characterises it as
+the _gregarious instinct_: by which we mean that the inherited nature of
+the Curlew, as a tribe, is so constituted that, given the appropriate
+internal conditions and adequate external stimulation, every individual
+will respond in a similar manner--that is, the behaviour is primarily
+determined by racial preparation. This is what we mean by the
+_gregarious instinct_ biologically considered. We may resolve our own
+experience in relation to the crowd into its simplest constituents,
+project our own primitive feelings into the Curlew, and say that the
+bird feels uneasiness in isolation and satisfaction in being one of the
+flock. But in truth we know nothing, save by analogy, of the correlated
+psychical state. All the knowledge we possess is derived from a study of
+the objective aspect of the behaviour, which in simple terms may be
+expressed thus: the individual is drawn towards its companions; there is
+a relation between the size of the flock and the strength of the
+attraction; and all Curlew behave similarly under similar circumstances.
+
+This instinct controls the movements of many birds from early autumn to
+the commencement of the breeding season. And so powerful is the control
+that the individual is suppressed and its activities subordinated to the
+welfare of the community as a whole. Flocks of Waders roam about the
+tidal estuaries in search of food, and different kinds of Gulls assemble
+there and preen their feathers or sleep; Warblers alter their mode of
+life, and in the osier bed, or amongst the elders, seek their food
+together in peace; Finches, Buntings, Pipits, and Wagtails, though food
+is everywhere abundant, gather themselves together respectively into
+bands which, as winter approaches, grow into flocks and even into
+composite flocks; and as the Warblers leave for the south, so their
+places are filled by flocks of Thrushes and Finches from the north. In
+whatever direction we turn, when the days begin to shorten, it is the
+community, not the individual, that thrusts itself upon our attention;
+and throughout the winter continues to be the outstanding feature of
+bird life.
+
+With the approach of the breeding season we witness that remarkable
+change which I have endeavoured to make clear in the previous
+chapters--the disintegration of the flock and the reinstatement of the
+individual. Instead of continuing with the flock, the individual now
+goes forth to seek the appropriate breeding ground; and having arrived
+there, is not only content to remain in isolation, but so behaves that
+isolation is insured. Intolerant of the approach of a stranger,
+intolerant even of the approach of the very members of the community
+whose companionship was previously welcomed, it not only fights to
+maintain the position it has selected, but fights indeed for the
+possession of ground already occupied, and, until reproduction is
+completed, asserts its individuality and exercises dominion over its
+territory. What, then, is the prospective value, biologically
+considered, of the changing interest that A displays in B, and to what
+will such changes lead? These are the questions to which we will now
+direct inquiry.
+
+The annual life-history of a bird is in broad outline conditioned by
+two powerful and at first sight opposing impulses--the one to live in
+society, the other to live solitary. But, manifestly, a bird cannot be
+governed by opposing impulses. It has but one character, within which,
+according to the season and the circumstances, different impulses
+predominate. But these impulses, no matter how different they may appear
+to be, have their respective parts to play in furthering the life of the
+individual. Hence they cannot oppose, though they may conflict, if the
+resultant behaviour contributes towards survival.
+
+The majority of birds live to-day in constant danger from predatory
+species, and that this danger was still greater in bygone ages there can
+be but little doubt. A curious mode of behaviour of the Curlew,
+Whimbrel, and Godwit demonstrates this, for it must be the outcome of
+the necessity for constant watchfulness. Whilst resting with its head
+turned back and its beak buried in the feathers of the mantle, the bird
+constantly moves the axis of its body, so that an observer, if placed in
+a direct line behind it, sees at one moment the right eye and at another
+the left. No movement of the feet or of the legs is perceptible, and the
+shifting of the body continues whether the eyes are open or closed. This
+body movement enables the bird to survey a much larger area of ground
+than it would otherwise be capable of doing, and thus adds to its
+security. As far as my experience goes, the movement is less evident
+amongst the members of a flock than when an individual is resting alone,
+or even with a few companions, which may be due to the fact that since
+some members are always awake and watchful, a bird of prey would have
+more difficulty in approaching a flock unawares than it would have in
+approaching a single individual. With the greatest ease a Sparrow-Hawk
+can pick up a Thrush as it feeds on the meadow by itself, but if it
+attempts to seize one of a flock, the chances are that its approach is
+signalled and that its prey escapes. And not only do the different
+members give warning one to another of the approach of danger, but they
+also combine to harass or even to drive away an enemy. So that there can
+be no doubt that the gregarious instinct is serviceable in promoting the
+welfare of the race, and has, as its end, the preservation of the
+individual in order that it may take its share at the appropriate time
+in procreating its kind.
+
+In winter, then, the individual loses its individuality and is
+subordinated to the welfare of the community, whilst in spring it
+regains its individuality, and all its inherited instincts which then
+come into operation lead to its isolation from the flock. The impulse to
+seek isolation is dependent upon internal organic conditions which are
+peculiar to a certain season; whereas the gregarious impulse depends
+upon internal organic conditions which inhere at all times, though its
+functioning is inhibited by the functioning of the former impulse. The
+evidence which leads to this conclusion is to be found in the fact that
+a male often deserts its territory temporarily and joins the flock,
+where it remains at peace with its companions--an aspect of behaviour
+which we have discussed on various occasions. The former impulse becomes
+dominant in the spring owing to its innately superior strength; the
+latter becomes dominant in the autumn because the organic condition
+which determines the functioning of the former then subsides. The
+impulse to seek the appropriate breeding ground and to dwell there would
+seem to be the strongest of all the impulses save one--the sexual.
+When, however, I speak of the sexual, I refer to the actual discharge of
+the sexual function, which is the consummation of the whole process. But
+the territory and all that appertains to it is part of that process--the
+search for the breeding ground, the dwelling there, and the intolerance
+of intrusion are but different stages, each one of which must have an
+impulse peculiar to it; and since the completion of the sexual act can
+only be successfully accomplished providing that success is attained at
+every stage, the probability is that, of the impulses concerned, one is
+neither more powerful nor less powerful than another.
+
+So that we have two impulses operating at different seasons and guiding
+the behaviour into widely divergent channels. But though the proximate
+end to which the behaviour is directed is apparently different, there
+are not two biological ends in view, but one--the attainment of
+reproduction; and the changes that we witness are not contrary but
+complementary, and their prospective value lies in the circumstance that
+they contribute towards the preservation of the race.
+
+If, then, every male is driven by inherited impulse to seek the
+appropriate breeding ground each recurring season; if, having arrived
+there, it is driven to seek a position of its own; if, in order to
+secure isolation it is obliged to attack other males or to ward off the
+attacks of intruders; if, in short, success can only be attained
+providing that the inherited nature is so adjusted that the bird can
+accomplish all that is here demanded--what will be the general result?
+That the individual will rear its offspring in safety and that they will
+inherit the peculiarities of their parents, enabling them, in their
+turn, to procreate their kind; all this will certainly follow. We are
+not concerned, however, at the moment, with the direct effect upon the
+individual, but with the consequences that will accrue to the species as
+a whole.
+
+Now certain facts are presented to observation which enable us not only
+to understand the nature of the change that is wrought in the history of
+the species, but to foreshadow, with no small degree of certainty, the
+extent of that change. I suppose that it has come within the experience
+of most of us to observe, at one time or another, the ebb and flow of a
+given species in a given district. Some favourite haunt is deserted for
+a year, or for a term of years, and is then revisited; or, if it is
+always occupied, the number of inhabitants fluctuates--plenty of pairs
+in this season, only a few in that. Many intricate relationships, both
+external and internal, contribute towards this state of affairs.
+Fluctuation in a downward direction, or temporary extinction, is brought
+about by changes in the physical world, by changes in the available
+supply of food, by the increase of enemies, or by adverse climatic
+conditions; whilst fluctuation in an upward direction, though due
+indirectly to a combination of circumstances in the external world
+favourable to the survival of large numbers of individuals, is directly
+determined by the impulse to seek isolation. As individuals of
+different species establish themselves, and form kingdoms and lesser
+kingdoms, we can watch the gradual quickening into life of moorland and
+forest and we can observe the manner in which it all comes to pass.
+Males that for weeks or months have lived in society, drifting from
+locality to locality according to the abundance of food or its scarcity,
+now set forth alone and settle first here and then there in search of
+isolation. Lapwings settle in the water meadows, and, finding themselves
+forestalled, pass on in search of other ground; Blackbirds arrive in a
+coppice or in a hedgerow and, meeting with opposition, disappear; and
+the Curlew, wandering with no fixed abode but apparently with a fixity
+of purpose, searches out the moorland where it can find the particular
+environmental conditions to which its inherited nature will respond. In
+fact, wherever we choose to look, we can observe in a general way the
+gradual appropriation of breeding ground; and if we fix our attention
+upon particular males, we can watch the method by which success or
+failure is achieved.
+
+On more than one occasion I have watched the efforts of Reed-Buntings to
+appropriate territories in a marsh that was already inhabited. Sometimes
+their efforts met with success, at other times with failure. In the
+former case, the males, whose ground was intruded upon, were severally
+forced to yield part of their holding and were thus left in possession
+of a smaller area. The success of the intruder seemed to depend upon
+persistent determination, rather than upon superior skill in battle.
+Recently I had an opportunity of observing the intrusion of a male
+Willow-Warbler upon ground already occupied. By persistent effort it
+succeeded in appropriating one half of the territory of its rival. The
+intruder occupied some trees on the outskirts of the territory it was
+invading, and used them as a base from which it made repeated efforts to
+enter the ground of its rival. These efforts were time after time
+frustrated. No sooner did it leave its base than it was seen and
+intercepted, or else attacked; and no matter from which direction it
+attempted to effect an entrance, its efforts, for a time, were all to no
+purpose. The fighting was of a determined character, and after each
+attack the owner of the territory showed signs of great excitement, and,
+sitting upright upon a branch, spread and waved its wings, which is the
+specific emotional manifestation during the period of sexual activity.
+Eventually the intruding male succeeded by persistent effort in
+appropriating part of the occupied ground.
+
+Thus we can actually witness the efforts of the individual to isolate
+itself from members of its own kind, and can observe the immediate
+consequences that follow from success or from failure. And from these
+consequences we can infer that, within a certain range but in accordance
+with the relative abundance of the species that dwell in it, every
+corner of the available breeding ground will be explored and every
+situation that evokes the appropriate response will be occupied.
+Moreover, since the annual dispersion is not merely a repetition in this
+season of that which occurred in a previous one, a progressive increase
+in the area occupied will follow. Yet, if the majority of species desert
+their breeding ground so soon as reproduction is ended, how can this be?
+An answer to the question will be found in the fact that a bird has an
+innate capacity to return to the neighbourhood of its birthplace, or to
+the place wherein it had previously reared offspring--which means that
+the results of prior process persist as the basis and starting-point of
+subsequent process.
+
+Bearing then in mind that the seeming peace in bird life around us in
+the spring is but the expression of transitory adjustments in the
+distribution of individuals and of species; bearing in mind how
+widespread is the search for isolation each recurring season, how
+frequently the search leads to competition and competition to failure,
+and how failure implies a renewal of the search; bearing in mind that
+situations, which appear to be eminently suitable for breeding purposes,
+are passed by year after year and remain unoccupied, just because, for
+reasons which have yet to be ascertained, the environment fails to
+supply some condition which is essential if the inherited nature of the
+bird is to respond--can there be any doubt that the general result of
+the functioning of the disposition will be expansion; or, since no limit
+is placed upon it from within but only from without--that is, by
+unfavourable circumstances in the external world, that the expansion
+will not merely be in one direction but in every direction?
+
+If now, when reproduction is ended, all the impulses relating to it die
+away, and the gregarious instinct again predominates, what are the
+consequences to which this change will lead? Just as the consequences
+which flow from the functioning of the former impulse are accessible to
+observation, so likewise can we observe the change that is wrought by
+the latter impulse. The process is a gradual one. Less and less
+attention is paid by the individual to intruders, more and more is it
+disposed to pass beyond its accustomed limits. Little by little,
+accompanied by its young or without them, as the case may be, the bird
+deserts its territory and wanders out into the wilderness. Here it
+associates with others, and finds in them a new interest and, I doubt
+not, a new enjoyment. All this we can observe as it takes place. But
+just as there is an innate capacity to seek, in the spring, the place
+where the pleasures of breeding had formerly been enjoyed, so we are
+bound to infer the existence in the adult of an innate capacity to
+revisit the former area of association; and this capacity will
+strengthen and confirm the gregarious instinct and set the direction of
+the general course of movement.
+
+We have seen, then, that the interest displayed by one bird in another
+changes with the seasons; we have seen that it is so modified as to be
+in useful relation to different environmental circumstances; as far as
+possible we have traced out the consequences, and have reached the
+conclusion that the change of behaviour must, on the one hand, lead to
+expansion, and on the other, to contraction; and we have seen that this
+conclusion is in accord with the facts of observation--that is the
+general result of our inquiry into the functioning of the two powerful
+impulses, the impulse associated with the disposition to secure a
+territory and the gregarious impulse.
+
+
+The phenomenon of migration embraces a number of separate problems, each
+one of which presents features of great interest and of still greater
+difficulty. On some of these problems I do not intend to touch; I seek
+only to ascertain whether the impulses that are concerned in the
+securing of a territory, and in the search for society, bear any
+relation to the problem as a whole. I hold that the origin of migration
+is not to be found merely in conditions peculiar to a remote past, but
+that the conditions inhere in the organic complex of the bird, and are
+thus handed down from generation to generation. Starting with this
+assumption I examined the behaviour which normally accompanies the
+seasonal life-history of the individual, and found, in that behaviour,
+manifestations of cyclical change leading to definite biological
+consequences. I now propose to inquire whether those consequences are
+such as might, in the course of time, give rise to the seasonal change
+of abode.
+
+We are apt to think of migration in terms of the Warbler that enlivens
+our hedgerows in the spring after travelling hundreds of miles from the
+south, or of the Redwing that comes from the far north and seeks its
+food during the winter on the meadows, or perhaps of the American Golden
+Plover that each year covers a vast expanse of ocean in its journey from
+its breeding ground. The length of the distance strikes the imagination
+and constrains us to focus attention upon the extremes.
+
+But migration is of much wider significance than is here represented. I
+sit beside the River Severn in April and watch Swallows, Tree-Pipits,
+and Yellow Wagtails passing in twos and threes, in small parties, or it
+may be in small flocks; and I observe that while some establish
+themselves in the neighbourhood, others pass on. Or I watch
+Herring-Gulls returning to the breeding station at Bolt Head, an endless
+stream of individuals coming from the east as far as eye can reach;
+following them for some miles inland I see them still, first as specks
+upon the horizon, then passing beside me as they beat their way slowly
+against the strong south-westerly winds, and finally disappearing from
+view in the direction of the cliffs. Or again, I watch Buntings and
+Finches deserting the flock and seeking stations in the marsh, or
+amongst the furze-bushes on the common, or in the spinneys. In each case
+the proximate end of the behaviour is alike--wherein then lies the
+difference? Only in the distance which separates the territory from the
+area in which the birds formerly associated. And intermediate between
+the extremes, I doubt not, if we had a sufficient body of observations,
+that we should find numerous gradations, the lesser merging step by step
+into the greater. Is the Swallow a migrant and the Herring-Gull not; is
+the Tree-Pipit a migrant and the Bunting not; must a bird cross many
+miles of sea or of land before it can be considered a migrant; is the
+length of the distance traversed a criterion of migration? Surely not.
+The distance traversed is merely a collateral consequence of the process
+as a whole.
+
+The annual life-history of a bird presents, as we have seen, two
+distinct phases--the one in which the individual dominates the
+situation, the other in which it is subordinated to the welfare of the
+community. Let us take these two phases separately and endeavour to see
+how they may have influenced the seasonal movements; and first let us
+take the more important of the two, namely that one which is directly
+concerned in the continuance of the race.
+
+In this phase we must consider the three factors to which allusion has
+already been made:--(1) the internal impulse, (2) the innate ability to
+return to the former breeding ground, (3) the conditions in the external
+environment. These three work in close relation and, as I shall
+endeavour to show, lead to important results.
+
+(1) If there were nothing in the inherited nature beyond an impulse to
+seek the breeding ground, if, that is to say, when the appropriate
+locality were reached, the bird took no further interest in the
+developing situation, the attainment of reproduction would become
+largely a matter of chance. A male in a congested district, having no
+incentive to seek fresh ground, would remain inactive until a female
+happened to cross its path and stimulate its sexual impulse, when its
+activity would take another form. Hence some districts would be
+over-populated, whilst others would remain unexplored. But the system of
+reproduction does not consist merely of a search for the breeding
+ground, and of the discharge of the sexual function; it is a much more
+complex business, yet withal more complete. Nothing is left to chance;
+the end is attained step by step; and each successive stage marks the
+appearance of some specific factor which contributes towards the success
+of the whole. We start with the appropriate organic condition under
+which, when adequate stimulation is provided, the disposition to secure
+a territory comes into functional activity. Within the field of this
+disposition we can distinguish certain specific impulses. In sequential
+order we have the impulse to seek the breeding ground; the appropriate
+situation which gives rise to an impulse to dwell in it; and the act of
+establishment which supplies the condition under which the impulse to
+drive away intruders is rendered susceptible to stimulation. Grouping
+these impulses, for the convenience of treatment, under one general
+heading, I speak of an impulse to seek isolation. It implies some kind
+of action with some kind of change as its correlated effect; and from it
+there flows a ceaseless energy directed towards a definite end which for
+us, who can perceive its prospective value, is isolation in an
+appropriate environment. The emphasis here is on "isolation," for it
+involves competition, and there cannot be competition without some
+change in the relative positions occupied by different individuals; so
+that in each recurring season there will be not only a re-arrangement of
+ground formerly occupied but an arrangement of ground formerly deserted.
+
+(2) That the older birds return to the locality wherein they had
+formerly reared offspring, and the younger to the neighbourhood of their
+birthplace, was always deemed probable. But in recent years evidence
+which cannot be rebutted has been supplied by the marking of birds. This
+evidence, details of which can be found in the summary of results
+published annually by Mr. Witherby in _British Birds_, demonstrates that
+the adult frequently returns not only to the same locality in which it
+formerly bred, but even to the same station; that it does so year after
+year; that this mode of behaviour is not peculiar to one sex; and that
+many of the young breed in the locality in which they were reared. Such
+being well-established facts, we can infer the existence of an innate
+ability to revisit the place wherein the enjoyment of breeding, or of
+birth, had formerly been experienced. Of its nature we know little or
+nothing. It would almost seem as if there must be some recollection of
+past enjoyment, but all that can be definitely asserted is--that past
+experience somehow becomes ingrained in the life of the individual and
+determines present behaviour. What, however, is of importance to us at
+the moment is not the _ad hoc_ nature of the bird, but the biological
+consequences to which the behaviour leads. For if, on the average,
+individuals return to their former haunts, it follows that the annual
+dispersion will not be merely a repetition in this season of that which
+had occurred in a previous one, but that the little added this year will
+become the basis for further additions in the next. The innate ability
+is handed down from generation to generation, and, in so far as it
+contributes to success, is fostered and developed by selection; and the
+modifications of behaviour to which it leads, since the results of prior
+process in the parent persist as the basis and starting-point of
+subsequent process in the offspring may in a sense also be said to be
+handed down.
+
+(3) The conditions in the external world may be organic or inorganic. By
+organic I mean the conditions which depend upon the number of
+competitors or enemies by which a bird is surrounded. The competitors
+may include other species which require a similar environment; and the
+enemies, species which prey upon it, or animals which take its young or
+its eggs. They vary in different seasons, in different districts, and
+in nature and extent--the success of one species leads to the failure of
+another, and the multiplication of the Jay or of the Magpie robs us of
+many a songster.
+
+By inorganic I refer to the changes in the climate and in the surface of
+the earth. The nourishment of the young depends upon a regular supply of
+food, and the supply of food depends upon the climate which alters in
+different periods; in one decade the temperature falls below, whilst in
+another it rises above, the normal, and, as the insect life fluctuates,
+so there is fluctuation in the bird population. The changes in the
+surface of the earth are manifold. Little by little the alder (_Alnus
+glutinosa_) overspreads the marsh. Young shoots spring up here and
+there, in a few years grow into bushes, and in a few more years are
+trees; and the dense masses of rush which seemed to choke their growth,
+yielding their position of importance, slowly disappear. And where
+formerly the _Orchis latifolia_, _Orchis mascula_, and _Juncus communis_
+grew in mingled confusion, nothing but water, moss, and the spreading
+roots of alder cover the ground. As the rush disappears, many birds that
+for generations have inhabited that marsh must seek accommodation
+elsewhere. Ancient breeding haunts thus disappear, new ones come into
+being, and even those which appear to be permanent are almost
+imperceptibly changing.
+
+Now the bird inherits a nervous system, which works under internal
+excitation and external stimulation. Given the appropriate organic
+condition and adequate stimulation, and the impulse to seek isolation
+comes into functional activity. What the organic condition is and how it
+arises we do not exactly know; all we know is that organic changes do
+take place in the breeding season, that these changes profoundly modify
+character, and that they correspond with the seasonal growth of the
+sexual organs. And with regard to the question of stimulation, we have
+again to confess to much ignorance, although certain facts are presented
+to observation which seem to indicate the direction in which the
+stimulus lies. For example, it is well known that abnormal climatic
+conditions influence behaviour; we see migrants retracing their flight
+along the very course they travelled a short time previously--driven
+headlong by the blizzard, that at least is what we say. But if the wind,
+instead of being cold and from the north, is warm and from the west, do
+they retrace their flight? I have not found it so. And if there be no
+wind and the temperature is low, are they still affected? Again, I have
+not found it so. When, as we commonly say, they fly before the storm,
+some change takes place in their organic complex, some new impulse
+receives stimulation or the former one lacks it. If, after Lapwings have
+established themselves in their territories, the weather becomes
+exceptionally severe, the birds collect together again in flocks and
+revert to their winter routine; and under similar circumstances,
+Buntings fail to sing and temporarily desert their territories. In such
+cases it is clear that the impulse to seek isolation ceases for a time
+to dominate the situation. The inference, therefore, is that atmospheric
+changes bear some relation to the functioning of the instinct; but
+whether it be temperature, or humidity, or the direction and velocity of
+the wind, or a combination of two or more of these factors that supplies
+the stimulus, we cannot tell.
+
+The appropriate organic condition and the stimulus have then still to be
+determined, and we must pursue our inquiry from the point at which the
+impulse comes into functional activity. We will take a simple case, and
+one free from complication.
+
+Let us suppose that there is an area bereft of bird life, if it can be
+so imagined, but in proximity to other inhabited areas. Into this area,
+whilst in search of isolation, let us imagine that a Yellow Bunting
+finds its way. After the manner of its race it establishes a territory
+and occupies, let us say at a low computation, half an acre of ground.
+It then obtains a mate, breeds, and rears offspring, two of which we
+will assume are males. Reproduction ended, the birds desert the area,
+and in the following spring, when the impulse again asserts itself,
+parents and offspring seek again their former haunts. We now have three
+males, each of which occupies half an acre, and each of which rears two
+offspring--that is the position at the close of the second year. In the
+third year the number will have increased to nine and the area occupied
+to 4½ acres; and so on in succeeding years, until by the beginning of
+the eleventh year, we have 59,048 Yellow Buntings occupying 29,524½
+acres or 46 square miles. This, then, will be the result of the
+operation of the impulse, providing that all the individuals survive and
+that no complications supervene.
+
+But of course complications are numerous, some of which retard while
+others accelerate the rate of expansion. These complications arise from
+various sources--in the first place from natural enemies which prey upon
+the birds or upon their eggs; in the next place from climate which, if
+it happens to be unfavourable, may mean that food is scarce and that
+only a small percentage of the young survive; and lastly from
+rivals--and by rivals I mean closely related forms that require a
+similar station and similar food--which, by occupying available ground,
+may check expansion, or, by forcing a continuation of the search, may
+widen it.
+
+Now when individuals fail as many do fail in their initial attempt to
+secure territory, the activity of the impulse still persists, and there
+is no control over the direction in which the bird continues to wander
+whilst in search of its end. Some therefore seek in this direction,
+others in that; some wander inwards into inhabited areas and fail to
+find accommodation, or, according to the relative strength of their
+impulse, perhaps succeed and so set free a new competitor, others wander
+outwards into country uninhabited by the species. These latter we will
+call "pioneers." They may find accommodation within a comparatively
+short distance of their base, or they may come into competition with
+rivals and fail, not necessarily on account of any congenital weakness
+of ability, but because being warned by an alien song, they may be
+precluded from coming into contact with just the environing conditions
+which can supply the stimulus and allow behaviour to run its further
+course--and so be obliged to extend their search into remoter districts.
+But it must not be overlooked that they will be placed in a most
+advantageous position so far as the attainment of reproduction is
+concerned. In their search for territory they will meet with little
+opposition and will be free to select whatsoever ground they will; and
+be free also from intrusion by neighbouring males, which is so frequent
+in occurrence and continues for so long in congested areas. Moreover, in
+thinly populated districts, the pressure upon the available means of
+support will not be so great, neither will natural enemies be so
+plentiful; and since the offspring, guided by prior experience, return
+to the neighbourhood of their birthplace, the advantages thus gained
+will be shared by the succeeding generation. It follows, then, that the
+range of a species will not always be continuous, will not, that is to
+say, proceed by a series of successive steps, but that sometimes in this
+direction and at other times in that, the chain of territories will be
+interrupted and different individuals separated by distances of greater
+or lesser extent. New colonies will thus come into being; and as the
+unlimited increase of the population over limited areas gradually
+reintroduces into them the struggle for territory, new centres of
+distribution, where the process will repeat itself and from which
+expansion will proceed afresh, will be formed. Hence, though it is
+clearly impossible for the progeny of one pair of Yellow Buntings to
+overspread the whole of the 46 square miles, it is by no means
+impossible for the limits of their range to exceed even those limits
+within the eleven years.
+
+To sum up our knowledge regarding this phase. Of the organic condition
+which renders the impulse responsive to stimulation we know very little;
+and though certain facts of observation seem to indicate the direction
+in which the stimulus is to be found, we must here again confess to much
+ignorance. So far as can be seen, however, the impulse to seek isolation
+with its correlative territory, leads to constant modification in the
+breeding range of most species. The occupation of the small space of
+ground which each individual requires, the extent of which has been
+gradually adjusted to suit the needs of different species, results in
+expansion not only in one direction but in every direction, and not only
+in one season but in every season. And if there were no complications in
+the external world this expansion would proceed, as we have seen, with
+astonishing rapidity. But complications, some of which are favourable
+and others unfavourable, are numerous, and it is difficult to estimate
+their importance or to indicate their precise effect; the former,
+however, accelerate the rate of expansion, whilst the latter retard it.
+Those individuals that wander outwards and seek territory on the
+outskirts of the range we have called "pioneers." They will have
+advantages over others that, wandering inwards, seek isolation in
+congested districts, and will succeed where the latter fail; and since
+there is in the young an innate ability to return to the district
+wherein they were reared, the advantages so gained may be said to be
+handed on from generation to generation.
+
+Let us now turn to the contra-phase, and endeavour to ascertain whether
+the gregarious instinct bears any relation to the seasonal desertion of
+the breeding ground. The conclusion at which we have already arrived
+regarding this instinct is that it forms part of the inherited nature of
+most species; that its functioning is suppressed when a bird is actually
+in occupation of a territory; and that it is serviceable in promoting
+the welfare of the individual. We cannot of course observe the instinct.
+What we observe, when reproduction is ended, is a change in the
+relations of different individuals; instead of arousing mutual
+hostility, they attract one another, from which we infer the existence
+of something which determines their conduct, and this "something" we
+speak of as an instinct.
+
+To what does this change lead? Let us suppose that there is an area
+inhabited by one species; that the number of inhabitants has reached the
+maximum that the means of sustenance will allow; and that the season of
+reproduction is drawing to a close. The position will then be as
+follows. All the available breeding ground is divided into territories;
+each territory is occupied by one unit, the family, and each individual
+is able to fend for itself; changes both internal and external begin to
+take place, the gregarious instinct comes into functional operation, and
+the supply of food diminishes--that roughly is the position. The
+internal factor operates so that the sight of this individual or the
+call of that, instead of evoking hostility as heretofore and keeping
+different units apart, proves now an irresistible attraction; so that in
+place of a number of individuals evenly dispersed over the whole of this
+area, a small number of flocks of various dimensions are stationed at
+certain points, which points are determined partly by experience, partly
+by the supply of food, and partly by accident. This implies for each
+individual some movement in some direction. But since the population of
+this imaginary area has reached the maximum, and the supply of food,
+though limited in distribution, is nevertheless plentiful, such
+movements will be irregular and will proceed in no definite direction.
+
+Now let us suppose that the breeding range extends and that fresh ground
+is occupied by pioneers. When reproduction and the rearing of broods are
+ended and the gregarious instinct becomes dominant, these pioneers, or
+at least some of them, will revisit the area wherein formerly they
+associated with companions. Their offspring, however, though they will
+have the inherited impulse and the innate tendency, will not have the
+experience; how then will they behave? There can be no doubt that some
+will accompany the older birds, and, being led by them, will share the
+experience of a former generation; nor any question that others will
+collect together in the neighbourhood of their birthplace and, if their
+impulse is satisfied, will remain there so long as food is to be found.
+Thus the gregarious instinct, working in close relation with acquired
+experience, will on the one hand lead to the formation of organised
+movements in certain directions, whilst on the other it will lead to the
+formation of new areas of association which will follow in the wake of
+the expansion.
+
+We have assumed, in the imaginary case which we have just taken, that
+the conditions in the external world are such as enable the birds to
+endure throughout the year--in short, that there are no complications
+regarding the supply of food. But we must bear in mind that so long as
+conditions are favourable during the period of reproduction, which is of
+short duration, the breeding range can continue to expand, and that
+therefore, in the course of centuries, regions will come to be occupied
+wherein, owing to alternations of climate or physical changes in the
+surface of the earth, food will be impossible, or at any rate difficult
+to obtain at certain seasons. Hence there will come a time when the area
+of association ceases to follow in the wake of the expansion, and the
+breeding area begins to diverge from the subsistence area.
+
+How, then, is the gulf between these two areas to be bridged? We can of
+course say that those individuals which, in virtue of some slight
+variation of hereditary tendency, return to regions where food is
+plentiful will survive; whilst others, less well endowed, will perish.
+We can state the position in some such general terms, and doubtless
+there would be truth in the statement, but it does not carry us far; we
+wish to know more of the nature of the tendency, and of the manner in
+which it has evolved. Well now, in this new situation which arises, two
+things are apparent--that the struggle for existence becomes a struggle
+for the means of subsistence, and that anything in the inherited
+constitution of the bird which can be organised to subserve the
+biological end in view becomes of selection value. So long as food can
+always be procured in the new areas of association, the individuals that
+behave in accordance with ancestral routine gain thereby no particular
+advantage; but directly the breeding range extends into regions where
+the supply fluctuates, traditional experience becomes a factor in
+survival, and those individuals that come under its influence will, on
+the average, be more likely to endure and so to procreate their kind and
+maintain the tradition. Let it once be granted that there is an innate
+capacity to retain in later phases of routine the experience gained in
+earlier phases, and it is difficult to see how traditional guidance can
+be refused recognition as a factor in the developing situation. But only
+_a_ factor, and by no means the most important one; for observation has
+shown that the young are capable of performing the return journey
+without guidance. Something therefore _is_ inherited, some impulse
+which comes into functional activity at a specified time, and leads the
+bird to set forth in a given direction.
+
+There are no grounds for supposing that the experience of one generation
+forms any part of the hereditary equipment of subsequent generations. In
+what direction then are we to look for the congenital factor? What is
+given is an inherited tendency to co-operation and mutual help, and an
+innate capacity to make use of the results of experience. The inherited
+tendency, as we have seen, leads on the one hand to the formation of new
+areas of association, whilst on the other, since it is the means of
+bringing isolated individuals into contact, it leads to experience being
+handed on from generation to generation, which, in its turn, results in
+a certain amount of backward movement along the line of expansion. It
+forms part of the hereditary equipment of many species, and is
+serviceable in promoting the welfare of the individual. Moreover, there
+is reason to believe that its origin dates back to an early period in
+the evolution of the higher forms of life; and if in the subsequent
+course of evolution it could have been so organised as to serve a double
+purpose, so much the more reason would there have been for its survival.
+In what does the instinct consist? Is it merely that the sight of this
+individual or the call of that proves at some particular moment an
+irresistible attraction, or does the appropriate organic condition give
+rise, as is generally supposed, to some preceding state of uneasiness?
+In the former case, the temporarily isolated individual or colony would
+have but little chance of sharing in the benefits which mutual
+association confers upon the associates; in the latter, the feeling of
+discomfort would lead to restlessness, and would thus bring the bird
+into touch with the environing circumstances under which instinctive
+behaviour could run its further course. So that it is probable that the
+movements of each individual, prior to its becoming a unit in the flock,
+are not accidental but are determined in some measure by racial
+preparation.
+
+Now if the fundamental assumption of the doctrine of the struggle for
+existence be true, the gregarious instinct will not be quite alike in
+all the members of different broods, nor even in each member of the same
+brood; that is, variation will occur in all possible directions. And we
+shall not, I think, exceed the limits of probability if we assume that
+different individuals vary in the persistency with which they strive to
+attain their unknown end, and in the direction in which they travel in
+pursuit of it. So that in each generation they will fall into three
+classes: (1) those which are inert, (2) those which wander along the
+line of expansion, (3) those which wander in other directions. If then
+the struggle for life at this particular juncture in the evolution of
+the breeding range is a struggle for the means of subsistence, the
+members of these three classes will not be in a like satisfactory
+position so far as the competition for food is concerned. Those in the
+first class--_i.e._, those in which the activity feelings are weak--will
+neither gain the benefits which arise from mutual help, nor will they
+have much prospect of enduring through the season of scarcity. Those in
+the third class will, it is true, derive some assistance one from
+another, and so be in a better position to discover what food may be
+available; but inasmuch as they will remain in regions where the climate
+alternates and the supply of food is liable to fall below the minimum
+required, the chances are that a high percentage will fail in the
+struggle for existence. We come now to those in the second class, and it
+is upon them that I wish more particularly to focus attention. The
+initial movement in their case will be in the direction from which
+outward expansion has all along taken place. Within a comparatively
+short distance they will reach districts where the species is plentiful,
+and here, associating with others that have some traditional experience,
+they will be guided by them and will find themselves in regions where
+food is plentiful. Hence in each generation those will survive that,
+owing to some congenital variation of their instinct, seek satisfaction
+for their impulse in a direction which brings them under the influence
+of tradition. And though at first but slight and not in themselves of
+survival value, such variations, since they coincide with modifications
+of behaviour due to acquired experience, will be preserved and in the
+process of time so accumulated as to be capable of determining the
+direction and extent of the movement.
+
+But the young Cuckoo deserts this country many weeks after its parents,
+and there is no reason to suppose that it lives in society when
+eventually its destination is reached; and the young Falcon passes to
+the south, and is certainly not gregarious--how then can we explain
+their behaviour in terms of something which they show no signs of
+possessing? I do not wish to make light of a difficulty which
+admittedly, at first sight, is a grave objection to the view that the
+gregarious instinct has been operative in the manner here claimed for
+it. It must, however, be borne in mind that this instinct, though
+originally developed to serve the purpose of mutual protection, supplies
+the material upon which evolution works when the extension of the
+breeding range creates a situation requiring readjustment on the part of
+the organism to new conditions of life; and that those variations which
+can be so modified as to be in useful relation to the new environmental
+circumstances are seized upon by natural selection and, being
+transmitted, form the foundation of a specific inherited response, no
+longer dependent upon, though operating in close relation with the
+primitive response whence originally it sprang. Thus the primordial
+instinct becomes so organised as to serve a secondary purpose, that of
+rendering secure a means of access to a certain food supply. In the
+course of evolution species were bound to arise which, owing to some
+peculiar conditions, derived greater advantage from living solitary than
+from living in society. Does it then follow, because such species
+manifest no inclination to live in society, that the instinct never has
+played any part in their lives? Or because the primary purpose has
+lapsed, does it follow that the secondary no longer exists?
+
+
+Let me recapitulate the principal considerations which I have discussed
+in this chapter.
+
+Though I have been advancing a theory, and though I have taken much for
+granted, yet it will, I think, be admitted that both the theory and what
+has been taken for granted rest on observational grounds. As our
+starting-point we have a bird whose inherited nature alternates
+according to the season, and in whose nature we can distinguish two
+contra-phases--the one to live in society, the other to live solitary.
+While both have their part to play in furthering the life of the
+individual, for biological interpretation there is only one end, the
+prospective value of which is the continuance of the race. We may say
+that the latter phase is the more important of the two because it is
+directly concerned with reproduction. But we shall make a great mistake
+if we attach peculiar importance to one phase, or to one mode of
+behaviour within that phase, or to one action within that mode of
+behaviour; for if there is one thing certain it is that the whole is an
+inter-related whole in which each part depends for its success upon that
+which precedes it.
+
+In that phase in which the territory is the central feature of the
+situation, the struggle for existence is in operation in its acutest
+form; all the congenital and acquired capacities of the bird--pugnacity,
+song, capacity to utilise in later phases the experience gained in prior
+phases, all these are organised to subserve an end--a proximate
+end--which in its simplest terms may be described as "isolation."
+Isolation is then the first step in the process of reproduction, and any
+individual that fails to make it good, fails to procreate its kind. But
+isolation implies separation, and the degree of separation varies in
+different species, from the few square feet of cliff required by the
+Guillemot to the few square miles of barren moor over which the
+Peregrine exercises dominion. One species must occupy sufficient ground
+to enable it to secure food for its young; another requires sufficient,
+but no more, upon which to deposit its egg; and a third must secure a
+position for its nest within the community. Hence it follows that the
+degree of separation varies with the conditions of existence. Since,
+however, the conditions in the external world are constantly changing
+according to the relative abundance or scarcity of enemies, the rise or
+fall of rivals, the physical changes in the earth's surface, and the
+alterations of climate, it is clear that isolation can only be obtained
+with difficulty, and that the competition for it must be severe. Some
+individuals therefore fail to breed, whilst others, perhaps because
+their impulse is stronger, persevere and seek stations elsewhere. What
+are their prospects of finding them? By extending the field of their
+activities, they will wander into districts remote from the scene of
+competition, districts where not only food is plentiful but where
+enemies and rivals are scarce; and to these pioneers, if to any, success
+in reproduction will most certainly be assured. But not only is it they
+who will benefit; their offspring also, when the time comes for them to
+take their part in the maintenance of the race, will share in the
+success of their parents, for even though they may not escape
+competition from individuals of closely related forms, they will meet
+with but little from those of their own kind. Now species which live
+throughout the year in the vicinity of their territory are comparatively
+few, the majority are obliged to wander in search of food so soon as
+reproduction is ended, and their behaviour is determined not only by its
+abundance or scarcity, but also by the powerful gregarious impulse which
+waxes in proportion as the instincts connected with reproduction wane.
+If, then, when the sexual instinct again becomes predominant, the
+experience of the former season nowise affects their movements, little
+or no progress will be made in the expansion of the range. But just as a
+certain entrance into the bush and pathway through it, when once made
+use of in the process of building, becomes so firmly established as to
+form the sole highway to and from the nest, so likewise, when the
+impulse to seek isolation repeats itself, the bird is constrained to
+seek the neighbourhood wherein it had experienced the enjoyment of
+breeding or of birth. Thus the little that is added one year becomes the
+basis for further additions in the next, and new centres of distribution
+are continually being formed from which expansion proceeds anew.
+
+Now as the range gradually extends into regions where the climate
+alternates and food at certain seasons is consequently scarce, the
+distance between the customary area of association and that of
+reproduction must perforce widen. The question then arises: How will the
+young that have no experience find their way to regions wherein they can
+endure? The forces which may have been organised to subserve the end in
+view are three: (1) Acquired experience, (2) tradition, (3) the
+gregarious instinct. The pioneer that carries the range a little further
+forward starts from a base where it has associated with companions and
+found food plentiful; and when the impulse to live in society again
+asserts itself, it not only repeats its former experience but hands on
+the habit thus acquired to those of the next generation that happen to
+accompany it. Granting, however, that by successive increments in the
+distance traversed, traditional guidance may in time accomplish much, it
+cannot account for all the known facts, it cannot at any rate explain
+the fact that in some cases the inexperienced offspring finds its way to
+the food area without guidance. Something, therefore, _is_ inherited.
+And my suggestion is this: That the gregarious instinct, the ancient
+origin of which we can infer from its manifestation in so many and
+diverse forms of life, supplies the material upon which evolution works;
+that variations of the initial impulse, at first slight and not in
+themselves of selection value, in so far as they coincide in direction
+with modifications of procedure due to experience or tradition, are
+preserved; and that, in the process of time, they are so accumulated as
+to form a specific congenital endowment determining a definite mode of
+behaviour.
+
+
+  FOOTNOTES:
+
+  [1] June 1915, R. M. Barrington.
+
+  [2] _Dictionary of Birds_, p. 556.
+
+  [3] _Social Psychology._
+
+  [4] _Manual of Psychology._
+
+  [5] _Ibis_, April 1918.
+
+  [6] _Zoologist_, 1912, p. 327.
+
+
+
+
+  INDEX
+
+
+  Acquired experience, 300
+
+  Adjustments, transitory, of distribution, 275
+
+  Alarm notes, 119
+
+  Arrival, advantages and disadvantages of late, 33-44
+
+  Assemblies in winter, 262, 263
+
+  Assembly grounds, 173
+
+  Attainment of reproduction, 171
+
+
+  Barrington, R. M., on the sex of migrants, 25
+
+  Battle between two male Cuckoos, 82
+
+  ---- between two Moor-Hens, 86, 92, 93, 94
+
+  ---- ---- Pied Wagtails, 86
+
+  ---- ---- Raven and Buzzard, 217
+
+  ---- ---- Raven and Peregrine, 216
+    law of, 13,19
+
+  Behaviour routine, 262
+
+  ---- sexual, 3
+
+  Bickerings, 96
+
+  Birthplace, return to, 43, 50
+
+  Blackbird, 87, 182, 222, 244
+
+  Blackcap, 81, 156, 224, 230
+
+  Black Grouse, 63
+
+  Black-tailed Godwit, 53
+
+  Boundaries, 1, 5
+
+  ---- conflicts for retention of, 7, 62
+
+  ---- disputes as to, 1
+
+  Brambling, 124
+
+  Breeding ground, search for appropriate, 270, 271
+
+  ---- range, extension of, 291-92
+
+  ---- site, acquirement of, 3
+
+  ---- stations, evolution of, 15-19
+
+  ---- ---- repeatedly visited long before nesting-time, 64
+
+  ---- territory, 2, 3, 7
+
+  ---- ---- evolution of, 18
+
+  ---- ---- foundation of, 7
+
+  ---- ---- innate capacity to return to former, 279-81
+
+  Bridled Guillemot, 64
+
+  Brooding, 180
+
+  ---- impulse, 191
+
+  Bunting, Cirl, 28, 140
+
+  ---- Corn, 28
+
+  ---- Reed, 28, 68, 69, 85, 104, 132, 158, 160, 244
+
+  ---- Yellow, 28, 30, 47, 64, 140, 159, 162, 183, 187, 188, 189,
+    235, 236, 286
+
+  Buzzard, 217
+
+
+  Capacity, innate, to return to former breeding territory, 279-81
+
+  Carrion Crow, 226
+
+  Chaffinch, 28, 31, 32, 33, 45, 87, 103, 156, 159, 235, 236, 244
+
+  ---- Donegal, 160
+
+  Change of breeding quarters owing to unsuitableness, 50
+
+  Chiffchaff, 49, 51, 80, 139, 140, 221, 224, 244
+
+  Cirl Bunting, 28, 140
+
+  Clarke, W. Eagle, _Studies in Bird Migration_, 24
+
+  Cleanliness of nest, 180
+
+  Cliff-breeding species, 63
+
+  Climatic changes, alteration of routine, due to, 284
+
+  ---- changes, food dependent on, 283
+
+  ---- conditions, influence of, 20
+
+  Communities, 202
+
+  ---- birds after breeding-season remain in, 265-67
+
+  Competition, female, for males, 13
+
+  Complexity of strife, 84-85
+
+  Conflicts between males during the mating period, 74, 86
+
+  ---- between males during the nesting period, 87
+
+  ---- for areas, 10, 11, 13, 62
+
+  ---- of Ruff, 54
+
+  ---- sexual, 10
+
+  Congenital disposition, 135
+
+  Contests between males for possession of females, 80
+
+  Coot, 61
+
+  Corn-Bunting, 28
+
+  Corncrake, 39
+
+  Crow, Carrion, 226, 227
+
+  Crow, Hooded, 202
+
+  Cuckoo, 52, 82, 144, 296
+
+  ---- restricted breeding area, 52
+
+  Curlew, 119, 138, 140, 250, 262, 263, 265, 273
+
+
+  Danger warnings, 269
+
+  Darwin, C., _Descent of Man_, 35
+
+  ---- on the arrival of males before females, 35
+
+  Defence of territory, 6
+
+  Development, sexual, 6
+
+  Disposition, congenital, 135
+
+  ---- functioning of, 74
+
+  ---- inherited, 5
+
+  ---- to defend the territory, 73-118
+
+  ---- to mate, 27
+
+  ---- to remain in a particular place in a particular environment, 6
+
+  ---- to secure a territory, 6, 20-72
+
+  Distribution, adjustment of, 275
+
+  Dove, Turtle, 126, 232
+
+  Dunlin, 250
+
+
+  Emotional behaviour, 53, 82, 114
+
+  ---- manifestation, 90, 283
+
+  ---- response, 26
+
+  Enemies, 282
+
+  Energy, waste of, 219
+
+  Environment, 6
+
+  ---- and food, 56
+
+  ---- changes of, 283
+
+  ---- external, conditions in, 279, 282
+
+  Equipment, hereditary, 6
+
+  Evolution of breeding stations or territory, 15, 19
+
+  ---- of the territory, 176
+
+  ---- of the voice, 163
+
+  Existence, struggle for, 294
+
+  Experience, acquired, 300
+
+  Experiments, removal of nests for, 181, 185, 190, 213, 214
+
+  Exposure, its effect on nestlings, 180
+
+  External environment, conditions in, 279, 282
+
+
+  Falcon, 48, 71
+
+  Feeding grounds, neutral, 125 in communities, 70
+
+  Females, fighting amongst, 109-118
+
+  ---- sexual impulse of, 13
+
+  Fieldfare, 124
+
+  Fighting instinct, 79, 82
+
+  Flight, emotional behaviour of Godwit during, 53
+
+  Flocks, in winter, birds collect together in, 262
+
+  Flycatcher, 244
+
+  Food, procuring of, 5
+
+  ---- abundance, or scarcity of, its relation to prosperity of young,
+         15, 16
+
+  ---- its bearing, on the movement of flocks, 262
+
+  ---- rearing of young dependent on rapid and regular, 179, 195
+
+  ---- supply, proximity to, necessary for rearing young, 179, 195
+
+  Fortuitous mating, 174
+
+  Fowler, Ward, on the value of communities, Rooks, 202
+
+  Fulmar, 121, 247
+
+  Functional activity, 259
+
+  ---- instinct of Reeve, 173
+
+  Functioning of the disposition, 275
+
+  ---- of the primary dispositions, 100
+
+
+  Garden Warbler, 223, 225, 230
+
+  Gätke, H., _Birds of Heligoland_, 24
+
+  ---- on the absence of song in birds on Heligoland, 124
+
+  ---- on the early arrival of Guillemots on Heligoland, 64
+
+  Godwit, emotional behaviour of, during flight, 53
+
+  ---- Black-tailed, 53
+
+  Grasshopper Warbler, 39, 131, 139, 153, 155, 187, 244
+
+  Greenfinch, 28, 33, 140, 235, 236
+
+  Gregarious instinct, 20, 61, 141, 265-66, 269, 276, 289, 290, 291,
+    296, 300
+
+  Grouse, Black, 63
+
+  Guillemot, Bridled, 64
+
+  ---- Common, 63, 64, 121, 192, 195, 206, 211, 247
+
+  ---- Ringed, 64
+
+  Gull, Common, 119
+
+  ---- Herring, 210, 278
+
+
+  Habit formation, law of, 8, 62, 65, 66, 67, 205
+
+  Hawfinch, 28
+
+  Headquarters, 176, 206, 207, 274
+
+  ---- restricted, 8, 9, 30, 50, 58, 64, 127
+
+  Hedge-Sparrow, 213, 221, 244
+
+  Hereditary equipment, 6
+
+  Herring-Gull, 210, 278
+
+  Hooded-Crow, 202
+
+  Hostility and territory, relationship between, 242
+
+  House-Sparrow, 218
+
+
+  Imitation, vocal, powers of, 156, 157, 161
+
+  Impulse, internal, 279
+
+  ---- to brood, 191
+
+  Inherited disposition, 5
+
+  Instinct, fighting, 79-82
+
+  ---- gregarious, 20, 61, 141, 265, 266, 269, 276, 289, 290, 291, 296,
+         300
+
+  ---- migratory, 37
+
+  ---- of song related to establishment of territory, 125
+
+  ---- sexual, reawakening of, 4, 18
+
+  Instinctive response, 180
+
+  Instincts susceptible to stimulation, 259
+
+  Internal impulse, 279
+
+  Internal stimulation, 62, 123
+
+  Interpretation of battles, 75
+
+  Intolerance of other birds, 218, 219
+
+  Intrusion resented, 274
+
+  Isolation, impulse to seek, 288
+
+  ---- of male, 12, 62, 65, 73, 81
+
+  ---- of male during breeding season, 267, 272, 273, 275, 281
+
+
+  Jay, 87, 156, 283
+
+
+  Kestrel, 228
+
+  Kittiwake, 116, 200, 247
+
+
+  Lapwing, 58, 59, 61, 62, 64, 84, 103, 104, 126, 189, 190, 220, 251, 284
+
+  Lapwing, life-history of, 58-61
+
+  Late arrival, advantages and disadvantages of, 33-44
+
+  Law of battle, 74, 75, 86
+
+  Lesser Whitethroat, 230, 244
+
+  Linnet, 156
+
+
+  M'Dougall, Dr, _Social Psychology_, 77
+
+  Magpie, 219, 283
+
+  Males arrive before advent of females, 24
+
+  Marsh-Warbler, 39, 40, 52, 81, 132, 140, 153, 155, 156, 165, 225
+
+  Martin, 201, 218
+
+  Mating, difficulties of, 172
+
+  ---- fortuitous, 174
+
+  Maximum number supportable in a given locality, 49
+
+  Meadow-Pipit, 188
+
+  Meeting places for antics, 54, 63
+
+  Mental Image, 77
+
+  Merlin, 227
+
+  Migration, 3-4
+
+  ---- distance no criterion, 279
+
+  ---- its relation to territory, 259
+
+  Migration, origin of, 260, 277
+
+  ---- phenomenon of, 277
+
+  Migratory instinct, 37
+
+  ---- species more highly specialised than resident species, 56
+
+  Missel-Thrush, 21
+
+  Mobility of the land and stability of the water, 260
+
+  Moor-hen, 61, 85, 103, 218, 250, 251
+
+  Morgan, Professor Lloyd, on instinctive behaviour, 74
+
+  ---- on emotional behaviour, 114
+
+
+  Nest, cleaning of, 180
+
+  ---- construction of, 3
+
+  Nests, removal of, for experiments, 181, 185, 190, 213, 214
+
+  Neutral feeding grounds, 62, 125
+
+  ---- ground, 98
+
+  Newton, E., on the arrival at breeding stations of males before female,
+    24, 35
+
+  Nightingale, 39, 156
+
+  Notes of alarm, 119
+
+  ---- of anger, 119
+
+  ---- of recognition, 139
+
+  ---- of warning, 119, 139, 141, 145, 151, 153
+
+
+  Offspring, rearing of, 3, 4
+
+  Organic change, sexual, 92, 123
+
+  ---- changes, 65
+
+  ---- condition of Reeve, 173
+
+  Owl, Wood, 156
+
+
+  Paired for life, 55-56
+
+  Parental instinctive response, failure of, 185
+
+  Partridge, 87, 218
+
+  Persecution, Carrion Crow and Magpie, 226
+
+  Persecution, Carrion Crow and Rook, 227
+
+  ---- House Sparrow and Martin, 218
+
+  ---- Lapwing and Snipe, 220
+
+  ---- Raven and Buzzard, 217
+
+  ---- ---- and Peregrine, 216
+
+  ---- Starling and Woodpecker, 218, 237
+
+  Persistency to remain in territory, 68
+
+  Pied-Wagtail, 86, 155
+
+  Pigeon, Wood, 219
+
+  Pipit, Meadow, 188
+
+  ---- Tree, 51, 188, 189, 222, 244, 278
+
+  Polyandrous females, 144
+
+  Predatory species, 268
+
+  Promiscuous pairing of Ruffs, 172
+
+  Proximity to food-supply necessary for rearing young, 179, 195
+
+  _Psychology, Manual of_, 1
+
+  Puffin, 63, 116, 200
+
+  Pugnacious instinct, 87-109
+
+  Pugnacity, 11, 62
+
+  ---- of females to obtain mates, 109-118
+
+  ---- of males, prior to mating-season, 77-81
+
+  ---- of Moor-Hen, 218
+
+
+  Racial preparation, 41, 43, 46, 67, 205, 206, 266
+
+  Rail, Water, 218
+
+  Raven, 48, 202, 216
+
+  Razor-bill, 63, 64, 200, 247
+
+  Readjustment of territory, 146
+
+  Rearing of offspring, 3, 4
+
+  Red-backed Shrike, 39, 50, 51, 156
+
+  Redbreast, 47
+
+  Redshank, 139
+
+  Redwing, 124
+
+  Redstart, 230, 244
+
+  Reed-Bunting, 28, 68, 69, 85, 104, 132, 156, 158, 160, 244, 246, 273
+
+  Reed-Warbler, 49, 51, 68, 81, 132, 140, 152, 153, 211, 225
+
+  Reeve, 171
+
+  Relation of song to the territory, 119-68
+
+  ---- of territory to migration, 259
+
+  ---- of territory to the system of reproduction, 169-214
+
+  Relationship to a territory, 169
+
+  Reproduction, 14, 15
+
+  ---- and territory, 169-214
+
+  ---- attainment of, 2, 6, 37
+
+  ---- goal of, 6
+
+  Ringed Guillemot, 64
+
+  Robbery of territory, 104-107
+
+  Rock-formation, suitability for Guillemots nesting on, 196
+
+  Rook, 202, 227
+
+  Routine behaviour, 262
+
+  Ruff, 54, 63, 172
+
+  ---- meeting places for conflicts, 54
+
+  Ruffs, promiscuous pairing of, 172
+
+
+  Savi's Warbler, 139
+
+  Sedge-Warbler, 25, 44, 152, 226, 244
+
+  Selous, E., on the life-history of Ruffs and Reeves, 172
+
+  ---- on meeting places for conflicts and antics, 54
+
+  ---- on the meeting places of Black Grouse, 63
+
+  Service, Robert, on flocks of unmated Sedge-Warblers, 44, 45
+
+  Sexual behaviour, 3
+
+  ---- conflicts, 10
+
+  ---- development, 6
+
+  ---- function, discharge of, 2, 3, 26
+
+  ---- impulse of females, 13
+
+  Sexual instinct in the migratory male, 26
+
+  ---- of Reeve, 173
+
+  ---- ---- reawakening of, 4, 18
+
+  ---- life of birds, 1
+
+  ---- maturity, males arrive at, before females, 36
+
+  ---- organic change, 92, 123
+
+  ---- selection, 166
+
+  Shag, 121
+
+  Shrike, Red-backed, 39, 50, 51, 156
+
+  Skylark, 188, 236, 244
+
+  Snipe, 153, 156, 219, 220
+
+  Sociability when not paired, 125, 126
+
+  Song, as an aid in searching for a mate, 12
+
+  ---- its influence on mating, 167
+
+  ---- origin of, 138
+
+  ---- relation to reproduction, 123
+
+  ---- relation to territory, 119-168
+
+  ---- volume of, influenced by age, seasonal sexual development,
+         or isolation, 166
+
+  Song-Thrush, 222, 244
+
+  Sparrow, House, 218
+
+  Sparrow-Hawk, 269
+
+  Spring, at approach of, birds lose their shyness, 138
+
+  Stability of the water and mobility of the land, 260
+
+  Starling, 217, 218, 237, 251
+
+  Stimulation, internal, 62, 123
+
+  ---- question of, 284
+
+  Stonechat, 87 187, 188, 189, 222, 233, 234
+
+  Stout, Dr, _Manual of Psychology_, 1, 77
+
+  Struggle for existence, 294
+
+  Susceptibility to position, 96
+
+  Swallow, 21, 156, 278
+
+
+  Territory, 1, 5
+
+  ---- adjustment of, 10
+
+  Territory and reproduction, 169-214
+
+  ---- breeding, 2, 3, 7
+
+  ---- dates of acquisition of, 33
+
+  ---- defence of, 6
+
+  ---- desertion of, after rearing young, 276
+
+  ---- disposition to defend, 73-118
+
+  ---- disposition to secure, 6, 20-72
+
+  ---- establishment of, 74, 285
+
+  ---- evolution of, 176
+
+  ---- failure to secure, 286
+
+  ---- fights for, 10, 11, 13, 62
+
+  ---- ownership of, 189
+
+  ---- possession of, a stimulus to song, 136
+
+  ---- its relation to migration, 259
+
+  ---- its relation to reproduction, 169-214
+
+  ---- readjustment of, 147
+
+  ---- restriction of, advantageous for mating, 172
+
+  ---- restricted, 8, 9, 30, 50, 58, 64
+
+  ---- separate for male and female Cuckoo, 144
+
+  ---- song, its relation to the, 119-68
+
+  ---- temporary desertion of, 28, 35, 58, 59
+
+  ---- and hostility, relationship between, 242
+
+  Thrush, Song, 222, 244
+
+  Tit, Blue, 221, 226
+
+  ---- Great, 221
+
+  ---- Long-tailed, 226
+
+  Tradition, 300
+
+  Tree-Pipit, 51, 188, 189, 222, 232, 244, 278
+
+  Turtle-Dove, 126, 232
+
+
+  Union of sexes, 12
+
+  Ussher, H. B., on the hostility between Choughs and Hooded Crows
+    and Choughs and Ravens, 227
+
+
+  Vocal Imitation, 156, 157, 161
+
+  Voice calls of Curlew, 263
+
+
+  Wagtail, Pied, 86, 155
+
+  ---- Yellow, 278
+
+  Wanderings from land, Guillemots, 193
+
+  Warbler, Garden, 223, 225, 230
+
+  ---- Grasshopper, 39, 131, 139, 155, 187, 244
+
+  ---- Marsh, 39, 40, 52, 81, 132, 140, 155, 156, 225
+
+  ---- Reed, 49, 51, 68, 81, 132, 140, 152, 153, 211, 225
+
+  ---- Savi's, 139
+
+  ---- Sedge, 25, 44, 152, 226, 244
+
+  ---- Willow, 25, 47, 50, 51, 80, 91, 140, 187, 211, 232, 244, 273
+
+  ---- Wood, 50, 51, 132, 221
+
+  Warfare between different species and its relation to the territory,
+    215-58
+
+  Warning notes, 119
+
+  ---- of danger, 269
+
+  Water Rail, 218
+
+  Wheatear, 25, 51
+
+  Whimbrel, 140
+
+  Whinchat, 39, 50, 51, 81, 222, 232, 233, 234, 244
+
+  Whitethroat, 25, 50, 68, 69, 124, 140, 182, 187, 189, 190, 213, 230,
+    244
+
+  ---- Lesser, 230, 244
+
+  Wild Duck, 250
+
+  Will, the, to fight, 102
+
+  Willow-Warbler, 25, 47, 50, 51, 80, 91, 140, 187, 211, 232, 244, 273
+
+  Winter assemblies, 262-63
+
+  Witherby, H. F., in _British Birds_, on the return to former
+    breeding-ground, 281
+
+  Wood-Owl, 156
+
+  Wood-Pigeon, 219
+
+  Wood-Warbler, 50, 51, 132, 221
+
+  Woodpecker, Lesser Spotted, 237
+
+  ---- Great Spotted, 237, 238
+
+  ---- Green, 20, 71, 156, 208, 218, 237
+
+  Wren, 244
+
+
+  Yellow Bunting, 28, 30, 47, 64, 140, 159, 162, 183, 187, 188, 189,
+    235, 236, 286
+
+  Young die in nest from exposure, 184, 185
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+The Project Gutenberg EBook of Territory in Bird Life, by H. Eliot Howard
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: Territory in Bird Life
+
+Author: H. Eliot Howard
+
+Illustrator: G. E. Lodge
+             H. Grönvold
+
+Release Date: April 14, 2010 [EBook #31987]
+
+Language: English
+
+Character set encoding: ISO-8859-1
+
+*** START OF THIS PROJECT GUTENBERG EBOOK TERRITORY IN BIRD LIFE ***
+
+
+
+
+Produced by Chris Curnow, Turgut Dincer, Joseph Cooper and
+the Online Distributed Proofreading Team at
+https://www.pgdp.net
+
+
+
+
+
+
+
+  +-------------------------------------------------------+
+  |  TRANSCRIBER'S NOTE:                                  |
+  |                                                       |
+  |  There are a large number of compound words in        |
+  |  this book including bird names which occur joined,   |
+  |  spaced and hyphenated. No attempt has been made to   |
+  |  correct these discrepancies as these are mostly      |
+  |  alternative spellings of the same word. In the case  |
+  |  of bird names it is difficult to decide as           |
+  |  ornithologists are still debating on this subject.   |
+  +-------------------------------------------------------+
+
+
+  TERRITORY IN BIRD LIFE
+
+
+  [Illustration: A pair of Lesser Spotted Woodpeckers attacking a Great
+     Spotted Woodpecker
+
+  Emery Walker ph.sc.]
+
+
+  TERRITORY IN
+  BIRD LIFE
+
+  BY H. ELIOT HOWARD
+
+
+  WITH ILLUSTRATIONS BY
+  G. E. LODGE AND H. GRÖNVOLD
+
+
+  NEW YORK
+  E. P. DUTTON AND COMPANY
+  1920
+
+
+
+
+PREFACE
+
+
+When studying the Warblers some twenty years ago, I became aware of the
+fact that each male isolates itself at the commencement of the breeding
+season and exercises dominion over a restricted area of ground. Further
+investigation, pursued with a view to ascertaining the relation of this
+particular mode of behaviour to the system of reproduction, led to my
+studying various species, not only those of close affinity, but those
+widely remote in the tree of avian life. The present work is the outcome
+of those investigations. In it I have endeavoured to interpret the
+prospective value of the behaviour, and to trace out the relationships
+in the organic and inorganic world which have determined its survival.
+Much is mere speculation; much with fuller knowledge may be found to be
+wrong. But I venture to hope that a nucleus will remain upon which a
+more complete territorial system may one day be established.
+
+I have to thank Mr. G. E. Lodge and Mr. H. Grönvold for the trouble they
+have taken in executing my wishes; I also want to record my indebtedness
+to the late E. W. Hopewell; and to Professor Lloyd Morgan, F.R.S., I am
+beholden more than I can tell.
+
+
+
+
+  CONTENTS
+
+                                                        PAGE
+  CHAPTER I
+
+  INTRODUCTION                                             1
+
+
+  CHAPTER II
+
+  THE DISPOSITION TO SECURE A TERRITORY                   20
+
+
+  CHAPTER III
+
+  THE DISPOSITION TO DEFEND THE TERRITORY                 73
+
+
+  CHAPTER IV
+
+  THE RELATION OF SONG TO THE TERRITORY                  119
+
+
+  CHAPTER V
+
+  THE RELATION OF THE TERRITORY TO THE SYSTEM
+    OF REPRODUCTION                                      169
+
+
+  CHAPTER VI
+
+  THE WARFARE BETWEEN DIFFERENT SPECIES AND ITS
+    RELATION TO THE TERRITORY                            216
+
+
+  CHAPTER VII
+
+  THE RELATION OF THE TERRITORY TO MIGRATION             259
+
+
+  INDEX                                                  302
+
+
+
+  LIST OF ILLUSTRATIONS
+
+
+                                                             _Face page_
+
+  A pair of Lesser Spotted Woodpeckers attacking a Great
+      Spotted Woodpecker                                  _Frontispiece_
+
+  Territorial flight of the Black-tailed Godwit                       54
+
+  Competition for territory is seldom more severe than
+      among cliff-breeding seabirds, and the efforts of
+      individual Razorbills to secure positions on the
+      crowded ledges lead to desperate struggles                      64
+
+  Male Blackbirds fighting for the possession of territory.
+      The bare skin on the crown of the defeated bird shows
+      the nature of the injuries from which it succumbed              74
+
+  Male Cuckoos fighting before the arrival of a female                82
+
+  Two pairs of Pied Wagtails fighting in defence of their
+      territories                                                     86
+
+  Long-tailed Tit: males fighting for the possession of
+      territory. The feathers have been torn from the crown
+      of the defeated and dying rival                                 96
+
+  A battle between two pairs of Jays                                 106
+
+  The Female Chaffinch shares in the defence of the territory
+      and attacks other females                                      110
+
+  Peregrine Falcon attacking a Raven                                 216
+
+  A battle between a pair of Green Woodpeckers and a
+      Great Spotted Woodpecker for the possession of a hole
+      in an oak-tree                                                 238
+
+  Plans of the Water-meadow showing the Territories
+      occupied by Lapwings in 1915 and 1916          _Between_ 58 and 59
+
+
+SCIENTIFIC NAMES OF BIRDS MENTIONED IN THE TEXT
+
+  Raven                       _Corvus corax._
+
+  Carrion-Crow                _Corvus corone._
+
+  Hooded Crow                 _Corvus cornix._
+
+  Rook                        _Corvus frugilegus._
+
+  Magpie                      _Pica pica._
+
+  Jay                         _Garrulus glandarius rufitergum._
+
+  Chough                      _Pyrrhocorax pyrrhocorax._
+
+  Starling                    _Sturnus vulgaris._
+
+  Greenfinch                  _Chloris chloris._
+
+  Hawfinch                    _Coccothraustes coccothraustes._
+
+  House-Sparrow               _Passer domesticus._
+
+  Chaffinch                   _Fringilla coelebs._
+
+  Brambling                   _Fringilla montifringilla._
+
+  Linnet                      _Acanthis cannabina._
+
+  Corn-Bunting                _Emberiza calandra._
+
+  Yellow Bunting              _Emberiza citrinella._
+
+  Cirl Bunting                _Emberiza cirlus._
+
+  Reed-Bunting                _Emberiza schoeniclus._
+
+  Sky-Lark                    _Alauda arvensis._
+
+  Pied Wagtail                _Motacilla lugubris._
+
+  Tree-Pipit                  _Anthus trivialis._
+
+  Meadow-Pipit                _Anthus pratensis._
+
+  Great Titmouse              _Parus major newtoni._
+
+  Blue Titmouse               _Parus coeruleus obscurus._
+
+  Long-tailed Titmouse        _Ægithalus caudatus roseus._
+
+  Red-backed Shrike           _Lanius collurio._
+
+  Whitethroat                 _Sylvia communis._
+
+  Lesser Whitethroat          _Sylvia curruca._
+
+  Blackcap                    _Sylvia atricapilla._
+
+  Grasshopper-Warbler         _Locustella noevia._
+
+  Savi's Warbler              _Locustella luscinioides._
+
+  Reed-Warbler                _Acrocephalus scirpaceus._
+
+  Marsh-Warbler               _Acrocephalus palustris._
+
+  Sedge-Warbler               _Acrocephalus schoenobænus._
+
+  Willow-Warbler              _Phylloscopus trochilus._
+
+  Wood-Warbler                _Phylloscopus sibilatrix._
+
+  Chiffchaff                  _Phylloscopus collybita._
+
+  Song-Thrush                 _Turdus musicus clarkii._
+
+  Redwing                     _Turdus iliacus._
+
+  Blackbird                   _Turdus merula._
+
+  Redstart                    _Phoenicurus phoenicurus._
+
+  Redbreast                   _Erithacus rubecula melophilus._
+
+  Nightingale                 _Luscinia megarhyncha._
+
+  Stonechat                   _Saxicola rubicola._
+
+  Whinchat                    _Saxicola rubetra._
+
+  Wheatear                    _OEnanthe oenanthe._
+
+  Hedge-Sparrow               _Accentor modularis._
+
+  Wren                        _Troglodytes troglodytes._
+
+  Spotted Flycatcher          _Muscicapa striata._
+
+  Swallow                     _Hirundo rustica._
+
+  Martin                      _Delichon urbica._
+
+  Sand-Martin                 _Riparia riparia._
+
+  Great Spotted Woodpecker    _Dryobates major anglicus._
+
+  Lesser Spotted Woodpecker   _Dryobates minor._
+
+  Green Woodpecker            _Picus viridis._
+
+  Cuckoo                      _Cuculus canorus._
+
+  Tawny Owl                   _Strix aluco._
+
+  Buzzard                     _Buteo buteo._
+
+  Sparrow-Hawk                _Accipiter nisus._
+
+  Peregrine Falcon            _Falco peregrinus._
+
+  Merlin                      _Falco æsalon._
+
+  Kestrel                     _Falco tinnunculus._
+
+  Shag                        _Phalacrocorax graculus._
+
+  Wild Duck                   _Anas boschas._
+
+  Snipe                       _Gallinago gallinago._
+
+  Dunlin                      _Tringa alpina._
+
+  Ruff                        _Machetes pugnax._
+
+  Redshank                    _Totanus totanus._
+
+  Black-tailed Godwit         _Limosa limosa._
+
+  Curlew                      _Numenius arquata._
+
+  Whimbrel                    _Numenius phæopus._
+
+  American Golden Plover      _Charadrius dominicus._
+
+  Lapwing                     _Vanellus vanellus._
+
+  Oyster-Catcher              _Hæmatopus ostralegus._
+
+  Herring-Gull                _Larus argentatus._
+
+  Kittiwake                   _Rissa tridactyla._
+
+  Razorbill                   _Alca torda._
+
+  Guillemot                   _Uria troille._
+
+  Puffin                      _Fratercula arctica._
+
+  Fulmar                      _Fulmarus glacialis._
+
+  Water-Rail                  _Rallus aquaticus._
+
+  Corn-Crake                  _Crex crex._
+
+  Moor-Hen                    _Gallinula chloropus._
+
+  Coot                        _Fulica atra._
+
+  Wood-Pigeon                 _Columba palumbus._
+
+  Turtle-Dove                 _Streptopelia turtur._
+
+  Partridge                   _Perdix perdix._
+
+  Black Grouse                _Lyrurus tetrix britannicus._
+
+  Red Grouse                  _Lagopus scoticus._
+
+
+
+
+TERRITORY IN BIRD LIFE
+
+
+
+
+CHAPTER I
+
+INTRODUCTION
+
+
+In his _Manual of Psychology_ Dr Stout reminds us that "Human language
+is especially constructed to describe the mental states of human beings,
+and this means that it is especially constructed so as to mislead us
+when we attempt to describe the working of minds that differ in a great
+degree from the human."
+
+The use of the word "territory" in connection with the sexual life of
+birds is open to the danger which we are here asked to guard against,
+and I propose, therefore, before attempting to establish the theory on
+general grounds, to give some explanation of what the word is intended
+to represent and some account of the exact position that representation
+is supposed to occupy in the drama of bird life.
+
+The word is capable of much expansion. There cannot be territories
+without boundaries of some description; there cannot well be boundaries
+without disputes arising as to those boundaries; nor, one would
+imagine, can there be disputes without consciousness as a factor
+entering into the situation; and so on, until by a simple mental
+process we conceive of a state in bird life analogous to that which we
+know to be customary amongst ourselves. Now, although the term "breeding
+territory," when applied to the sexual life of birds, is not altogether
+a happy one, it is difficult to know how otherwise to give expression to
+the facts observed. Let it then be clearly understood that the
+expression "securing a territory" is used to denote a process, or rather
+part of a process, which, in order to insure success to the individual
+in the attainment of reproduction, has been gradually evolved to meet
+the exigencies of diverse circumstances. Regarded thus, we avoid the
+risk of conceiving of the act of securing a territory as a detached
+event in the life of a bird, and avoid, I hope, the risk of a conception
+based upon the meaning of the word when used to describe human as
+opposed to animal procedure.
+
+Success in the attainment of reproduction is rightly considered to be
+the goal towards which many processes in nature are tending. But what is
+meant by success? Is it determined by the actual discharge of the sexual
+function? So many and so wonderful are the contrivances which have
+slowly been evolved to insure this discharge, that it is scarcely
+surprising to find attention focused upon this one aspect of the
+problem. Yet a moment's reflection will show that so limited a
+definition of the term "success" can only be held to apply to certain
+forms of life; for where the young have to be cared for, fostered, and
+protected from molestation for periods of varying lengths, the actual
+discharge of the sexual function marks but one stage in a process which
+can only succeed if all the contributory factors adequately meet the
+essential conditions of the continuance of the species.
+
+Securing a territory is then part of a process which has for its goal
+the successful rearing of offspring. In this process the functioning of
+the primary impulse, the acquirement of a place suitable for breeding
+purposes, the advent of a female, the discharge of the sexual function,
+the construction of the nest, and the rearing of offspring follow one
+another in orderly sequence. But since we know so little of the organic
+changes which determine sexual behaviour, and have no means of
+ascertaining the nature of the impulse which is first aroused, we can
+only deal with the situation from the point at which the internal
+organic changes reflect themselves in the behaviour to a degree which is
+visible to an external observer. That point is reached when large
+numbers of species, forsaking the normal routine of existence to which
+they have been accustomed for some months, suddenly adopt a radical
+change in their mode of behaviour. How is this change made known to us?
+By vast numbers of individuals hurrying from one part of the globe to
+another, from one country to another, and even from mid-ocean to the
+coasts; by detachments travelling from one district to another; by
+isolated individuals deserting this place for that; by all those
+movements, in fact, which the term migration, widely applied, is held to
+denote. Now the impulse which prompts these travelling hosts must be
+similar in kind whether the journey be long or short; and it were
+better, one would think, to regard such movements as a whole than to
+fix the attention on some one particular journey which fills us with
+amazement on account of the magnitude of the distance traversed or the
+nature of the difficulties overcome. For, after all, what does each
+individual seek? There may be some immature birds which, though they
+have not reached the necessary stage of development, happen to fall in
+with others in whom the impulse is strong and are led by them--they know
+not where. But the majority seek neither continent nor country, neither
+district nor locality is their aim, but a place wherein the rearing of
+offspring can be safely accomplished; and the search for this place is
+the earliest visible manifestation in many species of the reawakening of
+the sexual instinct.
+
+The movements of each individual are then directed towards a similar
+goal, namely, the occupation of a definite station; and this involves
+for many species a distinct change in the routine of behaviour to which
+previously they had been accustomed. Observe, for example, one of the
+numerous flocks of Finches that roam about the fields throughout the
+winter. Though it may be composed of large numbers of individuals of
+different kinds, yet the various units form an amicable society actuated
+by one motive--the procuring of food. And since it is to the advantage
+of all that the individual should be subordinated to the welfare of the
+community as a whole there is no dissension, apart from an occasional
+quarrel here and there.
+
+In response, however, to some internal organic change, which occurs
+early in the season, individuality emerges as a factor in the developing
+situation, and one by one the males betake themselves to secluded
+positions, where each one, occupying a limited area, isolates itself
+from companions. Thereafter we no longer find that certain fields are
+tenanted by flocks of greater or less dimensions, while acres of land
+are uninhabited, but we observe that the hedgerows and thickets are
+divided up into so many territories, each one of which contains its
+owner. This procedure, with of course varying detail, is typical of that
+of many species that breed in Western Europe. And since such a radical
+departure from the normal routine of behaviour could scarcely appear
+generation after generation in so many widely divergent forms, and still
+be so uniform in occurrence each returning season, if it were not
+founded upon some congenital basis, it is probable that the journey,
+whether it be the extensive one of the Warbler or the short one of the
+Reed-Bunting, is undertaken in response to some inherited disposition,
+and probable also that the disposition bears some relation to the few
+acres in which the bird ultimately finds a resting place. Whilst for the
+purpose of the theory I shall give expression to this behaviour in terms
+of that theory, and speak of it as a disposition to secure a territory,
+using the word disposition, which has been rendered current in recent
+discussion, for that part of the inherited nature which has been
+organised to subserve a specific biological purpose--strict compliance
+with the rules of psychological analysis requires a simpler definition;
+let us therefore say "disposition to remain in a particular place in a
+particular environment."
+
+But even granting that this disposition forms part of the hereditary
+equipment of the bird, how is the process of reproduction furthered? The
+mere fact of remaining in or about a particular spot cannot render the
+attainment of reproduction any less arduous, and may indeed add to the
+difficulties, for any number of individuals might congregate together
+and mutually affect one another's interests. A second disposition comes,
+however, into functional activity at much the same stage of sexual
+development, and manifests itself in the male's intolerance of other
+individuals. And the two combined open up an avenue through which the
+individual can approach the goal of reproduction. In terms of the theory
+I shall refer to this second disposition as the one which is concerned
+with the defence of the territory.
+
+Broadly speaking, these two dispositions may be regarded as the basis
+upon which the breeding territory is founded. Yet inasmuch as the
+survival value of the dispositions themselves must have depended upon
+the success of the process as a whole, it is manifest that peculiar
+significance must not be attached to just the area occupied, which
+happens to be so susceptible of observation; other contributory factors
+must also receive attention, for the process is but an order of
+relationships in which the various units have each had their share in
+determining the nature and course of subsequent process, so that, as Dr
+Stout says, when they were modified, it was modified.
+
+Now the male inherits a disposition which leads it to remain in a
+restricted area, but the disposition cannot determine the extent of that
+area. How then are the boundaries fixed? That they are sometimes adhered
+to with remarkable precision, that they can only be encroached upon at
+the risk of a conflict--all of this can be observed with little
+difficulty. But if we regard them as so many lines definitely delimiting
+an area of which the bird is cognisant, we place the whole behaviour on
+a different level of mental development, and incidentally alter the
+complexion of the whole process. It would be a mistake, I think, to do
+this. Though conscious intention as a factor may enter the situation,
+there is no necessity for it to do so; there is no necessity, that is to
+say, for the bird to form a mental image of the area to be occupied and
+shape its course accordingly. The same result can be obtained without
+our having recourse to so complex a principle of explanation, and that
+by the law of habit formation. In common with other animals, birds are
+subject to this law in a marked degree. An acquired mode of activity
+becomes by repetition ingrained in the life of the individual, so that
+an action performed to-day is liable to be repeated to-morrow so long as
+it does not prejudice the existence or annul the fertility of the
+individual.
+
+Let us see how this may have operated in determining the limits of the
+area acquired, and for this purpose let us suppose that we are observing
+a male Reed-Bunting recently established in some secluded piece of marsh
+land. Scattered about this particular marsh are a number of small
+willows and young alder trees, each one of which is capable of providing
+plenty of branches suitable for the bird to perch upon, and all are in a
+like favourable position so far as the outlook therefrom is concerned.
+Well, we should expect to find that each respective tree would be made
+use of according to the position in which the bird happened to find
+itself. But what actually do we find--one tree singled out and resorted
+to with ever-increasing certainty until it becomes an important point in
+relation to the occupied area, a headquarters from which the bird
+advertises its presence by song, keeps watch upon the movements of its
+neighbours, and sets out for the purpose of securing food. We then take
+note of its wanderings in the immediate vicinity of the headquarters,
+especially as regards the direction, frequency, and extent of the
+journeys; and we discover not only that these journeys proceed from and
+terminate in the special tree, but that there is a sameness about the
+actual path that is followed. The bird takes a short flight, searches a
+bush here and some rushes there, returns, and after a while repeats the
+performance; we on our part mark the extreme limits reached in each
+direction, and by continued observation discover that these limits are
+seldom exceeded, that definition grows more and more pronounced, and
+that by degrees the movements of the bird are confined within a
+restricted area. In outline, this is what happens in a host of cases. By
+repetition certain performances become stereotyped, certain paths fixed,
+and a routine is thus established which becomes increasingly definite as
+the season advances.
+
+But while it would be quite untrue to say that this routine is never
+departed from, and equally profitless to attempt to find a point beyond
+which the bird will under no circumstances wander, yet there is enough
+definition and more than enough to answer the purpose for which the
+territory has, I believe, been evolved, that is to say the biological
+end of reproduction. Again, however, the process of adjustment is a
+complex one. Habit plays its part in determining the boundaries in a
+rough and ready manner, but the congenital basis, which is to be found
+in the behaviour adapted to a particular environment, is an important
+factor in the situation. For example, if instead of resting content with
+just a bare position sufficient for the purpose of reproduction, the
+Guillemot were to hustle its neighbours from adjoining ledges, the
+Guillemot as a species would probably disappear; or if instead of
+securing an area capable of supplying sufficient food both for itself
+and its young, the Chiffchaff were to confine itself to a single tree,
+and, after the manner of the Guillemot, trust to spasmodic excursions
+into neutral ground for the purpose of obtaining food, the Chiffchaff
+as a species would probably not endure. All such adjustments have,
+however, been brought about by relationships which have gradually become
+interwoven in the tissue of the race.
+
+The intolerance that the male displays towards other individuals,
+usually of the same sex, leads to a vast amount of strife. Nowhere in
+the animal world are conflicts more frequent, more prolonged, and more
+determined than in the sexual life of birds; and though they are
+acknowledged to be an important factor in the life of the individual,
+yet there is much difference of opinion as to the exact position they
+occupy in the drama of bird life. Partly because they frequently happen
+to be in evidence, partly because they are numerically inferior, and
+partly, I suppose, because the competition thus created would be a means
+of maintaining efficiency, the females, by common consent, are supposed
+to supply the condition under which the pugnacious nature of the male is
+rendered susceptible to appropriate stimulation. And so long as the
+evidence seemed to show that battles were confined to the male sex, so
+long were there grounds for hoping that their origin might be traced to
+such competition. But female fights with female, pair with pair, and,
+which is still more remarkable, a pair will attack a single male or a
+single female; moreover, males that reach their destination in advance
+of their prospective mates engage in serious warfare. How then is it
+possible to look upon the individuals of one sex as directly
+responsible for the strife amongst those of the other, or how can the
+female supply the necessary condition? As long as an attempt is made to
+explain it in terms of the female, the fighting will appear to be of a
+confused order; regard it, however, as part of a larger process which
+demands, amongst other essential conditions of the breeding situation,
+the occupation of a definite territory, and order will reign in place of
+confusion.
+
+But even supposing that the male inherits a disposition to acquire a
+suitable area, even supposing that it inherits a disposition which
+results indirectly in the defence of that area, how does it obtain a
+mate? If the female behaved in a like manner, if she, too, were to
+isolate herself and remain in one place definitely, that would only add
+to the difficulties of mutual discovery. We find, however, in the
+migrants, that the males are earlier than the females in reaching the
+breeding grounds, and, in resident species, that they desert the females
+and retire alone to their prospective territories, so that there is a
+difference in the behaviour of the sexes at the very commencement of the
+sexual process. What is the immediate consequence? Since the male
+isolates itself, it follows, if the union of the sexes is to be
+effected, that the discovery of a mate must rest largely with the
+female. This of course reverses the accepted course of procedure. But
+after all, what reason is there to suppose that, the male seeks the
+female, or that a mutual search takes place; what reason to think that
+this part of the process is subject to no control except such as may be
+supplied by the laws of chance?
+
+Now, clearly, much will depend upon the rapidity with which the female
+can discover a male fit to breed; for if the course of reproduction is
+to flow smoothly, there must be neither undue delay nor waste of energy
+incurred in the search--some guidance is therefore necessary, some
+control in her external environment. Here the song, or the mechanically
+produced sound, comes into play, and assists in the attainment of this
+end. Nevertheless if every male were to make use of its powers whether
+it were in occupation of a territory or not, if the wandering individual
+had an equal chance of attracting a mate, then it would be idle to
+attempt to establish any relation between "song" on the one hand, and
+"territory" on the other, and impossible to regard the voice as the
+medium through which an effectual union of the sexes is procured. But
+there is reason to believe that the males utilise their powers of
+producing sound only under certain well-defined conditions. For
+instance, when they are on their way to the breeding grounds, or moving
+from locality to locality in search of isolation, or when they desert
+their territories temporarily, as certain of the residents often do,
+they are generally silent; but when they are in occupation of their
+territories they become vociferous--and this is notoriously the case
+during the early hours of the day, which is the period of maximum
+activity so far as sexual behaviour is concerned. So that just at the
+moment when the sexual impulse of the female is most susceptible to
+stimulation, the males are betraying their positions and are thus a
+guide to her movements. Nevertheless, even though she may have
+discovered a male ready to breed, success is not necessarily assured to
+her; for with multitudes of individuals striving to procreate their
+kind, it would be surprising if there were no clashing of interests, if
+no two females were ever to meet in the same occupied territory.
+Competition of this kind is not uncommon, and the final appeal is to the
+law of battle, just as an appeal to physical strength sometimes decides
+the question of the initial ownership of a territory.
+
+I shall try to make clear the relations of the various parts to the
+whole with the assistance of whatever facts I can command. I shall do so
+not only for the purposes of the theory, but because one so often finds
+the more important features of sexual behaviour regarded as so many
+distinct phenomena requiring separate treatment, whereas they are
+mutually dependent, and follow one another in ordered sequence. I spoke
+of the process as a series of relationships. Some of these relationships
+have already been touched upon; others will become apparent if we
+consider for a moment the purposes for which the territory has been
+evolved. Indirectly its purpose is that of the whole process, the
+rearing of offspring. But inasmuch as a certain measure of success could
+be attained, and that perhaps often, without all the complications
+introduced by the territory, there are manifestly advantages to be
+gained by its inclusion in the scheme. The difficulties which beset the
+path of reproduction are by no means always the same--all manner of
+adjustments have to be made to suit the needs of different species.
+There are direct relationships, such as we have been speaking of, which
+are essential to the every-day working of the process, and others which
+are indirect, though none the less important for they must have
+exercised an influence throughout the ages. These latter are furnished
+by the physical--the inorganic world, by climate, by the supply of the
+particular kind of breeding stations, by the scarcity or abundance of
+the necessary food and by the relative position of the food supply to
+the places suitable for breeding. Why does the Reed-Bunting cling so
+tenaciously to an acre or more of marshy ground, while the Guillemot
+rests content with a few square feet on a particular ledge of rock? The
+answer is the same in both cases--to facilitate reproduction. But why
+should a small bird require so many square yards, whilst a very much
+larger one is satisfied with so small an area? The explanation must be
+sought in the conditions of existence. The Reed-Bunting has no
+difficulty in finding a position suitable for the construction of its
+nest; there are acres of waste land and reedy swamps capable of
+supplying food for large numbers of individuals, and the necessary
+situations for countless nests. But its young, like those of many
+another species, are born in a very helpless state. For all practical
+purposes they are without covering of any description and consequently
+require protection from the elements, warmth from the body of the
+brooding bird, and repeated supplies of nourishment. A threefold burden
+is thus imposed upon the parents: they must find food for themselves,
+they must afford protection to the young by brooding, and they must
+supply them with the necessary food at regular intervals. And their
+ability to do all this that is demanded of them will be severely taxed
+by the brooding which must perforce curtail the time available for the
+collection of food.
+
+Let us then suppose that the Reed-Buntings inhabiting a certain piece of
+marsh are divided into two classes, those which are pugnacious and
+intolerant of the approach of strangers, and those which welcome their
+presence. The nests of the former will be built in isolation, those of
+the latter in close proximity. In due course eggs will be laid and
+incubation performed, and thus far all alike will probably be
+successful. Here, however, a critical point is reached. If the young are
+to be freed from the risk of exposure, the parents must find the
+necessary supply of food rapidly. But manifestly all will not be in a
+like satisfactory position to accomplish this, for whereas the isolated
+pairs will have free access to all the food in the immediate vicinity of
+the nest, those which have built in proximity to one another, meeting
+competition in every direction, will be compelled to roam farther
+afield and waste much valuable time by doing so; and under conditions
+which can well be imagined, even this slight loss of time will be
+sufficient to impede the growth of the delicate offspring, or to lead
+perhaps to still greater disaster. If any one doubts this, let him first
+examine one of the fragile offspring; let him then study the conditions
+under which it is reared, observing the proportion of time it passes in
+sleep and the anxiety of the parent bird to brood; and finally let him
+picture to himself its plight in a wet season if, in order to collect
+the necessary food, the parents were obliged to absent themselves for
+periods of long duration.
+
+Now take the case of the Guillemot. Its young at birth are by no means
+helpless in the sense that the young Reed-Bunting is, and food is
+readily procured. But breeding stations are scarce, for although there
+are many miles of cliff-bound coast, yet not every type of rock
+formation produces the fissures and ledges upon which the bird rests.
+Hence vast stretches of coast-line remain uninhabited, and the birds are
+forced to concentrate at certain points, where year after year they
+assemble in countless numbers from distant parts of the ocean. If, then,
+different individuals were to jostle one another from adjoining
+positions, and each one were to attempt to occupy a ledge in solitary
+State, not only would the successful ones gain no advantage from the
+additional space over which they exercised dominion, but inasmuch as
+many members that were fitted to breed would be precluded from doing
+so, the status of the species as a whole would be seriously affected.
+The amount of space occupied by each individual is therefore a matter of
+urgent importance. A few square feet of rock sufficient for the
+immediate purpose of incubation is all that can be allowed if the
+species is to maintain its position in the struggle for existence.
+
+Our difficulty in estimating the importance of the various factors that
+make for success or failure arises from our inability to see more than a
+small part of the scene as it slowly unfolds itself. The peculiar
+circumstances under which these cliff-breeding forms dwell does,
+however, enable us to picture, on the one hand, the precarious situation
+of an individual that was incapable of winning or holding a position at
+the accustomed breeding station, and, on the other, the plight of the
+species as a whole if each one exercised authority over too large an
+area. With the majority of species it is difficult to do this. So many
+square miles of suitable breeding ground are inhabited by so few
+Reed-Buntings that, even supposing certain members were to establish an
+ascendency over too wide an area, it would be impossible to discover by
+actual observation whether the race as a whole were being adversely
+affected. Competition doubtless varies at different periods and in
+different districts according to the numerical standing of the species
+in a given locality and according to the numerical standing of others
+that require similar conditions of existence; at times it may even be
+absent, just as at any moment it may become acute. These examples show
+how profoundly the evolution of the breeding territory may have been
+influenced by relationships in the inorganic world, and they give some
+idea of the intricate nature of the problem with which we have to deal.
+
+I mentioned that the first visible manifestation of the revival of the
+sexual instinct was to be found in the movements undertaken by the males
+at the commencement of the breeding season. Such movements are
+characterised by a definiteness of purpose, whether they involve a
+protracted journey of some hundreds of miles or merely embrace a parish
+or so in extent, and that purpose is the acquirement of a territory
+suitable for rearing offspring. They are thus directly related to the
+territory, and the question arises as to whether their origin may not be
+traced to such relatedness. So long as we fix our attention solely upon
+the magnitude of the distance traversed the suggestion may seem a
+fanciful one. Nevertheless, if the battles between males of the same
+species _are_ directly related to the occupation of a position suitable
+for breeding purposes, if those which occur between males of closely
+related forms _can_ be traced to a similar source, if the females take
+their share in the defence of the ground that is occupied, if, in short,
+the competition is as severe as I believe it to be, and is wholly
+responsible for the strife which is prevalent at the commencement of the
+breeding season--then such competition must have introduced profound
+modifications in the distribution of species; it must have even
+influenced the question of the survival of certain forms and the
+elimination of others; and since the powers of locomotion of a bird are
+so highly developed it must have led to an extension of breeding range,
+limited only by unfavourable conditions of existence.
+
+
+
+
+CHAPTER II
+
+THE DISPOSITION TO SECURE A TERRITORY
+
+
+Those who have studied bird life throughout the year are aware that the
+distribution of individuals changes with the changing seasons. During
+autumn and winter, food is not so plentiful and can only be found in
+certain places, and so, partly by force of circumstances and partly on
+account of the gregarious instinct which then comes into functional
+activity, different individuals are drawn together and form flocks of
+greater or less dimensions, which come and go according to the
+prevailing climatic conditions. But with the advent of spring a change
+comes over the scene: flocks disperse, family parties break up, summer
+migrants begin to arrive, and the hedgerows and plantations are suddenly
+quickened into life. The silence of the winter is broken by an outburst
+of song from the throats of many different species, and individuals
+appear in their old haunts and vie with one another in advertising their
+presence by the aid of whatever vocal powers they happen to possess--the
+Woodpecker utters its monotonous call from the accustomed oak; the
+Missel-Thrush, perched upon the topmost branches of the elm,
+persistently repeats its few wild notes; and the Swallow returns to the
+barn.
+
+All of this we observe each season, and our thoughts probably travel to
+the delicate piece of architecture in the undergrowth, or to the hole
+excavated with such skill in the tree trunk; to the beautifully shaped
+eggs; to the parent birds carrying out their work with devoted zeal--in
+fact, to the whole series of events which complete the sexual life of
+the individual; and the attachment of a particular bird to a particular
+spot is readily accounted for in terms of one or other of the emotions
+which centre round the human home.
+
+But if this behaviour is to be understood aright; if, that is to say,
+the exact position it occupies in the drama of bird life is to be
+properly determined, and its biological significance estimated at its
+true value, it is above all things necessary to refrain from appealing
+to any one of the emotions which we are accustomed to associate with
+ourselves, unless our ground for doing so is more than ordinarily
+secure. I shall try to show that, in the case of many species, the male
+inherits a disposition to secure a territory; or, inasmuch as the word
+"secure" carries with it too much prospective meaning, a disposition to
+remain in a particular place when the appropriate time arrives.
+
+If the part which the breeding territory plays in the sexual life of
+birds is the important one I believe it to be, it follows that the
+necessary physiological condition must arise at an early stage in the
+cycle of events which follow one another in ordered sequence and make
+towards the goal of reproduction, and that the behaviour to which it
+leads must be one of the earliest visible manifestations of the seasonal
+development of the sexual instinct. When does this seasonal development
+occur? For how long does the instinct lie dormant? In some species there
+is evidence of this first step in the process of reproduction early in
+February; there is reason to believe that in others the latter part of
+January is the period of revival; and the possibility must not be
+overlooked of still earlier awakenings, marked with little definiteness,
+though nevertheless of sufficient strength to call into functional
+activity the primary impulse in the sexual cycle. Here, then, we meet
+with a difficulty so far as direct observation is concerned, for the
+duration of the period of dormancy and the precise date of revival vary
+in different species; and, if accurate information is to be obtained,
+the study of the series of events which culminate in the attainment of
+reproduction ought certainly to begin the moment behaviour is
+influenced by the internal changes, whatever they may be, which are
+responsible for the awakening of the sexual instinct.
+
+In considering how this difficulty might be met, the importance of
+migratory species as a channel of information was gradually borne in
+upon me; for it seemed that the definiteness with which the initial
+stage in the sexual process was marked off, as a result of the incidence
+of migration, would go far towards removing much of the obscurity which
+appeared to surround the earlier stages of the breeding problem in the
+case of resident species. Recent observation has shown that I
+exaggerated this difficulty, and that it is generally possible to
+determine with reasonable accuracy the approximate date at which the
+internal changes begin to exert an influence on the behaviour of
+resident species also. Nevertheless, the specialised behaviour of the
+migrants furnished a clue, and pointed out the direction which further
+inquiry ought to take.
+
+Those who are accustomed to notice the arrival of the migrants are aware
+that the woods, thickets, and marshes do not suddenly become occupied by
+large numbers of individuals, but that the process of "filling up" is a
+gradual one. An individual appears here, another there; then after a
+pause there is a further addition, and so on with increasing volume
+until the tide reaches its maximum, then activity wanes, and the slowly
+decreasing number of fresh arrivals passes unnoticed in the wealth of
+new life that everywhere forces itself upon our attention. If now,
+instead of surveying the migrants as a whole, our attention be directed
+to one species only, this gradual arrival of single individuals in their
+accustomed haunts will become even more apparent; and if the
+investigation be pursued still further and these single individuals
+observed more closely, it will be found that in nearly every case they
+belong to the male sex. Males therefore arrive before females. This does
+not mean, however, that the respective times of arrival of the males and
+females belonging to any one species are definitely divided, for males
+continue to arrive even after some of the females have reached their
+destination; and thus a certain amount of overlapping occurs. A truer
+definition of the order of migration would be as follows:--Some males
+arrive before others, and some females arrive before others, but on the
+average males arrive before females. This fact has long been known.
+Gätke refers to it in his _Birds of Heligoland_. "Here in Heligoland,"
+he says, "the forerunners of the spring migration are invariably old
+males; a week or two later, solitary old females make their appearance;
+and after several weeks, both sexes occur mixed, _i.e._, females and
+younger males; while finally only young birds of the previous year are
+met with." Newton alludes to it as follows:--"It has been ascertained by
+repeated observation that in the spring movement of most species of the
+northern hemisphere, the cock birds are always in the van of the
+advancing army, and that they appear some days, or perhaps weeks, before
+the hens"; and Dr Eagle Clarke, in his _Studies in Bird Migration_,
+makes the following statement:--"Another characteristic of the spring
+is that the males, the more ardent suitors, of most species, travel in
+advance of the females, and arrive at their meeting quarters some days,
+it is said in some cases even weeks, before their consorts." Some
+interesting details were given in _British Birds_[1] in regard to the
+sex of the migrants that were killed by striking the lantern at the
+Tuskar Rock, Co. Wexford, on the 30th April 1914. In all, there were
+twenty-four Whitethroats, nine Willow-Warblers, eight Sedge-Warblers,
+and six Wheatears; and on dissection it was found that twenty
+Whitethroats, seven Willow-Warblers, eight Sedge-Warblers, and one
+Wheatear were males.
+
+What a curious departure this seems from the usual custom in the animal
+world! Here we have the spectacle afforded us of the males, in whom
+presumably the sexual instinct has awakened, deserting the females just
+at the moment when we might reasonably expect their impulse to accompany
+them would be strongest; and this because of their inherited disposition
+to reach the breeding grounds. If, in order to attain to reproduction,
+the male depended primarily upon securing a female--whether by winning
+or fighting matters not at the moment--if her possession constituted the
+sole difference in his external environment between success and failure,
+then surely one would suppose that an advantage must rest with those
+individuals which, instead of rushing forward and inflicting upon
+themselves a life of temporary isolation, remained with the females and
+increased their opportunities for developing that mutual appreciation
+which, by some, is held to be a necessary prelude to the completion of
+the sexual act, and to which close companionship would tend to impart a
+stimulus.
+
+In thus speaking, however, we assume that the revival of the sexual
+instinct in the migratory male is coincident in time with its return to
+the breeding quarters; and we do so because the act of migrating is
+believed to be the first step in the breeding process. But it is well to
+bear in mind just how much of this assumption is based upon fact, and
+how much is due to questionable inference. All that can be definitely
+asserted is this, that appropriate dissection reveals in most of the
+migrants, upon arrival at their destination, unquestionable evidence of
+seasonal increase in the size of the sexual organs. Beyond this there is
+nothing to go upon. Yet if the term "sexual instinct" is held to
+comprise the whole series of complex relationships which are manifest to
+us in numerous and specialised modes of behaviour, which ultimately lead
+to reproduction, and which have gradually become interwoven in the
+tissue of the race, there can be little doubt that the assumption is a
+reasonable one. To some, the term may recall the fierce conflicts which
+are characteristic of the season; to others, emotional response; to not
+a few, perhaps, the actual discharge of the sexual function--all of
+these, it is true, are different aspects of the one instinct; but at the
+same time each one marks a stage in the process, and the different
+stages follow one another in ordered sequence. However, we are not
+concerned at the moment with the term in its wider application; we wish
+to know the precise stage at which the disposition to mate influences
+the behaviour of the male. Is the female to him, from the moment the
+seasonal change in his sexual organs takes place, a goal that at all
+costs must be attained? Or is it only when the cycle of events which
+leads up to reproduction is nearing completion that she looms upon his
+horizon? One would like to be in a position to answer these questions,
+but there is nothing in the way of experimental evidence to go upon; and
+if I say that there is reason to believe that, in the earlier stages,
+the female is but a shadow in the external environment of the male, it
+must be taken merely as an expression of opinion, though based in some
+measure upon a general observation of the behaviour of various species.
+
+Before attempting to explain the difference in the times of arrival of
+the male and female migrant, let us examine the behaviour of some
+resident species at a corresponding period. My investigations have been
+made principally amongst the smaller species--the Finches and the
+Buntings--which often pass the winter in or near the localities wherein
+they brought up offspring or were reared. It is true that they wander
+from one field to another according to the abundance or scarcity of
+food; it is also true that, if the weather is of a type which precludes
+the possibility of finding the necessary food, these wanderings may
+become extensive or even develop into partial migrations. But under the
+normal climatic conditions which prevail in many parts of Britain, these
+smaller resident species seem to find all that they require without
+travelling any great distance from their breeding haunts. Flocks
+composed of Yellow Buntings, Cirl Buntings, Corn-Buntings, Chaffinches,
+Greenfinches, etc., can be observed round the farmsteads or upon arable
+land; small flocks of Reed-Buntings take up their abode on pieces of
+waste land and remain there until the supply of food is exhausted,
+deserting their feeding ground only towards evening when they retire to
+the nearest reed-bed to pass the night; flocks of Hawfinches visit the
+same holly-trees day after day so long as there is an abundance of
+berries on the ground beneath; and so on.
+
+I have mentioned the Reed-Bunting; let us take it as our first example
+and try to follow its movements when the influence exerted by the
+internal secretions begins to be reflected on the course of its
+behaviour. First, it will be necessary to discover the exact localities
+in any given district to which the species habitually returns for the
+purpose of procreation; otherwise the earlier symptoms of any
+disposition to secure a territory may quite possibly be overlooked in
+the search for its breeding haunts.
+
+In open weather Reed-Buntings pass the winter either singly, in twos or
+threes, or in small flocks, on bare arable ground, upon seed fields, or
+in the vicinity of water-courses; but in the breeding season they
+resort to marshy ground where the _Juncus communis_ grows in abundance,
+to the dense masses of the common reed (_Arundo phragmites_), and such
+like places. During the winter, the male's routine of existence is of a
+somewhat monotonous order, limited to the necessary search for food
+during the few short hours of daylight and enforced inactivity during
+the longer hours of darkness. But towards the middle of February a
+distinct change manifests itself in the bird's behaviour. Observe what
+then happens. When they leave the reed-bed in the morning, instead of
+flying with their companions to the accustomed feeding grounds, the
+males isolate themselves and scatter in different directions. The
+purpose of their behaviour is not, however, to find fresh feeding
+grounds, nor even to search for food as they have been wont to do, but
+rather to discover stations suitable for the purpose of breeding; and,
+having done so, each male behaves in a like manner--it selects some
+willow, alder, or prominent reed, and, perching thereon, leads a quiet
+life, singing or preening its feathers. Now if the movements of one
+particular male are kept in view, it will be noticed that only part of
+its time is spent in its territory. At intervals it disappears. I do not
+mean that one merely loses sight of it, but that it actually deserts its
+territory. As if seized with a sudden impulse it rises into the air and
+flies away, often for a considerable distance and often in the same
+direction, and is absent for a period which may vary in length from a
+few minutes to an hour or even more. But these periodical desertions
+become progressively less and less frequent in occurrence until the
+whole of its life is spent in the few acres in which it has established
+itself.
+
+The behaviour of the Yellow Bunting is similar. In any roadside hedge
+two or more males can generally be found within a short distance of one
+another, and in such a place their movements can be closely and
+conveniently followed. Under normal conditions the ordinary winter
+routine continues until early in February; but the male then deserts the
+flock, seeks a position of its own, and becomes isolated from its
+companions. Now the position which it selects does not, as a rule,
+embrace a very large area--a few acres perhaps at the most. But there is
+always some one point which is singled out and resorted to with marked
+frequency--a tree, a bush, a gate-post, a railing, anything in fact
+which can form a convenient perch, and eventually it becomes a central
+part of the bird's environment. Here it spends the greater part of its
+time, here it utters its song persistently, and here it keeps watch upon
+intruders. The process of establishment is nevertheless a gradual one.
+The male does not appear in its few acres suddenly and remain there
+permanently as does the migrant; at first it may not even roost in the
+prospective territory. The course of procedure is somewhat as
+follows:--At dawn it arrives and for a while utters its song, preens its
+feathers, or searches for food; then it vanishes, rising into the air
+and flying in one fixed direction as far as the eye can follow, until it
+becomes a speck upon the horizon and is ultimately lost to view. During
+these excursions it rejoins the small composite flocks which still
+frequent the fields and farm buildings. For a time the hedgerow is
+deserted and the bird remains with its companions. But one does not have
+to wait long for the return; it reappears as suddenly as it vanished,
+flying straight back to the few acres which constitute its territory,
+back even to the same gate-post or railing, where it again sings. This
+simple routine may be repeated quite a number of times during the first
+two hours or so of daylight, with, of course, a certain amount of
+variation; on one occasion the bird may be away for a few minutes only,
+on another for perhaps half an hour, whilst sometimes it will fly for a
+few hundred yards, hesitate, and then return--all of which shows clearly
+enough that these few acres possess some peculiar significance and are
+capable of exercising a powerful influence upon the course of its
+behaviour. And so the disposition in relation to the territory becomes
+dominant in the life of the bird.
+
+Or take the case of the Chaffinch. In winter large or small flocks can
+be found in many varied situations. But in the latter part of February,
+or the early days of March, these flocks begin to disperse. At daylight
+males can then be observed in all kinds of situations, either calling
+loudly, uttering their spring note, or exercising their vocal powers to
+the full; and it will be found that, in the majority of instances, these
+males are solitary individuals, that they pass the early hours of the
+morning alone, and that their normal routine of calling, singing, or
+searching for food, is only interrupted by quarrels with their
+neighbours. The same locality is visited regularly--not only the same
+acre or so of ground, but even the same elm or oak, has, as its daily
+occupant, the same cock Chaffinch. And temporary desertions from the
+territory occur also, much like those referred to in the life of the
+Bunting, but perhaps not so frequently. One has grown so accustomed
+during the dark days of winter to the sociable side of Chaffinch
+behaviour--to the large flocks searching for food, to the endless stream
+of individuals returning in the evening to roost in the holly-trees, to
+the absence of song--that this radical departure from the normal routine
+comes as something of a surprise; for the days are still short, the
+temperature is still low, the nesting season is still many weeks ahead,
+and yet for part of the day, and for just that part when the promptings
+of hunger must be strongest, the male, instead of joining the flock,
+isolates itself and expends a good deal of energy in insuring that its
+isolation shall be complete. And in place of the silence we hear from
+all directions the cheerful song uttered with such marked persistency
+that it almost seems as if the bird itself must be aware that by doing
+so it was advertising the fact of its occupation of a territory. This is
+surely a remarkable change, and the females in the meantime continue
+their winter routine.
+
+One other example. The monotonous call of the Greenfinch is probably
+familiar to all. In winter these birds accompany other Finches and form
+with them flocks of varying sizes, but in the spring the flocks
+disperse, and the Greenfinch, in common with other units of the flock,
+alters its mode of life. But whereas the Chaffinch or the Bunting begins
+to acquire its territory in February, the Greenfinch only does so in
+April. When the organic changes do at length begin to make themselves
+felt, the male seeks a position of its own, and having found one remains
+there, uttering its characteristic call. But owing probably to the fact
+that it is much later than the aforementioned species in acquiring a
+territory, temporary desertions are not so much in evidence. The species
+is so very plentiful, and the bird is so prone to nest in gardens and
+shrubberies surrounding human habitations, that this seasonal change in
+its routine of existence cannot fail to be noticed. One can hear its
+call in every direction, one can watch the same individual in the same
+tree; and it is the male that is thus seen and heard, the female appears
+later. Thus the behaviour falls into line with that of the Bunting or
+the Chaffinch.
+
+The behaviour of these resident species throws some light upon the early
+arrival of the males which we are endeavouring to explain in the case of
+the migrants. Let us see how their actions compare. The male resident
+deserts the female early in the year and establishes itself in a
+definite position, where it advertises its presence by song; the male
+migrant travels from a great distance, arrives later, and also
+establishes itself in a definite position, where it, too, advertises its
+presence by song. The male resident passes only the earlier part of the
+day in its territory at the commencement of the period of occupation;
+the male migrant remains there continuously from the moment it arrives.
+The male resident deserts its territory at intervals, even in the
+morning; the male migrant betrays no inclination to do so. Thus there is
+a very close correspondence between the behaviour of the two, and what
+difference there is--slight after all--cannot be said to affect the main
+biological end of securing territory. One is apt to think of the problem
+of migration in terms of the species instead of in terms of the
+individual. One pictures a vast army of birds travelling each spring
+over many miles of sea and land, and finally establishing themselves in
+different quarters of the globe; and so it comes about, I suppose, that
+a country or some well-defined but extensive area is regarded as the
+destination, the ultimate goal, of the wanderers. But the resident male
+has a journey to perform, short though it may be; it, too, has a
+destination to reach, neither a country nor a locality, but a place
+wherein the rearing of offspring can be safely accomplished, and it,
+too, arrives in that place in advance of the female.
+
+With these facts at our disposal, we will endeavour to find an
+explanation. It is unlikely that specialised behaviour would occur in
+generation after generation under such widely divergent conditions,
+and, moreover, expose the birds to risk of special dangers, if it were
+but an hereditary peculiarity to which no meaning could be attached.
+Hence the appearance of the males in their breeding haunts ahead of the
+females becomes a fact of some importance, and suggests that the
+extensive journey in the one case, and the short journey in the other,
+may both have a similar biological end to serve.
+
+Darwin evidently attached importance to this difference between the
+males and the females in their times of arrival. In the _Descent of Man_
+he referred to it as follows: "Those males which annually first migrated
+in any country, or which in spring were first ready to breed, or were
+the most eager, would leave the largest number of offspring; and these
+would tend to inherit similar instincts and constitutions. It must be
+borne in mind that it would have been impossible to change very
+materially the time of sexual maturity in the females without at the
+same time interfering with the period of the production of the young--a
+period which must be determined by the season of the year." Newton
+suggested the following explanation[2]: "It is not difficult to
+imagine that, in the course of a journey prolonged through some 50° or
+60° of latitude, the stronger individuals should outstrip the weaker by
+a very perceptible distance, and it can hardly be doubted that in most
+species the males are stouter, as they are bigger than the females."
+Granting that the males are the stronger, how can this account for
+their outstripping the females by a week, ten days, or even a fortnight,
+in a journey of perhaps 1500 miles? To expect the birds to accomplish
+such a distance in seven days is surely not estimating their
+capabilities too highly, and any slight inequality in the power of
+flight or endurance could give the males an advantage of a few hours
+only. But this explanation, based upon inequalities in the power of
+flight and endurance on the one hand, and the magnitude of the distance
+traversed on the other, cannot afford a solution of the behaviour of the
+resident males, and is less likely, therefore, to be a true solution of
+that of the migrants.
+
+There is another theory, simple enough in its way, which will probably
+occur to many. It is based on the assumption that the males reach sexual
+maturity before the females; and it is contended that the functioning of
+the instincts which contribute towards the biological end of
+reproduction depend upon the organic changes which the term "sexual
+maturity" is held to embrace, and that, inasmuch as the migratory
+instinct belongs to the group of such instincts, the males must be the
+first to leave their winter quarters.
+
+What is meant by the "migratory instinct"? To speak of it as one of the
+instincts concerned in reproduction is not enough. Reproduction involves
+the actual discharge of the sexual function, which involves the
+females; but the first visible manifestation of organic change in the
+male is its desertion of the females. Yet this is the behaviour which is
+referred to as the "migratory instinct," and which comes into play,
+according to this theory, because the bird has reached sexual maturity.
+Manifestly we must have some clear understanding as to what these terms
+represent. That organic changes determine the functioning of certain
+definite instincts at certain specified times there can be no doubt;
+that these changes may occur at a somewhat earlier date in the male than
+in the female is more than probable, but that this explains the
+behaviour in question I do not believe. One wants to know why the
+changes should occur earlier in the male, what disposition it is which
+first comes into functional activity, and to what such disposition is
+related.
+
+It may, however, be urged that, after all, this apparent eagerness to
+reach the breeding grounds is but a modification of hereditary procedure
+under the guiding hand of experience. What more likely result would
+follow from the enjoyment associated with previous success in the
+attainment of reproduction than a craving to repeat the experience? What
+stronger incentive to a hurried return could be imagined? It must be
+admitted that there are certain facts which might be used in support of
+an appeal to experience as a reasonable explanation. For example, the
+first males to arrive often display that richness of colouring which is
+generally supposed to indicate a fuller maturity. Gätke even speaks of
+the "most handsome old birds being invariably the first to hasten back
+to their old homes." But if experience is a factor, if some dim
+recollection of the past is held to explain the hurried departure of the
+male migrant, one wants to know with what such recollection is
+associated. Is it associated with the former female, or with the former
+breeding place, or with both? I take it that any recollection, no matter
+how vague, must be primarily associated with the particular place
+wherein reproduction had previously been accomplished; and I grant that
+if the first individuals to appear were invariably the older and
+experienced birds, their early return might be explained on the basis of
+such an association. But if there is reason to believe that a proportion
+are young birds on the verge of carrying out their instinctive routine
+for the first time, then we cannot appeal to past experience in
+explanation of their behaviour.
+
+The age of a bird is difficult to determine. Experience leads me to
+believe that some of the males that arrive before the females are birds
+born the previous season; one finds, for instance, individuals with
+plumage of a duller hue, which denotes immaturity, amongst the first
+batch of arrivals. But though plumage may sometimes be a satisfactory
+guide, yet to rely upon it alone, or upon a more perfect development of
+feather, is to exceed the limits of safety. How, then, can we ascertain
+whether all the males that arrive before the females have had some
+previous experience of reproduction? Well, we take a particular locality
+and note the migrants that visit it year after year, and we find that
+the respective numbers of the different species are subject to wide
+annual fluctuations. Not every species lends itself to an inquiry of
+this kind: some are always plentiful and fluctuation is consequently
+difficult to discern; others are scarce and variation is easily
+determined. Those which are of local distribution but conspicuous by
+their plumage, or easily traced by the beauty or the peculiarity of
+their song, afford the more suitable subjects for investigation. For
+example, the Grasshopper-Warbler, Marsh-Warbler, Nightingale, Corncrake,
+Red-backed Shrike, or Whinchat have each some distinctive peculiarity
+which makes them conspicuous, and each one is subject to marked
+fluctuation in numbers. The small plantation or wooded bank may hold a
+Nightingale one year, but we miss its song there the next; the osier bed
+or gorse-covered common which vibrates with the trill of the
+Grasshopper-Warbler one April is deserted the following season; the
+plantation which is occupied by a host of common migrants this summer
+may be enlivened next year by the song of the rarer Marsh-Warbler also;
+and so on. The fluctuation is considerable: we observe desertion on the
+one hand, appropriation on the other, and yet males appear before
+females whether the particular plantation, osier bed, or swamp had been
+inhabited or not the previous season. This fact is not without
+significance. It shows that similar conditions prevail both amongst the
+males that appropriate breeding grounds new to them, and amongst those
+that return to some well-established haunt; and on the assumption that
+the earlier arrivals are experienced males, the same birds evidently do
+not return to the same place year after year. Granting, then, that the
+males which appropriate new breeding-grounds are young birds, how can
+their earlier arrival be explained in terms of past experience; and
+granting that they are old, and therefore experienced, how can it be
+explained in terms of association?
+
+Again, it may be urged that if there is some biological end to be
+furthered by this hurried return, and if recollection of past experience
+is a means towards that end, such recollection need not necessarily be
+associated with a definite place, but only in a vague way with the whole
+series of events leading up to reproduction--in which series the
+migratory journey may even have acquired meaning. Whether there be any
+recollection of a previous journey or of a nest with young, I do not
+know. But the young bird is capable of performing its journey, of
+building its nest, and of rearing its young antecedent to
+experience--racial preparation has fitted it thus far; why then exclude
+the other event in the series, the earlier departure of the male, from
+hereditary equipment? If the journey were a casual affair without any
+goal attaching to it, if the males upon arrival wandered about in search
+of a mate, there would be some ground for thinking that a vague
+recollection of the whole former experience was sufficient to explain
+the hurried return; but since the pleasurable effect of association,
+founded upon previous experience of a definite place, cannot well be
+established, and since it is so difficult to study the objective aspect
+of the behaviour in question without coming to the conclusion that the
+journey is related to the appropriation of a place suitable for the
+rearing of offspring, one is tempted to ask whether the hurried return
+may not also be so related.
+
+Now the males of some of the migratory species, especially of those
+which are accustomed to return to their breeding haunts early in the
+season, are called upon to face greater dangers and have a greater
+strain imposed upon their strength by starting forth upon their journey
+ten days or a fortnight before their prospective mates. The blizzards
+which so often sweep across the northern parts of Europe in the latter
+half of March, destroying in their course the all too scanty supply of
+insect life, may take toll of their numbers; or the westerly gales,
+which are not infrequent at that period, may meet them in mid-ocean and
+add to the perils of their journey; or the temperature of the previous
+weeks may have been sufficiently low to arrest the development of insect
+life--and yet males are annually exposed to these risks in hurrying to
+their breeding grounds. For what purpose? The answer will largely depend
+upon the way in which we regard those few acres wherein a resting place
+is ultimately found. For myself, I believe that they are of importance,
+inasmuch as the securing of a place suitable for the rearing of
+offspring is a primary condition of success in the attainment of
+reproduction; and if this be so, it is evident that the interests of
+the race will be better served by the males making good this first step
+before the females are ready to pair, otherwise they might oscillate
+between two modes of behaviour, created by the premature functioning of
+conflicting impulses.
+
+The different steps in the process seem to follow one another in ordered
+sequence. The male inherits a disposition--which for us, of course, has
+prospective meaning--to seek the appropriate breeding ground and there
+to establish itself; and as early a functioning of this disposition as
+possible, consonant with the conditions of existence in the external
+environment, may have been evolved for the following reasons--firstly,
+the earlier individuals will meet with less interference wherever they
+may settle, every locality will be open to them, every acre free, their
+only need being that particular environment for which racial preparation
+has fitted them. In the second place, being already established when
+other males appear upon the scene, and advertising their presence by
+song, they will be less liable to molestation; thirdly, in those cases
+in which a long journey is undertaken, they will have ample time to
+recover from the fatigue, and, if attacked by later arrivals, will thus
+be in a better position to defend their territories; and lastly, a
+greater uniformity in their distribution will be insured before the
+females begin their search.
+
+There is, besides, another good reason for thinking that the earlier
+males will have an advantage. We will assume--and from the abundant
+evidence supplied by the marking of birds, it is quite a reasonable
+assumption--that there is a tendency, generally speaking, for
+individuals to return to the neighbourhood of their birthplace, or to
+the place in which they had previously reared their offspring. Now the
+earlier arrivals will have no difficulty in securing territories; those
+that come later may have to search more diligently, still they will gain
+all that they require so long as any available space remains. Then comes
+the point when all suitable ground is occupied, and yet there are males
+to be provided for. What will be the position of these males? Urged by
+their inherited nature, they will leave the district and possibly
+continue their search into those adjoining, only, however, to add to the
+difficulties of the males there similarly situated; and even allowing
+that they are at length successful in establishing themselves, what are
+their prospects of securing mates? Since the earlier females will not
+extend their wanderings farther than is absolutely necessary, but will
+pair whenever the opportunity for doing so arises, it is to the later
+females, forced onwards by competition, that the late males must look
+for mates; so that when at length pairing does take place, much valuable
+time will have been lost.
+
+The disadvantages which the late arrivals have to face are therefore
+great, and it is probable that the percentage which attain to
+reproduction will on the average be somewhat lower than the percentage
+in the case of the earlier arrivals. The district in which my
+observations have been made lies well within the limits of the breeding
+range of most of our common species, and it is not surprising that I
+should have met with little evidence of failure to breed as a result of
+failure to secure territory. Some interesting information was supplied
+to me, however, by the late Robert Service. He found, in certain seasons
+in Dumfriesshire, flocks of from ten to fifty unmated Sedge-Warblers,
+which, from the time of their arrival in May until the middle of July,
+haunted reed-filled spaces along stagnant streams. These flocks appeared
+to him to be composed of loosely-attached individuals of a migrant flock
+that had failed to find things congenial enough to entice them to
+disperse. But may they not have been composed of males that had failed
+to secure territories, or of females that had failed to discover males
+in possession of territories, or of both?
+
+
+We have seen that, in the case of many species, each male establishes
+itself in a particular place at the commencement of the breeding season,
+even though this may mean a partial or perhaps a complete severance from
+former companions. We must now discuss this fact in greater detail
+because it is opposed to the views often held regarding the sexual
+behaviour of birds, and is manifestly of importance when considering
+the theory of breeding territory.
+
+First, however, there is a point which requires some explanation. I
+speak of the _same_ male being in the _same_ place. How can I prove its
+identity? In the first place it is highly improbable that a bird which
+roams about within the same small area of ground, makes regular use of a
+certain tree and a certain branch of that tree, and observes a similar
+routine day after day, can be other than the same individual. But, apart
+from this general consideration, are there any means by which
+individuals of the same species can be identified? Well, there is
+variation in the plumage. Supposing we take a dozen cock Chaffinches and
+examine them carefully, we shall find slight differences in pattern and
+in colour--more grey here or a duller red there, as the case may be--and
+though these differences may not be sufficient to enable us to pick out
+a bird at a distance, they are nevertheless conspicuous when it is close
+at hand. Then again there is variation in the song; and the more highly
+developed the vocal powers the greater scope there is for variation. But
+even the phrases of a simple song can be split up and recombined in
+different ways. If one were asked casually whether the different phrases
+of the Reed-Bunting's song always followed one another in the same
+sequence, the answer would probably be that they certainly did so,
+whereas the bird is capable of combining the few notes it possesses in a
+surprising number of different ways. And lastly, there are differences
+in just the particular way in which specific behaviour, founded upon a
+congenital basis, is adapted by each individual to its own special
+environment. Racial preparation determines behaviour as a whole, but the
+individual is allowed some latitude in the execution of details which
+are in themselves of small moment--the selection of a particular tree as
+a headquarters and a particular branch upon that tree, the direction of
+the distant excursion, and the direction of the limited wanderings
+within the small area surrounding the headquarters which in the course
+of time determine the extent of the territory, are matters for each
+individual to decide when the occasion for doing so arises. Moreover
+instances of abnormal coloration or abnormal song are not rare, and they
+are valuable since they place the identity of the individual beyond
+dispute. I can recall the case of a Willow-Warbler whose song was unlike
+that of its own or any other species, and of a Redbreast whose voice
+puzzled me not a little. I can recollect also a male Yellow Bunting
+whose foot was injured or deformed. Of this bird's behaviour I kept a
+record for two months or so; and inasmuch as it inhabited a roadside
+hedge, and was of fearless disposition, the deformed foot could plainly
+be seen whenever it settled upon the road to search for food.
+Identification is not, therefore, a difficulty. There is always some
+small difference in colour or in song, or some well-defined routine
+which makes recognition possible.
+
+Owing to their great powers of locomotion, birds have generally been
+regarded as wanderers more or less; anything in the nature of a fixed
+abode, apart from the actual nest, having been accounted foreign to
+their mode of life; and even the locality immediately surrounding the
+nest has not been apprehended as possessing any meaning for the owner of
+that nest. No doubt the supply of food determines their movements for a
+considerable part of the year; they seek it where they can find it, here
+to-day, there to-morrow--in fact few species fail to move their quarters
+at one season or another, so that there is much truth in the notion that
+birds are wanderers. Yet to suppose that every individual one sees or
+hears--every Lapwing on the meadow, or Nightingale in the withy bed--is
+in that particular spot just because it happens to alight there as it
+roams from place to place, is to take a view which the observed facts do
+not support. For as soon as the question of reproduction dominates the
+situation, a new condition arises, and the habits formed during the
+previous months are reversed, and the males, avoiding one another, or
+even becoming actively hostile, prefer a life of seclusion to their
+former gregariousness--all of which occurs just at the moment when we
+might reasonably expect them to exhibit an increased liveliness and
+restlessness as a result of their endeavour to secure mates; and so
+universal is the change that it might almost be described as an
+accompaniment of the sexual life of birds generally.
+
+That the Raven and certain birds of prey exert an influence over the
+particular area which they inhabit has long been known, and it has been
+recognised more especially in the case of the Peregrine Falcon,
+possibly because the bird lives in a wild and attractive country, and,
+forcing itself under the notice of naturalists, has thus had a larger
+share of attention devoted to its habits. Moreover, when a species is
+represented by comparatively few individuals, and each pair occupies a
+comparatively large tract of country, it is a simple matter to trace the
+movements and analyse the behaviour of the birds. There is a rocky
+headland in the north-west of Co. Donegal comprising some seven miles or
+so of cliffs, where three pairs of Falcons and two pairs of Ravens have
+nested for many years. Each year the different pairs have been more or
+less successful in rearing their young; each year the young can be seen
+accompanying their parents up to the time when the sexual instinct
+arises; and yet the actual number of pairs is on the whole remarkably
+constant, and there is no perceptible increase. It seems as if the
+numbers of three and two respectively were the maximum the headland
+could maintain. But this is no exceptional case; it represents fairly
+the conditions which obtain as a rule amongst those species, granting,
+of course, a certain amount of variation in the size of each territory
+determined by the exigencies of diverse circumstances.
+
+If we take a given district, and devote our attention to the smaller
+migrants that visit Western Europe each returning spring for the purpose
+of procreation, we shall find that the movements of the males are
+subject to a very definite routine. This, however, is not true of every
+male; some may be wending their way to breeding grounds at a distance;
+others may be seeking the particular environment to which they may be
+adapted; others again, having found their old haunts destroyed, may
+consequently be seeking new.
+
+Of all this there is evidence. Small parties of Chiffchaffs pass through
+a district on their way to other breeding grounds, flitting from hedge
+to hedge as they move in a definite direction with apparently a definite
+purpose; Reed-Warblers settle in a garden or plantation, eminently
+unsuited to their requirements, and disappear; Wood-Warblers arrive in
+some old haunt, and finding it no longer suitable for their purpose,
+seek new ground. So that plenty of individuals are always to be found,
+which, for the time being at least, are wanderers.
+
+In the district which I have in mind, the wandering males form only a
+small part of the incoming bird population. The majority of individuals
+that fall under observation are those that have made this particular
+district their destination; and in doing so, they may possibly have been
+guided by their experience as owners or inmates of former nests, for it
+cannot be doubted that a return to the neighbourhood of the birthplace
+would lead to a more uniform distribution and therefore be advantageous,
+and the tendency to do so might consequently have become interwoven in
+the tissue of the race. How, then, do they behave? A certain amount of
+movement, an interchanging of positions, even though restricted to an
+area defined, let us say, by experience, might be expected under the
+circumstances--that, however, is not what we find; we observe the
+available situations plotted out into so many territories, each one of
+which is occupied by a male who passes the whole of his time therein.
+Take whatever species we will--Whitethroat, Whinchat, Willow-Warbler,
+Red-backed Shrike, it matters not which, for there is no essential
+difference in the general course of procedure--this condition will be
+found to prevail. Generally speaking, the behaviour in relation to the
+territory can be studied more conveniently where a number of individuals
+of the same species have established themselves in proximity to one
+another. Such species as the Chiffchaff, Willow-Warbler, or Wood-Warbler
+are often sufficiently common to allow of three or more of their
+respective males being kept in view at the same time; and the
+disposition to occupy a definite position can be readily observed. The
+Reed-Warbler is a suitable subject for an investigation of this kind;
+for since it is restricted by its habits to localities wherein the
+common reed (_Arundo phragmites_) grows in abundance, and since such
+localities are none too plentiful and often limited in extent, the area
+occupied by each individual is necessarily small--if it were not so the
+species would become extinct. Hence it is a simple matter to study the
+routine of the different individuals and to mark the extent of their
+wanderings.
+
+In this way the males of all the Warblers that breed commonly in Great
+Britain establish themselves, each one in its respective station at the
+respective breeding ground; so, too, do those of many other
+migrants--for example, the Whinchat, Wheatear, Tree-Pipit, and Red-backed
+Shrike. All of these, it is true, are common species--numbers of
+individuals can often be found in close proximity--and therefore it may
+be argued that they keep to one position more from pressure of
+population than from any inherited disposition working towards that end.
+But the rarer species behave similarly. Districts frequented by the
+Marsh-Warbler and offering plenty of situations of the type required by
+the bird are often inhabited by a few members only, and yet the
+disposition to remain in a definite position is just as marked.
+
+You will say, however, that these smaller migrants have no exceptional
+powers of flight; that they have besides just completed a long and
+arduous journey; and you will ask why they should be expected to wander,
+whether it is not more reasonable to expect that, in order to overcome
+their fatigue, they should remain where they settle. The Cuckoo is a
+wanderer in the wider sense of the term, and is gifted with considerable
+powers of flight. Upon arrival the male flies briskly from field to
+field, showing but little signs of weariness; yet we have only to follow
+its movements for a few days in succession to assure ourselves that the
+bird is no longer a wanderer; for just as the Warbler or the Chat moves
+only within a definitely delimited area, so the male Cuckoo, strange as
+it may seem, restricts itself to a particular tract of land. The area
+over which it wanders is often considerable and consequently it is not
+possible to keep the bird always in view, but inasmuch as the variation
+in the voices of different individuals is quite appreciable,
+identification is really a simple matter. If we cannot keep the bird in
+sight, we can trace its movements by sound and mark the extent of its
+wanderings, which by repetition become more and more defined, until a
+belt of trees here, or an orchard there, mark a rough and rarely passed
+boundary line.
+
+Let us take another example from the larger migrants--the Black-tailed
+Godwit, a bird common enough in the Dutch marshes but no longer breeding
+in this country. On suitable stretches of marsh land, numbers will be
+found in proximity one to another after the manner of the Lapwing, each
+male occupying a definite space of ground wherein it passes the time
+preening, searching for food, or in sleep--though at the same time
+keeping a strict watch over its territory. Now the preference shown for
+a particular piece of ground, and the determination with which it is
+resorted to, is the more remarkable when we take into consideration the
+specific emotional behaviour arising from the seasonal sexual condition.
+This behaviour is expressed in a peculiar flight. The bird rises high in
+the air, circles round with slowly beating wings above the marsh, and
+utters a call which, as far as my experience goes, is characteristic of
+the performance. The air is often full of individuals circling thus
+even beyond the confines of the marsh, for a male does not limit its
+flight to a space immediately above its territory; but nevertheless
+careful observation will show how unerringly each one returns to its own
+position on the breeding ground, no matter how extensive the aerial
+excursion may have been. And so, when the males of the smaller migrants
+confine their movements to an acre of ground at the completion of their
+long journey, they are acting no more under the influence of fatigue
+than the Cuckoo, which keeps within certain bounds yet flies about
+briskly, or the Godwit which, though holding to its few square yards on
+the ground, executes most tiring and extensive flights above the marsh.
+
+Of all the migrants, however, the behaviour of the Ruff is perhaps the
+most strange, and though it has long been known that these birds have
+their special meeting places where they perform antics and engage in
+serious strife, yet it is only within recent years that the primary
+purpose of these gatherings has been ascertained--that purpose being the
+actual discharge of the sexual function. Mr. Edmund Selous has carried
+out some exhaustive investigations into their activities at the meeting
+places, and he makes it clear that each bird has its allotted position.
+He says, for example, that "It begins to look as though different birds
+had little seraglios of their own in different parts of the ground,"
+that "each Ruff has certainly a place of its own," or again that "this
+Ruff indeed, which I think must be a tender-foot, does not seem to have
+a place of its own like the others." Nevertheless it is only at the
+meeting places that they have their special positions; there is no
+evidence to show that each one has a special territory, wherein it seeks
+its food, as the Warbler has, and therefore some may think that we are
+here confronted with behaviour of a different order. But we must bear in
+mind that the process has been adjusted to meet the requirements of
+different species: the size of the territory, the period of its daily
+occupation, the purpose which it serves--these all depend upon manifold
+relationships and do not affect the principle. Why it has been
+differentiated in different circumstances we shall have occasion to
+discuss later; for the moment it is enough that at the end of its
+migratory journey each Ruff occupies one position on the meeting ground.
+
+[Illustration: Territorial flight of the Black-tailed Godwit
+
+Emery Walker ph.sc.]
+
+Now birds that are paired for life, whose food-supply is not affected by
+alternations of climate, have no occasion to desert the locality wherein
+they have reared their offspring, and so their movements, being subject
+to a routine which would tend to become increasingly definite, must in
+the course of time and according to the law of habit formation become
+organised into the behaviour we observe. Is it necessary, therefore, to
+seek an explanation of their tendency to remain in one place in anything
+so complex as an inherited disposition? Again, since we have to confess
+to so very much ignorance on so many points connected with the whole
+phenomenon of migration, may there not be some condition, hitherto
+shrouded in mystery, which might place so different a complexion on the
+corresponding aspect of migrant behaviour as to rid us, in their case
+also, of the necessity of appealing to an inherited disposition? Such
+questions are justifiable. And if the life-histories of other species
+gave no further support to our interpretation, if, in short, the
+evidence were to break down at this point, then we should be forced to
+seek some other explanation more in keeping with the general body of
+facts.
+
+But far from placing any obstacle in the way of an interpretation in
+terms of inherited disposition, the behaviour of many of those residents
+which are not paired for life gives us even surer ground for that
+belief. Moreover in their case the initial stages in the process are
+more accessible to observation. I will endeavour to explain why. In the
+process of reproduction the environment has its part to play--whether in
+the manner here suggested, or indirectly through the question of
+food-supply, matters not at the moment. Now, migratory species are more
+highly specialised than resident species as regards food, and are
+affected more by variations of temperature, so that they can live for
+only a part of the year in the countries which they visit for the
+purpose of procreation. Hence the organic changes, which set the whole
+process in motion, must be coincident in time with the growth of
+appropriate conditions in the environment; for if it were not so, if the
+internal organic changes were to develop prematurely, the bird would
+undertake its journey only to find an insufficiency of food upon its
+arrival, and this would scarcely contribute towards survival. Definite
+limitations have therefore been imposed upon the period of organic
+change. But in the case of many resident species the conditions are
+somewhat different, for they remain in the same locality throughout the
+year, and a gradual unfolding of the reproductive process cannot
+therefore have a similarly harmful effect. Thus it comes about that the
+behaviour of the migrant, when it arrives at the breeding ground and
+first falls under observation, represents a stage in the process which,
+in the case of the resident, is only reached by slow degrees; and by
+closely observing the behaviour as it is presented to us in the life of
+the resident male, we not only gain a better insight into the changes in
+operation, but can actually witness the breaking down of the winter
+routine, stereotyped through repetition, by the new disposition as it
+arises.
+
+The first visible manifestations, even though they may be characterised
+by a certain amount of vagueness, are therefore of great importance if
+the behaviour is to be interpreted aright; and in order to insure that
+none of these earlier symptoms shall be missed, it is necessary to begin
+the daily record of the bird's movements at an early date in the season.
+As a rule the second week in February is sufficiently early for the
+purpose, but the date varies according to the prevailing climatic
+conditions. Even in species widely remote there is great similarity of
+procedure, and the behaviour of the Buntings is typical of that of many.
+With the rise of the appropriate organic state the male resorts at
+daybreak to a suitable environment, occupies a definite position, and
+singling out some tree or prominent bush, which will serve as a
+headquarters, advertises its presence there by song. At first the bird
+restricts its visits, which though frequent in occurrence are of short
+duration, for the most part to the early hours of the morning; it
+disappears as suddenly as it appeared, and one can trace its flight to
+the feeding grounds--a homestead or perhaps some newly sown field. But
+by degrees the impulse to seek the society of the flock grows less and
+less pronounced, the visits to the territory are more and more
+prolonged, and the occupation of it then becomes the outstanding feature
+of the bird's existence. This in outline is the course of procedure as
+it appears to an external observer.
+
+But although much can be learnt from the lives of these smaller species,
+there is no gain-saying the fact that a great deal of patient
+observation is required, and the process is apt to become tedious. There
+are others, however, which are more readily observed, whilst their
+life-histories afford just as clear an insight into the effect produced
+by the new disposition upon the developing situation; and among these
+the Lapwing takes a prominent position, because it is plentiful and
+inhabits open ground where it is easily kept in view.
+
+There is a water meadow with which I am familiar, where large numbers
+resort annually for the purpose of procreation. Here they begin to
+arrive towards the end of February, and at first collect in a small
+flock at one end of the meadow. A male, here and there, can then be seen
+to break away from the flock, and to establish itself in a definite
+position upon the unoccupied portion of the ground, where it remains
+isolated from its companions. Others do likewise until the greater part
+of the meadow is divided into territories. Six of these territories I
+kept under observation for approximately two months in the year 1915.
+The occupant of the one marked No. 6 upon the 1915 plan was a lame bird,
+a fortunate occurrence as it enabled me to follow its movements with
+some accuracy; and though it maintained its position for some weeks, it
+ultimately disappeared, as a result, I believe, of the persistent
+attacks of neighbouring males. The behaviour of the males during the
+first fortnight or so after they broke away from the flock was
+interesting. Though they retired to their territories and remained in
+them for the greater part of their time, yet it was only by degrees that
+they finally severed their connection with the flock, for so long as a
+nucleus of a flock remained, so long were they liable to desert their
+territories temporarily and to rejoin their companions.
+
+[Illustration: Emery Walker Ltd. sc.
+
+Plan of the water meadow showing the territories occupied by Lapwings in
+the year 1915.]
+
+[Illustration: Emery Walker Ltd. sc.
+
+Plan of the water meadow showing the territories occupied by Lapwings in
+the year 1916.
+
+_Between pages 58 and 59._]
+
+Lapwings, as is well known, collect in flocks during the winter months,
+and these flocks, which sometimes reach vast proportions, are to be
+found on tidal estuaries, water meadows, arable land, and such like
+places, according to the prevailing climatic conditions. This flocking
+may contribute towards survival, and may therefore be the result of
+congenital dispositions which have been determined on biological
+grounds. On the other hand, since food at that season is only to be
+obtained in a limited number of situations, the birds may be simply
+drawn together by accident. In the former case the behaviour would be
+instinctive, in the latter, though accidental at first, recurrent
+repetition would tend to make it habitual; but in either case the
+impulse to accompany the flock must be a powerful one, for on the one
+hand it would depend upon inherited, and on the other hand upon
+acquired, connections in the nervous system. Now observe that soon
+after the flock arrived in the meadow, single males detached themselves;
+there was no hesitation, they just retired from their companions and
+settled in their respective territories. They were not expelled, for if
+their leaving had been compulsory much commotion would have preceded
+their departure, and their return would certainly not have been
+welcomed. A reference to the plan will make the position clearer; the
+neutral zone inhabited by the flock is there shown as situated in one
+corner of the meadow, the territories that fell under observation are
+plotted out as far as possible to scale, and the more important zones of
+conflict are also marked.
+
+The males spent part of their time in their respective territories and
+part with the flock, so long as it remained in existence. When a male
+was in its territory it avoided companions and was openly hostile to
+intruders; when it was with the flock it wandered about with companions
+in search of food. The contrast between the two modes of behaviour was
+very marked, and it was evident that the gregarious instinct was
+gradually yielding its position of importance to the new factor--the
+territory. If there had been no flock, if a few solitary individuals had
+appeared here and there and had established themselves in different
+parts of the meadow, one would have had no definite evidence of the
+strength of the impulse in the male to seek a position of its own, one
+could only have argued from the general fact of males flocking in the
+winter and isolating themselves in spring that something more than
+accident was required to explain so radical a change. But since the
+birds returned in a flock to the ground upon which they intended to
+breed, and since the flock occupied temporarily part of the ground
+whilst the partitioning of the remainder was still proceeding, it was
+possible to gauge the strength of the impulse, which was forcing the
+males to isolate themselves in particular areas of ground, by comparing
+it with the impulse to accompany the flock--and the measure of its
+intensity was the rapidity with which the latter impulse yielded its
+position of importance.
+
+Like the Lapwing, the Coot and Moor-Hen are easily kept under
+observation, and since many individuals often breed in proximity, more
+than one can be watched at the same moment; moreover the area occupied
+by each male generally embraces an open piece of water as well as part
+of the fringe of reeds, so that the movements of the bird can be
+followed without much difficulty. Under favourable conditions
+manifestations of the developing situation become visible at a
+comparatively early date in the season--the middle or the latter part of
+February--and these manifestations resemble those of other species. But
+the Moor-Hen passes summer and winter alike in the same situation, and
+being therefore in a position to respond at once to internal
+stimulation, however vague, the change from the one state to the other
+is gradual. This, however, is a matter of detail; the main consideration
+lies in the fact that the impulse to retire to a definite position, to
+avoid companions, and to live in seclusion, is strongly marked, and
+produces a type of behaviour similar on the whole to that of the
+Lapwing. First of all there is the appropriation of a certain position,
+the limits of which are fixed according to the law of habit formation,
+and according to the pressure exerted by neighbouring individuals; then
+there is the neutral ground over which the birds wander amicably in
+search of food; and finally there is the contrast between the pugnacity
+of the male whilst in its territory, and its comparative friendliness
+when upon neutral ground.
+
+Evidence of similar behaviour is to be found in the life of the Black
+Grouse, a bird which has always excited the curiosity of naturalists on
+account of the special meeting places to which both sexes resort in the
+spring. Mr. Edmund Selous watched these birds in Scandinavia, where he
+kept a daily record at one of the meeting places. In various passages he
+refers to the appropriation of particular positions by particular males,
+and concludes thus: "It would seem from this that, like the Ruffs, each
+male Blackcock has its particular domain on the assembly ground, though
+the size of this is in proportion to the much greater space of the
+whole. On the other mornings, too, the same birds, as I now make no
+doubt they are, have flown down into approximately the same areas."
+
+The cliff-breeding species--Guillemots, Razorbills, and Puffins--are
+difficult to investigate because individuals vary so little, and the
+sexes resemble one another so closely; yet, despite these difficulties,
+we can gain some idea of the general purport of their activities. But
+when the ledges are crowded and the air is filled with countless
+multitudes, how is it possible to keep a single bird in view for a
+sufficient length of time to understand its routine? The difficulty is
+not an insuperable one. The flights, undertaken seemingly for no
+particular purpose, are often of short duration and are completed before
+the strain of observation becomes too great; moreover an individual
+sometimes possesses a special mark or characteristic which serves to
+make it conspicuous. For example, there is a well-marked variety of the
+Common Guillemot, the Ringed or Bridled Guillemot of science,
+distinguished by an unusual development of white round the eye and along
+the furrow behind it. One such individual I was fortunate in discovering
+upon a crowded cliff, and, as in the case of the Lapwing with the broken
+leg or the Yellow Bunting with the injured foot, the identity of the
+bird was beyond dispute, and one could observe that it appropriated to
+itself a particular position upon a particular ledge.
+
+Guillemots and Razorbills return at intervals to the breeding stations
+early in the season, and these visits are repeated with growing
+frequency until the birds are finally established. I have witnessed
+these periodic returns during March in the south of England, and during
+April in the north-west of Ireland, and I am informed that in the latter
+district such visits may occur as early as February. Gätke, who had
+ample opportunity of observing the birds in Heligoland, puts their
+return at an even earlier date. "They visit their breeding places," he
+says, "in flocks of thousands at the New Year, often even as early as
+December, as though they wanted to make sure of their former haunts
+being well preserved and ready for their reception." Such visits,
+however, are irregular in occurrence; the birds arrive, and, after
+spending a short time upon the ledges, disappear. And since there is not
+the same evidence in their coming and going of that method which we
+observe in the periodical returns of the Bunting or the Finch, it may be
+thought that needless importance is being attached to an episode in
+their lives which is quite intelligible in terms of a feeble response
+determined by a dawning organic change. While it may be quite
+intelligible in such terms it is not thereby explained; for every
+response must have as its antecedent an inherited connection in the
+nervous system determined on biological grounds. Besides, these early
+periodic returns conform in general to the type of behaviour displayed
+by other species, the males of which return to their breeding grounds
+many weeks before the real business of reproduction begins. Are we then
+justified in regarding them as accidents of the developing situation?
+Are we not rather bound to admit that they have some definite biological
+end to serve?
+
+[Illustration: Competition for territory is seldom more severe than
+amongst cliff-breeding sea birds, and the efforts of individual
+Razorbills to secure positions on the crowded ledges lead to desperate
+struggles.
+
+Emery Walker ph.sc.]
+
+These examples show that the males of many species reverse their mode of
+life at the commencement of the breeding season and proceed to isolate
+themselves, each one in a definitely delimited area.
+
+
+There are three ways in which we may attempt to interpret this
+particular mode of male behaviour. We may regard it as an accidental
+circumstance, nowise influencing the course of subsequent procedure; or,
+appealing to the law of habit formation, we may regard it as an
+individual acquirement; or again, we may invest it with a deeper
+significance and seek its origin in some specific congenital disposition
+determined on purely biological grounds.
+
+Which of these three shall we choose? The first by itself requires but
+little consideration; for though it might explain the initial visit, it
+cannot account for the persistency with which the plot of ground is
+afterwards resorted to. Supposing, however, that we combine the first
+and the second; supposing, that is to say, we assume, for the purpose of
+argument, that the initial visit is fortuitous, and that constancy is
+supplied by habit formation--would that be a satisfactory
+interpretation? It is a simple one, inasmuch as it only requires that a
+male shall alight by chance in a particular place for a few mornings in
+succession in order that the process may be set in motion. Now an
+essential condition of habit formation is recurrent repetition; given
+this repetition and, it is true, any mode of activity is liable to
+become firmly established. But how can we explain the repetition? Even
+if we are justified in assuming that the initial visit is purely an
+accidental occurrence, we cannot presume too far upon the laws of chance
+and assume that the repetition, at first, is also fortuitous.
+
+So that we come back to the congenital basis, the last of our three
+propositions. And it will, I think, be admitted that the facts give us
+some grounds for believing that the securing of the territory has its
+root in the inherited constitution of the bird. In comparing the
+behaviour of the migratory male with that of the resident, attention was
+drawn to the manner in which the occupation of a territory was effected:
+the former bird, it may be remembered, established itself without delay,
+whereas the latter did so only by degrees, and the difference was
+attributed to the incidence of migration which required a closer
+correspondence between organic process and external environment. But the
+significance for us just now lies in the fact that the definiteness,
+which accompanies the initial behaviour of the migratory male in
+relation to the territory, cannot have been acquired by repetition; for
+this reason, that when the male occupies its space of ground at the end
+of its long and arduous journey, it does so without preparation or
+experiment, even without hesitation, as if aware that it was making good
+the first step in the process of reproduction. No doubt, if it happened
+to be an individual that had already experienced the enjoyment of
+reproduction, it might be aware of the immediate results to be achieved
+and act accordingly. But among the hosts of migrants that one observes,
+there must be many males which have not previously mated; and yet, upon
+arrival, they all behave in a similarly definite manner--so that
+experience cannot well be the primary factor in the situation. If, then,
+the essential condition of habit formation is absent and experience is
+eliminated, there is nothing left but racial preparation to fall back
+upon.
+
+Nevertheless, it is true that many resident males seem to pass through
+a period of indecision before they establish themselves permanently in
+their respective territories; they come and go, their visits grow more
+and more prolonged, and only after the lapse of some considerable time
+does the process of establishment attain that degree of completeness
+which is represented in the initial behaviour of the migratory male.
+Their whole procedure seems therefore to bear the stamp of individual
+acquirement; and, if it stood alone, we might be content to construe it
+thus, but the example of the migratory male necessitates our looking
+elsewhere for the real meaning of the indecision.
+
+Let me first of all give some instances of the persistence with which a
+male remains in one spot, and this despite the fact that it has no mate.
+
+A Reed-Bunting occupied a central territory in a strip of marshy ground
+inhabited annually by four or five males of this species. Throughout
+April, May, and until the 19th June, it clung to its small plot of
+ground, tolerated no intrusion, and sang incessantly.
+
+Two Whitethroats arrived at much the same time--the 30th April
+approximately--and occupied the corner of a small plantation; the one
+obtained a mate the day following its arrival, the other remained
+unpaired for a fortnight.
+
+A Reed-Warbler established itself amongst some willows and alders
+adjoining a reed-bed and made its headquarters in a small willow bush.
+Not more than fifteen yards away, on the edge of the main portion of the
+reeds, another male was established and was paired on the 22nd May. Each
+morning the single male behaved in much the same way, singing
+continuously whilst perched upon the bush. And so the days passed by
+until it seemed improbable that it would ever secure a mate, but one
+appeared on the 20th June, and a nest was built forthwith.
+
+Now it is difficult to believe that a chance visit, even though repeated
+for a few mornings in succession, could have accounted for the
+Reed-Bunting remaining so persistently in the marsh, or the Whitethroat
+in one corner of the osier bed, or the Reed-Warbler in that one
+particular willow. Not only so, but if a habit of such evident strength
+can be acquired so readily, we have a right to ask why it should only be
+acquired in the spring--why not at every season? Considerations such as
+these lead to the belief that there must be some congenital basis to
+account for such persistent endeavour; the more so since it is difficult
+not to be impressed with the conative aspect of the male's behaviour. To
+a stranger, unacquainted with its previous history, the bird might
+appear to be leading a life of hesitation, whereas, if carefully
+watched, its whole attitude will be found to betray symptoms of a
+striving towards some end; and the frequent departure and return, which
+might be pointed to as the material from which a definite mode of
+procedure would be likely to emerge, is in reality behaviour of a
+determinate sort.
+
+My interpretation, then, of the apparent indecision in the behaviour of
+the resident male is this. During the winter most species live in
+societies, together they seek their food and together they retire in the
+evening to the accustomed roosting places; and the association of
+different individuals confers mutual benefits upon the associates. The
+movements of these societies are dominated by the question of food; all
+else is subservient, and the supply of the necessary sustenance may,
+under certain conditions, become a difficulty which can only be met by
+energy and resource. After the long night the sensation of hunger is
+strong, and the birds, on awakening, fly to the accustomed feeding
+grounds, returning again in the evening to the selected spot, and by
+frequent repetition a routine becomes established. Thus the behaviour of
+each individual is determined not only by the powerful gregarious
+impulse but also by the habits formed in connection therewith during
+many weeks in succession. Now with the rise of the appropriate organic
+state, the disposition to seek the breeding ground and there to
+establish itself becomes dominant in the male. But the process is a
+gradual one. There is no need, as happens amongst the migrants, for the
+period of organic change to conform rigidly to the growth of any
+particular condition in the environment, and hence for a time the bird
+oscillates between two modes of behaviour--between that one organised by
+frequent repetition and that one determined by the functioning of this
+new disposition.
+
+To look at the matter broadly, it is scarcely likely that so definite a
+mode of behaviour would recur with such regularity, generation after
+generation, in the individuals belonging to so many widely divergent
+forms, if it had no root in the inborn constitution of the bird. But the
+law of habit formation has its part to play also. By itself it is
+inadequate; yet it probably does assist very materially in adding still
+greater definition, and it probably is responsible in a large measure
+for determining the limits of the territory according to the conditions
+of existence of the species--thus the Falcon seeks its prey over wide
+tracts of land, and, by hunting over certain ground repeatedly,
+establishes a routine, which broadly fixes the area occupied; the
+Woodpecker cannot find food upon every tree, and every forest does not
+contain the necessary trees, and therefore the bird regulates its flight
+according to the position of the trees; and the Warbler, finding food
+close at hand, does not need to travel far, and the area it occupies is
+consequently small.
+
+So that the most likely solution of the problem will be found in a
+combination of our second and third propositions; that is to say, in an
+initial responsive behaviour provided for in the inherited constitution
+of the nervous system, and in a definiteness acquired by repetition and
+determined by relationships in the external environment.
+
+
+
+
+CHAPTER III
+
+THE DISPOSITION TO DEFEND THE TERRITORY
+
+
+In the previous chapter I endeavoured to show that each male establishes
+a territory at the commencement of the breeding season, and there
+isolates itself from members of its own sex. And further I gave my
+reasons for believing that this particular mode of behaviour is
+determined by the inherited nature of the bird, and that we are
+justified in speaking of it as "a disposition to secure a territory"
+because we can perceive its prospective value. But the act of
+establishment is only one step towards "securing." By itself it can
+achieve nothing; for any number of different individuals might fix upon
+the same situation, and if there were nothing in the inherited
+constitution of the bird to prevent this happening, where would be the
+security, or how could any benefit accrue to the species?
+
+In withdrawing from its companions in the spring, the male is breaking
+with the past, and this action marks a definite change in its routine of
+existence. But the change does not end in attempted isolation; it is
+carried farther and extends to the innermost life and affects what,
+humanly speaking, we should term its emotional nature, so that the bird
+becomes openly hostile towards other males with whom previously it had
+lived on amicable terms.
+
+The seasonal organic condition is responsible for the functioning of the
+disposition which results in this intolerance, just as it is for the
+functioning of the disposition which leads to the establishment of the
+territory; and the effect of these two dispositions is that a space of
+ground is not only occupied but made secure from intrusion. The process
+is a simple one. There is no reason to believe, there is no necessity to
+believe, that any part of the procedure is conditioned by anticipatory
+meaning; the behaviour is "instinctive" in Professor Lloyd Morgan's
+definition of the word, since it is of a "specific congenital type,
+dependent upon purely biological conditions, nowise guided by conscious
+experience though affording data for the life of consciousness."
+
+That the males of many animals are apt to become quarrelsome during the
+mating period is notorious. Darwin collected a number of facts, many of
+which related to birds, showing the nature and extent of the strife when
+the sexual instinct dominated the situation. And pondering over these
+facts, he deduced therefrom a "law of battle," which, he believed, bore
+a direct relation to the possession of a female. And it must be admitted
+that he had excellent ground for his conclusion in the fact not only
+that the conflicts occur mainly during the pairing season, but that
+the female is often a spectator and seems even to pair with the victor.
+I accepted it, therefore, as the most reasonable interpretation of the
+facts. But, as time passed by, incidents of a conflicting character led
+me to think that after all there might be another solution of the
+problem. And when it was no longer possible to doubt that there was a
+widespread tendency to establish territories, it at once became manifest
+that the battles might have an important part to play in the whole
+scheme. But how was this to be proved? What sort of evidence could show
+whether the proximate end for which the males were fighting had
+reference to the female or to the territory? Clearly nothing but a
+complete record of the whole series of events leading up to reproduction
+could supply the necessary data upon which a decision might rest. In the
+present chapter I shall give, in the first place, the reasons which lead
+me to think that the origin of the fighting cannot be traced to the
+female; afterwards, the evidence which seems to show that it must be
+sought in the territory; and finally, I shall make a suggestion as to
+the part the female may play in the whole scheme.
+
+[Illustration: Male Blackbirds fighting for the possession of territory.
+The bare skin on the crown of the defeated bird shows the nature of the
+injuries from which it succumbed.
+
+Emery Walker ph.sc.]
+
+The facts upon which the "law of battle" was founded were ample to
+establish the truth of its main doctrine. But the evidence upon which
+the interpretation of the battles was based was somewhat superficial. It
+was based mainly upon the general observation that one or more females
+could frequently be observed to accompany the combatants; and if this
+were the sole condition under which the fighting occurred, one must
+admit that this view would have much to recommend it. But it is not
+merely a question of males disputing in the presence of a female; for
+males fight when no female is present, pair attacks pair, or a male may
+even attack a female--in fact there is a complexity of strife which is
+bewildering.
+
+In attributing the rivalry to the presence of the female, it is assumed
+that males are in a preponderance, and that consequently two or more are
+always ready to compete for a mate. Her presence is presumably the
+condition under which his pugnacious nature is rendered susceptible to
+its appropriate stimulus, the stimulus being, of course, supplied by the
+opponent. There would be nothing against this interpretation if it were
+in accord with the facts; but it can, I think, be shown that the males
+are just as pugnacious and the conflicts just as severe even when the
+question of securing a mate is definitely excluded; and I shall now give
+the evidence which has led me to this conclusion.
+
+In the previous chapter we had occasion to refer to the difference in
+the times of arrival of the male and female migrants, and we came to the
+conclusion, it may be remembered, that this was a fact of some
+importance, because it gave us a clue to the meaning of much that was
+otherwise obscure in their behaviour. But it is also of importance in
+connection with the particular aspect of the problem which we now have
+in view, for if it can be shown that males, when they first reach their
+breeding grounds, are even then intolerant of one another's presence, if
+their actions and attitudes betray similar symptoms of quasi-conation,
+if disputes are rife and the struggles of a kind to preclude all doubt
+as to their reality, then it is manifest that in such cases their
+intolerance cannot be due to the presence of the female.
+
+Here, however, I must refer to a view which is held by some
+psychologists, namely, that amongst the higher animals, even on the
+occasion of the first performance of an instinctive act, there is some
+vague awareness of the proximate end to be attained. Discussing the
+nature of instincts, Dr M'Dougall[3] says, "Nor does our definition
+insist, as some do, that the instinctive action is performed without
+awareness of the end towards which it tends, for this, too, is not
+essential; it may be, and in the case of the lower animals no doubt
+often is, so performed, as also by the very young child, but in the case
+of the higher animals some prevision of the immediate end, however
+vague, probably accompanies an instinctive action that has often been
+repeated." A similar view seems to be held by Dr Stout.[4] "As I have
+already shown," he says, "animals in their instinctive actions do
+actually behave from the outset as if they were continuously interested
+in the development of what is for them one and the same situation or
+course of events; they actually behave as if they were continuously
+attentive, looking forward beyond the immediately present experience in
+preparation for what is to come. They apparently watch, wait, search,
+are on the alert. They also behave exactly as if they appreciated a
+difference between relative success and failure, trying again when a
+certain perceptible result is not attained and varying their procedure
+in so far as it has been unsuccessful. All these characters are found in
+the first nest-building of birds as well as in the second; they are
+found also in courses of conduct which occur only once in the lifetime
+of the animal." Both these writers would, I imagine, contend that, even
+when a female is absent, the idea of the female, as the end in view
+throughout, is present; and they would argue that the fact of her
+absence during the fighting in no way disposes of the belief that she is
+the condition under which the pugnacious instinct of the male is
+rendered susceptible to stimulation. What reason is there to think that
+this interpretation is applicable to the case under consideration? When
+a female is present, we observe that the males are pugnacious, and, when
+she is absent, that they still continue to be hostile--that is to say,
+they behave _as if_ she were present. Now, as far as I can ascertain,
+the "_as if_" is the only ground there is for supposing that the female
+is represented in imaginal form--there is no evidence of the fact, if
+fact it be. On the contrary, the behaviour of the male affords some
+fairly conclusive evidence that no such image is the primary factor in
+exciting the instinctive reaction. For if it be the actual presence of
+the female, or, in the absence of such, a mental image, that renders the
+pugnacious nature of the male responsive; provided the usual stimulus
+were present, the instinct ought surely to respond, not only under one
+particular circumstance, but under all circumstances. Yet, as we shall
+presently see, a male is by no means consistently intolerant of other
+males. It may be sociable at one moment or pugnacious at another, but
+the pugnacity is always peculiar to a certain occasion--the occupation
+of a territory. What shall we say then--that a mental image is a
+situational item only when the territory is occupied? It may be so; it
+may be that the fact of occupation gives rise to the mental image which,
+in its turn, renders the fighting instinct explosive, which again
+renders the possession of the territory secure. That such an
+interpretation is possible we must all admit. But if it were true,
+though it would not affect the main consideration, namely, whether the
+fighting has reference to the possession of a particular female, or to
+the protection of the territory, it would make further discussion as to
+which of these is the condition of the fighting unprofitable, for each
+would have its part to play in the process, the territory remaining,
+however, the principal factor in the situation.
+
+Now the difference in the times of arrival of the male and female
+migrant varies in different species from a few days to a fortnight or
+even more. It is most marked in those that return to their breeding
+grounds early in the season, and the greater the margin of difference
+the greater scope is there for observation. In my records for the past
+twelve years, there are frequent references to these initial male
+contests in the life of the Willow-Warbler and of the Chiffchaff; and in
+the district which I have in mind, these two species arrive early in the
+season, the males preceding the females by a week or even as much as a
+fortnight. Suppose, then, that two Chiffchaffs establish themselves in
+adjoining territories; or suppose that a male settles in a territory
+already occupied; what is the result? Well, scenes of hostility soon
+become apparent; as the birds approach one another they become more and
+more restive, their song ceases, they no longer search for food in the
+usual methodical manner, but instead their movements are hurried and
+their call-notes are uttered rapidly--all of which betrays a heightened
+emotional tone. Then the climax is reached, there is a momentary
+fluttering of tiny wings, a clicking of bills, and for the time being
+that may be all. But unless one or other of the combatants retires, this
+scene may be repeated many times in the course of a few hours, and
+repeated with varying degrees of severity. Yet the fighting, even in the
+most extreme form, when the birds locked together fall slowly to the
+ground, is seldom of an impressive kind, and one has to bear in mind the
+capabilities of the actors, remembering that the most severe struggle
+might readily be interpreted as a game if it were not for certain
+symptoms which reveal its inner nature.
+
+The males of many other migrants can frequently be observed to fight
+when there was every reason to believe that females had still to arrive.
+The Blackcap is notoriously pugnacious, but not more so than the
+Marsh-Warbler or the Whinchat. Here in Worcestershire, the _Arundo
+phragmites_ grows mainly on certain sheets of water which are
+comparatively few and far between, and the Reed-Warbler is consequently
+restricted to isolated and more or less confined areas. The males arrive
+early in May before the new growth of reeds has attained any
+considerable height, and each one has its own position in the reed-bed,
+sings there, and throughout the whole period of reproduction actively
+resists intrusion on the part of other males. I have kept watch upon a
+small area of reeds daily from the date of the first arrival; each
+individual was known to me, and as the growing reeds were only a few
+inches in height, a female could scarcely have escaped detection. Yet
+time and again disputes arose, and males pursued and pecked one
+another, striving to attain that isolation for which racial preparation
+had fitted them.
+
+But on account of their violence, or their novelty, or because the
+absence of a female was beyond question, some battles stand out in one's
+memory more prominently than others. An instance of this was a struggle
+between two Whitethroats which happened in the latter part of April and
+lasted for three successive days. The scene of its occurrence was more
+or less the same on each occasion, and the area over which the birds
+wandered was comparatively small. The fighting was characterised by
+persistent effort and was of a most determined kind, and so engrossed
+did the assailants become that they even fluttered to the ground at my
+feet. No trace of a female was to be seen at any time during these three
+days, nor, during the pauses in the conflict, was the emotional
+behaviour of a kind which led me to suppose that a female was anywhere
+in the vicinity. And, if she had been near, she must have made her
+presence known, for the belief that she is a timid creature, skulking on
+such occasions in the undergrowth, is by no means borne out by
+experience.
+
+Even more impressive was a battle between two male Cuckoos. It occurred
+high up in the air above the tops of some tall elm-trees which roughly
+marked the boundary line between their respective areas, and the actions
+of the birds were plainly visible. At the moment of actual collision
+the opponents were generally in a vertical position, and wings, feet,
+and beaks were made use of in turn; one could plainly see them strike at
+one another with their feet, and one could observe the open bill which
+generally denotes exhaustion, but may of course have been due to anger,
+or used as a means of producing terror. Yet no female appeared in the
+locality until six days after the occurrence of this struggle--and
+she certainly is not easily overlooked, for her note is unmistakable
+even when the behaviour of the male does not betray her arrival.
+
+[Illustration: Male Cuckoos fighting before the arrival of a female
+
+Emery Walker ph.sc.]
+
+That the actual presence of the respective females exercised any
+influence on the course of these struggles is more than doubtful. Not
+only did one fail to detect them, but one's failure to do so was
+confirmed by the knowledge that they had not yet arrived in those
+particular localities. Hence the fact of the male preceding the female
+is a valuable aid to the interpretation of subsequent behaviour; and one
+appreciates it the more after having experienced the difficulty of
+deciding whether she is present during the conflicts between resident
+males, for no matter how carefully we may observe the conditions which
+lead up to, and which accompany, such conflicts, or how closely we may
+scrutinise the surrounding trees, undergrowth, or ground, there always
+remains the possibility that she may, after all, have been overlooked.
+But this must not be taken to imply that in such cases direct
+observation alone can lead to no serviceable result, or that the
+evidence gained therefrom is worthless. Far from it. Failure to detect a
+female is so very common an occurrence that, even if we lacked the
+corroborative evidence supplied in the life of the migratory male, it
+would still be unreasonable to suppose that it were solely due to
+mistaken observation. We mark her absence during the conflicts between
+the respective males of many common species--the Finches, Buntings, and
+Thrushes that occupy their territories early in the season when the
+hedgerows and trees are still bare; but more frequently amongst those
+that inhabit open ground, because the movements of the birds are there
+more accessible to observation. For instance, half a dozen or more
+Lapwings can be kept in view at the same time, and as they stand at dawn
+in solitary state, keeping watch upon their respective territories, they
+are conspicuous objects on the short, frosted grass; no stranger can
+enter the arena without the observer being aware of it, no commotion can
+occur but one detects it, no movement however small need be missed. And
+so they fight, in a manner which leaves no doubt as to the reality of
+the struggle, when their prospective mates are absent not only from the
+particular territories in which the conflicts take place, but absent too
+from those adjoining.
+
+If the fact that males fight before they are paired and in the absence
+of a female could be placed beyond all question, it would no longer be
+possible to regard her possession as the end for which they are
+contending, and consequently there would be no need to produce further
+evidence. But the examples which I have given refer, of course, to only
+a few migrants and a few residents--and moreover it must be admitted
+that a female _is_ often conspicuous during the battles--so that by
+themselves they must be regarded, and rightly so, as inconclusive. We
+must therefore pass on to consider evidence of a somewhat different
+character.
+
+I spoke of the complexity of the strife. By this I mean that it is not
+merely a matter of disputes between adjoining males, but that it is a
+far more comprehensive business involving both sexes. Thus female fights
+with female and pair with pair, or a male will attack a female, or,
+again, a pair will combine against a single male or a single female. And
+from all this complexity of strife we gain much valuable evidence in
+regard to the question immediately before us. For when one pair attacks
+another, or males that are definitely paired fight with one another, or
+an unpaired male attacks either sex of a neighbouring pair
+indiscriminately, there is surely little ground for supposing that the
+possession of a mate is the reason of it all.
+
+The battles between pairs of the same species are by no means uncommon.
+Observe, for example, the central pair of three pairs of Reed-Buntings
+occupying adjoining territories, and keep a daily record of the routine
+of activity practised by both sexes during the early hours of the
+morning; then, at the close of the season, summarise all the fighting
+under different headings, and it will be found that the number of
+occasions upon which the central pair attacked, or was attacked by,
+neighbouring pairs will form a considerable portion of the whole.
+
+Or watch the Moor-Hen, and for the purpose choose some sheet of water
+large enough to accommodate three or more pairs, and so situated that
+the birds can always be kept in view. Early in February the pool will be
+haunted by numbers of individuals of both sexes, all swimming about
+together, and, if the pool is surrounded by arable land, wandering over
+that land subject to no territorial restrictions, apparently free to
+seek food where they will. But as time goes by, their number gradually
+decreases until a few pairs only remain, and these will occupy definite
+areas. If careful watch is then kept and the relations of the pairs
+closely studied, there will be no difficulty in observing the particular
+kind of warfare to which I am alluding, and it will be noticed that the
+encounters are of a particularly violent description. Thus two pairs
+approach one another, and, when they meet, throw themselves upon their
+backs, each bird striking at its adversary with its feet or seizing hold
+of it with its beak; and though, in the commotion that ensues, it is
+almost impossible to determine what exactly is happening, there is
+reason to believe that the sexes attack one another indiscriminately.
+
+A struggle between two pairs of Pied Wagtails is worth mentioning. It
+impressed itself upon my memory because of the unusual vigour with which
+it was conducted. The battle lasted for fifteen minutes or more, and
+the four birds, collecting together, pursued and attacked one
+another--at one moment in the air, at another upon the roof of a house
+where they would alight and flutter about on the slates, uttering their
+call-note without ceasing--until finally they disappeared from view,
+still, however, continuing the struggle.
+
+[Illustration: Two pairs of Pied Wagtails fighting in defence of their
+territories.
+
+Emery Walker ph.sc.]
+
+Such is the nature of the warfare which prevails between neighbouring
+pairs, and which can be observed in the life of many other species--the
+Chaffinch, Stonechat, Blackbird, Partridge, Jay, to mention but a few.
+
+The conflicts between males that are definitely paired are of such
+common occurrence that it is scarcely necessary to mention specific
+instances. But the occasions on which a male attacks either sex of a
+neighbouring pair indiscriminately, or on which a pair combine to attack
+a female, are less frequent.
+
+Now if it be true that males fight for no other purpose than to gain
+possession of a mate, what meaning are we to attach to the battles
+between the pairs, or what explanation are we to give of the fact that
+paired males are so frequently hostile? Those who hold this view will
+probably argue thus: "The presence of the female is the condition under
+which the pugnacious instinct of the male is rendered susceptible to
+appropriate stimulation, and the stimulus is supplied by a rival male;
+we admit that all the fighting which occurs after pairing has taken
+place has nothing to do strictly speaking with gaining a mate, but,
+inasmuch as the fact of possession is always liable to be
+challenged--and no male can differentiate between a paired and an
+unpaired intruder--we contend that it would add to the security of
+possession if the pugnacious instinct remained susceptible to
+stimulation so long as there were any possibility of challenge from an
+unpaired male; and we think that the waste of energy involved in the
+struggles between paired birds, and which we grant is purposeless, would
+be more than balanced by the added security." This is a possible
+explanation and requires consideration. It cannot account for all the
+diverse ways in which the sexes are mixed up in the fighting--it cannot,
+for instance, explain the fact that an unpaired male will attack either
+sex of an adjoining pair indiscriminately--but nevertheless it appears
+at first sight to be a reasonable explanation of some of them. We must
+remember, however, that fighting continues throughout the whole period
+of reproduction. Even after the discharge of the sexual function has
+ceased, and the female is engaged in incubation or in tending her young,
+the male is still intolerant of intruders; and it is difficult to
+believe that, at so late a stage in the process, a female could be any
+attraction sexually to an unpaired male. But apart from any theoretical
+objection, there remains the fact--namely that there is no evidence
+that a male, after having once paired, is liable to be robbed of its
+mate. And in support of this fact I have only to state that I have met
+with no single instance of failure to obtain and hold a mate when once a
+territory had been secured. Bearing in mind then that both sexes
+participate in the fighting, and that individuals of the opposite sex
+frequently attack one another; that all such conflicts are characterised
+by persistent effort, and that they are not limited to just the
+particular period when the sexual instinct is dominant but continue
+throughout the breeding season; bearing in mind that in at least one
+form of this promiscuous warfare the influence of the female can be
+definitely excluded, and that, in the remaining forms, the evidence
+which is required to link them up with the biological end of securing
+mates is lacking--can it be denied that the complexity of the strife
+makes against the view that the possession of a female is the proximate
+end for which the males are fighting?
+
+We started with the most simple aspect of the whole problem, the
+fighting of two males in the presence of one female--the aspect upon
+which attention has usually been fixed. And if it remained at that, if
+observation failed to disclose any further development in the situation,
+then there would be no need to probe the matter deeper, there would be
+no reason to doubt the assertion that the quarrel had direct reference
+to the female. But assuredly no one can ponder over the diversity of
+battle and still believe that the possession of a mate furnishes an
+adequate solution of the mystery. Clearly such an hypothesis cannot
+cover all the known facts; there are conflicts between separate pairs,
+and there are conflicts between males when females are known to be
+absent and when their mates are even engaged in the work of
+incubation--these cannot be due to an impulse in a member of one sex to
+gain or keep possession of one of the other sex. So that taking all
+these facts into consideration, we are justified, I think, in hesitating
+to accept this view, and must look elsewhere for the real condition
+under which the pugnacious nature of the male is rendered susceptible to
+appropriate stimulation.
+
+
+What then is the meaning of all this warfare? The process of
+reproduction is a complex one, built up of a number of different parts
+forming one inter-related whole; it is not merely a question of
+"battle," or of "territory," or of "song," or of "emotional
+manifestation," but of all these together. The fighting is thus one link
+in a chain of events whose end is the attainment of reproduction; it is
+a relationship in an inter-related process, and to speak of it as being
+even directly related to the territory is scarcely sufficient, for it is
+intimately associated with the disposition which is manifested in the
+isolation of the male from its companions, and forms therewith an
+_imperium in imperio_ from which our concept of breeding territory is
+taken. But let me say at once that it is no easy matter to prove this,
+for since so many modes of behaviour, which can be interpreted as
+lending support to this view, are likewise interpretable on the view
+that the presence of a female is a necessary condition of the fighting,
+it is difficult to find just the sort of evidence that is required.
+Nevertheless, after hearing the whole of the evidence and at the same
+time keeping in mind the conclusion which we have already reached, I
+venture to think that the close relationship between the warfare on the
+one hand and the territory on the other will be fully admitted.
+
+Formerly I deemed the spring rivalry to be the result of accidental
+encounters, and I believed that an issue to a struggle was only reached
+when one of the combatants succumbed or disappeared from the locality, a
+view which neither recognised method nor admitted control. Recent
+experience has shown, however, that I was wrong, and that there is a
+very definite control over and above that which is supplied by the
+physical capabilities of the birds.
+
+Let us take some common species, the Willow-Warbler being our first
+example; and, having found three adjoining territories occupied by
+unpaired males, let us study the conflicts at each stage in the sexual
+life of the three individuals, observing them before females have
+arrived upon the scene, again when one or two of the three males have
+secured mates, and yet again when all three have paired. Now we shall
+find that the conditions which lead up to and which terminate the
+conflicts are remarkably alike at each of these periods. A male
+intrudes, and the intrusion evokes an immediate display of irritation on
+the part of the owner of the territory, who, rapidly uttering its song
+and jerking its wings, begins hostilities. Flying towards the intruder,
+it attacks viciously, and there follows much fluttering of wings and
+snapping or clicking of bills. At one moment the birds are in the
+tree-tops, at another in the air, and sometimes even on the ground, and
+fighting thus they gradually approach and pass beyond the limits of the
+territory. Whereupon a change comes over the scene; the male whose
+territory was intruded upon and who all along had displayed such
+animosity, betrays no further interest in the conflict--it ceases to
+attack, searches around for food, or sings, and slowly makes its way
+back towards the centre of the territory.
+
+Scenes of this kind are of almost daily occurrence wherever a species is
+so common, or the environment to which it is adapted so limited in
+extent, that males are obliged to occupy adjacent ground. The Moor-Hen
+abounds on all suitable sheets of water, and it is a bird that can be
+conveniently studied because, as a rule, there is nothing, except the
+rushes that fringe the pool, to hinder us from obtaining a panoramic
+view of the whole proceedings, and moreover the area occupied by each
+individual is comparatively small. Towards the middle of February,
+symptoms of sexual organic change make themselves apparent, and the pool
+is then no longer the resort of a peaceable community; quarrels become
+frequent, and as different portions of the surface of the water are
+gradually appropriated, so the fighting becomes more incessant and more
+severe. Each individual has its own particular territory, embracing a
+piece of open water as well as a part of the rush-covered fringe, within
+which it moves and lives. But in the early part of the season, when the
+territories are still in process of being established, and definiteness
+has still to be acquired, trespassing is of frequent occurrence, and the
+conflicts are often conspicuous for their severity.
+
+Now these conflicts are not confined to unpaired individuals, nor to one
+sex, nor to one member of a pair--every individual that has settled upon
+the pool for the purpose of breeding will at one time or another be
+involved in a struggle with its neighbour. If then we single out certain
+pairs and day by day observe their actions and their attitude towards
+intruders, we shall notice that, instead of their routine of existence
+consisting, as a casual acquaintance with the pool and its inmates might
+lead us to believe, of an endless series of meaningless disputes, the
+behaviour of each individual is directed towards a similar goal--the
+increasing of the security of its possession; and further, if we pay
+particular attention to the circumstances which lead up to the quarrels
+and the circumstances under which such quarrels come to an end, we shall
+find, when we have accumulated a sufficient body of observations, that
+the disputes always originate in trespass, and that hostilities always
+cease when the trespasser returns again to its own territory. By careful
+observation it is possible to make oneself acquainted with the
+boundaries--I know not what other term to use--which separate this
+territory from that; and it is the conduct of the birds on or near these
+boundaries to which attention must be drawn. A bird may be feeding
+quietly in one corner of its territory when an intruder enters. Becoming
+aware of what is happening it ceases to search for food, and approaching
+the intruder, at first swimming slowly but gradually increasing its
+pace, it finally rises and attacks with wings and beak, and drives its
+rival back again beyond the boundary. Thereupon its attitude undergoes a
+remarkable change; ceasing to attack, but remaining standing for a few
+moments as if still keeping guard, it betrays no further interest in the
+bird with which a few seconds previously it was fighting furiously. On
+one occasion I watched a trespasser settle upon a conspicuous clump of
+rushes situated near the boundary. The owner, who was at the moment some
+distance away, approached in the usual manner, and, having driven off
+the trespasser, returned immediately to the clump, where it remained
+erect and motionless.
+
+A feature which marks all the fighting, and which we cannot afford to
+disregard, is the conative aspect of the behaviour of the owner of the
+territory. The bird attacks with apparent deliberation _as if_ it were
+striving to attain some definite end. I recollect an incident which was
+interesting from this point of view. A pair of Reed-Buntings were
+disturbed by a Weasel which had approached their nest containing young.
+Both birds betrayed symptoms of excitement; as the Weasel threaded its
+way amongst the rushes, so they fluttered from clump to clump or clung
+to the stems, uttering a note which is peculiar to times of distress,
+and followed it thus until finally it disappeared in a hedge. The
+rapidly uttered note and the excitement of the birds caused some
+commotion, and the male from an adjoining territory approached the
+scene. Now one would have expected that the presence of this bird, and
+possibly its aid in driving away a common enemy, would have been
+welcomed; one would have thought that all else would have been
+subservient to the common danger, and that so real a menace to the
+offspring would have evoked an impulse in the parent powerful enough to
+dominate the situation and subordinate all the activities of the bird to
+the attainment of its end. But what happened? Three times during this
+incident, the male, whose young were in danger, abandoned the pursuit of
+the Weasel and pursued the intruder. It was not merely that he objected
+to the presence of this neighbouring male in a passive way, nor even
+that he had a momentary skirmish with it, but that he determinedly drove
+the intruder beyond the boundary and only then returned to harass the
+Weasel.
+
+Thus it seems clear that the proximate end to which the fighting is
+directed is not necessarily the defeat of the intruder, but its removal
+from a certain position. And inasmuch as this result will be obtained
+whether the retreat is brought about by fear of an opponent or by
+physical exhaustion, it is manifest that too much significance need not
+be attached to the amount of injury inflicted. It is necessary to bear
+this in mind, because it is held by some, who have carefully observed
+the actions of various species, that overmuch importance is attached to
+the conflicts, that in a large number of instances they are mere
+"bickerings" and lead to nothing, and that they are now only "formal,"
+which means, I suppose, that they are vestigial--fragments of warfare
+that determined the survival of the species in bygone ages. But if the
+conclusion at which we have just arrived be correct, if we can recognise
+a single aim passing through the whole of the warfare--and that one the
+removal of an intruder from a certain position, then we need no longer
+concern ourselves as to the degree of severity of the battles--we see it
+all in true perspective. Neither exhaustion nor physical inability are
+the sole factors which determine the nature and extent of the fighting;
+there is a more important factor still--position. According, that is to
+say, to the position which a bird occupies whilst fighting is in
+progress, so its pugnacious nature gains or loses susceptibility, and it
+is this gain or loss of susceptibility which I refer to when I speak of
+the fighting as being controlled.
+
+What we have then to consider is the relation of "susceptibility" to
+"position." We can explain the relationship in two ways. We can say that
+the part of the nature of the male which leads to the occupation of a
+territory, and is partly hereditary and partly acquired, is stronger
+than the part which leads the bird to fight, and which is conditioned by
+the presence of a female, and that consequently when the male passes the
+boundary, the impulse to return asserts itself and the conflict ceases;
+or we can say that the occupation of a territory is the condition under
+which the pugnacious instinct is rendered susceptible to stimulation,
+that the stimulus is supplied by the intruder, and that when the male
+passes outside the accustomed area its instinct is no longer so
+susceptible and it therefore retires from the conflict.
+
+[Illustration: Long-tailed Tit Males fighting for possession of
+territory. The feathers have been torn from the crown of the defeated
+and dying rival.
+
+Emery Walker ph.sc.]
+
+Of these explanations, the first is not altogether satisfactory. It
+requires the presence of a female and, as we have seen, a female is by
+no means always present. Then it attributes to the one side of the
+inherited nature an influence which is not borne out by the facts, for
+in the ordinary routine of existence, without the incentive of battle,
+every individual is liable to wander occasionally beyond its boundary
+and to intrude temporarily upon its neighbours; and this it could
+scarcely do, providing its nature to remain within the territory were
+powerful enough to dominate its movements and curtail its activities
+even during the excitement of an encounter. But there is nothing
+inherently improbable in the alternative hypothesis, nor anything that
+is at all inconsistent with the behaviour as observed; on the contrary,
+if it is admitted, the facts become connected together and exhibit a
+meaning which they otherwise would not have possessed.
+
+So much for the controlling influence of "position," which alone seems
+to me sufficient ground for believing that the fighting has reference to
+the territory. But it is not the whole of the evidence.
+
+Now if it were possible to demonstrate by actual observation that those
+males which had not established territories were not pugnacious, we
+should have something in the nature of proof of the correctness of this
+view. Demonstrative evidence of this kind is, however, unattainable. Yet
+we can come very near to obtaining it by reason of a peculiar feature
+which marks the process of acquiring territory--the neutral ground. The
+Lapwing will serve as an illustration. In the previous chapter I
+referred to the small flocks that appeared in the accustomed water
+meadow early in February, and I described how they settled day after day
+in that meadow, but only in a limited part of it, where they passed
+their time in rest, in preening their feathers, or in running this way
+and that lazily searching for food; and how, at length, the flock
+dwindled by reason of individuals breaking away in order to secure
+positions on the remaining part of the meadow. Here the neutral ground
+is adjacent to the territories, and, while still occupied by the flock,
+is resorted to by the males that had deserted that flock in order to
+establish those territories.
+
+Suppose now that we have the whole meadow in view from some point of
+vantage. In front of us are the territories, in the distance the neutral
+ground; and in each territory there is a solitary male, while on the
+neutral ground a number of individuals of both sexes are assembled, and
+move about freely one amongst another. So that the scene presented to
+view is somewhat as follows: a flat meadow, at one end of which, and at
+fairly regular intervals, a few solitary individuals are dotted about,
+each one keeping at a distance from its neighbours; while at the other
+end a number of individuals are collected together in a comparatively
+small space, apparently deriving some satisfaction from their close
+association. That surely is a very remarkable contrast. But let us
+continue our investigation, first fixing our attention upon the solitary
+individuals; one is standing preening its feathers, another is squatting
+upon the ground, a third runs a few yards in this direction then a few
+yards in that, stimulated apparently by the sight of food, and so on.
+Moreover, each one keeps strictly to a well-defined area and makes no
+attempt to associate with its fellows. One of the males, however, whilst
+roaming backwards and forwards approaches the limit of its territory,
+and this brings the neighbouring bird, whose boundary is threatened,
+rapidly to the spot. In an upright position both stand face to face, and
+the battle then begins; with their wings they attempt to beat one
+another about the body, with their beaks they aim blows at the head, and
+in the mêlée wings and legs seem to be inextricably mixed; whilst at
+intervals, driven backwards by the force of the collision, they are
+compelled to separate, only, however, to return to the charge--and the
+sound of beating wings and the feathers that float in the air are tokens
+of earnestness. Such scenes are of frequent occurrence; but the
+conflicts vary in intensity, and the circumstances under which they
+occur vary too, and females come and go without leaving any clue as to
+their ultimate intentions.
+
+Turning now to the flock one is impressed with the friendship that seems
+to exist between the various members. There are, it is true, occasional
+displays of pugnacity which never seem to develop into anything very
+serious; for instance, one bird will fly at another, and a momentary
+scuffle is followed by a short pursuit but nothing more--nothing, that
+is to say, in the least comparable with the battle previously described.
+Of what is the flock composed? Of members of both sexes. There is no
+difficulty in assuring oneself that this is so. But is it entirely
+composed of individuals in whom development has not reached a stage
+adequate for the functioning of the primary dispositions? No, not
+entirely; for it will be observed that its number is a fluctuating one,
+that birds come and go, and, if a close watch is kept upon the different
+individuals as they leave, it will be noticed that some at least are
+inmates of the territories at the opposite end of the meadow--the
+solitary members whose behaviour we were recently watching. This fact is
+an important one. We were impressed, it may be remembered, with the
+contrast between the general behaviour of the birds at the opposite
+ends of the meadow. But now it appears as if the contrast were not
+between this individual and that, but between the behaviour of the same
+one under different circumstances. The male, that is to say, which,
+while in its territory, tolerates the approach of no other male, flies
+to the flock and is there welcomed by the very individuals with whom a
+short time previously it had been engaged in serious conflict.
+
+But if the conditions are reversed and the flock happens to settle in an
+occupied territory, the attitude of the owner towards the flock is very
+different. In the year 1916 an incident of this kind occurred in the
+meadow to which reference has already been made. The weather had been
+exceptionally severe--very cold easterly and north-easterly winds,
+frost, and frequent falls of snow had affected the behaviour of the
+Lapwings, and seemed to have checked the normal development of their
+sexual routine. The males would attempt to establish themselves, and
+then, when the temperature fell and the ground was covered with snow,
+would collect again in flocks and follow their winter routine. It was on
+the 9th March, during one of the spells of milder weather, that the
+flock on the neutral ground was disturbed and settled mainly in the
+territory marked No. 3 on the 1916 plan, but partly on that marked No.
+2. The owners thereupon began to attack the different members of the
+invading flock. Fixing attention upon a particular bird whilst ignoring
+the remainder, the No. 3 male drove it away, and then after a pause
+drove another away, and so on until by degrees all the invaders were
+banished, and the No. 2 male did likewise. The interest of this incident
+lies, however, in the behaviour of the different individuals of which
+the flock was composed; when attacked they made no real show of
+resistance, but accepted the situation and left. The will to fight was
+clearly lacking, yet their presence was a source of annoyance to the
+owners of the territories. A short time previously a female had
+accompanied one of the males and was at that time somewhere in the
+vicinity, but beyond this there was no evidence to show that either of
+them were paired, and even if the presence of the female were the reason
+of the pugnacity of the one, it could not well account for that of the
+other.
+
+The neutral ground does not always happen to be so close at hand as in
+the case of the meadow referred to. Sometimes the birds will resort to a
+particular field, attracted probably by a plentiful supply of food, and
+here they collect and behave as they do during the winter, running this
+way and that as the fancy takes them, meeting together by accident at
+one moment, parting at another, according to the direction in which they
+happen to wander. Of animosity there is little sign; the season might be
+the middle of winter instead of the middle of March for all the
+indication there is of sexual development, and yet one knows that they
+will behave differently when they leave this ground, as presently they
+will, and return to their territories in the surrounding neighbourhood,
+and that there each one will fight if necessary to preserve its acre
+from intrusion.
+
+It would seem, then, from this that the fighting must bear some relation
+to the particular area of ground in which it occurs; and unless it can
+be shown that there is some other factor in the external environment of
+the male, that is the direction in which we must look for the condition
+under which the instinct is rendered susceptible. One's thoughts turn,
+of course, to the female, but she too passes backwards and forwards
+between the territories and the neutral ground, and if her presence were
+really a _conditio sine qua non_ of the strife, one would like to know
+why, when she leaves those territories and joins the flock and the males
+do likewise, similar conflicts should not prevail there also.
+
+Other species have their neutral ground, but the environment seldom
+affords such facilities for observation as does that of the Lapwing.
+Even though the Moor-Hens, who are so conspicuously intolerant upon the
+pool, _do_ feed together amicably upon the meadows adjoining; and the
+Chaffinch that is so pugnacious in the morning, _does_ seek out the
+flock later in the day; yet their conditions of existence prevent our
+obtaining a panoramic view of the whole proceeding, and we have to study
+each scene separately before discovering that the relationship between
+intolerance and the territory on the one hand, and friendship and the
+neutral ground on the other, is just as strong a feature as it is in the
+behaviour of the Lapwing.
+
+I shall now give a brief account of the conduct of a male Reed-Bunting
+which by persistent effort established itself late in the season, and I
+shall do so because its behaviour tends to confirm much that has been
+said in the preceding pages.
+
+Early in March three male Reed-Buntings occupied a small water meadow
+overgrown with the common rush, and by the third week all of them were
+paired. On the 30th March two of the males were unusually pugnacious,
+and on the following day fighting continued and at times was very
+severe. Now I knew that the occupants of the ground in which the
+fighting was taking place were paired, and not doubting that the
+combatants were the owners of two territories marked for convenience
+sake Nos. 1 and 2, I was at a loss to understand the meaning of so
+determined and persistent a struggle. My attention, however, was
+presently drawn to a third bird, which also joined in the conflict and
+made the whole situation still more perplexing. This bird, as it soon
+became clear, was none other than the owner of No. 2 territory, and the
+one that I had previously regarded as such was a new arrival. On the
+following day, the 1st April, fighting continued, and in my record for
+that day there is a note to the effect that "No. 2 female seems to be of
+no interest to No. 5 male (the new arrival); its purpose seems to be to
+drive away intruders." On the 2nd April and subsequent days, this bird
+attacked every other male that approached, and not only maintained its
+position but ultimately succeeded in securing a mate. Here then we have
+two territories occupied by two males, both of which had obtained a
+mate. The relation of these two birds was normal, a month's routine had
+defined their boundaries, and conflicts were less frequent than
+formerly. But upon this comparatively peaceful scene a strange male
+intrudes. Observe the manner of the intrusion. The stranger does not
+wander about first in this direction and then in that, but acts _as if_
+it had some definite end in view, and establishing itself in a small
+alder bush which it uses as a base or headquarters, it gradually extends
+its dominion, gains the mastery over the surrounding ground, part of
+which belonged to No. 1 male and part to No. 2, and finally drives a
+wedge, so to speak, between the two territories.
+
+How is its behaviour to be explained, and why did its presence cause
+such commotion? No one could have watched the gradual unfolding of this
+incident day by day and not have been impressed by the persistent
+endeavour with which this male maintained its position in one small part
+of the meadow. This is the first and most important consideration. Then
+there is the attitude, also significant, which it adopted towards the
+females; for I take it that, apart from the question of territory, the
+explanation of its intrusion must be sought in the necessity for
+securing a mate--that it was attracted by the presence of the females,
+and that the proximate end of its behaviour was the possession of one of
+them. But if there is one thing that emerges from the facts more clearly
+than another it is that the course of its behaviour was in no way
+influenced by the presence or absence of either of the females. My
+reasons for saying so are the following: in the first place, it made no
+attempt to pursue or to thrust its attention upon either one or the
+other of them; secondly, it even went so far as to attack and drive them
+away when they approached too closely; and in the third place, when an
+unpaired female did at length appear, it adopted a different attitude
+and forthwith paired. And bearing in mind that these two females had
+already been with their respective mates for some considerable time, and
+that there was reason to believe that coition had actually taken place,
+is it likely that any counter-attraction would have proved successful in
+tempting either of them away from its mate, or probable, if they were
+the sole attraction, that the intruding male would have been so
+persistent in remaining? How very much simpler it is to fit the pieces
+together, if for the time being we ignore the female and fix our
+attention upon the territory. Each item of behaviour then falls into its
+proper place, and the fighting which seemed so perplexing and
+meaningless becomes a factor of prime importance. First of all the male
+arrives; then it establishes itself in a small alder bush and advertises
+its presence by song; next, by persistent effort in attacking the
+neighbouring males, it frees a piece of ground from their dominion; and
+finally, in proper sequence, a female arrives, pairing takes place, and
+reproduction is secured.
+
+[Illustration: A battle between two pairs of Jays
+
+Emery Walker ph.sc.]
+
+How then does the whole matter stand? If it were males only that engaged
+in serious conflict, and if they fought only in the presence of a
+female, the problem would resolve itself into one simply of obtaining
+mates. But the warfare extends in a variety of directions, it is not
+confined to one sex, nor to unpaired individuals, nor need the opponents
+necessarily be of the same sex; it involves both sexes alike singly or
+combined. Now the view that the biological end of battle is, in its
+primary aspect, related to the female, cannot, as we have seen, apply to
+the conflicts between different pairs, and only by much stretching of
+the imagination can it be held responsible for the hostility that males
+frequently display towards females or _vice versa_. It is valid only for
+a certain form of warfare. But that form represents, you will say, a
+large proportion of the whole, which is true; and so long as we ignore
+the remainder, we might rest content in the belief that we had solved
+the major part of the problem. But can we ignore the remainder? Can we
+say that the conflicts between paired males, for example, are simply
+offshoots of the pugnacious disposition, and have no part to play in the
+process of reproduction? They recur with marked persistency season after
+season and generation after generation; they are to be found in species
+widely remote; they are frequent in occurrence; and no one who had
+observed them and noted the vigour with which they are conducted, could,
+I think, conclude that they were meaningless--and be satisfied. They
+must somehow be explained. So that if anyone thinks fit to maintain that
+possession of a mate is an adequate explanation of part of the
+hostilities, it is clearly impossible to regard all the fighting as a
+manifestation of one principle directed towards a common biological end.
+
+But wherever we extend our researches, we find that the facts give
+precision to the view that the occupation of a territory is the
+condition under which the pugnacious instinct is rendered susceptible to
+stimulation. The Lapwing, when in its territory, displays hostility
+towards other males of its own species, but when upon neutral ground,
+treats them with indifference; the Chiffchaff pursues its rival up to
+the boundary and is then apparently satisfied that its object has been
+achieved; the cock Chaffinch in March permits no other male to intrude
+upon its acre or so of ground during the early hours of the morning, but
+for the rest of the day it joins the flock and is sociable; the
+Herring-Gull resents the approach of strangers so long as it occupies
+its few square feet of cliff, but welcomes companions whilst it is
+following the plough--all of which points to a relation between the
+territory and the fighting. And this view has at least one merit--it
+accounts for all the fighting no matter what degree of severity may be
+reached or in what way the sexes may be involved. The complexity of the
+strife presents no obstacle; for if the biological end of the fighting
+is to render the territory, which has already been established, secure
+from intrusion, each sex will have its allotted part to play at the
+allotted time: thus the battles between the males before females appear
+on the scene will decide the initial question of ownership; those
+between the females will give an advantage to the more virile members
+and insure an even distribution of mates for the successful males; the
+constant struggles between paired males will roughly maintain the
+boundaries and prevent such encroachment as might hamper the supply of
+food for the young; and the co-operation of male and female in defence
+of the territory will be an additional safeguard. Each form of battle
+will contribute some share towards the main biological function of
+reproduction.
+
+
+Hitherto we have dealt principally with the male. We have referred, it
+is true, to the fact that the female co-operates with her mate in order
+to drive away intruders, but beyond this, we have made no attempt to
+trace what part, if any, she plays in the whole scheme. We must do so
+now.
+
+The various steps by which the territory is not only established but
+made secure from invasion, imply an inherited nature nicely balanced in
+many directions--first of all the male must be so attuned as to be ready
+to search for a territory at the right moment; then it must be capable
+of selecting a suitable environment; and, having established itself, it
+must be prepared to defend its area from a rival, and to resist
+encroachment by its neighbours--and if it failed in any one of these
+respects, it would run the risk of failure in the attainment of
+reproduction. Each individual has therefore to pass, so to speak,
+through a number of sieves--the meshes of which are none too
+wide--before it can have a reasonable prospect of success. This being
+so, we ask, in the first place, whether the female, too, may not have an
+eliminating test to pass; and in the second place, whether she may not
+also assist in furthering the biological end of securing the territory.
+
+Now the answer to the first of these questions will be found to be in
+the affirmative. Just as, in the securing of a territory, the ultimate
+appeal is to the physical strength of the male, so, in the course of her
+search for a mate, the female may be called upon to challenge, or may be
+challenged by a rival, and the issue is decided by force. My attention
+was first drawn to this fact by a struggle between two female
+Whitethroats, which I have described elsewhere. The scene of its
+occurrence was the corner of a small osier bed occupied by one male, and
+the females that took part in it had only recently arrived, but the
+male, an unpaired bird, had been in possession of its territory for some
+days. The sequel to this struggle, which was protracted and severe, was
+the disappearance of both females, the male being left without a mate
+for a further ten days.
+
+[Illustration: Emery Walker ph.sc.
+
+The female Chaffinch shares in the defence of the territory and attacks
+other females.]
+
+Numerous instances have since come under my notice. Hen Chaffinches
+become so absorbed that they fall to the ground and there continue the
+struggle. Seizing hold of one another by the feathers of the head, they
+roll from side to side, and then, without relaxing their grip, lie
+exhausted--the quickened heart-beat, altered respiration, tightly
+compressed feathers and partially expanded wings betraying the intensity
+of the conflict.
+
+As the breeding season approaches, hen Blackbirds grow more pugnacious.
+Individuals that early in the year have frequented the same spot daily
+and have even shown every sign of friendship, become openly hostile. For
+two years in succession I had an opportunity of observing females under
+such conditions, and of studying the gradual change in their
+relationship. Each morning at break of day and for some hours afterwards
+they could be seen in the same place, one following the other as they
+searched for food first in this direction and then in that, as if they
+derived some special pleasure from the fact of their companionship. Then
+a change began to manifest itself. Indications of animosity became
+apparent; one would run towards the other in a threatening attitude and,
+in a half-hearted manner, peck at it; and gradually the hostility grew,
+until the tentative pecking developed into a scuffle and the scuffle
+into a conflict.
+
+Much fighting also occurs between the females of the Reed-Bunting, and
+likewise between those of the Moor-Hen, and because these two species
+are not only common but inhabit respectively open stretches of marshy
+ground or large sheets of water, the fighting can be readily observed.
+
+Why do the females fight before they are definitely paired? To obtain
+mates? This certainly seems to be the obvious explanation because any
+question of securing territory can be excluded; yet if it be true that
+their sex is numerically inferior, it is difficult to understand the
+necessity for such strenuous competition. But what is the condition
+under which the pugnacious instinct of the female is rendered
+susceptible to stimulation? It cannot be merely the presence of a male
+ready to breed, for then there would be endless commotion amongst the
+flocks of Chaffinches or of Lapwings which in March are composed of both
+sexes, including even males that have secured territories. There must be
+some other circumstance; and, judging by experience, it is to be found
+in the territory--a male, that is to say, in occupation of one, is the
+condition under which the inherited nature of the female is allowed free
+play. We must bear in mind, however, that the competition between the
+males is very severe, that large numbers probably fail to pass even this
+preliminary test, and that only a proportion are in a position to offer
+to the female the condition under which her process can successfully run
+its course; so that the presumption is--though it is incapable of
+demonstration--that there is a competition for such males each recurring
+season, and that, on the average, the weaker females fail to procreate
+their kind.
+
+But apart from any direct assistance she may give in driving away
+intruders, does she in any way help to further the biological end of
+reproduction? This is a difficult question to answer, and the suggestion
+I have to make can only apply in those cases in which the territory is
+occupied throughout the breeding season. Much of the fighting between
+the males occurs in her presence, and it must be admitted--though it is
+difficult to speak with any degree of certainty--that such fighting,
+taken as a whole, bears the stamp of exceptional determination. Let us
+then grant that the excitement of a male does, under these
+circumstances, reach a higher level of intensity, and let us see how
+this will add to the security of the territory. The fact that the male
+has established itself and obtained a mate is not alone sufficient to
+accomplish the end for which the territory has been evolved. During the
+period between the initial discharge of the sexual function and the time
+when incubation draws to a close, much may happen to prejudice the
+future of the offspring; there is always the possibility of invasion by
+an individual whose development is backward or which has been
+unsuccessful in making good the first step, and, as we saw in the case
+of the Reed-Bunting, a portion of the ground won may be lost; there is
+always the danger of gradual encroachment by neighbouring owners; and
+there is even a possibility that a pair may be so persistently harassed
+by more virile neighbours as to forsake the locality permanently. If
+then a male is to attain a full measure of success it must be capable
+of keeping its boundaries intact up to the time when the young are able
+to fend for themselves, and consequently it is important that its
+intolerant nature should remain susceptible to stimulation throughout
+the greater part of the season.
+
+Does the presence of a female serve to promote this end? Now we know
+very little of the influence exerted by one sex upon the other.
+Professor Lloyd Morgan has suggested that the male raises the emotional
+tone of the female, a suggestion which seems to me in accordance with
+the facts. There is reason to believe, however, that the converse is
+also true--namely that the excitement of the male reaches a higher level
+of intensity when a female is present. Granting then that his emotional
+tone is raised, how will this affect the question? So great is the
+difference of opinion as to the part that the emotions play in
+furthering the life of the individual that one hesitates to accept any
+particular one. But it seems to be generally admitted that emotion adds
+to the efficacy of behaviour, and this is the view of Professor Lloyd
+Morgan. "Whatever may be the exact psychological nature of the emotions,
+it may be regarded," he says, "as certain that they introduce into the
+conscious situation elements which contribute not a little to the energy
+of behaviour. They are important conditions to vigorous and sustained
+conation." Therefore, if it be true that the female raises the emotional
+tone of the male, the result will be an increased flow of energy into
+all the specific modes of behaviour connected with reproduction, amongst
+which those directly concerned in the securing and defence of the
+territory will receive their share; so that instead of a progressive
+weakening of just those elements in the situation which make for
+success, the level of their efficiency will be maintained as a result of
+such reinforcement. But the female becomes intolerant of her own sex
+when she has discovered a male ready to breed, and, later, assists her
+mate in resisting intrusion; and by raising her emotional tone, he may
+be the means of furthering more strenuous behaviour on her part. Each
+member of the pair would in this way contribute towards the energy of
+behaviour of its mate, and hence add indirectly to the security of the
+territory.
+
+It may be well to illustrate the foregoing remarks. Suppose that there
+is a small piece of woodland barely sufficient to hold three pairs of
+Willow-Warblers, and suppose that the male and female in the middle
+territory did not respond to one another's influence quite as readily as
+the adjoining males and females, what would be the result? The emotional
+tone of the central pair would stand at a lower level of intensity; and,
+since their congenital dispositions would lack the necessary
+reinforcement, the birds would tend to become less and less punctilious
+in keeping their boundaries intact, whereas the adjoining pairs, always
+on the alert and meeting with little opposition, would encroach more and
+more and gradually extend their dominion. And so, by the time the young
+were hatched, the parents would be in occupation of an area too limited
+in extent to insure the necessarily rapid supply of food, and would be
+compelled to intrude upon the adjoining ground. But knowing how routine
+becomes ingrained in the life of the individual, knowing that for weeks
+this pair had submitted to their neighbours, can we believe that they
+would be capable of asserting their authority and that the young would
+be properly cared for? Or suppose that different pairs of Kittiwake
+Gulls on the crowded ledges, or different pairs of Puffins in the
+crowded burrows, varied in like manner, would they all have equal
+chances of rearing their offspring? The struggle for reproduction is
+nowhere more severe than amongst the cliff-breeding sea birds; it is not
+for nothing that one sees Kittiwake Gulls, locked together, fall into
+the water hundreds of feet below and struggle to the point of
+exhaustion, or, as has been reported, to the point of death; it is not
+for nothing that Puffins fight with such desperation. And surely success
+will be attained by that pair whose emotional tone stands high and whose
+impulse to fight is therefore strong, rather than to the ill-assorted
+couple.
+
+
+The argument, then, is briefly this. In the spring, a marked change
+takes place in the character of the males of very many species; instead
+of being gregarious they either avoid one another and become hostile,
+or, if their conditions of existence require that they shall still live
+together, they become irritable and pugnacious. This change is made
+known to us by the battles of varying degrees of severity which are such
+a feature of bird life in the spring; and since a female can commonly be
+observed to accompany the combatants, the possession of a mate appears
+at first sight to be the proximate end for which the males are
+contending. But when the circumstances which lead up to the quarrels are
+investigated closely, the problem becomes more difficult; for it is not
+merely a question of males fighting in the presence of a female, as is
+generally supposed to be the case, but on the contrary there is a
+complexity of strife which is bewildering--males attack females or _vice
+versa_; female fights with female; or a pair combine to drive away
+another pair, or even a solitary individual no matter of which sex. This
+complexity of strife makes against the view that the possession of a
+mate is the reason of the fighting. But an even stronger objection is to
+be found in the fact that males are hostile when no female is
+present--and hence we must seek elsewhere for the true explanation.
+
+Now if the behaviour of a male be closely observed, it will be found
+that its pugnacious instinct gains or loses susceptibility according to
+the position which it happens to occupy--when its ground is trespassed
+upon, the impulse to fight is strong; but when it crosses the boundary
+it seems to lose all interest in the intruder. Moreover, in some
+species, the male rejoins the flock at intervals during the early part
+of the season and for a time leads a double existence, passing backwards
+and forwards between its territory and the neutral ground. Its behaviour
+under these circumstances affords some valuable evidence, for the bird
+displays little if any hostility when accompanying the flock, yet when
+it returns to the ground over which it exercises dominion, no male can
+approach without being attacked. The conclusion, therefore, seems to be
+inevitable, namely that the actual occupation of a territory is the
+condition under which the pugnacious nature of the male is rendered
+susceptible to appropriate stimulation.
+
+
+
+
+CHAPTER IV
+
+THE RELATION OF SONG TO THE TERRITORY
+
+
+If we listen to the voices of the Waders as, in search of food, they
+follow the slowly ebbing tide, we shall notice that each species has a
+number of different cries, some of which are uttered frequently and
+others only occasionally. Not only so, but if we study the circumstances
+under which they are uttered, we shall in time learn to associate
+certain specific notes with certain definite situations.
+
+The Curlew, when surprised, utters a cry with which most of us, I
+suppose, are familiar; but when with lowered head it drives away another
+individual from the feeding ground, it gives expression to its feelings
+by a low, raucous sound, which again is different from its cry when a
+Common Gull steals the _arenicola_ that has been drawn out of the mud
+with such labour.
+
+Thus we come to speak of "alarm notes," "notes of anger," "warning
+notes"--naming each according to the situations which normally accompany
+their utterance. And so, all species, or at least a large majority of
+them, have, in greater or lesser variety, cries and calls which are
+peculiar to certain seasons and certain situations; and since on many
+occasions we have indisputable evidence of the utility of the sound
+produced--as when, upon the alarm being given by one individual, the
+flock of Lapwing rises, or when, in response to a particular note of the
+parent, the nestling Blackcap ceases to call--so are we bound to infer
+that all the cries are, in one way or another, serviceable in furthering
+the life of the individual.
+
+But besides these call-notes, birds produce special sounds during the
+season of reproduction--some by instrument, others by voice, others
+again by the aid of mechanical device. And not only is this the case,
+but many accompany their songs with peculiar flights, such as soaring to
+a great height, or circling, or floating in the air upon outstretched
+wings. These special sounds and special flights are those with which I
+now propose to deal, including under the heading "song" all sounds
+whether harsh or monotonous or beautiful, and whether vocally or
+otherwise produced; and I shall endeavour to show not only that they are
+related to the "territory," but that they contribute not a little to the
+successful attainment of reproduction.
+
+The vocal productions are infinite in variety and combination. At the
+one extreme we have songs composed of a single note repeated slowly or
+rapidly as the case may be, whilst at the other we have the complex
+productions of the Warblers; and between these two extremes, notes and
+phrases are combined and recombined in ways innumerable. And just as
+there is a rich variety of combination, so there is a very wide
+variation in the purity and character of the notes--some are harsh,
+others melodious, some flute-like, others more of a whistle, and others
+again such as can only be likened to the notes of a stringed instrument.
+Hence in variety of phrase combination added to variety in the character
+of the note, there is a possibility of infinite modes of expression.
+
+If, in the latter part of May, we take up a position at dawn in some
+osier bed, we listen to songs which have reached a high degree of
+specialisation, songs, moreover, which appeal to us on account of their
+beauty; if, on the other hand, we climb down the face of the sea cliff,
+we hear an entirely different class of songs--harsh, guttural, weird,
+monotonous sounds, which, appeal to us though they may, lack the music
+of the voices in the osier bed. And just as, in the osier bed, we can
+recognise each species by its voice, so we can distinguish the "cackle"
+of the Fulmar, the "croak" of the Guillemot, or the "grunt" of the Shag.
+In the osier bed, however, there is considerable variation in the song
+of different individuals of the same species, so much so that we can
+recognise this one from that; whereas on the cliff we cannot distinguish
+between the voices of different individuals. And the more highly
+developed the song, the greater the range of variation appears to be;
+but notwithstanding this--notwithstanding the fact that the pitch may
+differ, the phrase combination may differ, and the timbre may
+differ--the song remains nevertheless specific. So that the two
+principal features of "song," broadly speaking, are "diversity" and
+"specific character."
+
+In contrast with the call-notes, the majority of which can be heard at
+all times of the year, the song is restricted as a rule to one season,
+and that one the season of reproduction. It is true, of course, that
+some birds sing during the autumn, and, if the climatic conditions are
+favourable, in the winter also, just as others betray, in the autumn,
+symptoms of emotional manifestation peculiar to the spring; but just as
+the manifestation of the latter is feeble and vestigial, so, too, does
+the song of the former lack the vigour and persistency which is
+characteristic of the spring. Again, in contrast with the call-notes,
+which are common alike to both sexes, song is confined to one sex--a
+peculiar property of the males.
+
+Now all, I think, will agree that it must serve some biological
+purpose--this at least seems to be the conclusion to be drawn from the
+two outstanding features of "diversity" and "specific character"; and
+since the voices of different individuals of the same species vary, it
+has been suggested that, by creating a more effective pairing situation,
+it is serviceable in furthering the life of the individual. I do not
+propose at the moment to enquire whether this doctrine be true, but
+rather to direct attention to other ways in which the song may be
+useful.
+
+Is the instinct susceptible to stimulation under all conditions during
+the season of reproduction, or only under some well-defined condition?
+This is the question to which we will first direct inquiry.
+
+Song in its full development belongs, as we have seen, to the season of
+reproduction; it is heard at the dawn of the seasonal sexual process,
+and is the most conspicuous outward manifestation of the internal
+organic changes which ultimately lead to reproduction. These changes
+would appear, at first sight, to be the primary condition which renders
+the instinct susceptible to appropriate stimulation. But while this is
+true up to a point, in so far, that is to say, as organic changes are a
+necessary antecedent of all behaviour connected with the attainment of
+reproduction, closer acquaintance with the circumstances under which the
+instinct is allowed full play leads to the belief that they are not
+alone sufficient to account for the facts as observed. In order to
+arrive at a decision we must seek out the specific factors in the
+external environment with which "song" is definitely related.
+
+Some birds cross whole continents on their way to the breeding grounds,
+others travel many miles, others again find suitable accommodation in a
+neighbouring parish--nearly all have a journey to perform, it may be
+short or it may be long. The flocks of Finches gradually decrease and we
+observe the males scattering in different directions in search of
+territories; we watch the summer migrants on their way--small parties
+halting for a few hours in the hedgerows and then continuing their
+journey, single individuals alighting on trees and bushes and resting
+there for a few minutes, and the constant passage of flocks of various
+dimensions at various altitudes; and we see Fieldfares, Redwings, and
+Bramblings slowly making their way from the south and the west to their
+homes in the far north. Occasionally we hear their song, not the
+emotional outburst customary at this season, but, except in isolated
+cases, a weak and tentative performance. Gätke speaks of the absence of
+song on the Island of Heligoland, and refers to the Whitethroat as one
+of the few migrants that enliven that desolate rock with their melody.
+On the other hand, many migrants that rest temporarily on the Isle of
+May sing vigorously.[5] But on the whole there is, I think, no question
+that the male whilst travelling to its breeding grounds, and, even after
+its arrival, whilst in search of a territory, sings but little--and that
+little lacks the persistency characteristic of the period of sexual
+activity. Yet, when a suitable territory is eventually secured, the
+nature of the bird seems to change; for, instead of being silent and
+retiring, as if aware of some end not fully attained, it not only makes
+itself conspicuous but advertises its presence by a song uttered with
+such perseverance as to suggest that that end is at length attained.
+Hence, in a general way, the instinct of song seems to be related to the
+establishment of a territory.
+
+Now the subsequent course of behaviour tends to confirm this view. We
+have already had occasion to refer to the fact that the males of some
+species desert their territories temporarily and join together on ground
+which is regarded by the birds that associate there as neutral, and that
+they do so not merely for the purpose of securing food but because they
+derive some special pleasure from the act of association, and we shall
+find that the altered behaviour of the male when it leaves its territory
+to seek food or to join the flock is an important point for us just now.
+
+Buntings desert their territories temporarily and collect in flocks on
+the newly sown fields of grain. Some of the males are single, others are
+paired, and accompanied, it may be, by their mates; they wander over the
+ground in search of food, uttering their call-notes from time to time,
+or, settling upon the hedges and trees surrounding the field, rest there
+and preen their feathers. But even though a male may be surrounded by
+other males, even though it may occupy a position where it is
+conspicuous to all around, even though, that is to say, it is
+apparently in contact with just those stimulating circumstances which
+will evoke a response when it returns to its territory, yet it makes no
+attempt to sing.
+
+Lapwings, when they resort to the neutral ground, run this way and that
+in full enjoyment of one another's companionship, behaving as they do
+when they flock in autumn and winter. Specific emotional manifestation
+is, however, absent, and their actions seem to be in nowise affected by
+the powerful impulse which only a few minutes previously determined
+their conduct, for of the characteristic flight with its accompanying
+cry there is no sign.
+
+Early in the season Turtle Doves often collect from the surrounding
+country at certain spots where their favourite food is abundant. The
+croak of this Dove--its true song--is a familiar sound during the
+summer, but in addition the bird has a sexual note characteristic of the
+race. I watched a flock of upwards of one hundred on some derelict
+ground approximately eight acres in extent. Here, in May, the birds were
+attracted by the seeds of _Stellaria media_ which was growing in
+profusion. After 5 A.M. there was continuous traffic between this piece
+of ground and the surrounding neighbourhood, a constant arrival and
+departure of single individuals or pairs; and, as they fed, the sexual
+note could be heard in all directions. Now some of the males occupied
+territories close at hand, and one could watch their passage to and
+fro; yet in no single instance did I hear the true song uttered on the
+feeding ground, although the moment a male returned to its territory its
+monotonous croak could be heard, uttered moreover with that persistence
+which is so marked a feature of all song or of the sounds that
+correspond to it.
+
+Thus it will be seen that, even after the internal organic changes have
+taken place, the instinct of song is not susceptible to stimulation at
+all times and under all circumstances, but only at certain specified
+times and under special circumstances which can be observed to
+correspond with the occupation of the territory.
+
+In many species each male singles out within its territory some
+prominent position to which it resorts with growing frequency. This
+position is an important feature of the territory, and exercises a
+dominating influence on the life of the bird. I have referred to it as
+the "headquarters," and it may be a solitary tree or bush, an
+outstanding mound or mole hillock, a gatepost or a railing--anything in
+fact that supplies a convenient resting place so long as it fulfils one
+condition, namely that the bird when it is there is conspicuous. It need
+not, however, be a tree or a mound or indeed anything upon which the
+bird can perch, for there is reason to think that the soaring flight
+undertaken at this season by so many males, since it is generally
+accompanied by the specific sexual sound, answers the same purpose as
+the topmost branch of a tree.
+
+Now there is nothing in the external environment to which the song is
+more definitely related than to the "headquarters"--this at least is the
+conclusion to be drawn from the behaviour, and I will indicate the sort
+of evidence upon which such conclusion is based. There is, first of all,
+the persistency with which the male resorts to the same tree, even to
+the same branch, and, as it seems, solely for the purpose of
+advertisement. We know by experience the approximate routine of the
+male's behaviour; we know where to seek it, where to hear it, and when
+once we have discovered its headquarters, we know that there it will
+sing day after day for weeks or it may be for months together--perhaps
+the most striking feature of its behaviour at this season. Next, we find
+that other trees, though made use of, are not made use of to a similar
+extent for the purpose of song. The area occupied varies much according
+to the nature of the environment; it is sometimes extensive, and seldom
+less than half an acre or so in extent; but in most instances it
+contains plenty of trees and bushes which could, one would imagine,
+serve the purpose of a "headquarters" just as well as the particular one
+selected, and yet the bird, when there, betrays no inclination to sing
+at all comparable with that which can be observed when it occupies its
+accustomed perch. Further evidence is afforded in the behaviour of those
+species that make temporary excursions from their territories. The male,
+on its return, flies as a rule direct to its special tree and sings.
+Sometimes, however, it settles upon the ground, not unfrequently
+accompanied by the female, and while there remains silent; but presently
+rising from the ground and deserting its mate, it flies to the
+headquarters and sings. Again, nearly every male at one time or another
+in the course of the season is aroused to action by the intrusion of a
+rival. The emotional tone of the owner of the territory is then raised,
+and the intruder is pursued and attacked; but this alone is not
+sufficient, it seems as if the chain of instinctive activities, when
+once aroused by appropriate stimulation, must pursue its course to the
+end--and the end in such a case is only reached and complete
+satisfaction only gained when the bird has not merely returned to his
+"headquarters" but has given vocal expression to his emotion. Finally,
+we must bear in mind these two facts, that the "headquarters" is
+occupied solely by the male--it forms no part of the life of the
+female--and that it is the male only that sings.
+
+Many such subtle incidents of behaviour as the foregoing can be
+perceived but not readily described, and trifling though they may seem
+to be in themselves, yet in the aggregate they yield full assurance of a
+close relationship.
+
+The distant song of a male, or the presence of an intruding male, have
+also stimulating effects, though in somewhat different ways. The former
+evokes the normal reply, that is to say the bird, if silent, is liable
+to utter a corresponding reply; the latter arouses hostility into which
+is infused much feeling tone, the bird sings hurriedly while in pursuit
+of its rival, and, which is more remarkable still, even in the midst of
+an encounter. Both the normal reply and the emotional song must be
+similar in origin--different aspects of the same situation--and both are
+clearly related to the other male.
+
+The arrival of a female may also be followed by an emotional outburst
+which can be heard at intervals for some days; on the other hand, the
+song may continue as before or, for a time, entirely cease.
+
+To take the emotional outburst first. This would appear to be
+susceptible of explanation on the hypothesis that the voice contributes
+to a more effective pairing situation; an hypothesis which admittedly,
+at first sight, gains some support from the fact that a second or a
+third male is frequently present. But, in truth, the presence of a
+second male makes the situation, so far as the relationship between the
+song and the female is concerned, all the more perplexing; for, as we
+have already seen, the instinct of pugnacity, when aroused by the
+appearance of an intruder, is also liable to be accompanied by a
+similarly extravagant song. On each occasion the vocal effort is infused
+with much feeling tone, and it would be impossible to point to any one
+feature which is peculiar to only one occasion. The question therefore
+arises as to whether the emotional outburst which we are attributing to
+the arrival of a female may not after all be due to the presence of an
+intruding male. It may be so. But although I can recall no single
+instance in which the presence of an intruder could be definitely
+excluded, yet I should hesitate to base upon this any broad
+generalisation.
+
+When the normal course of the song is not interrupted by the arrival of
+a female, when, that is to say, the male still pursues the routine to
+which he has all along been accustomed, and still sings at stated
+intervals in stated places with a voice that betrays no heightened
+emotional tone, even though the song may convey some meaning to the
+delicate perceptual powers of the female, we have nothing to lay hold
+upon which can be construed as an indication of direct relationship
+between the song and the presence of the female.
+
+The partial or complete suspension of the song after pairing has taken
+place is the most interesting, as it is the most noticeable, feature.
+Not that it is by any means universal--if it were so, some of the
+difficulties that beset the path of interpretation would be removed, but
+it is sufficiently widespread to demand explanation. In nearly every
+case it is, however, only temporary, the period during which the male is
+silent varying from a few days to a few weeks. The male
+Grasshopper-Warbler, when it first reaches us, sings persistently, but
+when it is joined by a female a change becomes apparent; instead of the
+incessant trill, there are spasmodic outbursts of short duration, and in
+the course of a few days the bird lapses into a silence which may be
+broken for a short while at dawn, or late in the evening, but is often
+complete. More striking still is the change in the case of the
+Marsh-Warbler, and the sudden deterioration, or even suspension, of
+strains so beautiful and so varied, at a moment, too, when it might
+least be expected, at once arrests the attention. The Reed-Warbler that
+had its headquarters in a willow sang vigorously from the middle of May
+until a female arrived on the 20th June, when its voice was hushed,
+except for occasional outbursts which lacked force and were of short
+duration. When the Wood-Warbler secures a territory it repeats its
+sibilant trill with unwearying zeal, yet no sooner does a mate appear
+than its emotion is manifested in other directions. The Reed-Bunting is
+vociferous during February and March; but when a female arrives, periods
+of silence are frequent and the instinct of the bird becomes
+progressively less susceptible to stimulation. After the manner of the
+race the male makes temporary excursions from its territory accompanied
+by his mate, and it is noteworthy that when he returns and she is absent
+he sings, but that the moment she joins him, or even comes into sight,
+he is silent. In fact, in greater or less degree, a change is noticeable
+in the song of many resident and migratory species under similar
+circumstances, a deterioration so marked that we learn by experience to
+regard it as a certain indication of the arrival of a mate.
+
+Thus it becomes clear that there are certain specific factors in the
+external environment with which the instinct can be definitely related,
+and in the order of their importance they are (1) the territory as a
+whole; (2) the headquarters; (3) an intruding male; (4) the female.
+
+To what extent are these relationships interrelated? Are they all
+mutually dependent upon one another, or is there one which conditions
+the remainder?
+
+In the first place it is evident that if a male were not to establish a
+territory, no opportunity would be afforded for making use of any
+special post or for acquiring a habit in relation to it, and so without
+further consideration we may say that the connection between the song
+and the headquarters, whatever it may be, is primarily dependent upon
+the establishment of a territory.
+
+Next, we have the fact that the distant voice, or still more so the
+presence, of another male has an exciting influence and evokes a
+corresponding reply. Here we have a direct relationship, and one which
+at first sight appears to be exclusive of cross-correlation. But is it
+really so; does no circumstance arise under which even the proximity of
+a rival fails to evoke response? The reply is not doubtful. Such a
+circumstance _does_ arise--when a male for one reason or another passes
+outside the limits of its accustomed area. This aspect of behaviour has
+already been fully discussed in connection with the question of
+hostility, and everyone, I imagine, must by now be pretty well familiar
+with the facts. However, it does not often happen that we are given
+such an aid to interpretation as is vouchsafed to us in the altered
+behaviour of the male when it joins the flock, and if, as I believe,
+song and hostility are intimately associated, forming part of an
+inter-related whole which, for biological interpretation, has, as its
+end, the attainment of reproduction, it is not surprising that
+circumstances which lead to the modification of the one should likewise
+affect the other; I offer no apology, therefore, for adverting to this
+aspect of behaviour once again.
+
+Now a male may leave its territory for three reasons--to pursue an
+intruder, to join the flock on neutral ground, or to find the necessary
+means of subsistence on other feeding grounds. On each of these
+occasions it hears the song of, and is in close contact with, other
+males; and if the relationship of which we are speaking be really
+exclusive of cross-correlation, its instinct ought to respond with the
+customary freedom. But what happens? A male pursues its rival, betraying
+much emotion and singing extravagantly, until the boundary is passed,
+when emotion subsides and it is silent; or, it flies to the flock on
+neutral ground, and, although surrounded by the very males that a short
+time previously evoked response, is there unresponsive; or again, it
+goes in search of food and collects with other males bent on a similar
+errand, and in presence of what we know would be an exciting influence
+under other circumstances, it nevertheless remains silent. Hence the
+relationship between the song and a male rival seems, as in the case of
+the headquarters, to depend in the first instance upon the occupation
+of a territory.
+
+So that the relationship between the song and the territory as a whole
+is clearly of a different order from that which obtains between the song
+and the headquarters, or the song and a male rival; for the first, as
+far as can be judged by observation, is exclusive of, whilst the second
+and the third involve, cross-correlation. How are these facts to be
+explained? We have already seen that it belongs to the nature of the
+male during the season of reproduction to establish itself in a definite
+place, and this action is just as much a part of its hereditary nature
+as the building of the nest is of that of the female, and it is just as
+necessary for the successful attainment of reproduction. What exactly
+the stimulus is to this mode of behaviour we do not know; we can go no
+further back than the internal organic changes which are known to occur
+and which we assume, not without some reason, are responsible for its
+initiation. Granting, then, that there is this congenital disposition,
+what relation does it bear to the song? Without a doubt the song is
+likewise founded upon a congenital basis; it is truly instinctive, and
+as such requires appropriate stimulation; furthermore the male sings
+only when in occupation of its territory. Having regard to these two
+facts we might say that the territory is the stimulus to the song. But
+this can scarcely be a true interpretation, for inasmuch as the stimulus
+would be relatively constant, a relatively constant response ought to
+follow, and even a slight acquaintance with the daily round of
+behaviour will furnish plenty of evidence to the contrary, seeing that
+the song, though persistent, is never continuous--in fact there are long
+periods of silence during the daytime, and only in the morning and the
+evening does the male become really vociferous. What then is the
+stimulus? Through awareness of something in the environment the male
+responds to stimulation, and the only reply we can give is that the
+headquarters, or a distant song, or the proximity of another male--with
+all of which, as we have seen, the instinct is definitely related--are
+the specific factors which normally evoke response--and experience
+teaches us that the periods of quiescence are just those when life is at
+its lowest ebb and these stimulating factors less in evidence. Bearing
+this in mind, bearing in mind the fact that when a male joins the flock
+or crosses the boundary its instinct ceases to respond, bearing in mind,
+that is to say, that there is evidence of relationship between these
+specific factors and the song only when the territory is actually
+occupied, the conclusion seems inevitable that we have here the
+determining condition which renders the instinct susceptible to
+appropriate stimulation.
+
+There remains the female. I place her last in order of importance, not
+because I regard her influence as of small consequence, but because the
+evidence is of a varied and complex kind, so much so that it is
+difficult to ascertain by observation just how far she is a situational
+item. It will be remembered that the only direct evidence we had of such
+influence was a deterioration or, in some instances, a complete
+cessation of vocal manifestation. Clearly then we are confronted with a
+relationship of a different kind from that which we have been
+discussing; for not only is anything in the nature of stimulation
+absent, but, and this is a remarkable fact, the other items in the
+environment which formerly evoked response no longer do so in quite the
+same way. Is there any awareness on the part of the male of the relation
+between his voice and the mate that is to be, or is it merely that as
+the sexual situation increases in complexity some inhibiting influence
+comes into play? These are questions which lead up to difficult
+problems. But it is no part of my task to discuss the psychological
+aspect of the behaviour; my purpose is merely to show that the situation
+on the arrival of a female undergoes marked modification, that the
+instinct of the male is then less susceptible to stimulation, and that
+the factors in the external environment which formerly elicited response
+become relatively neutral.
+
+Hence the appearance of the female on the scene marks the opening of a
+new stage in the life-history of the male, and, to judge by the course
+of events, it would seem as if the song with its network of
+relationships had now served its main biological purpose.
+
+And now, what is the purpose, and what the origin, of song? Is it, as
+some naturalists have conceived, a means of raising the emotional tone
+of the female, of creating a more effective pairing situation, and so
+of removing a barrier to the successful discharge of the sexual
+function; or, is the emphasis here too much upon the emotional, too
+little upon the strictly utilitarian, aspect? All, I think, will agree
+that it must serve some biological purpose, and the position we have so
+far reached is that the determining condition of its manifestation is
+not merely the establishment, but the actual occupation of a territory,
+and that there are no factors in the external environment which can
+evoke response in the absence of such condition. This being so, the
+further questions arise as to whether it contributes towards the
+attainment of the end for which the whole territorial system has been
+built up, and what precisely is the way in which it does so.
+
+Everyone knows that in the spring the shyest of birds no longer practise
+the art of concealment. The Curlew soars to a great height, and upon
+outstretched wings hovers in the air whilst uttering its plaintive wail;
+the cock Grouse, as if dissatisfied with its "crowing," springs into the
+air and becomes a conspicuous object of the moor; the wary Redshank,
+poised on flickering wings, forgets its mournful alarm cry, and finds
+again its melodious song; and even the secretive Grasshopper-Warbler
+crawls out of the midst of the thicket in order to "reel," just as, for
+a similar reason, Savi's Warbler climbs to the top of a tall reed. In
+fact the males of most species, when they are finally established on the
+breeding grounds, make themselves as conspicuous as possible by sight
+and by sound. And since the sounds produced by no two species are
+exactly alike, the females are able to recognise their prospective
+mates, and the males that are still in search of ground have ample
+warning if that upon which they are treading is already occupied. So
+that you see, from the remarkable development of the vocal powers in the
+male, there follow two important results--"recognition" and "warning."
+
+We here turn from song as the expression of an instinctive disposition,
+and the question of what calls forth this expression, to the impression
+produced by the song on the hearer.
+
+Most birds have a call-note or a number of call-notes, which, generally
+speaking, are specifically distinct. But to the human ear they are not
+always so, perhaps because our power of hearing is less sensitive than
+that of a bird, and unable to appreciate delicate differences of tone.
+Be this as it may, however, the fact remains that we often find it
+difficult, and in not a few cases impossible, to recognise a bird merely
+by its call. The plaintive notes of the Willow-Warbler and of the
+Chiffchaff are to our ears very closely akin, so, too, are those of the
+Marsh-Warbler and of the Reed-Warbler, and there is a great resemblance
+between the hissing sound produced by the two Whitethroats. In Co.
+Donegal I have been deceived by the spring-call of the Chaffinch which,
+owing possibly to the humidity of the atmosphere, is, there, almost
+indistinguishable from the corresponding note of the Greenfinch. The
+Yellow Bunting and the Cirl Bunting frequently make use of a similar
+note, so do the Curlew and the Whimbrel. In fact, numberless instances
+could be quoted in which notes appear to us identical, and, as a rule,
+the more closely related the species, the more difficult it becomes to
+distinguish the sounds--alike in plumage, alike in behaviour, alike in
+emotional manifestation, it would be surprising if they were not alike
+in voice. But the moment we pass from the call-notes to a consideration
+of the songs we are faced with a very remarkable fact, for not only are
+these readily distinguished, but in many cases they bear no resemblance
+in any single characteristic. What could be more unlike than the songs
+of the Willow-Warbler and of the Chiffchaff, of the Marsh-Warbler and
+the Reed-Warbler, or of the Yellow Bunting and the Cirl Bunting?
+
+Now when different individuals collect in flocks at certain seasons,
+they assist one another in finding food, and afford mutual protection by
+giving timely warning of the approach of a common enemy, and the
+gregarious instinct is thus of great advantage to the species; but no
+matter how powerful the impulse to flock might be, if there were no
+adequate means of communication, the different units would frequently
+fail to discover their neighbours. Here the specific cries and calls
+come into play, enabling them as they move about in search of food, or
+change their feeding grounds, or whilst they are on migration, to keep
+constantly in touch with one another; and hence one purpose that these
+call-notes serve is that of recognition. Moreover, they convey their
+meaning to individuals of other species and are acted upon, and are thus
+in every sense socially serviceable; but on the other hand, whilst
+there is much evidence to show that the song is of great individual
+value, there is none to show that it is in any like manner of direct
+advantage to the community.
+
+If, then, there is in the call-notes an adequate means of communication
+and of recognition, why do I suggest that the song has also been evolved
+primarily for the purpose of recognition?
+
+What, first of all, are the conditions in the life behaviour during the
+season of reproduction that make the intervention of the voice a
+consideration of such importance? The general result of our
+investigation might be summed up thus: we found that the male inherits a
+disposition to secure a territory, that at the proper season this
+disposition comes into functional activity and leads to its
+establishment in a definite place, and that it cannot search for a mate
+because its freedom of action in this respect is forbidden by law; that
+the female inherits no such disposition, that she is free to move from
+place to place, free to satisfy her predominant inclination, and to seek
+a mate where she wills; and, since the appropriate organic condition
+which leads to pairing must coincide with appropriate conditions in the
+environment, that the union of the sexes must be accomplished without
+undue delay. Furthermore we found that a territory is essential if the
+offspring are to be successfully reared; that, since the available
+breeding ground is limited, competition for it is severe, and that the
+male is precluded from leaving the ground which he has selected, and is
+obliged, in order to secure a mate, to make himself conspicuous. That
+was our general result. Now there are two ways by which the male can
+make himself conspicuous--by occupying such a position that he can be
+readily seen, or by producing some special sound which will be audible
+to the female and direct her to the spot. The former, by itself, is
+insufficient; in the dim light of the early dawn, when life is at its
+highest, and mating proceeds apace, what aid would it be for a male to
+perch on the topmost branch of a tree, how slender a guide in the depth
+of the forest? But whether in the twilight or in the dark, in the
+thicket or the jungle, on the mountain or on the moor, the voice can
+always be heard--and the voice is the principal medium through which the
+sexes are brought into contact.
+
+Well now, we come back to the question, why, if all species have a
+serviceable recognition call, that call should not be sufficient for the
+purpose, just as, without a doubt, it is adequate for all purposes at
+other seasons? The answer is, I think, clear. The recognition call is
+not confined to one sex, nor only to breeding birds; it is the common
+property of all the individuals of the species, and if the female were
+to rely upon it as a guide she might at one moment pursue another
+female, at another a non-breeding male; she might even be guided to a
+paired female or to a paired male, and time would be wasted and much
+confusion arise. So that no matter how much a male might advertise
+himself by cries and calls which were common alike to all the
+individuals of the species, it would not assist the biological end which
+we have in view. Something else is therefore required to meet the
+peculiar circumstances, some special sound bearing a definite meaning by
+which the female can recognise, amongst the host of individuals of no
+consequence to her, just those particular males in a position to breed
+and ready to receive mates. Hence the vocal powers, the power of
+producing sounds instrumentally, and the power of flight, have been
+organised to subserve the biological end of "recognition."
+
+And this view is strengthened, it seems to me, by the erratic behaviour
+of certain species, more particularly by one remarkable case, the case
+of the Cuckoo. The male, after having established himself, utters his
+call persistently from the day of arrival until approximately the middle
+of June; but, in contrast with the large majority of species, the female
+has a characteristic call which she, too, utters at frequent intervals.
+The female is polyandrous and has a sphere of influence embracing the
+territories of a number of males; she wanders from place to place, is
+often silent, and not unfrequently is engaged in dealing with her egg or
+in searching for a nest in which to deposit it, and therefore she is not
+always in touch with a male, still less with any particular one. Now
+there is much evidence to show that the discharge of the sexual function
+amongst birds is subject to control, and that this control operates
+through the female--through her physiological state becoming
+susceptible to stimulation only at certain periods. So that we have
+these considerations, that the female is polyandrous, that she has a
+territory distinct from that of the male, and that her sexual impulse is
+periodical; and the further consideration that the impulse, since it is
+periodical, is of limited duration and must receive immediate
+satisfaction. Such being the circumstances of the case, would the voice
+of the male serve to insure the union of the sexes at the appropriate
+moment? Well, the fact that she is polyandrous implies that every male
+in her sphere of influence is not always capable of satisfying her
+sexual instinct. Is, then, the male's call an indication of his
+readiness to yield to stimulation? Without a doubt it is an index of the
+general physiological state which generates the sexual impulse, without
+a doubt it denotes a general preparedness to breed, but there is no
+evidence to show that it denotes the degree of ardour of the male at any
+particular moment, and much that proves the contrary. So that only by
+the female producing some special sound which will attract the males
+that are eager and bring them rapidly to the spot where she happens to
+be, only thus is it possible to insure the consummation of the sexual
+act. This, it seems to me, is the purpose of the peculiar call of the
+female--a call which, so far as biological interpretation is concerned,
+is just as much a song as the melody of the Marsh-Warbler--and its
+interest for us just now lies in this, that here we have a special case
+in which the sexes have separate territories, the female is polyandrous,
+and the voice of the male is not sufficient by itself to bring to pass
+the union of the sexes; and in which, consequently, if the purpose of
+song be that of recognition, we should expect to find, as we do find,
+that the female had a distinct and penetrating call.
+
+We now come to the question of "warning," by no means the least
+important purpose of song. I pointed out that one of the chief
+differences between the call-notes and the song was that the former were
+socially serviceable, whereas the latter was only serviceable to certain
+individuals; and in making this statement, I had in mind the direct
+benefits to the community which proceeded from an appreciation of sounds
+having a mutually beneficial meaning, not the indirect, though none the
+less beneficial, consequences to the species as a whole. Biologically
+considered, song, if it acts as a warning and thereby leads in one way
+or another to more complete success in the rearing of offspring, may be
+spoken of as socially serviceable; but it is legitimate to draw a
+distinction between the prospective value of remote relationships which
+we can foresee, and the mutual assistance which the individuals of a
+community derive from their close association.
+
+If there were always sufficient breeding ground to support the offspring
+of all the individuals of each species, if the individuals were always
+so distributed that there was no possibility of overcrowding in any
+particular area, and if the conditions of existence of different
+species were so widely divergent that the presence of this one in no way
+affected the interests of that, no opportunity would be afforded for the
+development of so complex a system as is involved in the "territory" and
+all that appertains to it. But the available breeding ground is by no
+means unlimited. The supply of food, which is a determining factor in
+the environment, is always fluctuating according to the climate and
+according to the changes in the earth's surface; and so the distribution
+of the bird population in any given area, though it may be suitably
+adjusted for one year or even for a period of years, is bound in the
+course of time to require readjustment. Now there cannot be readjustment
+without competition, nor competition without combat. But the appeal to
+physical force is only a means to an end, and, since no male can endure
+incessant warfare and the perpetual strain of always being on the alert,
+without experiencing such physical exhaustion as might affect his power
+of reproduction, its direct effect upon the combatants cannot be
+otherwise than harmful--in fact it is a necessary evil which for the
+good of the species must be kept strictly within bounds. Bearing in
+mind, then, these two facts, namely that the distribution of the males
+is never stable and that overmuch fighting may defeat the end in view,
+we can appreciate the importance of any factor which will lead to a more
+uniform distribution and at the same time insure security by peaceable
+means.
+
+The proximate end of the male's behaviour is isolation--how is it to be
+obtained? If, after having occupied a territory, the bird were to remain
+silent, it would run the risk of being approached by rivals; if, on the
+other hand, it were merely to utter the recognition call of the species,
+it would but attract them. In neither case would the end in view be
+furthered, and isolation would solely depend upon alertness and the
+capacity to eject intruders. Supposing, however, that the song, just as
+it serves to attract the females, serves to repel other males, a new
+element is introduced deserving of recognition; for those males that had
+established themselves would not only be spared the necessity of many a
+conflict, but they would be spared also the necessity of constant
+watchfulness, and so, being free to pursue their normal routine--to seek
+food, to rest, and, if migrants, to recover from the fatigue of the
+journey, they would be better fitted to withstand the strain of
+reproduction; and those that were still seeking isolation in an
+appropriate environment, instead of settling first here and then there
+only to find themselves forestalled, would avoid and pass by positions
+that were occupied, establishing themselves without loss of time in
+those that were vacant. Without the aid of something beyond mere
+physical encounter to regulate dispersal, it is difficult to imagine how
+in the short time at disposal anything approaching uniformity of
+distribution could be obtained. Hence, both in the direction of limiting
+combat, of insuring accommodation for the maximum number of pairs in the
+minimum area, and of conserving energy, the song, by conveying a
+warning, plays an important part in the whole scheme.
+
+And if this be so, if the song repels instead of attracting, it follows
+that the more distinct the sounds, the less likelihood will there be of
+confusion; for supposing that different species were to develop similar
+songs, whole areas might be left without their complement of pairs just
+because this male mistook the voice of that, and avoided it when there
+was no necessity for doing so. So that just as from the point of view of
+"recognition" each female must be able to distinguish the voice of its
+own kind, so likewise the warning can only be adequate providing that
+the sounds are specifically distinct. A point, however, arises here in
+regard to closely related forms. Some species require similar food and
+live under similar conditions of existence; they meet in competition and
+fight with one another; and, if they did not do so, the food-supply of a
+given area would be inadequate to support the offspring of all the pairs
+inhabiting that area. Generally speaking, the more closely related the
+forms happen to be, the more severe the competition tends to become; and
+it may be argued that in such cases a similar song would contribute to
+more effective distribution and in some measure provide against the
+necessity of physical encounter; that, in fact, it would stand in like
+relation to the success of all the individuals concerned, as does the
+song to the individuals of the same species. But we must bear in mind
+that the primary purpose of song is to direct the females to those males
+that are in a position to breed; and to risk the possibility of prompt
+recognition in order that the males of closely related species should
+fight the less, would be to sacrifice that which is indispensable for a
+more remote and less important advantage.
+
+What meaning does the song convey to a male that is unestablished? Does
+the bird recognise that it is forestalled; does it foresee and fear the
+possibility of a conflict, and conclude that the attempt to settle is
+not worth while? I do not imagine that it thinks about it at all. How
+then does the warning warn? We will endeavour to answer this question,
+but, in order to do so, we must review the stages by which a territory
+is secured.
+
+We take as our starting point the internal organic changes which are
+known to occur. These changes are correlated with other changes,
+manifested by a conspicuous alteration in behaviour--to wit, the
+disappearance of sociability and its replacement by isolation. Having
+found a station which meets the requirements of its racial
+characteristics, the male establishes itself for a season, becomes
+vociferous, displays hostility towards others of its kind, and in due
+course is discovered by a female. The whole is thus an inter-related
+whole, a chain of activities which follow one another in ordered
+sequence. Now we have seen that it is neither pugnacious nor vociferous
+until the territory is actually occupied; we have seen that the fact of
+occupation is the condition under which the instincts of pugnacity and
+of song are rendered susceptible to appropriate stimulation; we have
+discussed the nature of the stimulus in each case, and we wish to know
+the sort of meaning that the song conveys to an individual which is
+still in the preliminary stage of seeking a station. In sequential order
+we have the following: (1) internal organic changes which lead to
+isolation, (2) the appropriate environment which gives rise to an
+impulse to remain in it, (3) the occupation of a territory which is the
+condition under which the instincts are rendered susceptible to
+stimulation, (4) the various stimuli. Each is dependent upon that which
+precedes it, and no part can be subtracted without failure of the
+biological end in view, neither can the different stages be combined in
+different order. So that, in considering the significance of song to an
+unestablished male, we are dealing with the situation at a point at
+which all the latent activities have not been fully felt, for all that
+so far has occurred is the change from sociability to isolation
+determined by internal organic changes. The bird has not established a
+territory because it has not come into contact with the appropriate
+environment, and it is not pugnacious because the condition which
+renders its instinct susceptible is absent; and so, as it wanders from
+place to place and hears the voices of males here or males there, it
+merely behaves in accordance with that part of its nature which
+predominates just at that particular moment--the impulse to avoid them.
+
+But given the appropriate environment, given, that is to say, just that
+combination of circumstances which might bring into functional activity
+all the latent instincts of the intruder, and no matter how vociferous
+the occupant of a territory might be, it would not be preserved from
+molestation. The advantage of the song, biologically considered, is then
+this, that it will often prove just sufficient to preclude males in
+search of isolation from coming into contact with the environmental
+conditions adequate to supply the stimulus to their latent activities
+and to convert them into rivals.
+
+If this interpretation be correct, if we are right in attributing the
+withdrawal solely to the fact that the first stage only in the
+relational series has been reached, it follows that the effect of song
+upon males that have reached subsequent stages in that series must be of
+a very different kind. We have dealt with the male when in the
+preliminary stage of seeking isolation, we must deal with it now when
+eventually it occupies a territory. How does it behave when it hears, as
+it is bound to do, the voices of rivals in its neighbourhood? You may
+remember that some allusion was made to the fact that an outburst of
+song from one individual was followed, not unfrequently, by a similar
+outburst on the part of other individuals in the immediate locality. For
+example, silence may reign in the reed-bed except for an occasional note
+of the Reed-Warbler or Sedge-Warbler. Suddenly, however, a dispute
+arises between two individuals, accompanied by a violent outburst of
+song, and forthwith other males in the vicinity begin to sing excitedly
+and continue doing so for some minutes in a strangely vigorous manner,
+the tumult of voices affording a striking contrast to the previous
+silence. Spasmodic outbursts of this kind, stimulated by an isolated
+utterance, are by no means uncommon. But not only does song stimulate
+song; under certain conditions it has the still more remarkable effect
+of arousing hostility. The boundary that separates two adjoining
+territories is by no means a definite line, but rather a fluid area
+wandered over by this owner at one moment, by that at another. Now so
+long as the bird is silent while in this area, the probability is that
+it will escape detection and remain unmolested; let it however sing--it
+often does so--and it will not merely be approached but attacked, and
+consequently this area is the scene of much strife. The point to be
+noticed here is that the song brings about no withdrawal; it elicits a
+response, attracts instead of repelling, and, in short, arouses the
+impulse that is always predominant in the nature of the male when
+eventually it occupies a territory--the impulse of self-assertiveness.
+Therefore it seems clear that the different stages in the process of
+reproduction mark the appearance of different conditions, each of which
+renders some new impulse susceptible to stimulation, and that the
+significance of song depends upon the stage which happens to have been
+reached. Hence when we speak of song acting as a "warning," we do not
+mean that it arouses any sensation of fear; it is but a stimulus to
+that part of the inherited nature of the hearer which predominates at
+the moment.
+
+Are we then justified in the use of such terms as "warning,"
+"significance," or even "meaning," when it is but a matter of stimulus
+and response? In what does the impulse to avoid other males consist?
+There is no reason to suppose that there is any sensation of fear in the
+first stage, and the course of behaviour demonstrates that there is none
+in the later stages. But it is difficult to conceive of an impulse which
+has, as its end, the isolation of the individual from members of its own
+sex and kind, without some feeling-tone, the reverse of pleasurable,
+entering into the situation; just as it is difficult to believe that the
+female experiences no pleasurable sensation when she hears the voice of
+the male that directs her search. So that the song may be actually
+repellent in the one case and attractive in the other; and it is none
+the less repellent when, as in the later stages, it attracts a
+neighbouring male, for the attraction is then of a different order,
+determined by the presence of the condition which renders the pugnacious
+nature susceptible and leads to attack. In a sense, therefore, we can
+speak of "meaning"--though not perhaps of "significance"--and of
+"warning," when we refer to the prospective value of the behaviour.
+
+So much for the purpose of "song"; there still remains the more
+difficult question--the question of origin. Let me make clear what I
+mean by origin. As we have already seen, there is infinite diversity in
+the sexual voice of different species; some are harsh and others
+monotonous, and some strike the imagination by their novelty whilst
+others are melodious; and to the naturalist each, in its particular way
+and in a particular degree, probably makes some appeal according to the
+associations that it arouses. But just why a Marsh-Warbler is gifted
+with a voice that is so beautiful and varied, whilst the
+Grasshopper-Warbler must perforce remain content with a monotonous
+trill; just why the tail feathers of the Snipe have developed into an
+instrument, whilst the Pied Woodpecker has developed muscles which
+enable it to make use of a decayed branch as an instrument--we know no
+more than we do of the nature of the forces which lead the Reed-Warbler
+to weave its nest to reeds, or the caterpillar of the Elephant Hawk Moth
+to assume so peculiar an attitude when disturbed. When therefore I speak
+of the origin, I do not refer to the mode of origin of variation; I take
+for granted that variations somehow arise, and I seek to ascertain
+whether there is anything in the phenomena which we have explored which
+might reasonably be held to determine the survival of this one in
+preference to that.
+
+When we reflect upon the problem of song and consider the numerous and
+diverse forms in which it is manifested, we are apt to draw a
+comparison between the sounds we hear and those produced by musical
+instruments, and hence to conclude that each bird is gifted with a
+special instrument in virtue of which it produces its characteristic
+melody. But there is a very remarkable phenomenon connected with the
+singing of birds which shows that this is really not the case--I mean
+the phenomenon of imitation. There are plenty of good imitators amongst
+our native species, and the power of imitation is not the exclusive
+property of those which have reached a high degree of vocal development,
+nor, for the matter of that, of song-birds at all. Even the Jay, than
+which few birds have a more raucous voice, that "hoots" like the
+Wood-Owl, or copies the sounds produced by the tail feathers of the
+Snipe, will occasionally imitate the most melodious strains of some
+other species; and the Red-backed Shrike, whose sexual call is
+principally a few harsh notes rapidly repeated, bursts at times into
+perfect imitations of the song of the Swallow, Linnet, or Chaffinch.
+Nevertheless it is amongst such typical songsters as the Warblers that
+we find the greatest volume of imitation, and no limit seems to be
+placed upon their capacity. The Marsh-Warbler can utter the call of the
+Green Woodpecker, or sing as the Nightingale does, with as much facility
+as it sings its own song; and the Blackcap is well-nigh as proficient in
+copying the cries and melodies of surrounding species--and so, if it
+were necessary, we might proceed to add to the list.
+
+These examples demonstrate that different songs are not represented by
+a corresponding number of different physiological contrivances; for if
+the difference were really attributable to some structural peculiarity,
+then the range of sounds embraced in the call-notes and the sexual call
+of any given species, must be the measure of the capacity of its
+instrument; and no matter how great its power of imitation may be, it
+follows that it will only be capable of copying those sounds which fall
+within that range. There is plenty of evidence to show that the power of
+imitation is almost unlimited, at all events that it is not confined
+within such narrow limits as are here demanded. Hence it seems clear
+that the diversity of song is not to be sought in structure, but in some
+innate capacity to play one tune in preference to another; and if this
+be so, and if out of the same instrument, which has been primarily
+evolved to further the biological end of intercommunication, all manner
+of diverse sounds can be made to proceed, the problem of the origin of
+song is to that extent simplified.
+
+We must next inquire into the nature of song, and endeavour to ascertain
+whether all the individuals of a species are alike proficient, or,
+failing this, whether there is any quality which can be observed to be
+constant under all conditions. I watch the Reed-Buntings in a marsh and
+find that there are three males occupying adjoining territories. Two of
+them are fully mature and their plumage is bright: that is to say the
+crown is black, the collar and breast are white, the flanks are dull
+white spotted with black, and the mantle is reddish-brown. The third is
+immature: the crown, instead of being black, is suffused with brown; the
+collar, instead of being white, is mottled with brown; and the flanks
+are more heavily streaked with brown. These three birds take up their
+positions in February, and, as is their wont, sing incessantly each day
+at daybreak. The song of the first two is normal, including the usual
+number of phrases which flow in no definite sequence, but are combined
+and recombined in different order, and the tone is pure; that of the
+third, the immature bird, is, however, very different; for just as in
+comparison its plumage is dull, so the phrases of its song are limited
+and reiterated with great monotony, the tone is impure, and the whole
+performance is dull and to our ears unmusical. I watch them from
+February to June, and observe the order in which they are mated--first a
+mature male; next, after a short interval, the immature male; and
+finally, after a still longer interval, the remaining bird gets a mate.
+As the season advances, still keeping watch on the development of the
+plumage and of the voice of the immature male, I observe that no very
+definite change takes place--that the colours remain dull, that there is
+a conspicuous absence in the song of certain phrases, and that the notes
+lack purity of tone.
+
+If now, instead of Reed-Buntings in a marsh, I watch Yellow Buntings on
+a furze-covered common, I find that, establishing themselves early in
+February, they sing persistently, and in a few weeks are paired. But
+what arrests my attention more particularly is the quality of the song;
+for although the voice is unmistakably the voice of the Yellow Bunting,
+yet it is incomplete and lacks the variety of phrases and musical
+notation which we customarily associate with the bird. Nevertheless, as
+the season advances, there is a progressive development in both these
+directions, and by the end of March or the beginning of April the song
+possesses all those qualities which appeal to us so forcibly.
+
+There is one other fact to which attention must be drawn--the variation
+in the song of the same species in different districts. As an
+illustration let us take the case of the Chaffinch. In Worcestershire
+the bird sings what I imagine to be a normal song--the notes are clear
+and the phrases are distinct and combined in numerous ways. With the
+notes fresh in mind I leave them and go to the west of Donegal, where I
+am at once conscious of a difference; not a subtle difference that
+perplexes the mind and is difficult to trace, but a change so remarkable
+that one is conscious of a passing doubt as to whether after all the
+voice is the voice of the Chaffinch; the song is pitched in a lower key,
+certain phrases are absent, the notes lack tone and are sometimes even
+harsh, and the bird seems wholly incapable of reaching the higher notes
+to which I am accustomed.
+
+Now the immature Reed-Bunting, though to our ears its song is but a poor
+representation of that of the adult, gains a mate; the Yellow Bunting
+pairs, and the discharge of the sexual function may even have taken
+place before its voice attains what we judge to be its full development;
+and there are no grounds for supposing that the Donegal Chaffinch, with
+its less musical notes, has on that account any the less chance of
+procreating its kind--facts which demonstrate that the biological value
+of song is neither to be sought in the purity of tone, nor in the
+variety and combination of phrases, nor, indeed, in any of those
+qualities by which the human voice gains or loses merit, and which leave
+us with no alternative but to dismiss from our minds all æsthetic
+considerations in the attempt to estimate its true significance.
+
+What, then, determines its value? Are there any qualities which, whether
+the bird is mature or immature, whether it is untrained or has acquired
+fuller expression by practice, whether it inhabits this district or
+that, are alike constant? Well, no matter how great the variation, no
+matter how much this voice falls below or exceeds the standard, judged
+from the human standpoint, attained by that, even we, with our duller
+perception, have no difficulty in recognising the species to which the
+owner of the voice belongs; in other words, the song is always specific,
+and this is the most noticeable, as it is the most remarkable,
+characteristic.
+
+There is still, however, another quality to which I would draw
+attention--that of loudness. The sounds produced are on the whole alike
+penetrative, and the individuals of any given district, even though the
+climate by affecting their vocal muscles may have modified the character
+of the song, are at no disadvantage in this respect; neither are the
+females on the same account the less likely to hear the undeveloped
+voice of the immature male.
+
+We have then the following considerations: firstly, there is the
+widespread and remarkable phenomenon of imitation, from which we can
+infer that the diversity of song is not due to structural differences
+but must be sought in some innate capacity to play one tune in
+preference to another; secondly, not all the individuals of the same
+species play a similar tune--we find that there is in certain directions
+a noticeable variation which nevertheless does not seem to affect the
+question of success or failure in the attainment of reproduction; in the
+third place, in contrast with this variation, we can observe a striking
+uniformity in two important particulars, namely in the specific
+character and penetrative power of the song--qualities which we know are
+essential for the purposes of "recognition" and "warning"; and finally,
+from the general course of our investigation, we can infer that if a
+male had no certain means of advertising its position, the territory
+would not be brought into useful relation in its life. Have we here
+sufficient ground on which to construct a theory of origin; in other
+words, has the evolution of song been incidental to, and contributory
+to, the evolution of the territory?
+
+We have all along spoken of the song and of the call-notes as if they
+were manifestations of separate emotional states having their respective
+and well-defined spheres of usefulness; and while, speaking generally,
+this is a true statement of the case, there is much evidence to show
+that the relationship between them is nevertheless very close. There
+are, for example, quite a number of cases in which a particular
+call-note is uttered with unusual energy during sexual emotion, and is
+attached to the song, of which it may be said to form a part; but a
+still closer connection can be traced in many simple melodies which are
+merely compositions of social and family calls repeated many times in
+succession, and even in some of the more complex productions there will
+be found indications of a similar construction. And since this is so,
+since moreover, in the seasonal vocal development of such a bird as the
+Yellow Bunting, we can observe the gradual elaboration from simple to
+complex--from the repetition of single notes to phrases and from phrases
+to the complete melody--we have every reason to suppose that it is along
+these lines that the evolution of the voice has proceeded.
+
+In all probability there was a time when vocal expression was limited
+to primitive social and family cries which would be called into play
+with special force during times of excitement, more particularly during
+the sexual season which is the period of maximum emotional excitement.
+But the excitement would express itself in all the congenital modes of
+behaviour peculiar to the season, and thus the repetition of these cries
+would become associated with combat, with extravagant feats of flight,
+and with other forms of motor response. Now the more emotional
+individuals would be the more pugnacious, and all the more likely
+therefore to secure territory and so to procreate their kind; and, being
+of an excitable disposition, they would at the same time be the more
+vociferous. Hence variations of the hereditary tendency to vocal
+expression, even though in themselves they were not of survival value,
+would be fostered and preserved, so long as they were not harmful, in
+virtue of their association with pugnacity. But if, instead of being
+neutral, they helped to further the biological end of combat, the
+relationship between the voice and pugnacity would be of a mutually
+beneficial kind; and those individuals in which variation in both
+directions happened to coincide, would have a better chance of success
+in the attainment of reproduction.
+
+A territorial system, closely corresponding to that which we have
+discussed, forms part of the life behaviour of certain mammals, and of
+its existence much lower in the scale of life evidence is not wanting;
+from which we can infer that it is not of recent origin, but that the
+conditions in the external environment demanded such a system at a
+remote period of avian development. Now even in its incipient stages the
+system must have involved a separation of the sexes, and howsoever
+slight the degree of separation may have been in comparison with that
+which can be observed to-day, inasmuch as the power of locomotion was
+then less highly developed, mating could only have proceeded
+satisfactorily providing that males fit to breed had some adequate means
+of disclosing their positions. Thus there is reason to think that from
+the very commencement of the process variations of emotional disposition
+expressed through the voice would have been of survival value.
+
+But expressed in what direction, in loudness and persistency of
+utterance, these are the qualities which, I imagine, would have been
+more likely to have facilitated the search of the female? Yet if she
+were uncertain as to the owner of the voice, neither loudness nor
+persistent repetition would avail much; and as species multiplied and
+the competition for the means of living became increasingly severe, so
+the necessity of a territory would have become intensified, and so, too,
+with the extension of range, would the separation of the sexes have been
+an ever-widening one; and as with their multiplication, irregularities
+and delays in mating, arising from the similarity of the calls, would
+have increased in frequency, so a distinctive call, which would have
+tended to minimise these risks, would have come to possess biological
+value.
+
+Here we have a theory of origin, but origin of what? Of certain
+characteristics of song--nothing more; and therefore to suppose that it
+furnishes a complete explanation, which satisfies all the requirements
+of scientific logic, of so wonderful an intonation as that, for example,
+of the Marsh-Warbler, or that no other relationships, except that of the
+territory, enter into the total emotional complex, simplifying here or
+elaborating there to meet the exigencies of diverse circumstances--to
+suppose this would be foolish. That there are many relationships which
+even to-day are leading to modifications in important particulars, but
+which at the present time are beyond our cognisance, of this there can
+be no doubt.
+
+There is one process by which song may have attained a fuller
+development, and which would account in some measure for the
+elaboration, inexplicable merely in terms of "recognition." It is this:
+the effect of the sexual call upon the female cannot well be neutral, it
+must be either pleasurable or the reverse--it must, that is to say, be
+accompanied by some suggestiveness, and by suggestion I mean the
+arousing of some emotion akin to that of the male; and if there are
+degrees of suggestiveness, which well there may be, some males will mate
+sooner than others and some will remain mateless--this is the theory of
+sexual selection. The question to be decided here is whether the
+biological emphasis is on loudness, or specific distinctness, or pitch,
+or modulation, or the manner in which the phrases are combined--that is,
+on some qualities in preference to others--or whether the emphasis is on
+the whole. We have already seen, and it is well known, that there is
+much variation in the voices of different individuals of the same
+species, and thus the first condition of the theory is fulfilled. Now
+the conditions which lead to variation are threefold--immaturity,
+seasonal sexual development, and isolation. Of the three, the variation
+in the case of the immature bird is the most instructive; the tone is
+not so pure, the combination of phrases is incomplete, and elaboration
+is imperfect, and yet, notwithstanding all these imperfections, we can
+observe that the bird pairs as readily as does the adult. But even if we
+lacked this demonstrative evidence, we should still be justified in
+assuming that such must be the case, for we know from experience in the
+preservation of game, where there is no surer way of reducing the stock
+than by leaving too high a percentage of old cocks, that for the young
+bird to be at any disadvantage in competition with the adult is
+detrimental, if not disastrous, to the species. So that while there is
+plenty of evidence of variation in those particular qualities which
+appeal to our æsthetic faculties, there is at the same time evidence
+which demonstrates that such variations exercise no influence on the
+course of mating; and inasmuch as it is difficult to conceive of any
+voice departing more from the normal type in these particular qualities
+than the immature does from the adult, if there be degrees of
+suggestive influence, we must seek it in some other direction. There
+remain the two other characteristics which we found to be constant under
+all circumstances, namely, loudness and specific distinctness; and if,
+in addition to serving the purpose of disclosing the positions of the
+males, they serve to evoke some emotion in the female, which helps to
+further the biological end of mating, so much the more reason is there
+for their survival.
+
+There can be no question that this ingenious and attractive theory, if
+it were true in its special application to song, would immensely
+simplify interpretation, and moreover that preferential mating would
+contribute not a little to the success of the whole territorial system.
+No one can deny the strength of the argument: that the sexual instinct,
+like all other instincts, must require a stimulus of an appropriate
+kind; that the effect of the sexual call upon the female cannot be
+neutral; and hence the probability that stimulation varies too; no one,
+I say, can question the strength of this evidence, and, one might add,
+of the evidence derived from the analogy of the human voice. But when we
+have said this, we have said all; and our acceptance of the hypothesis,
+so far as song is concerned, must remain provisional so long as the
+evidence remains but secondary evidence.
+
+
+
+
+CHAPTER V
+
+THE RELATION OF THE TERRITORY TO THE SYSTEM OF REPRODUCTION
+
+
+In the first two chapters I tried to show that the inherited nature of
+the male leads it to remain in a definite place at a definite season and
+to become intolerant of the approach of members of its own sex, and that
+a result is thus attained which the word "territory" in some measure
+describes. But the use of this word is nevertheless open to criticism,
+for it denotes a human end upon which the highest faculties have been
+brought to bear, and consequently we have to be on our guard lest our
+conception of the "territory" should tend to soar upwards into regions
+which require a level of mental development not attained by the bird. It
+is necessary to bear this in mind now we have come to consider the
+meaning of the territory, or rather the position that it occupies in the
+whole scheme of reproduction.
+
+Relationship to a territory within the interrelated whole of a bird's
+life serves more than one purpose, and not always the same purpose in
+the case of every species. We have only to glance at the life-histories
+of divergent forms to see that the territory has been gradually adjusted
+to suit their respective needs--limited in size here, expanded there, to
+meet new conditions as they arose. Now some may think that the theory
+would be more likely to be true if the territory had but one purpose to
+fulfil, and that one the same for every species; and they may see
+nothing but weakness in the multiplication of ways in which I shall
+suggest it may be serviceable. But such an objection, if it were raised,
+would arise from a mistaken conception, a conception which, instead of
+starting with a relationship and working up to the "territory," sees in
+the "territory" something of the bird's own selection and thence works
+back to its origin. Holding the view that it is nothing but a term in a
+complex relationship which has gradually become interwoven in the
+history of the individual, I see no reason why the fact of its serving a
+double or a treble purpose should not be a stronger argument for its
+survival. I now propose to examine the various ways in which the
+territory may have been of use in furthering the life of the individual,
+and the circumstances in the inorganic world which have helped to
+determine its survival.
+
+The purpose that it serves depends largely upon the conditions in the
+external environment--the climate, the supply of food, the supply of
+breeding-stations, and the presence of enemies. Hence its purpose varies
+with varying conditions of existence. But before we proceed to examine
+the particular ways in which it has been modified to suit the needs of
+particular classes of species, and the reason for such modifications, we
+must inquire whether there is not some way in which it has been
+serviceable alike to every species, or at least to a large majority of
+them.
+
+Success in the attainment of reproduction depends upon the successful
+discharge of the sexual function; and the discharge of the sexual
+function depends primarily upon an individual of one sex coming into
+contact with one of the opposite sex at the appropriate season and when
+its appropriate organic condition arises. Now the power of locomotion is
+so highly developed in birds that it may seem unreasonable to suppose
+that males and females would have any difficulty in meeting when their
+inherited nature required that they should do so, still less reasonable
+to suggest that this power might even act as a hindrance to successful
+mating. Nevertheless, if we try to picture to ourselves the conditions
+which would obtain if the movements of both sexes were in no wise
+controlled, and mating were solely dependent upon fortuitous gatherings,
+we shall come, I fancy, to no other conclusion than that much loss of
+valuable time and needless waste of energy would often be incurred in
+the search, and that many an individual would fail to breed just because
+its wanderings took it into districts in which, at the time, there
+happened to be too many of this sex or too few of that. And as the power
+of locomotion increased and the distribution of the sexes became more
+and more irregular, so the opportunity would be afforded for the
+development of any variation which would have tended to facilitate the
+process of pairing, and by so doing have conferred upon the individuals
+possessing it, some slight advantage over their fellows.
+
+What would have been the most likely direction for variation to have
+taken? Any restriction upon the freedom of movement of both sexes would
+only have added to the difficulties of mating; but if restriction had
+been imposed upon one sex, whilst the other had been left free to
+wander, some order would have been introduced into the process. That the
+territory serves to restrict the movements of the males and to
+distribute them uniformly throughout all suitable localities, there can
+be no question; and since the instinctive behaviour in relation to it is
+timed to appear at a very early stage in the seasonal sexual process,
+the males are in a position to receive mates before the impulse to mate
+begins to assert itself in the female.
+
+We will take the Ruff as an example. According to Mr. Edmund Selous,
+pairing, in this species, is promiscuous--the Ruffs are polygamous, the
+Reeves polyandrous. Suppose, then, that upon this island of some few
+miles in circumference, whereon his investigations were made, the
+movements of neither Ruff nor Reeve were subject to control, that the
+birds wandered in all directions, and that the union of the sexes were
+fortuitous, would the result have been satisfactory? We must remember
+that the Reeve requires more than one Ruff to satisfy her sexual
+instinct; we must also bear in mind the possibility that the functioning
+of her instinct may be subject to some periodicity, and we ask whether,
+under these circumstances, accidental gatherings would meet all the
+requirements of the situation. Now, manifestly, she must be in a
+position to find males when her appropriate organic condition arises.
+But in the absence of any system in the distribution of the sexes, how
+could delay be avoided, or how could a uniform discharge of the sexual
+function be assured? There is, however, a system. In the first place,
+there are the assembly grounds to which the birds repair season after
+season; and then, on the assembly grounds, there are the territories,
+represented, as Mr. Selous tells us, by depressions where the grass by
+long use has been worn away, and each depression is owned by one
+particular Ruff. The assembly grounds have the effect of splitting up
+and scattering the birds, and the number of Ruffs at any one particular
+meeting place is limited by the territories; with the result that Ruffs
+fit to breed are evenly distributed and always to be found in certain
+definite places, and the Reeves know by experience where to find them.
+
+The advantage of this territorial system is therefore apparent. Instead
+of this district being overcrowded and that one deserted; instead of
+there being too many of one sex here and too few of the other sex there;
+instead of a high percentage of individuals failing to procreate their
+kind, just because circumstances over which they have no control prevent
+their discovering one another at the appropriate time--each sex has its
+allotted part to play, each district has its allotted number of
+inhabitants, and the waste of energy and the loss of time incurred in
+the process of mating is reduced to a minimum.
+
+Let us return again to the question of fortuitous mating, and consider
+the position of a male and female that have discovered one another by
+accident and have paired; what will be the subsequent course of their
+behaviour? We are assuming, of course, that a territory forms no part of
+their life-history. If the discharge of the sexual function takes place
+immediately and the ovaries of the female are in an advanced state of
+seasonal development, the construction of the nest will proceed without
+delay--and the nest will answer the same purpose as the territory in so
+far as it serves to restrict the movements of the birds and tends to
+make them remain in, or return to, its vicinity; but if not, there will
+be an interval during which both sexes will continue to wander as
+before, guided only by the scarcity or abundance of food. In the first
+case, there will be the attraction of the nest to prevent any untimely
+separation; in the second, there will be nothing in the external
+environment to induce them to remain in any particular spot. Now if we
+turn to any common species and observe the sequence of events in the
+life of different pairs, we shall find that pairing is seldom followed
+by an immediate attempt to build; that an interval of inactivity is the
+rule rather than the exception, and that this interval varies in
+different species, in different individuals, and in different seasons.
+Our imaginary male and female will therefore be faced with considerable
+difficulty; for with nothing in the external environment to attract them
+and with no restriction imposed upon the direction or extent of their
+flight, their union will continue to be, as it began by being,
+fortuitous. Next, let us consider their position were a disposition to
+establish a territory to form part of the inherited nature of the male.
+Each one will then be free to seek food when and where it wills and to
+associate with other individuals without the risk of permanent
+separation from its mate; and, no matter how long an interval may elapse
+between mating and nest-building, each one will be in a position to find
+the other when the appropriate moment for doing so arrives. Hence, while
+preserving freedom of movement for each individual, the territory will
+render their future, as a pair, secure.
+
+No doubt the course of behaviour, as we observe it to-day in the lives
+of many species, is the outcome of, rather than the condition which has
+led to, the evolution of the territory. Thus, in many cases, we find
+that early mating is the rule rather than the exception; we find that
+the sexes frequently separate to seek their food, and fly away
+temporarily in different directions; and, under exceptional climatic
+conditions, we find that they even revert to their winter routine and
+form flocks; only, however, to return to their territories, as pairs,
+under more congenial conditions. Yellow Buntings, for example, pair
+comparatively early in the season--some in the latter part of February,
+others in March, and others again in April; and some build their nests
+in April, others in May. There is a gorse-covered common which I have in
+mind, a favourite breeding resort of this species. Between this common
+and the surrounding country, the birds constantly pass to and fro. If
+you watch a particular male you will observe that it sings for a while
+in its territory, that it then rises in the air and disappears from
+view, and finally that it returns to the tree, bush, or mound which
+constitutes its headquarters, where it again sings. Meanwhile the
+female, with which there is every reason to believe that this male has
+paired, behaves similarly; she, too, flies to the surrounding country
+and in time returns with equal certainty. Sometimes male and female
+accompany one another--that is, they leave simultaneously and likewise
+return; at other times, though they depart together, the male returns
+alone; or the male may disappear in one direction whilst the female does
+so in another--and, on the whole, there is a sameness in the direction
+of flight taken by the same pairs on different occasions. An interval of
+nearly two months may thus elapse between mating and nest-building,
+during which the sexes are not only often apart but often separated by a
+considerable distance.
+
+What does this species gain by the individuals belonging to it mating so
+early in the season? If the appropriate condition which leads the
+females to seek males were to arise in each individual at a late date,
+the first stage in the process--mating--would not be completed before
+the second--the discharge of the sexual function--were due to begin.
+Thus, instead of having ample time, the females would have but a short
+period in which to discover males; and this in some cases might lead to
+delay, in others to failure, and in others again to needlessly severe
+competition, entailing physical exhaustion at a critical moment in
+their lives. Hence those females in which the appropriate organic
+condition developed early in the season would not only be more likely to
+find males, but would be in a position to rear more broods than those in
+which it developed late; and they would have a better chance of leaving
+offspring, which, in their turn, would reproduce the peculiarities of
+their parents. Moreover, within certain limitations, the more these
+successful females varied in the date of their development, the less
+severe would be the competition, and the more uniformly successful would
+the mating of all the individuals in a given district tend to become.
+But all of this renders an interval of sexual inactivity unavoidable; an
+interval which must constitute a danger unless there were something in
+the external environment to prevent the male and female from drifting
+apart. Inasmuch, then, as the occupation of a territory serves to remove
+all possibility of permanent separation, I suggest that its evolution
+has afforded the condition under which this beneficial procedure has
+developed--free to mate when they will, free to seek food where they
+will, free to pursue their normal routine of existence, and to meet all
+exigencies as they arise in their ordinary daily life--whilst free to do
+this, their future, as a pair, is nevertheless secure.
+
+Thus far we have considered the territory in its relation to the
+discharge of the sexual function. In many of the lower forms of life,
+the success or the failure of reproduction, so far as the individual is
+concerned, may be said to end with the completion of the sexual act--the
+female has but to deposit her eggs in a suitable environment and then
+her work is done, because in due course and under normal conditions of
+temperature the young hatch out, and from the first are able to fend for
+themselves. And so, when we come to consider the question of
+reproduction in the higher forms of life, we are apt to focus attention
+too much upon the sexual function and too little upon the contributory
+factors, the failure of any one of which would mean failure of the
+whole. For a bird, success in the attainment of reproduction does not
+merely imply the successful discharge of the sexual function; much more
+is demanded; it must find somewhere to build its nest and to lay its
+eggs, it must shield its young from extremes of temperature and protect
+them from enemies, and it must be in a position to supply them with food
+at regular intervals. And, consequently, every situation is not equally
+favourable for rearing young; there must be a plentiful supply of food
+of the right kind in the immediate vicinity of the nest, and it must be
+in greatest abundance just at the moment when it is most urgently
+needed--that is to say, during the first few weeks after the birth of
+the young. Success, therefore, depends upon manifold relationships which
+centre in the station, and these relationships vary in intensity with
+the conditions of existence.
+
+First, then, let us examine the problem from the point of view of the
+food-supply. There are many species whose success in rearing offspring
+is largely dependent upon the rapidity with which they can obtain food;
+and it makes but little difference which species we choose out of
+many--Finch, Bunting, Warbler, or Chat. I shall choose the Buntings, as
+their life-history in broad outline conforms to the general type, and,
+moreover, their behaviour is fresh in my mind. The young are born in a
+very helpless state; they are without covering--fragile organisms,
+ill-fitted, one would think, to withstand extremes of temperature, and
+wholly incapable of protecting themselves from enemies of any
+description. For the first three days after they are hatched the female
+spends much of her time in brooding them, and, when she is thus
+occupied, the male sometimes brings food to her, which she proceeds to
+distribute or swallows. But all the young cannot be fed, neither are
+they ready to be fed, at the same moment; and the parents have besides
+to find food for themselves, and the nest has to be cleaned--all of
+which necessitates the young being exposed to the elements at frequent
+intervals. Now it is impossible to observe the instinctive routine of
+the parents, when the young need attention, without being impressed with
+the conative aspect of their behaviour. Why, we ask, are the movements
+of the female so brisk; why does she seek food and clean the nest so
+hurriedly; why, if her instinctive routine is interrupted, do her
+actions and her attitude betray such bewilderment? I take it that the
+only answer we can give to these questions is that the part of her
+inherited nature which predominates just at this particular time is to
+brood. But why is brooding of such importance? Partly to maintain the
+young at the proper temperature, and thereby to induce sleep--and sleep
+for offspring newly hatched is as important as food--and partly to
+protect them from the risk of exposure to extremes of temperature. This
+latter danger is no imaginary one. Examine a young bird that has
+recently left the egg; observe its nakedness; and consider what it has
+to withstand--a temperature that may rise to 70° F. or may fall to 40°
+F., the tropical rain of a thunderstorm or the persistent drizzle of
+many hours' duration, the scorching effect of a summer sun or the
+chilling effect of a cold north-easterly wind, and, constantly, the
+sudden change of temperature each time that the parent leaves the nest.
+One marvels that it ever does survive; one marvels at the evolution of a
+constitution sufficiently elastic to withstand such changes. But,
+however much the constitution may give us cause to wonder, it is clear
+that much depends upon the parents. A slight inefficiency of the
+instinctive response which the presence of the young evokes, a little
+slowness in searching for food or sluggishness in returning to the nest,
+might lead to exposure and prove fatal. And, however much is demanded of
+the parents, it is clear that much also depends upon the relationships
+in the external environment; for no matter how sensitive or how well
+attuned the instinctive response of the parent may be, it will avail but
+little in the presence of unfavourable conditions in the environment.
+
+Everything turns upon the question of the effect of exposure. And in
+order to ascertain how far extremes of temperature are injurious, I
+removed the nests of various species containing newly hatched young,
+and, placing them in surroundings that afforded the customary amount of
+protection from the elements, I made a note of the temperature and the
+atmospheric conditions and then observed the condition of the young at
+frequent intervals. Details of these experiments will be found at the
+end of the chapter.
+
+The experiments with the Blackbirds and the Whitethroats gave the most
+interesting results. Both broods of each species were respectively of
+much the same age, yet one brood of Blackbirds survived for five, and
+the other only for two and a half hours, and one brood of Whitethroats
+lived for twelve hours whilst the other succumbed in a little over an
+hour. This difference is rather remarkable; and it seems clear that the
+power of resistance of the young diminishes rapidly when the temperature
+falls below 52° F. It must be borne in mind, however, that the
+conditions under which the experiments were made were, on the whole,
+favourable--the weather was dry, the temperature was not unusually low,
+nor was the wind exceptionally strong or cold; and even in those cases
+in which the young succumbed so rapidly, the atmospheric conditions
+could by no means be regarded as abnormal.
+
+What, then, would happen in an unusually wet or cold breeding season?
+For how long would the young then survive? In the spring and early
+summer of the year 1916, I was fortunate in observing the effect of
+exposure under natural but inclement conditions. I happened to be
+watching the Yellow Buntings on Hartlebury Common--200 acres of Upper
+Soft Red Sandstone, profusely overgrown with cross-leaved heath (_Erica
+tetralix_), ling (_Calluna vulgaris_), and furze (_Ulex_)--in one corner
+of which eight males had established adjoining territories covering some
+fifteen acres of ground. The males obtained mates towards the end of
+March or at the beginning of April; nests were built in the middle of
+May, and the successful pairs hatched out their young in June. On the
+10th June the weather became exceptionally cold, and during the next ten
+days the temperature fell at times to 40° F. during the daytime. Slight
+frosts were registered at night in the district, and the young bracken,
+which covered the Common in places, had the appearance of having been
+scorched and eventually withered away. At the coldest period of this
+cold spell the young were hatched in two of the nests--in the first one
+on the 10th June, and in the second a day or so later; and on the
+morning of the 10th June, having found a suitable position near the
+first nest, I began to watch the movements of the parents, with the
+intention of keeping some record of their behaviour each day so long as
+the young needed attention. An hour passed without their appearing, and
+on examining the young I found that they were cold, feeble, and
+unresponsive, but the female presently arrived and went to the nest.
+Later in the day the young were lively and responded freely when the
+nest was approached, but nevertheless I was impressed with the length of
+time during which the parents were absent; for, judging by the
+experience of previous experiment, there seemed to be every likelihood
+of their losing their offspring in such abnormally cold weather, unless
+they brooded them more persistently. On the 11th June at 5.50 A.M.
+neither parent was to be seen and the young could scarcely be made to
+respond; but shortly afterwards both male and female appeared, and,
+after remaining a few minutes, again disappeared without even
+approaching the nest. At 6.45 A.M. no attempt had been made to brood and
+the young were then so feeble that they were scarcely able to open their
+mouths, and at 6 P.M. one was still alive but the remaining three were
+dead. Yet the parents returned and the female went to the nest; and,
+from a distance of a few feet, I watched her brooding the living and the
+dead. At 5.45 A.M. the following day the remaining young bird had
+succumbed, the temperature then being 49° F.
+
+At the second nest, I was unable to watch the behaviour of the parents
+so closely. On the 15th June the nest contained three young from three
+to four days old, and during the morning of that and the succeeding day
+nothing unusual occurred, with the exception that the period of exposure
+seemed, as in the former case, to be too long. On the 17th June at 3.10
+A.M. the young had collapsed and were stiff, but the parents were in
+their territory and anxious apparently to attend to their brood. At 9.15
+A.M. only two of the young were left in the nest, and though I searched
+amongst the undergrowth and in the gorse bush in which the nest was
+placed, no trace of the third bird was to be found. Of the two remaining
+young, one was alive and responsive but the other was dead, and though
+the female attended assiduously to the sole surviving offspring, yet it
+too had succumbed by the following morning.
+
+In a third territory, there was a nest containing four eggs. These eggs
+were due to hatch at much the same time as those in the two nests just
+referred to, but they failed to do so, and an examination showed that
+they contained well developed but dead chicks.
+
+To what can the death of the young and of the chicks in the eggs be
+attributed? Not to any failure in the instinctive response of the
+females, for they fed their young, they brooded them, they even brooded
+the dead as well as the living, and probably did all that racial
+preparation had fitted them to do. Yet the fact that the young in the
+second nest were lifeless and exposed at 3 A.M. seems to betoken absence
+on the part of the parents during the night, and may be interpreted as a
+failure of the parental instinctive response. Let us return for a moment
+to the experiments. These showed, it will be remembered, that a rise or
+fall in the temperature of but a few degrees was sufficient to make an
+astonishing difference in the length of time that the young were able to
+survive without their parents; that when the temperature reached 58° F.
+the bodies of the young retained their warmth, and that under such
+conditions even a night's exposure had little, if any, effect; so that
+even supposing that the parents were absent during the night, the death
+of the young cannot be said to have been due to a failure of the
+parental instinct, because under normal conditions--and under such has
+their instinctive routine been evolved--their absence would not have
+prejudiced the existence of the offspring. I attribute the collapse of
+the young solely to the exceptional cold that prevailed at just the most
+critical time, and I base this conclusion partly on the experience
+gained from experiment, but mainly on their condition observed at
+different intervals; for during exposure they collapsed rapidly, their
+flesh became cold and their movements sluggish, their response grew
+weak, and gradually they became more and more feeble until they could
+scarcely close their bills after the mandibles had been forced asunder.
+Yet, even after having reached so acute a stage of collapse, the warmth
+from the body of the brooding bird was sufficient to restore them
+temporarily; once more they would become lively and responsive, only,
+however, to revert to the previous condition soon after the parent had
+again abandoned them. Doubtless their power of resistance grew less and
+less during each successive period of exposure.
+
+If the nestling Bunting is to be freed from the risk of exposure, it is
+evident that there must be, in the vicinity of the nest, an adequate
+supply of food upon which the parents can draw liberally. Hence those
+pairs that exercise dominion over the few acres surrounding the nest,
+and are thus able to obtain food rapidly, will stand a better chance of
+rearing their offspring than others which have no certain supply to draw
+upon--and this, I believe, is one of the biological ends for which the
+territory has been evolved. But it must not be supposed that each pair
+finds, or even attempts to find, the whole of the food within its
+territory, or that it is necessary for the theory that it should do so;
+all that is required is that such overcrowding as might lead to
+prolonged absence on the part of the parents and inordinate exposure of
+the young shall be avoided. So that the problem has to be considered not
+merely from the point of view of the individual, but from the larger
+point of view of all the pairs inhabiting a given area.
+
+Now there were eight pairs of Yellow Buntings occupying the one corner
+of Hartlebury Common, and their territories in the aggregate covered
+some fifteen acres. The birds obtained part of their food-supply amongst
+the gorse and in some young scattered oak-trees, and part in an
+adjoining coppice and on the surrounding arable land. But they were not
+the sole occupants of this corner of the Common; other insectivorous
+species had territories there also--amongst which were Whitethroats,
+Grasshopper-Warblers, Willow-Warblers, Whinchats, Stonechats,
+Meadow-Pipits, Tree-Pipits, and Skylarks. Suppose then that there had
+been sixteen pairs of Yellow Buntings instead of eight; that there had
+been other pairs, which assuredly there were, inhabiting the locality;
+that they had also resorted, which assuredly they did, to the coppice
+and arable ground for the purpose of securing food; and that their
+numbers had also been increased in a similar ratio--would a supply of
+food for all have been forthcoming with the necessary regularity and
+promptitude? Well, the parents might have had to travel a little
+farther; but even if they had been compelled to do so, their absence
+would only have been prolonged by so many minutes the more, and under
+normal conditions what harmful result to the offspring could possibly
+have followed? The question for us, however, is not what might have
+occurred under normal conditions, but whether the life behaviour is so
+adjusted as to meet the exigencies of diverse, and in this case of
+abnormal, circumstances. Now the capacity of the young to resist
+exposure diminishes very rapidly when the temperature falls below the
+normal--the danger zone seems to be reached at approximately 52° F., and
+the length of time during which they survive then becomes astonishingly
+short--and moreover the fall in the temperature would tend to decrease
+the supply of insect life upon which they depend, so that if the size of
+the territories had been reduced by one half, and the parents in
+consequence had been compelled to seek their food at a greater distance,
+can it be doubted that the cumulative effect of even a few minutes of
+additional exposure would have been detrimental, if not disastrous, to
+the offspring?
+
+We speak, however, of the parents extending their journeys a little
+farther in this direction or a little farther in that, as though they
+could do so with impunity except in so far as it affected themselves, or
+their offspring, or the other Yellow Buntings inhabiting that particular
+area. But, most certainly, any extension would have meant so much
+encroachment upon the available means of support of other members of the
+species inhabiting adjoining areas, whose young in turn would have been
+liable to have been affected; and, with even greater certainty, the
+Whitethroats, the Stonechats, the Tree-Pipits, and the Willow-Warblers
+that had also established themselves in that one corner of the Common
+would have been hard pressed to find sufficient food with sufficient
+rapidity.
+
+Let me give another illustration of a somewhat different kind. Lapwings,
+as we saw in the previous chapters, establish territories and guard them
+from intrusion with scrupulous care. The young are able to leave the
+nest soon after they are hatched, and consequently the parents are not
+necessarily obliged to bring food _to_ them--they can, if they so
+choose, lead them _to_ the food. Whether each pair limits its search for
+food to its territory, I do not know. But even supposing that all
+ownership of territory were to lapse directly the young were hatched,
+that the boundaries were to cease to exist, and that the birds were free
+to wander at will without fear of molestation, the end for which the
+territory had been evolved would none the less have been obtained; for
+inasmuch as the parents are accompanied by their young, it matters not
+in what part of the meadow they seek their food; all that matters is
+that the number of families shall not exceed the available supply of
+food. So far, then, as the Lapwing is concerned, the territory fulfils
+its purpose when once it limits the number of males, since, by doing so,
+it limits the number of families and prevents undue pressure upon the
+means of support.
+
+Nevertheless, there are many birds that seem to rely entirely upon the
+territory to supply them with all that is necessary. Each Warbler seeks
+its food within the precincts of its own particular domain, and, except
+in occasional instances, neither resorts to neutral ground nor makes
+excursions into the locality immediately surrounding the territory, as
+does the Bunting. Probably it would be disastrous if it attempted to do
+so, for since its young at birth are so delicate and so susceptible to
+changes of temperature, it cannot afford to be absent from them for
+long. Of the two experiments made with young Whitethroats, one was made
+under favourable and the other under unfavourable conditions. In this
+latter case the temperature was 50° F., and the young, it may be
+remembered, only survived for a little over one hour. Now exposure at
+that temperature is evidently dangerous, but it would be still more
+dangerous if the weather were wet instead of dry, and the temperature
+46° F. instead of 50° F.; and it is, I imagine, on this account that the
+impulse to brood is so strongly implanted in the female. No sooner, it
+seems, does she depart than she returns with a small quantity of food
+which she hurriedly distributes and immediately settles down to brood;
+and if forcibly prevented from returning, her attitude betrays symptoms
+of what, humanly speaking, we should term great distress. If, then, the
+conditions in the external environment were such as would make it
+difficult for the female to obtain food rapidly, what advantage would
+she derive from so strongly developed an impulse? Might it not be a
+disadvantage? Might it not mean that she would abandon the search too
+readily and be content to return with an insufficient supply, and might
+not that be as injurious to the young as prolonged exposure? Manifestly
+the impulse to brood could only have developed strength in so far as it
+fitted in with all the other factors that make for survival; and the
+principal factor in the external environment seems to be the territory.
+How could the young have been freed from the risk of exposure if the
+impulse to brood had not been so strongly implanted in the parent? How
+could the impulse to brood have been free to develop if a supply of food
+had not been first insured? How could the supply of food have been
+insured if numbers of the same species had been allowed to breed in
+close proximity?
+
+From the foregoing facts it is clear that the young of many species are
+at birth susceptible to cold and unable to withstand prolonged exposure.
+The parents must therefore be in a position to obtain food rapidly, and
+consequently it is important that there should be an ample supply in the
+vicinity of the nest. This end the territory certainly serves to
+promote; it roughly insures that the bird population of a given area is
+in proportion to the available means of subsistence, and it thus reduces
+the risk of prolonged exposure to which the young are always liable.
+
+
+This leads on to a consideration of those cases in which the question of
+securing food is subordinate to the question of securing a station
+suitable for reproduction.
+
+I take the Guillemot as an example. In principle its behaviour is
+similar to that of the Bunting; the male repairs to a definite place,
+isolates itself, and becomes pugnacious. But the Guillemot is generally
+surrounded by other Guillemots, and the birds are often so densely
+packed along the ledges that there is scarcely standing room, so it
+seems, for all of them. Nevertheless the isolation of the individual is,
+in a sense, just as complete as that of the individual Bunting, for each
+one is just as vigilant in resisting intrusion upon its few square feet
+as the Bunting is in guarding its many square yards, so that the
+evidence seems to show that that part of the inherited nature which is
+the basis of the territory is much the same in both species. What we
+have then to consider is, What is the biological value to the Guillemot
+of an inherited nature which, for the Bunting, has utility in relation
+to the supply of food for the young? Up to a point, the act of securing
+a territory has like value for each respective species, whether the area
+occupied be large or small--that is to say, it enables the one sex to
+discover the other with reasonable promptitude.
+
+For the greater part of the year, Guillemots live at sea; singly, in
+twos or threes, or in small parties, they move upon the face of the
+waters, extending their wanderings far away from land, out into the
+broad ocean, where for weeks together they face the gales and heavy seas
+of the Atlantic. But in due course and in response to internal organic
+changes, they return, like the Warbler, to their breeding grounds--rocky
+headlands or islands appropriately situated and affording the
+appropriate rock formation. During all these months of wandering, the
+majority seem to ignore the land, to pass away from it altogether, and
+to spread themselves over the surface of the ocean regardless of
+mainland or island. Some useful observations, which throw some light on
+the distance that Guillemots are accustomed to wander from land, were
+made by Lieut. B. R. Stewart during a number of voyages between various
+ports in Great Britain and Ireland and ports in North America,
+principally New York and Quebec. Thus, on the 24th March, large numbers
+were seen in lat. 55° N., long. 24° W., five hundred miles approximately
+from land, though on the following day--four hundred miles off Tory
+Island--they were not so plentiful. Again, on the 1st October, in lat.
+53° N., long. 27° W., seven hundred miles or so from land, one bird was
+seen, whilst on the following day, in lat. 52° N., long. 21° W., a
+single individual was washed on board by the heavy seas and seemed
+little the worse for the adventure. Within two hundred miles of the west
+coast of Ireland, he found them plentiful on various occasions. From
+this it is clear that the circumstances under which the bird lives for
+many months in succession must impose a considerable strain upon its
+constitution; and how it is able to withstand the buffeting of wind and
+water, to secure its food, and to endure, is a mystery. It is important,
+therefore, that the young bird should be properly nourished and
+protected from anything that might harm its constitution, and important,
+too, that the parents should be freed from any undue strain during the
+course of reproduction.
+
+The conditions which the breeding station has to fulfil are threefold:
+in the first place, it must be in proximity to the food-supply;
+secondly, it must provide the necessary shelter for the egg and for the
+helpless offspring; and, in the third place, it must be so situated that
+the young can reach the water in safety. We will examine these
+conditions one by one.
+
+The proximity to the food-supply is a consideration of some importance.
+The life of the Guillemot during the winter is a strenuous one; we know
+that large numbers succumb in stormy weather, and we can infer that
+slight constitutional defects might make all the difference between
+failure and success; and, therefore, the less severely the constitution
+of the parent is taxed during reproduction, and the more securely the
+constitution of the offspring is built up, the greater prospect will
+both have of resisting the hardships of the winter successfully. Much,
+then, will depend upon the distance the parents have to travel in order
+to obtain food. The farther the breeding station is removed from the
+feeding ground the greater the physical strain which will be imposed
+upon the birds, and the greater the chance will there be of the
+offspring being improperly nourished. Now the food consists of small
+fish, largely of sand-eels, which are secured in deep water, and the
+abundance of which varies, possibly according to the nature of the
+currents. Hence cliffs which are situated away from the water, or from
+which the water recedes at low tide, or which are surrounded by an area
+of shallow water, and are thus not in proximity to the feeding ground,
+even though they may fulfil the second and third condition, will not
+answer the requirements of a breeding station.
+
+Of no less importance is the type of rock-formation. Not every formation
+affords the necessary ledges upon which the egg can be deposited with
+safety--the face of the cliff may be too smooth, or too jagged, or the
+shelves may run at too acute an angle. Many of the large assemblages of
+Guillemots in the British Islands are found where the rock is quartzite,
+mica-schist, limestone, or chalk. The reason of this is that such rocks
+are weathered along the planes of stratification, of jointing, of
+cleavage, or of foliation--the strata being probably of unequal
+durability--with the result that innumerable shelves, ledges, and
+caverns, which are taken advantage of by the birds, form a network over
+the face of the cliff. But only those ledges can be made use of which
+are placed at a considerable height above the water, because, when the
+cliff faces the open sea, the lower ones are liable to be washed in
+stormy weather by the incoming swell and thus become untenable. There is
+a small cove in the midst of the most precipitous part of the breeding
+station at Horn Head, wherein the shingly shore shelves rapidly to the
+Atlantic and faces to the west. Here, towards the end of July, young
+Kittiwake Gulls can sometimes be found washed up on the beach--some
+living, but in every stage of exhaustion, others dead, and in every
+stage of decomposition; here is the young bird, recently caught by the
+swell and thrown upon the shore, lying side by side with the remains of
+others that had previously succumbed to starvation--on every side
+evidence of the devastation wrought by the Atlantic. May not some of
+this destruction have been brought about by the nests having been placed
+upon the lower ledges within reach of an exceptionally heavy sea? Hence
+much depends upon the nature of the rock-formation, and many a mighty
+precipice, even though it may fulfil the first and third condition, is
+nevertheless valueless as a breeding station.
+
+Finally, the young bird must occupy a ledge from which it can reach the
+water in safety. There is much difference of opinion as to the manner in
+which it leaves the ledge, but all agree that it does so before it is
+capable of sustained flight. If, then, the face of the cliffs were made
+up of a series of broken precipices, or if the rocks at the base
+projected out into the water, or if detached rocks abounded in the
+waters beneath, the mortality amongst the chicks would no doubt be
+considerable.
+
+The coast-line of Co. Donegal will illustrate the foregoing remarks. On
+the southern and western side of the Slieve League promontory there is
+no real Guillemot station; only on the northern side--the quartzite in
+the vicinity of Tormore--are the birds to be found in large numbers.
+Northwards from here, a wild and rugged coast is passed over before
+other stations are reached--at the eastern end of Tory Island and on
+Horn Head; and beyond this, to the east, there are none, not even on the
+old rocks that form the promontory of Inishowen. Why, we ask, do
+countless numbers crowd the ledges of Horn Head, whilst they are absent
+from the precipices of Slieve League; why, too, are they absent from
+the granite cliffs of Owey? The reason is not far to seek. Either the
+face of the cliff is made up of a series of broken precipices, or the
+face of the precipices is too smooth, or the otherwise suitable ledges
+are situated too near the water, or the water recedes from the base of
+the cliff at low tide. Many miles of rock-bound coast are thus useless
+for the purpose of reproduction.
+
+Now when we bear in mind how large an expanse of coast is formed of
+blown sand or of rocks of low altitude, and how many miles of cliff fail
+to supply the three essential conditions that we have been considering,
+we can see that suitable breeding stations must be limited both in
+number and extent. From a wide expanse of ocean hosts of individuals are
+therefore obliged to converge at certain definite points; and hence,
+each recurring season, there must arise a competition for positions at
+the station, just as there is competition between individual Buntings
+for positions in the marsh. And the ability to obtain a position upon a
+suitable ledge involves, in the first place, an impulse to search for
+it; in the second place, an impulse to dwell in it; and in the third
+place, an impulse to resist intrusion upon it. It would be useless for
+an individual to be pugnacious if it had no fixed abode; equally useless
+for it to establish itself on a particular ledge if it had no power to
+defend it--all of which implies an inherited nature similar to that of
+the Bunting. But the proximate end to which the competition is directed
+is not alike in the case of both species. In the case of the Guillemot
+it has reference solely to the piece of rock whereon the egg is laid; in
+the case of the Bunting to a piece of ground capable of furnishing an
+adequate supply of food for the young; and the reason for the difference
+is this, that there is always an abundance of food in the water beneath
+the cliff, but breeding stations are scarce, whereas there is always an
+abundance of situations in the marsh in which the Bunting can place its
+nest, but the supply of food varies and at times can only be obtained
+with difficulty.
+
+If then the Guillemot were to behave after the manner of the Bunting and
+assign to itself a portion of the face of the cliff, or if it were only
+to occupy a few ledges, or an even lesser area--a single ledge--what
+would be the result? That it would attain to reproduction is beyond
+question; that the egg would be safely deposited there can be no manner
+of doubt; neither is there any reason to suppose that the offspring
+would not be successfully reared. But, indirectly, its behaviour would
+affect the Guillemot race. For if it be true, as the crowded ledges
+certainly seem to show, that there is a dearth of suitable breeding
+ground, no greater calamity could befall the species than that some
+members should exercise dominion over too large an area of the habitable
+part of the cliff and thus prevent others from breeding. Under such
+conditions the race could not endure, since in this, as in every case,
+its survival must depend upon a close correspondence between the
+behaviour of the individual and the circumstances in the external
+environment.
+
+Scarcity of suitable cliffs is the principal reason of the ledges being
+so closely packed with Guillemots, just as it accounts for this part of
+the precipice being crowded with Kittiwake Gulls, that part with
+Herring-Gulls, and that part again with Razorbills and Puffins. Yet each
+individual preserves its few square feet of rock or soil from
+molestation, and the area each one occupies varies according to the
+conditions of existence of the species. Thus the Herring-Gull occupies a
+comparatively small area, although one many times larger than that of
+the Guillemot. It requires more space than the latter, owing to the fact
+that it not only builds a nest but rears four instead of a single
+offspring, and it can be allowed this, because, since its young remain
+in the nest until they are capable of sustained flight, it can make use
+of many miles of cliff from which the tide recedes at the base, or which
+have, at their base, rocks jutting out into the sea; but manifestly it
+cannot be allowed so much space as the Bunting.
+
+Martins build in close proximity to one another, owing probably to
+shortage of accommodation, and, in their case, the nests have to be so
+situated as to be sheltered from the wet. If water drips upon them for
+any length of time, the mud, of which they are composed, crumbles and
+large pieces fall away, with the result that the eggs or the young are
+precipitated to the ground. Consequently, not every house or
+perpendicular cliff will answer the purpose of a breeding station. A few
+pairs build their nests beneath the eaves close against the walls of my
+house, and year after year the result is much the same; after every
+downfall of rain, the water collects into rivulets, trickles down over
+the eaves, is absorbed by the mud and destroys the nests. Thereupon, the
+birds set to work and rebuild; but again the nest is destroyed, and
+again they rebuild, and so on throughout the summer, and only on rare
+occasions do they succeed in rearing offspring at the proper season.
+Similar conditions must prevail in many situations; but, clearly, the
+more binding and plastic the building material, the longer the nest will
+withstand the action of the dripping water and the greater chance will
+there be of the young being reared in safety. Observe, therefore, how
+far-reaching an effect so small a detail as the nature of the mud can
+have upon the status of the species in any given locality. Where the
+conditions are favourable, there the birds must congregate to breed,
+and, like the Guillemot, if each individual exercised dominion over too
+large an area, the species as a whole would suffer.
+
+In all these examples, the fact of different individuals being in such
+close proximity may afford some protection from enemies both as regards
+the egg and the offspring, and in so far as there is a mutual advantage
+such assemblages may be spoken of as communities. A community, however,
+in the true sense of the word, is a collection of individuals brought
+together, not primarily as a result of shortage of breeding ground, but
+in consequence of advantages of communal ownership over individual
+ownership. A rookery is an example of a true community. Neither shortage
+of nesting accommodation nor scarcity of food can account for Rooks
+assembling together to breed; for if the different pairs which go to
+make up the rookery were to scatter throughout the surrounding
+neighbourhood, they would, as a rule, find plenty of trees in which to
+build their nests, and plenty of food.
+
+How, then, can the theory apply to a species that breeds under such
+conditions? What part can the territory play in furthering the life of
+the individual when large numbers of nests are built closely together in
+the same tree? There is much evidence to show that mutual protection is
+a necessary condition of the Rook's existence; many cases are on record
+of rookeries being destroyed by Carrion-Crows, Hooded Crows, and Ravens.
+For instance, Mr. Ward Fowler records a case in which a pair of Crows
+attacked a small rookery, ransacked the nests, and destroyed the eggs,
+with the result that not a single pair of Rooks was left in the
+settlement. Each Rook must therefore secure a position within the
+precincts of the community if it is to have a chance of success in the
+attainment of reproduction. But every locality cannot supply sufficient
+trees of the right kind, appropriately situated and in suitable relation
+to the food supply, in which numbers of nests can be built in close
+proximity; so that if more than one community were to attempt to
+establish itself in a limited area, the supply of food or the supply of
+trees might become a pressing problem. Each community must therefore be
+prepared to defend its own interests, and each must be regarded as one
+unit and the area occupied as one territory within which are included a
+number of lesser territories. The individual may fail to establish
+itself within a community, but, even if it succeeds, the community may
+fail to establish the rights of communal ownership; hence it has to face
+a twofold possibility of failure, and if it lacked the inherited nature
+which leads the Guillemot to secure a position upon the ledge, or the
+Bunting to obtain a position in the marsh, the chances are that it would
+fail in the attainment of reproduction.
+
+The question now arises as to how it comes about that the area occupied
+by each individual conforms in broad outline to that which has proved
+beneficial for the welfare of the species as a whole. We shall find that
+up to a point the answer is a simple one. No one could study the
+behaviour of animals without observing the important part that habit
+plays in the life of the individual; an action performed to-day is
+liable to be repeated to-morrow and the following day until it becomes
+ingrained in the life of the individual. This must not be taken to mean,
+however, that a particular action has to be performed for many days in
+succession before it becomes definitely fixed; if only it is repeated a
+number of times, even within the space of a few hours, it will acquire
+sufficient strength for its continuance; but continued repetition gives
+increased fixity, and, as time goes by, it becomes increasingly
+difficult for the creature to make a change unless the character of the
+situation necessitates readjustment.
+
+For example, when the organic condition which leads to nest-building
+becomes active, the bird tentatively collects some of the necessary
+material in its bill, flies round with it, and then drops it. After a
+while it collects some more, and this time leaves it perhaps in a bush.
+Later on it makes another attempt, and, meeting with a situation which
+calls forth the appropriate response, it thereupon lays the foundation
+of the structure. We will assume that the nest is placed in the midst of
+a tangled bush. Well, the bird lays the first strands of the foundation
+and then goes in search of more material. The next time it approaches
+the nest from the opposite side of the bush, and presently it finds yet
+a third entrance. But each entrance is not made use of in turn: one is
+employed more frequently than the other two, and in the course of time
+becomes the sole highway to and from the nest. Suppose now that, when
+the young are hatched, I cut away the foliage from the bush on the
+opposite side from that on which the bird customarily enters, and by so
+doing leave the nest exposed, what is the result? The female arrives
+with food, threads her way through the bush, and, when beside the nest,
+pauses as if aware that some change had taken place, and then flies away
+through the new opening. In a short time she returns, flits from twig to
+twig on the outskirts of the bush, and comes upon the new opening--there
+she hesitates. But though the nest is in full view and within a few
+inches of her perch, and though the young stretch out their necks, yet
+so strong is the former habit that she is compelled to return to the
+opposite side and approach the nest by the usual circuitous route before
+she distributes the food amongst her offspring.
+
+Let us see how far this law of habit formation may have been effective
+in defining the extent of the area occupied. When a male Warbler arrives
+at its destination in the spring it seeks out a suitable environment,
+and, having found a place unoccupied by any other male, settles in it
+and remains there--its behaviour up to this point being determined by
+racial preparation. After the fatigue of the journey its movements are
+at first sluggish; hunger, however, asserts itself and a search is made
+for food; wandering away from the position in which it first settled and
+which acts as a headquarters, it hunts through certain trees here or
+certain bushes there and returns, and presently it wanders away again,
+perhaps in another direction, but, as before, works its way back again
+to the headquarters. The journeys thus radiate outwards from the
+headquarters, and according to the success with which the bird meets,
+so, probably, it happens that some trees are searched more often than
+others and certain directions are taken more frequently than others, and
+by constant repetition a routine is established which limits the
+direction and scope of its wanderings.
+
+But in the case of the Guillemot the conditions of existence are
+reversed: food can be had in abundance but suitable breeding stations
+are scarce. The few square feet of ledge correspond to the tree or clump
+of bushes which acts as a headquarters for the Warbler, and the
+occupation of them is determined, as it is in the case of the Warbler,
+by racial preparation. Since, however, the ledge is only made use of for
+the immediate purpose of incubation and is in no way affected by
+questions relating to food, there is no occasion for the bird to wander
+along the ledge nor to encroach upon those adjoining. Hunger stimulates
+the Warbler to search the surrounding trees, and so to extend its area;
+but hunger takes the Guillemot down to the water, and hence the area
+which it primarily occupied remains unmodified.
+
+To sum up: the territory is useful in various ways, but not necessarily
+in the same way for every species. Reproduction would always have
+remained fortuitous, and the number of individuals that attained to it
+would seldom have reached the possible maximum unless some provision had
+been included in its system for insuring that the males and females
+could meet at the proper moment and afterwards remain in touch with one
+another, and that the number of pairs inhabiting a given area did not
+exceed the available means of support. I have tried to show that the
+inclusion of a disposition to secure a territory tends to remove these
+difficulties. In the first place, the disposition which leads to its
+occupation comes into functional activity (in the male) early in the
+season; and so, by the time that the appropriate pairing condition
+arises in the females, the process of acquiring territories is well
+advanced, and the males being regularly distributed, each in its
+respective position, are readily found by their prospective mates. The
+behaviour of each sex is thus adjusted to further the end of mutual
+discovery. Next, after mating has taken place, the position occupied by
+the male acts as a headquarters to which the birds can always repair,
+and becomes a bond of union which is serviceable in that it prevents any
+possibility of their drifting apart. And in the third place, the males
+become pugnacious and in this way secure for themselves areas which vary
+in size according to the conditions of existence of the species, so that
+there is no possibility of too many congregating in this locality, and
+all the less likelihood of too few finding their way to that; and hence,
+on the average, different pairs are distributed throughout all suitable
+localities. Furthermore, owing to the fact of their having a
+headquarters, the male and female are allowed a freedom of movement
+which otherwise they would only possess when the construction of the
+nest had actually begun; they can seek their food independently, and,
+even though paired, they can if necessary continue their winter routine
+without risk of separation. This means that the organic condition which
+leads to pairing, is free to develop in the female earlier than would be
+the case if there were nothing in the external environment to attract
+the pair to a particular spot; and the longer the period over which the
+process of pairing can be spread, the greater chance will females have
+of discovering mates, the less severe will the competition tend to
+become, and, consequently, the smaller the percentage of individuals
+that fail to obtain suitable partners.
+
+In these ways the territory has been serviceable alike to a number of
+species. But much as the questions of mutual discovery and regular
+distribution may have influenced the course of its development, there
+can, I think, be little doubt that, on the one hand, the supply of the
+necessary accommodation for rearing offspring, and on the other, the
+necessity for an adequate supply of food in close proximity to the nest,
+have been the main determining factors, and have led to a wide
+divergence in its function. At the one extreme the function is to insure
+a plentiful supply of food for the young; at the other, to insure a
+station suitable for rearing offspring. I took the Bunting and the
+Guillemot as types of the two extremes. The young of the former species
+are born in a very helpless state. They are susceptible to cold and
+unable to withstand prolonged exposure, and therefore it is essential
+that there should be an ample supply of food, upon which the parents can
+draw liberally, in the vicinity of the nest. But the nest is placed in a
+variety of situations, and accommodation in this respect may be said to
+be unlimited. The young of the latter species are not so susceptible to
+exposure, and moreover there is always an abundance of food in the
+waters beneath the cliff; but ledges of rock, upon which the egg can be
+securely deposited and the young successfully reared, are limited both
+in number and extent. The position then is as follows: there are
+situations in plenty in which hosts of Buntings can build their nests
+but the supply of food is a difficulty, and if the respective areas of
+different individuals were insufficient to supply them with the
+necessary food with the necessary rapidity, they would run the risk of
+losing their offspring and the species would not endure; on the other
+hand, cliffs upon which the Guillemot can rear its young are limited,
+but the supply of food presents no difficulty, and consequently the
+smaller the area over which each individual exercises dominion, the
+greater the number that will attain to reproduction and the greater
+prospect the species will have of survival. The emphasis in the one case
+lies on the fact that the area occupied must be sufficiently large; on
+the other, on its being just sufficient and no more to accommodate the
+egg. Hence the difference in the function at the opposite extremes is
+brought about, not by modifications of the instinctive behaviour which
+leads to the establishment and defence of the territory, but solely by
+modifications in the size of the area occupied, in accordance with the
+conditions prevailing in the external environment. No doubt, if we had
+the life-histories of a sufficient number of species worked out, we
+should find that the gradations were complete from the one extreme to
+the other. We are justified in thinking that this must be so because in
+many directions we can not only observe differences in the size of the
+area occupied, but can recognise a close correspondence between those
+differences and the conditions of life of the species. Thus the
+Herring-Gull occupies a comparatively small area, though one which is
+many times larger than that of the Guillemot. It requires more space
+because it not only builds a nest but rears four instead of a single
+offspring, and it can be allowed more space because the young remain in
+the nest until they are capable of sustained flight, and consequently it
+can make use of many miles of cliff from which the tide recedes at the
+base, and which on this account are denied to the Guillemot, but
+manifestly it cannot be allowed so much space as the Bunting, for then
+comparatively few individuals would attain to reproduction.
+
+Again, the Reed-Warbler inhabits swamps overgrown with the common reed,
+and in such places insect life is abundant just at the time when the
+young are hatched. But these swamps cover a comparatively small acreage
+in the breeding range of the bird, and if each pair were to attempt to
+establish dominion over an area equal, let us say, to that of the
+Willow-Warbler, the species would have but a poor chance in the struggle
+for existence. So that, in a case of this description, the supply of
+food and the comparative scarcity of breeding stations have been factors
+of like importance in the evolution of the territory.
+
+Finally we were led to inquire as to how it comes about that the extent
+of the area occupied by each individual is adapted to the circumstances
+in which the individual finds itself; and we came to the conclusion that
+the movements of the bird, subsequent to the initial act of establishing
+itself in a position, are regulated and defined by the law of habit
+formation. For example, the Warbler, in response to its inherited
+nature, takes up a position in an appropriate situation. It then
+proceeds to search for food; it makes short journeys first in this
+direction and then in that; it repeats these journeys, and gradually
+forms a habit which compels it to remain within more or less
+well-defined boundaries. But the actual distance that it traverses on
+the occasion of its first attempt must be determined by the relative
+abundance or scarcity of the particular kind of insect life which it
+requires. So that, although habit defines and in some measure helps to
+determine the boundaries of the territory, it is clear that in the last
+resort they must depend upon the nature of the conditions in the
+external environment.
+
+We have, then, the congenital basis which leads to the occupation of a
+position, and to the enmity shown by the owner of the position towards
+other individuals; and this congenital basis is found alike in many
+widely divergent forms, living under equally widely divergent
+conditions; we have acquired accommodation; and we have relationships in
+the organic and inorganic world--and the outcome of it all is a system
+of behaviour which we, who can perceive the end to which such behaviour
+is tending, are justified in speaking of as "a disposition to secure a
+territory." In the development of this system a primary value must be
+ascribed to the conditions in the external environment, for they
+determine the direction of the variations of instinctive procedure and
+of acquired habit which work towards the same goal--that of adjustment
+to the conditions of life.
+
+
+
+
+NOTE
+
+
+The following are the experiments referred to on page 181:--
+
+
+On the 14th May 1915, a nest of Blackbirds approximately four days old
+was removed at 6.45 A.M. The temperature was considerably below the
+normal, and snow lay on all the high ground in the neighbourhood. In a
+short time the birds collapsed, and at 9.15 A.M. were dead. On the 29th
+May, at 6 A.M., a second nest was removed, containing young of
+approximately the same age, and although the conditions were more
+normal, the temperature being 50° F., the birds collapsed at 8 A.M., and
+an hour later one of the brood showed little signs of life. The wind,
+however, then changed to the west, and the temperature rose one degree,
+with the result that they were still living at 11 A.M. A further
+experiment was made with Song-Thrushes on the 5th June. The wind was in
+the south and the temperature 63° F. The young, approximately four days
+old, were removed at 7.25 A.M., but as they showed no signs of collapse
+at 1 P.M. I replaced the nest in the original site.
+
+
+On the 30th May, a nest of Whitethroats three days old was removed at
+7.15 A.M. The wind was northerly and the weather fine, but the
+temperature low--50° F. At 8.15 A.M. the birds showed no sign of life. A
+second experiment with this species was made on the 10th June under more
+favourable circumstances, for although the sky was overcast and the wind
+northerly, the temperature was 59° F. In this case the young survived
+from 6.55 A.M. to 7 P.M.
+
+
+On the 27th May 1915, a nest of Hedge-Sparrows hatched the previous day
+was removed at 7 A.M. The temperature was below the normal, being 49° F.
+At 8 A.M. the young were cold and in a state of collapse, but they
+survived nevertheless until 3.20 P.M.
+
+
+On the 7th June 1915, a nest of young Skylarks three days old was
+removed at 7.15 A.M. The temperature was 62° F., and the birds survived
+until 4 A.M. the next day.
+
+
+On the 6th June 1916, a nest of Linnets just hatched was removed at 6.47
+A.M. The temperature was 51° F. At 7.50 A.M. the birds were cold and in
+a state of collapse, and only survived until 8.50 A.M.
+
+
+
+
+CHAPTER VI
+
+THE WARFARE BETWEEN DIFFERENT SPECIES AND ITS RELATION TO THE TERRITORY
+
+
+We have now considered the various ways in which the territory is useful
+in furthering the life of the individual. We have seen that, in some
+cases, there is competition for stations where the egg or eggs can be
+deposited and incubated in safety; that, in others, there is competition
+for stations capable of furnishing an adequate supply of food for the
+young; and that the establishment of "territories" not only renders the
+attainment of reproduction for the individual secure, but serves so to
+regulate the distribution of pairs that the maximum number can be
+accommodated in the minimum area. This being so, the question arises as
+to whether competition for territory is strictly limited to individuals
+of the same species, or whether it may not occur also between different
+kinds of birds, providing always that similar conditions of existence
+are required. First of all I shall relate a number of facts which will
+serve to show the nature and extent of the warfare, and I shall then
+give the reasons which lead me to believe that the fighting not only
+bears some relation to the "territory," but that it is an important
+factor in contributing to the attainment of that which for biological
+interpretation is the end for which the whole territorial system has
+been evolved.
+
+Those who have studied wild life on one of the rocky headlands, which
+are so numerous round our coasts, will probably be familiar with the
+rivalry that exists between the Raven and certain birds of prey. Where
+the Raven finds shelter for its nest, there, too, the Peregrine has its
+eyrie--and so it happens that these two species are continually at war.
+Now the warfare occurs not only during the season of reproduction but
+continues throughout the greater part of the year, and can even be
+observed in the late summer or early autumn--the period when we should
+expect to find the instinct least susceptible to appropriate
+stimulation. But it is of a more determined kind early in the spring,
+and it is then that we often witness those remarkable exhibitions of
+flight, the skill of which excites our admiration. The Falcon rises
+above the Raven, stoops at it, and when it seems no longer possible for
+a collision to be avoided, or, one would imagine, for the Raven to
+escape destruction, the Raven skilfully turns upon its back and
+momentarily faces its opponent, and the Falcon with equal skill changes
+its course, passing upwards and away. The attack, however, is soon
+repeated, and though no collision may actually take place, yet the fact
+that the Raven, when it turns to face its adversary, is obliged to drop
+the stick which it carries, is not only an indication of the character
+of the struggle, but it shows that a definite end is gained--that the
+efforts of the Raven to build in that particular locality are hampered.
+But the Falcon is not the only enemy that the Raven has to face;
+Buzzards are just as intolerant of the presence of Ravens in their
+neighbourhood as the Ravens are of them, and consequently there is
+incessant quarrelling wherever the same locality is inhabited. As a
+rule, the fighting occurs whilst the birds are on the wing; the Buzzard
+rises to a considerable height, and, closing its wings, stoops at the
+Raven below, and when within a short distance of its adversary, swerves
+upwards and gains a position from which it can again attack. The
+Buzzard, however, is by no means always the aggressor; I have watched
+one so persistently harassed by a Raven that at length it left the rock
+upon which it was resting and disappeared from view, still followed by
+its rival. Thus it seems as if they were evenly matched, and, when they
+occupy the same locality, it is interesting to notice how the initiative
+passes from the one to the other according to the position occupied by
+the birds in their respective territories.
+
+[Illustration: Peregrine Falcon attacking a Raven
+
+Emery Walker ph.sc.]
+
+That there is constant warfare between the Green Woodpecker and the
+Starling is well known, the purpose of the Starling being to gain
+possession of the hole which the Woodpecker with much skill has drilled
+for itself. As far as my experience goes, the Starling is always the
+aggressor, and there is only too good reason to fear that, in the course
+of time, the Green Woodpecker will disappear as a result of the greater
+fertility and tenacity of its enemy. The Martin suffers a similar kind
+of persecution from the House-Sparrow, and here again there is reason to
+believe that the greater virility of the Sparrow will hasten the
+extinction of its rival. In cases of this description the purpose of the
+fighting is clear, and one can understand why such divergent species
+should be hostile to one another; yet others, equally remote in the
+scale of nature, are hostile when no such ostensible reason can be
+assigned for their hostility. Few birds are more pugnacious than the
+Moor-Hen, and the determined manner in which different individuals fight
+with one another is notorious. But the intolerance it displays towards
+other species is no less remarkable, and its pugnacious instinct seems
+to be peculiarly susceptible to stimulation by different individuals
+belonging to widely divergent forms. At one moment a Lapwing may be
+attacked, at another a Thrush or a Starling, harmless strangers that
+have approached the pool to drink; even a Water-Rail, as it threads its
+way through the rushes, may fail to escape detection; and, which is
+still more curious, a covey of Partridges will evoke response if they
+approach the pool too closely.
+
+Here is a curious instance of apparent waste of energy. A pair of
+Magpies built their nest in an ilex tree. Early one morning there was a
+commotion in the tree, much flapping of wings and a medley of sounds
+which told of large birds engaged in a struggle--the Magpies were
+attacking a pair of Wood-Pigeons. There was no question as to the
+genuineness of the struggle, nor any doubt as to the proximate end for
+which the Magpies were striving, for their efforts continued so long as
+the Wood-Pigeons remained in the tree, and only ceased when they had
+succeeded in driving them away.
+
+Turning next to species which are less distantly related, we find that
+instances of intolerance are more numerous and that a wider range of
+species is involved. The hostility that the Lapwing displays towards the
+Snipe calls for special remark. It often happens that the marshes or
+water meadows, that are such favourite haunts of the Lapwing, are also
+resorted to by Snipe for the purpose of securing food, or it may be even
+for the purpose of reproduction. In such places both species are often
+abundant; the meadow is divided up into Lapwings' territories, and early
+in the season the Snipe wander over it in small parties, singly, or in
+pairs. Now, if it were only on isolated occasions that the Lapwing paid
+heed to the Snipe, one would not perhaps attach any peculiar
+significance to the fact; but the pugnacious instinct of the bird
+responds to the presence of this intruder almost as freely as it does to
+that of another Lapwing. Again and again, day after day, the Snipe are
+attacked and driven off in a manner which would be fittingly described
+as persistent persecution, for the Snipe has neither the physical
+capacity nor apparently any instinctive tendency to retaliate. Thus a
+Lapwing may come suddenly upon a small party of Snipe hidden from view
+in a dyke where they are probing the ground for food; the Snipe
+immediately rise and fly away and there is momentary confusion as the
+Lapwing darts first at this one, then at that; or, espying a Snipe at
+rest at the opposite end of its territory, it will first of all run
+rapidly towards it, and then fly after it, as, with twisting flight, it
+darts hither and thither a few feet above the ground; or again, it will
+attack and rapidly pursue solitary individuals as they skim across its
+territory and attempt to settle. Is this intolerance merely an exuberant
+expression of an instinct which is serviceable in another direction? The
+behaviour of the Lapwing scarcely justifies such a conclusion, for all
+its actions denote a striving towards some end which we can describe,
+and it seems to gain satisfaction only when the ejection of the intruder
+has been accomplished.
+
+Many of the Warblers display irritation when approached by other birds
+which we should scarcely expect would arouse their hostility. The
+Hedge-Sparrow, for example, is frequently regarded with suspicion, and
+it is by no means unusual to see it attacked by so small a bird as the
+Chiffchaff. The Wood-Warbler is also pugnacious, and will even attack a
+pair of Chaffinches. Between the Tit family and some of the smaller
+Warblers there are constant exhibitions of hostility; even the Great Tit
+is liable to be driven away, but the Blue Tit is especially marked out
+for persecution, though doubtless it is well able to hold its own.
+
+The following incident will show how real is the antagonism between
+these two families. A Chiffchaff occupied the corner of a small osier
+bed, and was particularly aggressive towards other closely-related forms
+in its immediate neighbourhood. On two mornings in succession ten Blue
+Tits invaded its ground, passing from end to end of it as they wended
+their way from tree to tree in search of food. Their presence evoked the
+usual hostile response, yet, withal, aroused the fear of the Chiffchaff,
+which, at times, appeared to be swayed by conflicting impulses. Now, in
+attempting to interpret the nature of the instinct which was evoked, one
+has to be guided, in a case of this description, by the similarity of
+the response to that which can be observed on other occasions and in
+other situations when the intention of the bird is clear. And on this
+occasion the Chiffchaff betrayed all the symptoms which normally precede
+an attack; it spread its tail, quivered its wings, uttered its
+high-pitched note rapidly, hopped from twig to twig, or flew restlessly
+from tree to tree, and seemed to be prevented from attacking only by the
+number of its opponents. This, indeed, was shown by its subsequent
+behaviour, for whenever a Tit became temporarily detached from its
+companions it hesitated no longer but forthwith attacked.
+
+There are other species which are no less aggressive than the
+Warblers--the Chats for example. The Stonechat regards with suspicion
+almost any bird of its own size, and will even pursue a Tree-Pipit if it
+approaches too closely. The same is true of the Whinchat, and one would
+scarcely expect to find this bird attacking Buntings as it sometimes
+does. A Whinchat that occupied some marshy ground was constantly at war
+with a pair of Reed-Buntings; their territories were adjacent and in
+some measure overlapped, and the Whinchat drove away either sex
+indiscriminately, and was not only always the aggressor but seemed to
+be master of the situation.
+
+Coming now to kindred forms, those, that is to say, which belong to the
+same family, we find that, both in intensity and extent, the warfare far
+exceeds anything that we have thus far considered. So frequent, indeed,
+are acts of intolerance, and so readily awakened into activity is the
+pugnacious nature of the bird, that the fighting will almost bear
+comparison in volume with that which occurs between individuals of the
+same species. Between the Thrush and the Blackbird there are incessant
+quarrels early in the year, and the initiative seems to pass from one
+to the other according to the circumstances in which they are placed. If
+the territory of a Thrush is invaded the Thrush is the aggressor, and,
+conversely, if that of the Blackbird is threatened, the Blackbird
+becomes the aggressor; and so, when the territories of the two birds are
+adjacent or overlap, as frequently they do, there is constant friction,
+resulting in quarrels which attract attention on account of the
+noisiness of the birds.
+
+All the Warblers are exceedingly pugnacious, the fighting being
+especially severe between those that are very closely related. The
+Blackcap and the Garden-Warbler are constant rivals, and the scenes
+which can be witnessed when the two meet in competition are interesting
+from many points of view. The birds not only pursue and fight with one
+another, but their emotional behaviour reaches a high level of
+intensity--excitable outbursts of song are indulged in, tails are
+outspread, wings are slowly flapped, and feathers raised--in fact the
+attitudes assumed are similar in all respects to those which occur
+during the contests which are so frequent between the respective
+individuals of each species; and it would be difficult to point to any
+one item of behaviour which is not also manifest at one time or another
+during the battles between these rivals, and still more difficult to
+trace any difference in the intensity of the excitement. And if we are
+satisfied that the fighting in the one case is purposive, so, too, must
+we regard it as having some biological purpose to serve in the other.
+But the Garden-Warbler is not the only bird that acts as a stimulus to
+the instinct of the Blackcap; Whitethroats are often attacked, and the
+Chiffchaff is a source of irritation. Even when a male Blackcap is
+engaged in incubation, it will leave its nest on the approach of a
+Chiffchaff, and, having driven away the intruder, proceed to sing
+excitedly. At other times both male and female will combine to attack
+this small intruder.
+
+But this does not mean that the Chiffchaff suffers persecution; it is
+itself most aggressive, as is shown by the fact that it will join in the
+Blackcap quarrels and attack the combatants indiscriminately. Its
+behaviour, however, requires further consideration, especially as
+regards its relations with its nearest of kin--the Willow-Warbler; for
+here we have a mutual intolerance which is somewhat remarkable, and
+evidence of it can be found wherever the birds occupy the same ground.
+Now it can be observed that the hostility is not limited merely to
+occasional acts of intolerance, but that there is organised warfare
+lasting, it may be, for many days in succession, and that the actions of
+the birds bear the stamp of a persistent striving towards some end. On
+one occasion the Willow-Warbler may be the aggressor, on another the
+Chiffchaff, and at times it is difficult to say which of the two is
+responsible for the quarrel. In size and in strength they are equal, and
+the "will to fight" is as strong in the one as in the other, so that it
+is seldom, if ever, possible to point to this one as the victor and that
+one as the vanquished. Success or failure probably depends more upon the
+cumulative effect of many combats entailing physical exhaustion, than
+upon the issue of any one particular battle; and whilst observation
+might quite well fail to distinguish any resultant change in the
+relative positions of the birds, or any harmful effect upon their
+constitutions, yet the area occupied by this one might be sufficiently
+curtailed to prejudice the welfare of the young, or the vitality of that
+one might be seriously impaired--and we should be none the wiser.
+
+Neither the Marsh-Warbler nor the Reed-Warbler will tolerate strangers
+within the small space of ground over which they exercise dominion. Of
+the two, the Marsh-Warbler is perhaps the more pugnacious, and will
+attack any other Warbler that approaches too closely; Whitethroats are
+often pursued and driven away, and less frequently, Garden-Warblers. In
+one case, a male occupied the same ground as a Sedge-Warbler, and there
+was a constant feud between them; a willow-tree formed its headquarters,
+and this same tree seemed to be the headquarters of the Sedge-Warbler,
+so that they often met and whenever they did so they quarrelled. As a
+rule the Marsh-Warbler was the aggressor and had the mastery over its
+opponent, and when it attacked, it uttered a peculiar harsh scolding
+note, raised the feathers on its back, spread out its wings, and
+betrayed the usual symptoms of emotional excitement.
+
+On the other hand, the Sedge-Warbler is most aggressive towards other
+kindred species, and when a male happens to occupy the same ground as a
+Reed-Warbler, there are frequent battles between them and incessant
+commotion; they fly at one another and meet in the air with an audible
+clicking of bills, or pursue one another amongst the reeds, each one
+uttering its characteristic scolding note.
+
+The Tits, as a family, are notoriously pugnacious. I have seen a pair of
+Blue Tits attack a single Long-tailed Tit with great determination, and
+not only did they pursue it, but, flying at it, struck it with
+considerable force.
+
+In giving an account of the domestic economy of the Carrion-Crow, Mr.
+Edmund Selous refers to the hostility between this bird and the Magpie.
+"About a week ago," he says,[6] "I saw a Crow busily engaged in chasing
+away several Magpies, not only from three or four tall slender trees
+close together, in one of which it had its nest, but also from various
+other trees, not far off, round about. In this the Crow had a good deal
+of trouble, as the Magpies were always returning. After a time it was
+joined by another crow, which however did not take so active a part in
+the drama, nor did I see either of the two actually go to the nest,
+though I could only explain their action by supposing it was their own.
+This morning I saw the same thing reversed, for a pair of Magpies, with
+an undoubted nest, kept attacking a Crow that insisted on settling in
+one of a row of trees--also tall and slender--in which it was placed.
+Both were equally persevering--the Crow, though often chased away,
+always returning, and settling generally in the last tree of the row,
+where he would be left alone sometimes for a minute or two, but before
+long one of the Magpies flew at him, and put him to flight. The Crow
+defended itself, but not, it would seem, very successfully, and in the
+last attack upon him, made, with great spirit, in the air, a large black
+feather floated to the ground, which I made no doubt was his. Yet this
+did not drive him from the trees, and it was only on my approaching
+nearer that he finally left them. Thus we see that both species look
+upon the approach of the other to within a moderate distance of their
+nest as an intrusion."
+
+That the Rook suffers persecution from the Carrion-Crow is a
+well-established fact, and there is reason to believe that it has
+another dangerous enemy in the Hooded Crow. According to the late
+Mr. Ussher, Choughs will attack both Hooded Crows and Ravens. "I once
+saw," he says, "two Choughs energetically attacking a pair of Ravens;
+they shot up into the air and darted down on the latter, whose heavy
+flight made them helpless against their agile tormentors."
+
+Birds of prey are often hostile to one another. The Merlin is
+exceptionally pugnacious, and its boldness in attacking intruders is
+well known. When, for example, a Kestrel approaches its territory, it
+leaves the tree, bush, or rock upon which it was resting, utters its
+characteristic cry, and soars rapidly upwards; then, rising to a
+considerable height, it swoops down upon the Kestrel, and by
+alternately stooping at and chasing its opponent, drives it away from
+the immediate neighbourhood.
+
+What we have, then, to consider is, Do these battles between different
+species contribute towards the attainment of the end for which the whole
+territorial system has been evolved?
+
+Let us take the individual and see whether we can establish any relation
+between the hostility it displays towards members of other species and
+its general disposition to secure a territory. We must remember that a
+male can have no knowledge of the prospective value of its behaviour,
+nor is it likely that it has any ulterior purpose in ejecting other
+males, beyond the pleasure it derives from satisfying its impulse to do
+so. The proximate end of its behaviour is to attack, nothing more, and
+this, of course, it can only do just in so far as the intruder evokes
+the appropriate instinct.
+
+Now the arguments we shall employ will, on the whole, be similar to
+those which we made use of in the second chapter, wherein we attempted
+to ascertain the conditions under which a male becomes intolerant of
+other males of its own species, and examined more especially the claims
+of the "territory" as opposed to those of the "female." But here we
+start on firmer ground, because the one factor which introduced an
+element of uncertainty--the female--can be definitely excluded; at least
+it seems so to me, for granting even that her presence is the condition
+under which the pugnacious nature of the male is rendered susceptible to
+stimulation, it is difficult to see why a male of a different species
+should supply that stimulus, or what biological purpose could be served
+by its doing so.
+
+When dealing with the attitude of a male towards others of its kind, we
+attached considerable significance to the fact that its pugnacious
+nature gained or lost susceptibility according to the position which it
+happened to occupy. We found, it will be remembered, that the same bird
+that was pugnacious in its own territory took no further interest in its
+opponent when the boundary was passed; and, moreover, that if it
+happened to wander into an adjoining one, it made no real effort to
+defend itself when attacked, but returned forthwith to its own
+headquarters. It remains to be shown whether the rivalry between
+different kinds of birds is similarly related to the position which the
+opponents happen to occupy at the time.
+
+First, then, there is the general consideration, namely, that the enmity
+occurs for the most part just at the time when the territories are in
+process of being established. During autumn and winter, many birds of
+more or less close affinity assemble together in flocks, wherever the
+supply of food is abundant, and are then not only sociable, but, so
+there is reason to believe, are mutually helpful both in discovering the
+necessary means of subsistence which are often none too plentiful, and
+in affording protection from enemies, which, on the contrary, are often
+numerous. That the different units of which these flocks are composed
+should live on amicable terms is therefore as necessary for the welfare
+of the whole community at this particular season as that the different
+individuals of the same species should do so. But just as the sociable
+relations, which obtain between these individuals throughout the winter,
+undergo a marked change at the commencement of the breeding season, so,
+too, do different species, which habitually associate together, suddenly
+become hostile to one another. This change is coincident in time with
+the rise of the organic condition which leads to the establishment of
+territories; and the hostility continues, though in diminishing degree,
+throughout the breeding season, and dies away the following autumn.
+
+For example, different Warblers resort to the elders (_Sambucus nigra_)
+in September, and there pass much time feeding on the fruit which is
+then ripe and often abundant. In the same bush there may be Blackcaps,
+Garden-Warblers, Whitethroats, and Lesser Whitethroats, some preening
+their feathers, others searching for the berries, others again, with
+feathers relaxed, making feeble attempts to sing. Occasionally there may
+be a scuffle, perhaps between a Blackcap and a Lesser Whitethroat, or
+between a Garden-Warbler and a Blackcap, but it is of short duration and
+lacks vigour. Apart, however, from such temporary disturbances, there is
+no real rupture in their relations, and certainly nothing to lead one to
+suppose that the bickerings are determined by the functioning of any
+specific instinct. Yet only a few months previously some of them were
+constantly at war, and their quarrels betrayed symptoms of great
+persistence; and if we remember how the observed behaviour of the birds
+suggests the fact that they were striving to attain something definite,
+we shall understand the nature and extent of the change, and shall, I
+fancy, be in a better position to estimate its biological worth at its
+true value.
+
+We can find many similar examples--flocks are to be found on arable
+ground, on the water meadows, and on the mud-flats; here different kinds
+of Thrushes feed on the berries of the yew, there different kinds of
+Tits travel together in parties; hosts of Finches collect in the hollies
+to pass the night and Buntings roost together in the gorse; and, in
+fact, in whatever direction we choose to look in the autumn and winter,
+we find various birds assembled together and living on amicable terms.
+All of this changes in the spring, and the relationship undergoes a
+gradual but noticeable alteration; so much so that whereas the
+outstanding feature of bird life in the winter is sociability, that of
+the spring is hostility.
+
+So much, then, for the seasonal change of relationship; let us now turn
+to particular cases and attempt to trace the condition which accompanies
+such change.
+
+Many migrants in the spring seem to follow the course of the Severn
+during their journey northwards through Worcestershire; and where the
+river bends to the north-west at Lincombe Lock, there they leave it, or,
+rather, continue in a north-easterly direction which takes them across
+the southern end of Hartlebury Common. As I have already mentioned, this
+Common is overgrown with gorse, heather, and ling, and scattered here
+and there are a number of dwarf oak-trees and small elder-bushes. The
+situation is therefore an ideal one for the smaller migrants to rest for
+a brief time, and, from the point of view of the observer, very suitable
+because it is open and the movements of the birds can be traced for some
+distance. Turtle Doves pass over at a great height, or skim across a few
+feet above the gorse; Redstarts settle for a few minutes and then
+disappear; Tree-Pipits, Whinchats, and Willow-Warblers pass from tree to
+tree or flit from bush to bush--and all in a north-easterly direction.
+They do not sing, they are restless, and, judging by their behaviour,
+they are anxious to conceal their presence, not to make it known. Yet we
+know that when they reach their destination, as presently they will, all
+this will change; that each of them will employ every means at its
+disposal to make itself conspicuous; and that each, as far as it is
+able, will resist intrusion on the part of other species.
+
+Now the southern end of the Common is always inhabited by individuals
+belonging to one of these species, or to others of close affinity; so
+that wherever these travellers settle whilst passing across it, the
+chances are that they will find the ground occupied--and their behaviour
+under such circumstances is no less interesting than the behaviour of
+the bird upon whose ground they are trespassing. We will take the case
+of the Whinchat. It arrives from the south-west, and, flying from bush
+to bush, works its way in a north-easterly direction. In doing so it
+intrudes upon the territory of a Stonechat; and the Stonechat, becoming
+excited, flies towards it, and it retires for a short distance in the
+direction from whence it came. Here again it is followed and attacked
+and again moves on, and then, flying in a circle as if to avoid the
+territory which blocked the path, resumes its former line of flight,
+though still followed by the Stonechat, which after continuing the
+pursuit for perhaps a quarter of a mile, suddenly turns in the air and
+returns to its headquarters.
+
+It is difficult to put oneself in the place of the Stonechat or of the
+Whinchat. But even after making due allowance for the danger inseparable
+from any attempt to do so, there remains the unquestionable fact that
+whereas the impulse to attack was strong in the one, the impulse to
+defend itself was wholly lacking in the other. Yet a Whinchat, when it
+has established itself, is most pugnacious; it not only attacks every
+bird of a similar size that approaches its position, but its behaviour
+under such circumstances bears the impress of unusual determination; and
+if we were to take a male and place it in the position of the Stonechat,
+we should find that its nature would change, that the presence of the
+Stonechat would evoke a hostile response, and, conversely, that the
+instinct of the Stonechat would not be susceptible to stimulation. Hence
+it is clear that the nature of a bird when on migration is not quite the
+same as it is when its destination is reached; that the positions
+occupied from time to time during the journey carry no meaning, or,
+rather, are not brought into relation with its life in quite the same
+way as is the position which it finally occupies; and further, it is
+clear that the interest it displays in other species undergoes a
+somewhat remarkable transformation when at length its destination is
+reached.
+
+This altered nature of the migrant is a fact of some importance in
+relation to our present subject, but it does not stand alone--the same
+characteristic is observable in other phases of bird life. Some of the
+residents, the Buntings and the Finches for example, occupy their
+breeding ground very early in the year, and it often happens that the
+situations which they select are not capable of supplying them with food
+so early in the season, though at a later date food will be there in
+abundance; so that they are compelled to resort to the surrounding
+neighbourhood, and since, even there, the available supply is sometimes
+scarce or, if plentiful, limited to certain areas, they are constrained
+from time to time to join together again in flocks. Thus, for part of
+the year, they may be said to lead a double existence; for just as the
+Whinchat, that is sociable on migration, betrays a changed nature when
+it reaches its destination, so too does the nature of these residents
+change from hour to hour according to whether they are seeking food or
+occupying the breeding ground.
+
+In the newly-sown fields of grain the birds frequently find a supply of
+food. Here Yellow Buntings, Greenfinches, and Chaffinches collect from
+the surrounding neighbourhood. The majority are somewhere in possession
+of territories, and not a few are paired. Between the territories and
+the feeding ground a highway is formed by individuals passing to and
+fro. Sometimes both members of the pair leave together in order to seek
+food, at other times they separate and the male may be in his territory
+whilst the female is with the flock. Apart from occasional
+manifestations of sexual emotion on the part of a male, there is nothing
+to disturb the harmony of the flock nor anything in the behaviour of the
+birds which would lead one to suspect that, when they return, their
+nature will change and that they will be no longer sociable; and, which
+is still more remarkable, no matter how great the provocation which an
+individual, when in company with the flock, may be called upon to
+endure, its customary hostile response will fail to be elicited. An
+incident which happened in the spring of 1917 will serve to make this
+clear. A flock of some thirty Yellow Buntings, Greenfinches, and
+Chaffinches were feeding in one corner of a field which had recently
+been sown with barley. As they sought their food they wandered outwards
+into the middle of the field, and in so doing, passed across the
+territory of a Skylark. Whereupon the Skylark became excited, uttered
+its call-note rapidly, and rising a few feet from the ground, attacked
+those members of the flock that were nearest, which happened to be the
+Yellow Buntings; and so determined were its onslaughts that the Yellow
+Buntings were forced to retire. The Skylark showed no discrimination as
+to sex, but attacked both males and females, and within a few minutes
+succeeded in driving away at least two pairs. One would have expected
+that the Yellow Buntings would have made some show of resistance; one
+would have thought that the fact of being violently attacked would have
+supplied a stimulus sufficiently strong to evoke a corresponding hostile
+response: yet there was no mistaking the lack of interest that they
+displayed in the contest--they made no effort to retaliate but seemed to
+accept the situation as unalterable and left.
+
+So far we have examined only those cases in which the pugnacious
+instinct was stimulated in one of the adversaries, and in which
+consequently the fighting seldom reached any high degree of severity. We
+must now consider some others in which each of the opponents acts as a
+stimulus to the pugnacious instinct of the other. It is here, of course,
+that we find the most violently contested battles, and it is here, too,
+that the purpose of the fighting seems clear. The persecution which the
+Green Woodpecker suffers from the Starling is well known. The purpose of
+the Starling's behaviour is clear, namely the possession of the hole
+occupied by the Woodpecker. Bird for bird, the Woodpecker is more than
+the equal of the Starling, but persistent endeavour ultimately wins the
+day. The Starlings perch close beside the hole, and, whenever the
+Woodpecker shows itself, attack with determination; and not only do they
+do so but they are assisted, so there is reason to believe, by other
+individuals or pairs in the attainment of their end, so that no matter
+how stoutly the Woodpecker defends itself, in time it is almost certain
+to be deprived of its ownership.
+
+In like manner different kinds of Woodpeckers contend with one another
+for the possession of a hole, and here the opponents are more equally
+matched. I have seen a pair of Lesser Spotted Woodpeckers endeavouring
+to drive away a Great Spotted Woodpecker. The excitement of all three
+birds was exceptional. Each of the Lesser Spotted Woodpeckers kept
+swooping in turn at their rival, sometimes in the air and sometimes when
+it was settled on the topmost branches of a dead tree, and the sounds
+produced reminded one of the piping of a flock of Oyster-Catchers in
+flight.
+
+A battle between a pair of Green Woodpeckers and a Great Spotted
+Woodpecker is worth mentioning. It occurred on the 24th of April.
+Passing through the middle of a wood, I noticed a Great Spotted
+Woodpecker fly out of a hole in an oak-tree. Shortly afterwards, a pair
+of Green Woodpeckers settled near the hole and then flew to some
+oak-trees close at hand, where they were joined by their rival and signs
+of hostility were soon apparent. Presently the Great Spotted Woodpecker
+returned to the hole and entered. Both of the Green Woodpeckers then
+flew into the tree; and one of them, settling upon the trunk, climbed
+up to the level of the hole and, when it became aware of the Great
+Spotted Woodpecker within, extended its wings fully and proceeded to
+peck viciously at its opponent. Whereupon there was a scuffle at the
+mouth of the hole and the Great Spotted Woodpecker hurriedly left. After
+this, all was quiet and the Green Woodpecker eventually descended and
+entered the hole. The Great Spotted Woodpecker, however, returned again,
+but, after fluttering around the hole, disappeared, leaving the Green
+Woodpeckers in possession.
+
+In this varied field of hostile behaviour which we have explored, one
+feature stands out prominently, namely, that the interest which a bird
+displays in other species varies not only at different seasons but even
+from hour to hour. I have used the word "nature" as equivalent to
+"interest," and I have spoken of the bird's nature changing or altering
+according to the circumstances in which it was placed. But its nature is
+its inborn constitution, and its constitution cannot change from day to
+day, still less from hour to hour. So that, in a sense, and having
+regard to strict scientific accuracy, it is misleading in this
+particular connotation to say that the bird's nature changes.
+
+[Illustration: H. Gronvold dcl. Emery Walker ph.sc.
+
+A battle between a pair of Green Woodpeckers and a pair of Great
+Spotted Woodpeckers for the possession of a hole in an oak tree.]
+
+What then does happen? The instinct of pugnacity must form just as much
+a part of the hereditary make-up of the migrant, when on migration, as
+when finally it reaches its destination; still more must it form part of
+the constitution of the Bunting when it leaves its headquarters
+temporarily and joins the flock. And, if it is there, the question
+arises as to why it does not respond. Now every instinct requires for
+its response a stimulus of an appropriate kind, and, therefore, a
+reasonable view to take would be that the necessary stimulus was
+lacking. But this is a view which we cannot uphold, because on all these
+occasions an opposing male was present--and, so far as it is possible to
+judge by observation, that is the stimulus which in the main evokes a
+hostile response. We must therefore look elsewhere than in its
+direction for a reason which will adequately explain the behaviour.
+
+Though it be true that every instinct requires for its functioning a
+stimulus of an appropriate kind, yet it is also true that the condition
+which will render it responsive must be present. What we have then to
+consider is whether the phenomena which we have explored give us any
+clue as to the particular nature of that condition. In the first place,
+we have the general fact that the hostility is not confined to a few
+species belonging to a few families, but that it is of wide
+application--birds of prey, Warblers, Woodpeckers, all supply us with
+evidence which serves to show, in greater or less degree, its nature and
+extent. Next, we found that the hostility was peculiar to a certain
+season--and that one the season of reproduction. And if the question
+were asked: What condition would then be most likely to render the
+instinct susceptible, the answer that would most certainly be given
+would be--the presence of a female. And in reply to a further question
+as to the particular nature of the stimulus to which the instinct would
+respond, we should be told--the presence of another male of the same
+species. Now the possible influence of the female on the course of the
+male's behaviour was the subject of inquiry in the second chapter,
+wherein we endeavoured to explain the hostility between males of the
+same species, and we came to the conclusion that it was not alone
+sufficient to account for the facts disclosed. Still less likely,
+therefore, is it that her presence can bear any direct relation to the
+hostility between different species, the more so since the biological
+end of securing a mate is definitely excluded. And we have something in
+the nature of proof of the correctness of this view in the fact that she
+accompanies her mate when he joins the flock, and that there his
+instinct is not susceptible to stimulation. We then proceeded to examine
+certain cases in which all the indications pointed to the fact that the
+"will to fight" was present in only one of the opponents; and we
+attached considerable importance to this circumstance, because we knew
+from experience that the same bird which seemed to lack courage, could
+at other times and in other situations be most aggressive. If then we
+ask what condition was present on the one occasion that was absent on
+the other, we have no difficulty in finding a reply--on every occasion
+on which the opponents appeared to be unevenly matched, one was in
+occupation of a territory and the other was not. And if we inquire
+further as to which of the two was the aggressor, the answer is again
+clear, namely, the bird that occupied a territory. Finally we considered
+some particular instances in which the "will to fight" was present alike
+in both opponents, and in which the battles were protracted and severe.
+
+But the fact that a bird has established a territory is not in itself
+sufficient to render its hostile nature susceptible; it must be actually
+in occupation if a response is to be elicited. We reach this conclusion
+step by step: the behaviour of the migrant, that lacks the "will to
+fight" when on migration but is pugnacious when it has secured a
+territory, shows it; the behaviour of the resident, which temporarily
+joins the flock and is there sociable, shows it; and it is shown also by
+the determination with which both opponents fight when the question of
+ownership of a station is in dispute. And of all the facts we have
+reviewed, this is perhaps the most important in relation to our present
+subject, for it demonstrates that the change from sociability to
+hostility is not merely an incident of the sexual season, not merely an
+indirect result of the functioning of the general disposition which
+leads to the establishment of a territory, but that it is intimately
+associated with the whole process, and that the particular part of the
+bird's nature which is concerned is so nicely balanced that it will
+respond under one condition and one only.
+
+Thus we are led to the only conclusion which seems consistent with the
+facts, namely that there is a relationship between the "territory" and
+the hostility.
+
+
+If we are satisfied that all this warfare is not merely an expression of
+an instinct which is serviceable in another direction, what part does it
+play in the whole scheme of reproduction?
+
+The young of many birds are delicate at birth and unable to withstand
+exposure to cold, and in the previous chapter we came to the conclusion
+that the territory was serviceable in that it provided an adequate
+supply of food in the vicinity of the nest, and thus obviated the
+necessity of the parents being absent from them for long. But manifestly
+no matter how active a male may be in driving away members of its own
+sex and kind, it will neither make its position secure, nor insure a
+supply of food for its young, so long as any number of individuals of
+different kinds are allowed to establish themselves in the same space of
+ground. On the one hand, then, we have the fact that there is constant
+strife between males of close affinity, whilst on the other, we know
+that many species require like conditions of existence and are bound to
+assemble wherever these conditions are suitable; and we can infer that
+the territory would fail to serve its purpose if no restriction were
+imposed upon the measure of such assemblies.
+
+The question then arises: Does all this warfare contribute towards the
+attainment of reproduction? Not far from my house there is a small water
+meadow, three acres in extent, which for some years has been derelict
+and is now overgrown with the common rush (_Juncus communis_) and small
+alder trees. For three successive seasons I watched the bird life of
+this meadow, and more especially the Reed-Buntings whose behaviour I was
+studying at the time. In every respect the meadow was suitable for this
+bird; there was an abundance of food and numberless situations in which
+nests could be placed. Each year all the pairs were successful in
+rearing one, if not two broods, yet the number of pairs never exceeded
+five--the first year there were three; the second year five; and the
+third year four. In addition to the four pairs of Reed-Buntings, there
+were in the spring of 1915, six pairs of Whitethroats, one pair of
+Lesser Whitethroats, four pairs of Willow-Warblers, one pair of
+Sedge-Warblers, two pairs of Grasshopper-Warblers, one pair of
+Chiffchaffs, three pairs of Hedge-Sparrows, two pairs of Tree-Pipits,
+one pair of Skylarks, one pair of Whinchats, one pair of Flycatchers,
+two pairs of Song-Thrushes, one pair of Blackbirds, one pair of
+Redstarts, three pairs of Chaffinches, and one pair of Wrens--in all,
+thirty-five pairs, whose young were mainly dependent for their living
+upon the insect life of that meadow and the ground immediately
+surrounding it. If we allow three young to each pair--and this would
+take no account of second broods--we arrive at the following result,
+namely, that one hundred and five young and seventy adults had to be
+supplied with food from that locality, which would mean, if the search
+for food were strictly limited to that meadow, that 83 square yards
+would be allotted to each individual.
+
+Suppose now that the four male Reed-Buntings had each admitted one other
+male, and that they had secured mates, what would have been the effect
+upon the whole community? The four additional pairs with their young
+would have represented twenty individuals, which would have represented
+a decrease of 8.5 square yards in the space allotted to each individual.
+The pressure of the bird population upon the means of support would then
+have been materially increased; and not only the Buntings, but the
+Warblers, Pipits, and all the rest would have suffered. But the result
+would have been the same if, instead of the four additional male
+Reed-Buntings, four males of other kinds had been allowed to enter the
+marsh, and we can multiply the number four until we arrive at a point
+when the means of subsistence would no longer have been adequate for the
+adults, still less for the young. If, then, there were nothing to
+prevent this happening, many of the birds in that marsh would have no
+chance of rearing their young successfully. Hence, if the territory is
+adequately to serve the purpose for which we believe it has been
+evolved, some provision must have been included in the system to meet
+the difficulty.
+
+There are three ways by which this may have been
+accomplished--indirectly, by increasing the size of the area occupied by
+each individual, and thereby reducing the relative number of each
+species; or directly, by rendering the fighting instinct of the bird
+susceptible to stimulation by individuals of other species; or,
+possibly, by a combination of the two. There were four pairs of
+Reed-Buntings in the marsh, and their territories covered the whole of
+it. But inasmuch as other insectivorous birds were established there
+also, and found sufficient food to maintain both themselves and their
+families, it is clear that the area these Reed-Buntings occupied was in
+excess of that which they would have required if they had been the sole
+inhabitants. And such often appears to be the case. Many a Warbler
+allocates to itself a space of ground more than sufficient to supply it
+with all that it needs; so, too, does the Finch, or the Pipit, or the
+Falcon--if we take no account of kindred species. Thus there is reason
+to believe that, by limiting the number of individuals in a given
+locality, this apparently wasteful expanse of territory is serviceable
+in that it provides against the pressure of the bird population upon the
+available means of support becoming too great. But though a reduction in
+the numerical standing of the different species would certainly follow
+from any increase in the area occupied by the respective individuals,
+and with even greater certainty would place them in a more secure
+position as regards their supply of food, yet, when we remember how
+large a number are dependent upon a supply of insect life for their
+young, we can understand that it would not alone be a sufficient
+safeguard against the dangers attendant upon overcrowding. It is here, I
+believe, that we shall find the true explanation of the hostility; it
+roughly insures that the number of pairs in any given area does not
+exceed the available means of support, and indeed it is difficult to
+imagine how such uniformity of distribution as would free the young from
+the risk of exposure could be obtained without some such control.
+
+Some birds, however, have no difficulty in finding the necessary food
+for their young, yet have great difficulty in finding a station where
+they can rear their young in safety; and the area each one occupies has
+been reduced to the smallest proportions in order that the maximum
+number can be accommodated. Here, any increase in the size of the
+territory would inevitably lead to the extinction of the race, so that
+nothing stands between failure and success except the ability of the
+bird to defend its territory. If we study the bird population at one of
+the breeding stations on the coast, we find, generally speaking, that
+each kind of bird inhabits a particular portion of the cliff; on the
+lower ledges are the Guillemots and Kittiwake Gulls; higher up are
+Razorbills and Fulmars, and at the top, where the cliff is broken and
+the face of the rock covered with turf and soil, the Puffin finds
+shelter for its egg. At the same time there is much overlapping; the
+kind of ledge that suits a Razorbill is equally suitable for a Guillemot
+or a Fulmar, and so, no matter how successful the Razorbill may be in
+establishing a territory and preventing intrusion upon it by other
+Razorbills, it will be all to no purpose if it allows itself to be
+jostled out of its position by a Fulmar. Hence, inasmuch as breeding
+stations are limited and competition for territory so severe, only those
+forms in which the fighting instinct responds freely to a wide range of
+stimuli will be in a position to maintain a footing upon the cliff.
+
+In trying to estimate the importance of the hostility in its relation to
+the territory, we must bear in mind that competition varies in different
+seasons and in different localities. The surface of the land is
+constantly undergoing modification, partly owing to human and partly to
+physical agency--forests are cleared; marshes are drained; the face of
+the sea-cliffs is altered by the erosion of the waves; here the coast
+may be locally elevated, there locally depressed; and so forth. Many of
+these changes are slow and imperceptible, many can be observed in our
+own lifetime. The timber is felled and the undergrowth cleared in some
+wood, and the following spring we notice a change in the character of
+the bird population. Migrants which formerly found in it no suitable
+accommodation now begin to appear, and as the seasons pass by and the
+undergrowth affords more and more shelter for the nests and an
+increasing supply of insect life, so their numbers increase until the
+wood becomes an important breeding station, resonant with the song of
+many individuals. But slowly the growth increases; the bushes pass into
+saplings and the saplings into trees, and the undergrowth then
+disappears just as surely as do the migrants which can no longer find
+there the conditions which they require.
+
+Or, as an illustration of the effect produced by natural agency, let me
+describe a change which has taken place in a corner of Co. Donegal. The
+promontory of Horn Head is bounded on the west by extensive sand-hills,
+100 ft. or more in height. On the southern side it is divided from the
+mainland by a channel, which narrows down to 100 yards or so in width
+where it fringes the sand-hills, and then widens out again, covering an
+area of approximately 270 acres. As far as is known in the memory of
+man, this area has always been tidal. But in recent years a change has
+taken place, and the blown sand has silted up the channel, with the
+result that this tidal area has been transformed into a brackish lake.
+What has brought about the change is not easy to determine. There is
+evidence, however, of a slow alteration of the level of the shore-line;
+for in the midst of the sand-hills, situated 150 yards or so from the
+present sea-margin, and running parallel with it, there is an
+accumulation of pebbles some 3 feet high by 4 feet deep. This raised
+beach is now separated from the Atlantic by sand-drifts of considerable
+height, and consequently there are some grounds for believing that
+secular elevation is taking place, which, if it be the case, will
+account for the change in progress. Now the effect on the bird
+population can be seen even now, and will doubtless become more apparent
+as the years pass by. Sand-Martins used to find plenty of places to
+breed amongst the sand-drifts, and moreover do so still. But their
+nesting sites are constantly changing and disappearing, and the
+breeding-place of one colony, that was situated in the bank of a stream
+twelve years ago, is now buried 10 feet or more below the surface of the
+sand. The area that was once tidal, but is now a brackish lake, is fed
+by mountain streams, and as the fresh water predominates, so in course
+of time will it become fringed with vegetation; and instead of the
+flocks of Curlew, Dunlin, and other waders that, at low water, resorted
+there to feed, Coots will fight with one another for the possession of
+territories, and the Wild Duck will teach her young to seek their food.
+
+In whatever direction we turn, we find that many breeding grounds are
+subject to incessant change. Ancient haunts disappear, new ones come
+into being, a change which makes life impossible for this bird, as
+likely as not benefits that one, and so on. There is no stability. Hence
+in any given district each recurring season there must needs be a large
+number of individuals which are obliged to seek new stations, and if
+there were no control over their distribution, if each one were free to
+establish itself wherever it chanced to alight, this locality might be
+overcrowded and that one deserted; and, bearing in mind how many species
+there are that require similar conditions of existence, we can infer
+that the successful attainment of reproduction would become impossible
+for many of those individuals so long as each species was indifferent
+to the presence of the others. On the other hand, if there were no
+control over the range of the intolerance, the smaller bird would have
+no chance in competition with the larger, and it is doubtful whether the
+larger would gain an advantage commensurate with the energy it would
+expend in ridding its area of the smaller. I have described battles in
+which the opponents were only distantly related; for instance, the
+Moor-Hen will attack almost any bird--Partridge, Lapwing, or
+Starling--that approaches its territory even temporarily. Nevertheless
+the antagonism between kindred forms is more prevalent, and, as a rule,
+characterised by more persistent effort; and thus it seems as if the
+susceptibility of the fighting instinct has its limitations, the degree
+of the responsiveness being dependent upon the affinity of the
+opponents.
+
+Suppose now that we take an area inhabited by a number of different
+species requiring like conditions of existence, divide it into three
+sections, and imagine that in one they were all sociable, that in
+another they were all hostile, and that in a third those which were
+closely related were intolerant of one another. Let us suppose further
+that each one of them was represented by the full number of individuals
+that the law of territory would allow. In the first section an
+individual would establish itself, and, becoming intolerant of its own
+kind, would exercise dominion over an area roughly sufficient, providing
+conditions were normal, to insure an adequate supply of food for its
+young. But it would take no account of other species, and since any
+number might occupy the same ground, the fact of its having established
+a territory would not alone suffice to render its supply of food
+secure. Success in the attainment of reproduction would then become
+largely a matter of chance, depending upon the number of individuals
+that happened to settle in this place or in that. In the second section
+there would be perpetual warfare; for whereas the appropriate organic
+condition which leads to pairing arises in different species at
+different times, fresh claimants to occupied ground would constantly be
+appearing, and the efforts of the inhabitants to preserve their
+boundaries intact would have to be maintained throughout the whole
+period of reproduction; and while the stronger or more persistent forms
+would be more likely to breed, they would do so at the expense of their
+young, to which they would be unable to devote proper attention, and
+with an expenditure of energy that would reflect itself upon the future
+of the race. But the conditions of life in the third section would be
+such as would be more likely to yield good results. The relations of the
+different members of the community would be more evenly balanced, for a
+male would only be called upon to compete with those of its own size and
+strength. Thus, on the one hand, accommodation would be so divided as to
+secure the breeding of the maximum number of individuals with the
+minimum of expenditure of energy, whilst on the other, any undue
+pressure upon the available means of subsistence would be prevented.
+
+There can be no question that in the latter section a higher percentage
+of individuals would succeed in rearing offspring. And so, by reason of
+the fighting instinct being more susceptible or less susceptible
+according to the affinity of the opponents, a control is established
+which, while preventing unnecessary extension of warfare, allows for
+sufficient extension to render the biological end secure.
+
+
+These, then, are the facts--this the conclusion which can be drawn from
+them. It may, however, be said of these facts, as it has been said, with
+even less justification, of the battles between individuals of the same
+species, that they do not afford evidence of genuine hostility. No doubt
+there are many naturalists who could supplement these facts with others
+in which the conflicts resulted in bodily injury, or terminated fatally,
+or at least were of a more determined kind. But I have already drawn
+attention to the fact that, so long as a definite result is attained,
+the severity of the struggle and the amount of injury inflicted are
+matters of small moment. Let us, however, run over the substance of the
+argument, and then briefly refer again to this point of view.
+
+After enumerating instances of hostility, sufficient in number, so it
+seemed, to constitute reasonable ground for the belief that they had a
+part to play in the life-history of the individual, the two questions we
+set ourselves to examine in this chapter were: Is there any circumstance
+in the life behaviour of the individual with which the hostility can be
+definitely related; and, will the hostility lead to the securing of a
+greater measure of success in the attainment of reproduction?
+
+Many different species assemble together in winter and roam from place
+to place in search of food. But in spring their behaviour undergoes a
+remarkable transformation; they avoid one another and become
+quarrelsome, so much so that whereas the outstanding feature of the
+winter is sociability, that of the spring is hostility. With this
+general fact before us, we proceeded to investigate this change of
+behaviour still further. First of all we took the case of a migrant,
+and, comparing its behaviour, as it journeyed, with that when finally it
+reached its destination, we found that the bird which was notoriously
+pugnacious when in occupation of a territory betrayed no interest in
+other species as it travelled to the accustomed breeding ground. Not
+only so, but even though it was attacked, we found that its pugnacious
+instinct still failed to respond. Here, however, it may be contended,
+and with reasonable justification, that in the interval which elapses
+before the ultimate destination is reached, some change in the organic
+condition of the bird may occur which will account for its altered
+behaviour; or, it may be urged, with no less justification, that whereas
+on migration the bird is unpaired, when the destination is reached it is
+probably in possession of a mate and is therefore quarrelsome. Now, at
+the most, the interval can only be a matter of a few days, and it is
+unlikely that organic changes sufficient to bring about so important an
+alteration of behaviour could occur in so short a time, still less
+likely that they could be timed to come into functional activity just at
+the moment when the bird reaches its breeding ground. And with regard to
+the suggestion that the change can be accounted for by the presence of a
+mate, we shall do well to remember not only that males as a rule precede
+the females by some days, but that a male may even remain in its
+territory, mateless, for some weeks, and yet display hostility.
+
+Nevertheless the case of the migrant did not, by itself, afford
+sufficient evidence upon which to base any conclusion. We therefore
+inquired into the behaviour of some of the residents at a corresponding
+period. The Bunting served as an illustration. Early in the season it
+establishes a territory, and because food is then scarce it is forced to
+seek it elsewhere than on the small plot of ground which it has
+acquired; and so it makes its way to some spot where the supply is
+abundant, and there, meeting with other species bent on a similar
+errand, forms with them a flock. Part of its time is then spent in the
+territory and part on the feeding ground, and between these two points a
+highway is formed by the bird passing constantly to and fro. But the
+attention which it pays to other species is very different on these two
+occasions--when in the territory it is intolerant of strangers, but when
+it accompanies the flock it displays no interest in their movements.
+From hour to hour its nature seems to change. But, as we saw, the inborn
+constitution of the bird cannot change, and therefore we came to the
+conclusion that an explanation of the altered behaviour was to be found
+in the fact that the pugnacious instinct is only rendered susceptible
+under a certain condition. So that all the evidence tended to confirm
+the impression which we had gained from the course of events in the life
+of the migrant, namely, that the hostility bears a direct relation to
+the occupation of a territory.
+
+Finally we were led to inquire whether the hostility was serviceable in
+promoting the welfare of the individuals. We saw that many different
+species require similar conditions of existence, that ancient breeding
+haunts disappear and that new ones come into being, and that in the
+ordinary course of events such species must often assemble in the same
+area for the purpose of reproduction. So that even though a male might
+be successful in protecting its ground from intruders of its own kind,
+yet it might still fail to rear offspring, just because it happened to
+choose a position in which other kindred forms had gathered. Hence if
+the territory is adequately to serve its purpose, some control over the
+local distribution of species is of paramount importance. Nevertheless,
+if all the different forms that require similar conditions of existence
+were intolerant of one another in a like degree, the smaller bird would
+have no chance in competition with the larger. This, however, is not
+the case. Some, as we saw, arouse little or no animosity in others, in
+fact the more closely related the rivals, the more responsive their
+pugnacious nature seems to become.
+
+To return now to the view that the fighting is not really serious, but,
+on the contrary, that it is either vestigial and has no longer any part
+to play in furthering the life of the individual, or that it is a
+by-product of the seasonal sexual condition to which no meaning can be
+attached. First, there is the relationship with the territory, and this,
+it seems to me, is a fact of some importance; for if the fighting were
+merely an exuberant manifestation of sexual emotion, one would expect to
+find it occurring under all conditions, and not merely under one
+particular condition in the life of the bird. The hostility is too
+widespread, however, and too uniform in occurrence for us to suppose
+that it has no root in the inherited constitution of the bird; and if it
+served some useful purpose in the past, the instinct might still
+persist, so long as it were not harmful. Thus the view that the
+behaviour is vestigial is not perhaps unreasonable. But manifestly it
+makes no difference whether it be vestigial or a by-product of sexual
+emotion, whether the battle be fierce or so trivial as to appear to us
+to be more in the nature of "play," so long as some change in the
+relative prospects of the opponents is the result.
+
+For us, then, the main consideration lies in the question: Is the
+behaviour serviceable now in furthering the life of the individual?
+Whether the evidence which we have examined affords sufficient ground
+for the belief that the hostility is genuine and has a part to play in
+the whole scheme of reproduction, each must judge for himself.
+
+
+
+
+CHAPTER VII
+
+THE RELATION OF THE TERRITORY TO MIGRATION
+
+
+Coincident in time with the growth of appropriate conditions in the
+environment, organic changes take place rendering certain instincts
+susceptible to stimulation; and the stimulus being applied, the Warbler
+leaves the country wherein it had passed the winter and finds its way
+back, with apparently little difficulty, to the district in which it was
+reared or had previously reared offspring. What is the nature of these
+changes and of the impulse which is first brought into functional
+activity; whence comes the stimulus; and what directs the bird on its
+journey--these are all different aspects of one great problem, the
+problem of migration. I do not propose to discuss all these various
+aspects, for indeed I have no suggestions to offer which are in the
+least likely to be helpful, but I seek rather to ascertain whether the
+phenomena which we have explored bear any relation to the problem as a
+whole; whether, that is to say, the competition for territory and all
+that appertains to it can have supplied the conditions under which, in
+the process of time, this complex and definite mode of behaviour has
+evolved.
+
+We are sometimes told that we must seek the origin of migration in the
+physical changes that have occurred in the ancient history of the
+earth--in glacial conditions which gradually forced birds to the south,
+or in the "stability of the water and mobility of the land" which
+brought about a gradual separation of the feeding area from the breeding
+area--and which continued for a sufficient length of time to lead to the
+formation of an instinct, and that the instinct persists because it is
+serviceable in promoting the welfare of the race. But when we consider
+the lapse of time, and the changes that must have occurred in the
+character of the bird population--the appearance of new forms and the
+disappearance of the old, the ebb and flow of a given species in a given
+area--and bear in mind that, notwithstanding this, the migratory
+instinct, if not stronger, is assuredly no less strong, and the volume
+of migration, if not greater, is assuredly no less; in short, that the
+whole phenomenon is progressive rather than retrogressive, we shall find
+the view that the instinct owes its origin to conditions which no longer
+exist, receives but little encouragement.
+
+I doubt not that, throughout the ages, geological changes have been an
+important factor in directing or limiting the scope of migration, and
+moreover are so still; just as climatic changes and the relative
+abundance or scarcity of enemies have influenced the course of its
+evolution. These are all contributory factors operating in the external
+environment. But there are, besides, internal factors which form part of
+the inherited constitution of the bird, and, being passed on from
+generation to generation, afford the conditions under which migration is
+constantly being renewed. It is, I believe, in this field of organic
+change and relationship that the conditions of origin must be sought.
+
+Just as the moth in passing from the rudimentary to the perfect
+condition runs through a series of changes, each one of which is marked
+by a typical behaviour response adjusted to meet some particular
+circumstance in the external environment, so the annual history of a
+bird displays an ordered routine, each phase of which can be observed to
+correspond with one of the successive changes in the environment. In
+almost every direction, we find that this routine is characterised, in
+broad outline, by great uniformity; so much so that, providing we know
+the history of one species, we can forecast with no small degree of
+certainty the general course of behaviour of other members of the
+family. But only the _general_ course. There is endless variation in
+just the particular way in which the behaviour is adapted to meet the
+needs of particular species--the major details may be said to be
+specific, the minor details varietal.
+
+Now it is that part of the behaviour routine which has reference to the
+relationship between one bird and another upon which, for the time
+being, I wish to dwell; for the interest that A displays in B is by no
+means always the same--it changes according to the season, and this
+change can be observed to be uniform throughout a wide range of species.
+
+In winter, in whatsoever direction we turn, we observe not only that
+different individuals but that different species also collect together
+in flocks. And since food at that season is not always easy to obtain,
+and, moreover, is only to be found in certain situations, which are
+limited both in number and extent, it would seem that such assemblages
+are in the main determined by accident. No doubt the abundance or the
+scarcity of food does determine the movements of birds, and hence to
+that extent may be held to account for the flocks. But we shall but
+deceive ourselves if we think that it is the sole or even the principal
+reason, or that the situation is in no wise affected by internal
+factors. The behaviour of the individual in relation to the flock bears
+ample testimony to the presence of a gregarious impulse which derives
+satisfaction from the fact of close association.
+
+As an illustration, let us take a bird whose movements are easily
+watched, and in whose hereditary constitution the impulse to which I
+allude seems to be strongly implanted--the Curlew. When the breeding
+season is over, Curlew leave the mountain and the moor and return to
+the coast or tidal estuaries for the remainder of the year. Here, at low
+water, they find an abundant supply of food--crustaceans amongst the
+sea-weed upon the rocks, and lobworms (_Arenicola piscatorum_) in the
+mud as the tide advances or recedes. But when the tide is full, they
+retire to those parts of the shore that remain uncovered--to isolated
+rocks, or to sand-dunes, or it may even be to pasture-land in the
+neighbourhood. During this period of repose large numbers of individuals
+gather together on a comparatively small space of ground. They are not
+constrained to do so by any shortage of accommodation, nor by any
+question relative to food, nor, for the matter of that, by any
+circumstance in the external environment; they are brought together
+solely, this at least is the impression that one gains, by some
+inherited impulse working towards that end. And their subsequent course
+of behaviour tends to confirm that impression. For if we watch the
+gathering together of the different units of which the flock is
+composed, and study more particularly the emotional manifestation which
+accompanies their arrival and departure, we shall find that the coming
+of a companion arouses some emotion which is expressed by a vocal
+outburst that sweeps through the flock.
+
+Now each call, and the Curlew has a great variety, is not only peculiar,
+generally speaking, to certain occasions, but is accompanied by a
+specific type of behaviour, whence we can infer in broad outline the
+type of emotion which is aroused. Thus we come to recognise fear, anger,
+or sexual emotion, by just the particular sound which is emitted. But
+even if we are going too far in referring particular calls to particular
+emotions, we can, without a doubt, divide them into two broad
+categories--those which are pleasurable and those which are the reverse.
+And we need have no hesitation in placing the particular call to which I
+allude in the first of these two categories, not only on account of the
+nature of the sound produced, but because the activities which are
+aroused are not such as normally accompany irritation. This is well seen
+if the behaviour of different individuals be closely observed. After
+resting on one leg for some time, first one and then another is seized
+with cramp, and running a few yards in an ungainly way, bumps up against
+its companions as if it had not full control over its movements. Its
+behaviour produces irritation which is expressed by a vocal outburst,
+and followed by actions the meaning of which is clear. Moreover, the
+call is taken up by other individuals and sweeps over part of the flock
+as does the greeting. But the nature of the cry is entirely different
+from that which greets the arrival of a companion--humanly speaking it
+is a passionate and impatient utterance, the height of displeasure. The
+arrival, then, acts as a stimulus to something in the inherited
+constitution which is expressed in, and presumably is satisfied by, this
+vocal outburst; and, since the bird that arrives joins also in the
+chorus, there is reason to think that the impulse which determines its
+movements is similar to that which is temporarily aroused in the flock.
+
+Apart, however, from the evidence derived from the affective aspect of
+the operation of the instinct, the general course of behaviour lends
+support to the view that the assemblies are determined by internal
+factors, and are not merely the outcome of circumstances in the external
+environment. Observe, for example, the manner in which the flock is
+built up. Single individuals are content to rest alone so long as no
+assembly is in sight, but they are drawn towards their companions
+directly the opportunity arises, just as surely as the smaller
+aggregation is drawn towards the flock; and so, as the flock increases,
+it gradually absorbs all the lesser flocks and smaller parties, for the
+greater the flock the greater the attraction seems to be; and different
+individuals appear to gain some satisfaction from being in close bodily
+contact with one another.
+
+When the Curlew flies to that part of the mud-flat which is first
+exposed by the receding tide, and there associates with others, it does
+not then do so because it has any interest in its fellows, nor because
+they serve as an attraction, but because it is constrained by hunger--in
+other words, the association is determined by accident. But when, during
+periods of repose, it sees a flock, flies to it, and takes up a position
+in the midst of it, it does so not because suitable accommodation is
+lacking--not therefore because of external constraint--but because it
+derives some pleasure from satisfying something in its organic complex.
+We speak of this behaviour and of the emotion which characterises it as
+the _gregarious instinct_: by which we mean that the inherited nature of
+the Curlew, as a tribe, is so constituted that, given the appropriate
+internal conditions and adequate external stimulation, every individual
+will respond in a similar manner--that is, the behaviour is primarily
+determined by racial preparation. This is what we mean by the
+_gregarious instinct_ biologically considered. We may resolve our own
+experience in relation to the crowd into its simplest constituents,
+project our own primitive feelings into the Curlew, and say that the
+bird feels uneasiness in isolation and satisfaction in being one of the
+flock. But in truth we know nothing, save by analogy, of the correlated
+psychical state. All the knowledge we possess is derived from a study of
+the objective aspect of the behaviour, which in simple terms may be
+expressed thus: the individual is drawn towards its companions; there is
+a relation between the size of the flock and the strength of the
+attraction; and all Curlew behave similarly under similar circumstances.
+
+This instinct controls the movements of many birds from early autumn to
+the commencement of the breeding season. And so powerful is the control
+that the individual is suppressed and its activities subordinated to the
+welfare of the community as a whole. Flocks of Waders roam about the
+tidal estuaries in search of food, and different kinds of Gulls assemble
+there and preen their feathers or sleep; Warblers alter their mode of
+life, and in the osier bed, or amongst the elders, seek their food
+together in peace; Finches, Buntings, Pipits, and Wagtails, though food
+is everywhere abundant, gather themselves together respectively into
+bands which, as winter approaches, grow into flocks and even into
+composite flocks; and as the Warblers leave for the south, so their
+places are filled by flocks of Thrushes and Finches from the north. In
+whatever direction we turn, when the days begin to shorten, it is the
+community, not the individual, that thrusts itself upon our attention;
+and throughout the winter continues to be the outstanding feature of
+bird life.
+
+With the approach of the breeding season we witness that remarkable
+change which I have endeavoured to make clear in the previous
+chapters--the disintegration of the flock and the reinstatement of the
+individual. Instead of continuing with the flock, the individual now
+goes forth to seek the appropriate breeding ground; and having arrived
+there, is not only content to remain in isolation, but so behaves that
+isolation is insured. Intolerant of the approach of a stranger,
+intolerant even of the approach of the very members of the community
+whose companionship was previously welcomed, it not only fights to
+maintain the position it has selected, but fights indeed for the
+possession of ground already occupied, and, until reproduction is
+completed, asserts its individuality and exercises dominion over its
+territory. What, then, is the prospective value, biologically
+considered, of the changing interest that A displays in B, and to what
+will such changes lead? These are the questions to which we will now
+direct inquiry.
+
+The annual life-history of a bird is in broad outline conditioned by
+two powerful and at first sight opposing impulses--the one to live in
+society, the other to live solitary. But, manifestly, a bird cannot be
+governed by opposing impulses. It has but one character, within which,
+according to the season and the circumstances, different impulses
+predominate. But these impulses, no matter how different they may appear
+to be, have their respective parts to play in furthering the life of the
+individual. Hence they cannot oppose, though they may conflict, if the
+resultant behaviour contributes towards survival.
+
+The majority of birds live to-day in constant danger from predatory
+species, and that this danger was still greater in bygone ages there can
+be but little doubt. A curious mode of behaviour of the Curlew,
+Whimbrel, and Godwit demonstrates this, for it must be the outcome of
+the necessity for constant watchfulness. Whilst resting with its head
+turned back and its beak buried in the feathers of the mantle, the bird
+constantly moves the axis of its body, so that an observer, if placed in
+a direct line behind it, sees at one moment the right eye and at another
+the left. No movement of the feet or of the legs is perceptible, and the
+shifting of the body continues whether the eyes are open or closed. This
+body movement enables the bird to survey a much larger area of ground
+than it would otherwise be capable of doing, and thus adds to its
+security. As far as my experience goes, the movement is less evident
+amongst the members of a flock than when an individual is resting alone,
+or even with a few companions, which may be due to the fact that since
+some members are always awake and watchful, a bird of prey would have
+more difficulty in approaching a flock unawares than it would have in
+approaching a single individual. With the greatest ease a Sparrow-Hawk
+can pick up a Thrush as it feeds on the meadow by itself, but if it
+attempts to seize one of a flock, the chances are that its approach is
+signalled and that its prey escapes. And not only do the different
+members give warning one to another of the approach of danger, but they
+also combine to harass or even to drive away an enemy. So that there can
+be no doubt that the gregarious instinct is serviceable in promoting the
+welfare of the race, and has, as its end, the preservation of the
+individual in order that it may take its share at the appropriate time
+in procreating its kind.
+
+In winter, then, the individual loses its individuality and is
+subordinated to the welfare of the community, whilst in spring it
+regains its individuality, and all its inherited instincts which then
+come into operation lead to its isolation from the flock. The impulse to
+seek isolation is dependent upon internal organic conditions which are
+peculiar to a certain season; whereas the gregarious impulse depends
+upon internal organic conditions which inhere at all times, though its
+functioning is inhibited by the functioning of the former impulse. The
+evidence which leads to this conclusion is to be found in the fact that
+a male often deserts its territory temporarily and joins the flock,
+where it remains at peace with its companions--an aspect of behaviour
+which we have discussed on various occasions. The former impulse becomes
+dominant in the spring owing to its innately superior strength; the
+latter becomes dominant in the autumn because the organic condition
+which determines the functioning of the former then subsides. The
+impulse to seek the appropriate breeding ground and to dwell there would
+seem to be the strongest of all the impulses save one--the sexual.
+When, however, I speak of the sexual, I refer to the actual discharge of
+the sexual function, which is the consummation of the whole process. But
+the territory and all that appertains to it is part of that process--the
+search for the breeding ground, the dwelling there, and the intolerance
+of intrusion are but different stages, each one of which must have an
+impulse peculiar to it; and since the completion of the sexual act can
+only be successfully accomplished providing that success is attained at
+every stage, the probability is that, of the impulses concerned, one is
+neither more powerful nor less powerful than another.
+
+So that we have two impulses operating at different seasons and guiding
+the behaviour into widely divergent channels. But though the proximate
+end to which the behaviour is directed is apparently different, there
+are not two biological ends in view, but one--the attainment of
+reproduction; and the changes that we witness are not contrary but
+complementary, and their prospective value lies in the circumstance that
+they contribute towards the preservation of the race.
+
+If, then, every male is driven by inherited impulse to seek the
+appropriate breeding ground each recurring season; if, having arrived
+there, it is driven to seek a position of its own; if, in order to
+secure isolation it is obliged to attack other males or to ward off the
+attacks of intruders; if, in short, success can only be attained
+providing that the inherited nature is so adjusted that the bird can
+accomplish all that is here demanded--what will be the general result?
+That the individual will rear its offspring in safety and that they will
+inherit the peculiarities of their parents, enabling them, in their
+turn, to procreate their kind; all this will certainly follow. We are
+not concerned, however, at the moment, with the direct effect upon the
+individual, but with the consequences that will accrue to the species as
+a whole.
+
+Now certain facts are presented to observation which enable us not only
+to understand the nature of the change that is wrought in the history of
+the species, but to foreshadow, with no small degree of certainty, the
+extent of that change. I suppose that it has come within the experience
+of most of us to observe, at one time or another, the ebb and flow of a
+given species in a given district. Some favourite haunt is deserted for
+a year, or for a term of years, and is then revisited; or, if it is
+always occupied, the number of inhabitants fluctuates--plenty of pairs
+in this season, only a few in that. Many intricate relationships, both
+external and internal, contribute towards this state of affairs.
+Fluctuation in a downward direction, or temporary extinction, is brought
+about by changes in the physical world, by changes in the available
+supply of food, by the increase of enemies, or by adverse climatic
+conditions; whilst fluctuation in an upward direction, though due
+indirectly to a combination of circumstances in the external world
+favourable to the survival of large numbers of individuals, is directly
+determined by the impulse to seek isolation. As individuals of
+different species establish themselves, and form kingdoms and lesser
+kingdoms, we can watch the gradual quickening into life of moorland and
+forest and we can observe the manner in which it all comes to pass.
+Males that for weeks or months have lived in society, drifting from
+locality to locality according to the abundance of food or its scarcity,
+now set forth alone and settle first here and then there in search of
+isolation. Lapwings settle in the water meadows, and, finding themselves
+forestalled, pass on in search of other ground; Blackbirds arrive in a
+coppice or in a hedgerow and, meeting with opposition, disappear; and
+the Curlew, wandering with no fixed abode but apparently with a fixity
+of purpose, searches out the moorland where it can find the particular
+environmental conditions to which its inherited nature will respond. In
+fact, wherever we choose to look, we can observe in a general way the
+gradual appropriation of breeding ground; and if we fix our attention
+upon particular males, we can watch the method by which success or
+failure is achieved.
+
+On more than one occasion I have watched the efforts of Reed-Buntings to
+appropriate territories in a marsh that was already inhabited. Sometimes
+their efforts met with success, at other times with failure. In the
+former case, the males, whose ground was intruded upon, were severally
+forced to yield part of their holding and were thus left in possession
+of a smaller area. The success of the intruder seemed to depend upon
+persistent determination, rather than upon superior skill in battle.
+Recently I had an opportunity of observing the intrusion of a male
+Willow-Warbler upon ground already occupied. By persistent effort it
+succeeded in appropriating one half of the territory of its rival. The
+intruder occupied some trees on the outskirts of the territory it was
+invading, and used them as a base from which it made repeated efforts to
+enter the ground of its rival. These efforts were time after time
+frustrated. No sooner did it leave its base than it was seen and
+intercepted, or else attacked; and no matter from which direction it
+attempted to effect an entrance, its efforts, for a time, were all to no
+purpose. The fighting was of a determined character, and after each
+attack the owner of the territory showed signs of great excitement, and,
+sitting upright upon a branch, spread and waved its wings, which is the
+specific emotional manifestation during the period of sexual activity.
+Eventually the intruding male succeeded by persistent effort in
+appropriating part of the occupied ground.
+
+Thus we can actually witness the efforts of the individual to isolate
+itself from members of its own kind, and can observe the immediate
+consequences that follow from success or from failure. And from these
+consequences we can infer that, within a certain range but in accordance
+with the relative abundance of the species that dwell in it, every
+corner of the available breeding ground will be explored and every
+situation that evokes the appropriate response will be occupied.
+Moreover, since the annual dispersion is not merely a repetition in this
+season of that which occurred in a previous one, a progressive increase
+in the area occupied will follow. Yet, if the majority of species desert
+their breeding ground so soon as reproduction is ended, how can this be?
+An answer to the question will be found in the fact that a bird has an
+innate capacity to return to the neighbourhood of its birthplace, or to
+the place wherein it had previously reared offspring--which means that
+the results of prior process persist as the basis and starting-point of
+subsequent process.
+
+Bearing then in mind that the seeming peace in bird life around us in
+the spring is but the expression of transitory adjustments in the
+distribution of individuals and of species; bearing in mind how
+widespread is the search for isolation each recurring season, how
+frequently the search leads to competition and competition to failure,
+and how failure implies a renewal of the search; bearing in mind that
+situations, which appear to be eminently suitable for breeding purposes,
+are passed by year after year and remain unoccupied, just because, for
+reasons which have yet to be ascertained, the environment fails to
+supply some condition which is essential if the inherited nature of the
+bird is to respond--can there be any doubt that the general result of
+the functioning of the disposition will be expansion; or, since no limit
+is placed upon it from within but only from without--that is, by
+unfavourable circumstances in the external world, that the expansion
+will not merely be in one direction but in every direction?
+
+If now, when reproduction is ended, all the impulses relating to it die
+away, and the gregarious instinct again predominates, what are the
+consequences to which this change will lead? Just as the consequences
+which flow from the functioning of the former impulse are accessible to
+observation, so likewise can we observe the change that is wrought by
+the latter impulse. The process is a gradual one. Less and less
+attention is paid by the individual to intruders, more and more is it
+disposed to pass beyond its accustomed limits. Little by little,
+accompanied by its young or without them, as the case may be, the bird
+deserts its territory and wanders out into the wilderness. Here it
+associates with others, and finds in them a new interest and, I doubt
+not, a new enjoyment. All this we can observe as it takes place. But
+just as there is an innate capacity to seek, in the spring, the place
+where the pleasures of breeding had formerly been enjoyed, so we are
+bound to infer the existence in the adult of an innate capacity to
+revisit the former area of association; and this capacity will
+strengthen and confirm the gregarious instinct and set the direction of
+the general course of movement.
+
+We have seen, then, that the interest displayed by one bird in another
+changes with the seasons; we have seen that it is so modified as to be
+in useful relation to different environmental circumstances; as far as
+possible we have traced out the consequences, and have reached the
+conclusion that the change of behaviour must, on the one hand, lead to
+expansion, and on the other, to contraction; and we have seen that this
+conclusion is in accord with the facts of observation--that is the
+general result of our inquiry into the functioning of the two powerful
+impulses, the impulse associated with the disposition to secure a
+territory and the gregarious impulse.
+
+
+The phenomenon of migration embraces a number of separate problems, each
+one of which presents features of great interest and of still greater
+difficulty. On some of these problems I do not intend to touch; I seek
+only to ascertain whether the impulses that are concerned in the
+securing of a territory, and in the search for society, bear any
+relation to the problem as a whole. I hold that the origin of migration
+is not to be found merely in conditions peculiar to a remote past, but
+that the conditions inhere in the organic complex of the bird, and are
+thus handed down from generation to generation. Starting with this
+assumption I examined the behaviour which normally accompanies the
+seasonal life-history of the individual, and found, in that behaviour,
+manifestations of cyclical change leading to definite biological
+consequences. I now propose to inquire whether those consequences are
+such as might, in the course of time, give rise to the seasonal change
+of abode.
+
+We are apt to think of migration in terms of the Warbler that enlivens
+our hedgerows in the spring after travelling hundreds of miles from the
+south, or of the Redwing that comes from the far north and seeks its
+food during the winter on the meadows, or perhaps of the American Golden
+Plover that each year covers a vast expanse of ocean in its journey from
+its breeding ground. The length of the distance strikes the imagination
+and constrains us to focus attention upon the extremes.
+
+But migration is of much wider significance than is here represented. I
+sit beside the River Severn in April and watch Swallows, Tree-Pipits,
+and Yellow Wagtails passing in twos and threes, in small parties, or it
+may be in small flocks; and I observe that while some establish
+themselves in the neighbourhood, others pass on. Or I watch
+Herring-Gulls returning to the breeding station at Bolt Head, an endless
+stream of individuals coming from the east as far as eye can reach;
+following them for some miles inland I see them still, first as specks
+upon the horizon, then passing beside me as they beat their way slowly
+against the strong south-westerly winds, and finally disappearing from
+view in the direction of the cliffs. Or again, I watch Buntings and
+Finches deserting the flock and seeking stations in the marsh, or
+amongst the furze-bushes on the common, or in the spinneys. In each case
+the proximate end of the behaviour is alike--wherein then lies the
+difference? Only in the distance which separates the territory from the
+area in which the birds formerly associated. And intermediate between
+the extremes, I doubt not, if we had a sufficient body of observations,
+that we should find numerous gradations, the lesser merging step by step
+into the greater. Is the Swallow a migrant and the Herring-Gull not; is
+the Tree-Pipit a migrant and the Bunting not; must a bird cross many
+miles of sea or of land before it can be considered a migrant; is the
+length of the distance traversed a criterion of migration? Surely not.
+The distance traversed is merely a collateral consequence of the process
+as a whole.
+
+The annual life-history of a bird presents, as we have seen, two
+distinct phases--the one in which the individual dominates the
+situation, the other in which it is subordinated to the welfare of the
+community. Let us take these two phases separately and endeavour to see
+how they may have influenced the seasonal movements; and first let us
+take the more important of the two, namely that one which is directly
+concerned in the continuance of the race.
+
+In this phase we must consider the three factors to which allusion has
+already been made:--(1) the internal impulse, (2) the innate ability to
+return to the former breeding ground, (3) the conditions in the external
+environment. These three work in close relation and, as I shall
+endeavour to show, lead to important results.
+
+(1) If there were nothing in the inherited nature beyond an impulse to
+seek the breeding ground, if, that is to say, when the appropriate
+locality were reached, the bird took no further interest in the
+developing situation, the attainment of reproduction would become
+largely a matter of chance. A male in a congested district, having no
+incentive to seek fresh ground, would remain inactive until a female
+happened to cross its path and stimulate its sexual impulse, when its
+activity would take another form. Hence some districts would be
+over-populated, whilst others would remain unexplored. But the system of
+reproduction does not consist merely of a search for the breeding
+ground, and of the discharge of the sexual function; it is a much more
+complex business, yet withal more complete. Nothing is left to chance;
+the end is attained step by step; and each successive stage marks the
+appearance of some specific factor which contributes towards the success
+of the whole. We start with the appropriate organic condition under
+which, when adequate stimulation is provided, the disposition to secure
+a territory comes into functional activity. Within the field of this
+disposition we can distinguish certain specific impulses. In sequential
+order we have the impulse to seek the breeding ground; the appropriate
+situation which gives rise to an impulse to dwell in it; and the act of
+establishment which supplies the condition under which the impulse to
+drive away intruders is rendered susceptible to stimulation. Grouping
+these impulses, for the convenience of treatment, under one general
+heading, I speak of an impulse to seek isolation. It implies some kind
+of action with some kind of change as its correlated effect; and from it
+there flows a ceaseless energy directed towards a definite end which for
+us, who can perceive its prospective value, is isolation in an
+appropriate environment. The emphasis here is on "isolation," for it
+involves competition, and there cannot be competition without some
+change in the relative positions occupied by different individuals; so
+that in each recurring season there will be not only a re-arrangement of
+ground formerly occupied but an arrangement of ground formerly deserted.
+
+(2) That the older birds return to the locality wherein they had
+formerly reared offspring, and the younger to the neighbourhood of their
+birthplace, was always deemed probable. But in recent years evidence
+which cannot be rebutted has been supplied by the marking of birds. This
+evidence, details of which can be found in the summary of results
+published annually by Mr. Witherby in _British Birds_, demonstrates that
+the adult frequently returns not only to the same locality in which it
+formerly bred, but even to the same station; that it does so year after
+year; that this mode of behaviour is not peculiar to one sex; and that
+many of the young breed in the locality in which they were reared. Such
+being well-established facts, we can infer the existence of an innate
+ability to revisit the place wherein the enjoyment of breeding, or of
+birth, had formerly been experienced. Of its nature we know little or
+nothing. It would almost seem as if there must be some recollection of
+past enjoyment, but all that can be definitely asserted is--that past
+experience somehow becomes ingrained in the life of the individual and
+determines present behaviour. What, however, is of importance to us at
+the moment is not the _ad hoc_ nature of the bird, but the biological
+consequences to which the behaviour leads. For if, on the average,
+individuals return to their former haunts, it follows that the annual
+dispersion will not be merely a repetition in this season of that which
+had occurred in a previous one, but that the little added this year will
+become the basis for further additions in the next. The innate ability
+is handed down from generation to generation, and, in so far as it
+contributes to success, is fostered and developed by selection; and the
+modifications of behaviour to which it leads, since the results of prior
+process in the parent persist as the basis and starting-point of
+subsequent process in the offspring may in a sense also be said to be
+handed down.
+
+(3) The conditions in the external world may be organic or inorganic. By
+organic I mean the conditions which depend upon the number of
+competitors or enemies by which a bird is surrounded. The competitors
+may include other species which require a similar environment; and the
+enemies, species which prey upon it, or animals which take its young or
+its eggs. They vary in different seasons, in different districts, and
+in nature and extent--the success of one species leads to the failure of
+another, and the multiplication of the Jay or of the Magpie robs us of
+many a songster.
+
+By inorganic I refer to the changes in the climate and in the surface of
+the earth. The nourishment of the young depends upon a regular supply of
+food, and the supply of food depends upon the climate which alters in
+different periods; in one decade the temperature falls below, whilst in
+another it rises above, the normal, and, as the insect life fluctuates,
+so there is fluctuation in the bird population. The changes in the
+surface of the earth are manifold. Little by little the alder (_Alnus
+glutinosa_) overspreads the marsh. Young shoots spring up here and
+there, in a few years grow into bushes, and in a few more years are
+trees; and the dense masses of rush which seemed to choke their growth,
+yielding their position of importance, slowly disappear. And where
+formerly the _Orchis latifolia_, _Orchis mascula_, and _Juncus communis_
+grew in mingled confusion, nothing but water, moss, and the spreading
+roots of alder cover the ground. As the rush disappears, many birds that
+for generations have inhabited that marsh must seek accommodation
+elsewhere. Ancient breeding haunts thus disappear, new ones come into
+being, and even those which appear to be permanent are almost
+imperceptibly changing.
+
+Now the bird inherits a nervous system, which works under internal
+excitation and external stimulation. Given the appropriate organic
+condition and adequate stimulation, and the impulse to seek isolation
+comes into functional activity. What the organic condition is and how it
+arises we do not exactly know; all we know is that organic changes do
+take place in the breeding season, that these changes profoundly modify
+character, and that they correspond with the seasonal growth of the
+sexual organs. And with regard to the question of stimulation, we have
+again to confess to much ignorance, although certain facts are presented
+to observation which seem to indicate the direction in which the
+stimulus lies. For example, it is well known that abnormal climatic
+conditions influence behaviour; we see migrants retracing their flight
+along the very course they travelled a short time previously--driven
+headlong by the blizzard, that at least is what we say. But if the wind,
+instead of being cold and from the north, is warm and from the west, do
+they retrace their flight? I have not found it so. And if there be no
+wind and the temperature is low, are they still affected? Again, I have
+not found it so. When, as we commonly say, they fly before the storm,
+some change takes place in their organic complex, some new impulse
+receives stimulation or the former one lacks it. If, after Lapwings have
+established themselves in their territories, the weather becomes
+exceptionally severe, the birds collect together again in flocks and
+revert to their winter routine; and under similar circumstances,
+Buntings fail to sing and temporarily desert their territories. In such
+cases it is clear that the impulse to seek isolation ceases for a time
+to dominate the situation. The inference, therefore, is that atmospheric
+changes bear some relation to the functioning of the instinct; but
+whether it be temperature, or humidity, or the direction and velocity of
+the wind, or a combination of two or more of these factors that supplies
+the stimulus, we cannot tell.
+
+The appropriate organic condition and the stimulus have then still to be
+determined, and we must pursue our inquiry from the point at which the
+impulse comes into functional activity. We will take a simple case, and
+one free from complication.
+
+Let us suppose that there is an area bereft of bird life, if it can be
+so imagined, but in proximity to other inhabited areas. Into this area,
+whilst in search of isolation, let us imagine that a Yellow Bunting
+finds its way. After the manner of its race it establishes a territory
+and occupies, let us say at a low computation, half an acre of ground.
+It then obtains a mate, breeds, and rears offspring, two of which we
+will assume are males. Reproduction ended, the birds desert the area,
+and in the following spring, when the impulse again asserts itself,
+parents and offspring seek again their former haunts. We now have three
+males, each of which occupies half an acre, and each of which rears two
+offspring--that is the position at the close of the second year. In the
+third year the number will have increased to nine and the area occupied
+to 4-1/2 acres; and so on in succeeding years, until by the beginning of
+the eleventh year, we have 59,048 Yellow Buntings occupying 29,524-1/2
+acres or 46 square miles. This, then, will be the result of the
+operation of the impulse, providing that all the individuals survive and
+that no complications supervene.
+
+But of course complications are numerous, some of which retard while
+others accelerate the rate of expansion. These complications arise from
+various sources--in the first place from natural enemies which prey upon
+the birds or upon their eggs; in the next place from climate which, if
+it happens to be unfavourable, may mean that food is scarce and that
+only a small percentage of the young survive; and lastly from
+rivals--and by rivals I mean closely related forms that require a
+similar station and similar food--which, by occupying available ground,
+may check expansion, or, by forcing a continuation of the search, may
+widen it.
+
+Now when individuals fail as many do fail in their initial attempt to
+secure territory, the activity of the impulse still persists, and there
+is no control over the direction in which the bird continues to wander
+whilst in search of its end. Some therefore seek in this direction,
+others in that; some wander inwards into inhabited areas and fail to
+find accommodation, or, according to the relative strength of their
+impulse, perhaps succeed and so set free a new competitor, others wander
+outwards into country uninhabited by the species. These latter we will
+call "pioneers." They may find accommodation within a comparatively
+short distance of their base, or they may come into competition with
+rivals and fail, not necessarily on account of any congenital weakness
+of ability, but because being warned by an alien song, they may be
+precluded from coming into contact with just the environing conditions
+which can supply the stimulus and allow behaviour to run its further
+course--and so be obliged to extend their search into remoter districts.
+But it must not be overlooked that they will be placed in a most
+advantageous position so far as the attainment of reproduction is
+concerned. In their search for territory they will meet with little
+opposition and will be free to select whatsoever ground they will; and
+be free also from intrusion by neighbouring males, which is so frequent
+in occurrence and continues for so long in congested areas. Moreover, in
+thinly populated districts, the pressure upon the available means of
+support will not be so great, neither will natural enemies be so
+plentiful; and since the offspring, guided by prior experience, return
+to the neighbourhood of their birthplace, the advantages thus gained
+will be shared by the succeeding generation. It follows, then, that the
+range of a species will not always be continuous, will not, that is to
+say, proceed by a series of successive steps, but that sometimes in this
+direction and at other times in that, the chain of territories will be
+interrupted and different individuals separated by distances of greater
+or lesser extent. New colonies will thus come into being; and as the
+unlimited increase of the population over limited areas gradually
+reintroduces into them the struggle for territory, new centres of
+distribution, where the process will repeat itself and from which
+expansion will proceed afresh, will be formed. Hence, though it is
+clearly impossible for the progeny of one pair of Yellow Buntings to
+overspread the whole of the 46 square miles, it is by no means
+impossible for the limits of their range to exceed even those limits
+within the eleven years.
+
+To sum up our knowledge regarding this phase. Of the organic condition
+which renders the impulse responsive to stimulation we know very little;
+and though certain facts of observation seem to indicate the direction
+in which the stimulus is to be found, we must here again confess to much
+ignorance. So far as can be seen, however, the impulse to seek isolation
+with its correlative territory, leads to constant modification in the
+breeding range of most species. The occupation of the small space of
+ground which each individual requires, the extent of which has been
+gradually adjusted to suit the needs of different species, results in
+expansion not only in one direction but in every direction, and not only
+in one season but in every season. And if there were no complications in
+the external world this expansion would proceed, as we have seen, with
+astonishing rapidity. But complications, some of which are favourable
+and others unfavourable, are numerous, and it is difficult to estimate
+their importance or to indicate their precise effect; the former,
+however, accelerate the rate of expansion, whilst the latter retard it.
+Those individuals that wander outwards and seek territory on the
+outskirts of the range we have called "pioneers." They will have
+advantages over others that, wandering inwards, seek isolation in
+congested districts, and will succeed where the latter fail; and since
+there is in the young an innate ability to return to the district
+wherein they were reared, the advantages so gained may be said to be
+handed on from generation to generation.
+
+Let us now turn to the contra-phase, and endeavour to ascertain whether
+the gregarious instinct bears any relation to the seasonal desertion of
+the breeding ground. The conclusion at which we have already arrived
+regarding this instinct is that it forms part of the inherited nature of
+most species; that its functioning is suppressed when a bird is actually
+in occupation of a territory; and that it is serviceable in promoting
+the welfare of the individual. We cannot of course observe the instinct.
+What we observe, when reproduction is ended, is a change in the
+relations of different individuals; instead of arousing mutual
+hostility, they attract one another, from which we infer the existence
+of something which determines their conduct, and this "something" we
+speak of as an instinct.
+
+To what does this change lead? Let us suppose that there is an area
+inhabited by one species; that the number of inhabitants has reached the
+maximum that the means of sustenance will allow; and that the season of
+reproduction is drawing to a close. The position will then be as
+follows. All the available breeding ground is divided into territories;
+each territory is occupied by one unit, the family, and each individual
+is able to fend for itself; changes both internal and external begin to
+take place, the gregarious instinct comes into functional operation, and
+the supply of food diminishes--that roughly is the position. The
+internal factor operates so that the sight of this individual or the
+call of that, instead of evoking hostility as heretofore and keeping
+different units apart, proves now an irresistible attraction; so that in
+place of a number of individuals evenly dispersed over the whole of this
+area, a small number of flocks of various dimensions are stationed at
+certain points, which points are determined partly by experience, partly
+by the supply of food, and partly by accident. This implies for each
+individual some movement in some direction. But since the population of
+this imaginary area has reached the maximum, and the supply of food,
+though limited in distribution, is nevertheless plentiful, such
+movements will be irregular and will proceed in no definite direction.
+
+Now let us suppose that the breeding range extends and that fresh ground
+is occupied by pioneers. When reproduction and the rearing of broods are
+ended and the gregarious instinct becomes dominant, these pioneers, or
+at least some of them, will revisit the area wherein formerly they
+associated with companions. Their offspring, however, though they will
+have the inherited impulse and the innate tendency, will not have the
+experience; how then will they behave? There can be no doubt that some
+will accompany the older birds, and, being led by them, will share the
+experience of a former generation; nor any question that others will
+collect together in the neighbourhood of their birthplace and, if their
+impulse is satisfied, will remain there so long as food is to be found.
+Thus the gregarious instinct, working in close relation with acquired
+experience, will on the one hand lead to the formation of organised
+movements in certain directions, whilst on the other it will lead to the
+formation of new areas of association which will follow in the wake of
+the expansion.
+
+We have assumed, in the imaginary case which we have just taken, that
+the conditions in the external world are such as enable the birds to
+endure throughout the year--in short, that there are no complications
+regarding the supply of food. But we must bear in mind that so long as
+conditions are favourable during the period of reproduction, which is of
+short duration, the breeding range can continue to expand, and that
+therefore, in the course of centuries, regions will come to be occupied
+wherein, owing to alternations of climate or physical changes in the
+surface of the earth, food will be impossible, or at any rate difficult
+to obtain at certain seasons. Hence there will come a time when the area
+of association ceases to follow in the wake of the expansion, and the
+breeding area begins to diverge from the subsistence area.
+
+How, then, is the gulf between these two areas to be bridged? We can of
+course say that those individuals which, in virtue of some slight
+variation of hereditary tendency, return to regions where food is
+plentiful will survive; whilst others, less well endowed, will perish.
+We can state the position in some such general terms, and doubtless
+there would be truth in the statement, but it does not carry us far; we
+wish to know more of the nature of the tendency, and of the manner in
+which it has evolved. Well now, in this new situation which arises, two
+things are apparent--that the struggle for existence becomes a struggle
+for the means of subsistence, and that anything in the inherited
+constitution of the bird which can be organised to subserve the
+biological end in view becomes of selection value. So long as food can
+always be procured in the new areas of association, the individuals that
+behave in accordance with ancestral routine gain thereby no particular
+advantage; but directly the breeding range extends into regions where
+the supply fluctuates, traditional experience becomes a factor in
+survival, and those individuals that come under its influence will, on
+the average, be more likely to endure and so to procreate their kind and
+maintain the tradition. Let it once be granted that there is an innate
+capacity to retain in later phases of routine the experience gained in
+earlier phases, and it is difficult to see how traditional guidance can
+be refused recognition as a factor in the developing situation. But only
+_a_ factor, and by no means the most important one; for observation has
+shown that the young are capable of performing the return journey
+without guidance. Something therefore _is_ inherited, some impulse
+which comes into functional activity at a specified time, and leads the
+bird to set forth in a given direction.
+
+There are no grounds for supposing that the experience of one generation
+forms any part of the hereditary equipment of subsequent generations. In
+what direction then are we to look for the congenital factor? What is
+given is an inherited tendency to co-operation and mutual help, and an
+innate capacity to make use of the results of experience. The inherited
+tendency, as we have seen, leads on the one hand to the formation of new
+areas of association, whilst on the other, since it is the means of
+bringing isolated individuals into contact, it leads to experience being
+handed on from generation to generation, which, in its turn, results in
+a certain amount of backward movement along the line of expansion. It
+forms part of the hereditary equipment of many species, and is
+serviceable in promoting the welfare of the individual. Moreover, there
+is reason to believe that its origin dates back to an early period in
+the evolution of the higher forms of life; and if in the subsequent
+course of evolution it could have been so organised as to serve a double
+purpose, so much the more reason would there have been for its survival.
+In what does the instinct consist? Is it merely that the sight of this
+individual or the call of that proves at some particular moment an
+irresistible attraction, or does the appropriate organic condition give
+rise, as is generally supposed, to some preceding state of uneasiness?
+In the former case, the temporarily isolated individual or colony would
+have but little chance of sharing in the benefits which mutual
+association confers upon the associates; in the latter, the feeling of
+discomfort would lead to restlessness, and would thus bring the bird
+into touch with the environing circumstances under which instinctive
+behaviour could run its further course. So that it is probable that the
+movements of each individual, prior to its becoming a unit in the flock,
+are not accidental but are determined in some measure by racial
+preparation.
+
+Now if the fundamental assumption of the doctrine of the struggle for
+existence be true, the gregarious instinct will not be quite alike in
+all the members of different broods, nor even in each member of the same
+brood; that is, variation will occur in all possible directions. And we
+shall not, I think, exceed the limits of probability if we assume that
+different individuals vary in the persistency with which they strive to
+attain their unknown end, and in the direction in which they travel in
+pursuit of it. So that in each generation they will fall into three
+classes: (1) those which are inert, (2) those which wander along the
+line of expansion, (3) those which wander in other directions. If then
+the struggle for life at this particular juncture in the evolution of
+the breeding range is a struggle for the means of subsistence, the
+members of these three classes will not be in a like satisfactory
+position so far as the competition for food is concerned. Those in the
+first class--_i.e._, those in which the activity feelings are weak--will
+neither gain the benefits which arise from mutual help, nor will they
+have much prospect of enduring through the season of scarcity. Those in
+the third class will, it is true, derive some assistance one from
+another, and so be in a better position to discover what food may be
+available; but inasmuch as they will remain in regions where the climate
+alternates and the supply of food is liable to fall below the minimum
+required, the chances are that a high percentage will fail in the
+struggle for existence. We come now to those in the second class, and it
+is upon them that I wish more particularly to focus attention. The
+initial movement in their case will be in the direction from which
+outward expansion has all along taken place. Within a comparatively
+short distance they will reach districts where the species is plentiful,
+and here, associating with others that have some traditional experience,
+they will be guided by them and will find themselves in regions where
+food is plentiful. Hence in each generation those will survive that,
+owing to some congenital variation of their instinct, seek satisfaction
+for their impulse in a direction which brings them under the influence
+of tradition. And though at first but slight and not in themselves of
+survival value, such variations, since they coincide with modifications
+of behaviour due to acquired experience, will be preserved and in the
+process of time so accumulated as to be capable of determining the
+direction and extent of the movement.
+
+But the young Cuckoo deserts this country many weeks after its parents,
+and there is no reason to suppose that it lives in society when
+eventually its destination is reached; and the young Falcon passes to
+the south, and is certainly not gregarious--how then can we explain
+their behaviour in terms of something which they show no signs of
+possessing? I do not wish to make light of a difficulty which
+admittedly, at first sight, is a grave objection to the view that the
+gregarious instinct has been operative in the manner here claimed for
+it. It must, however, be borne in mind that this instinct, though
+originally developed to serve the purpose of mutual protection, supplies
+the material upon which evolution works when the extension of the
+breeding range creates a situation requiring readjustment on the part of
+the organism to new conditions of life; and that those variations which
+can be so modified as to be in useful relation to the new environmental
+circumstances are seized upon by natural selection and, being
+transmitted, form the foundation of a specific inherited response, no
+longer dependent upon, though operating in close relation with the
+primitive response whence originally it sprang. Thus the primordial
+instinct becomes so organised as to serve a secondary purpose, that of
+rendering secure a means of access to a certain food supply. In the
+course of evolution species were bound to arise which, owing to some
+peculiar conditions, derived greater advantage from living solitary than
+from living in society. Does it then follow, because such species
+manifest no inclination to live in society, that the instinct never has
+played any part in their lives? Or because the primary purpose has
+lapsed, does it follow that the secondary no longer exists?
+
+
+Let me recapitulate the principal considerations which I have discussed
+in this chapter.
+
+Though I have been advancing a theory, and though I have taken much for
+granted, yet it will, I think, be admitted that both the theory and what
+has been taken for granted rest on observational grounds. As our
+starting-point we have a bird whose inherited nature alternates
+according to the season, and in whose nature we can distinguish two
+contra-phases--the one to live in society, the other to live solitary.
+While both have their part to play in furthering the life of the
+individual, for biological interpretation there is only one end, the
+prospective value of which is the continuance of the race. We may say
+that the latter phase is the more important of the two because it is
+directly concerned with reproduction. But we shall make a great mistake
+if we attach peculiar importance to one phase, or to one mode of
+behaviour within that phase, or to one action within that mode of
+behaviour; for if there is one thing certain it is that the whole is an
+inter-related whole in which each part depends for its success upon that
+which precedes it.
+
+In that phase in which the territory is the central feature of the
+situation, the struggle for existence is in operation in its acutest
+form; all the congenital and acquired capacities of the bird--pugnacity,
+song, capacity to utilise in later phases the experience gained in prior
+phases, all these are organised to subserve an end--a proximate
+end--which in its simplest terms may be described as "isolation."
+Isolation is then the first step in the process of reproduction, and any
+individual that fails to make it good, fails to procreate its kind. But
+isolation implies separation, and the degree of separation varies in
+different species, from the few square feet of cliff required by the
+Guillemot to the few square miles of barren moor over which the
+Peregrine exercises dominion. One species must occupy sufficient ground
+to enable it to secure food for its young; another requires sufficient,
+but no more, upon which to deposit its egg; and a third must secure a
+position for its nest within the community. Hence it follows that the
+degree of separation varies with the conditions of existence. Since,
+however, the conditions in the external world are constantly changing
+according to the relative abundance or scarcity of enemies, the rise or
+fall of rivals, the physical changes in the earth's surface, and the
+alterations of climate, it is clear that isolation can only be obtained
+with difficulty, and that the competition for it must be severe. Some
+individuals therefore fail to breed, whilst others, perhaps because
+their impulse is stronger, persevere and seek stations elsewhere. What
+are their prospects of finding them? By extending the field of their
+activities, they will wander into districts remote from the scene of
+competition, districts where not only food is plentiful but where
+enemies and rivals are scarce; and to these pioneers, if to any, success
+in reproduction will most certainly be assured. But not only is it they
+who will benefit; their offspring also, when the time comes for them to
+take their part in the maintenance of the race, will share in the
+success of their parents, for even though they may not escape
+competition from individuals of closely related forms, they will meet
+with but little from those of their own kind. Now species which live
+throughout the year in the vicinity of their territory are comparatively
+few, the majority are obliged to wander in search of food so soon as
+reproduction is ended, and their behaviour is determined not only by its
+abundance or scarcity, but also by the powerful gregarious impulse which
+waxes in proportion as the instincts connected with reproduction wane.
+If, then, when the sexual instinct again becomes predominant, the
+experience of the former season nowise affects their movements, little
+or no progress will be made in the expansion of the range. But just as a
+certain entrance into the bush and pathway through it, when once made
+use of in the process of building, becomes so firmly established as to
+form the sole highway to and from the nest, so likewise, when the
+impulse to seek isolation repeats itself, the bird is constrained to
+seek the neighbourhood wherein it had experienced the enjoyment of
+breeding or of birth. Thus the little that is added one year becomes the
+basis for further additions in the next, and new centres of distribution
+are continually being formed from which expansion proceeds anew.
+
+Now as the range gradually extends into regions where the climate
+alternates and food at certain seasons is consequently scarce, the
+distance between the customary area of association and that of
+reproduction must perforce widen. The question then arises: How will the
+young that have no experience find their way to regions wherein they can
+endure? The forces which may have been organised to subserve the end in
+view are three: (1) Acquired experience, (2) tradition, (3) the
+gregarious instinct. The pioneer that carries the range a little further
+forward starts from a base where it has associated with companions and
+found food plentiful; and when the impulse to live in society again
+asserts itself, it not only repeats its former experience but hands on
+the habit thus acquired to those of the next generation that happen to
+accompany it. Granting, however, that by successive increments in the
+distance traversed, traditional guidance may in time accomplish much, it
+cannot account for all the known facts, it cannot at any rate explain
+the fact that in some cases the inexperienced offspring finds its way to
+the food area without guidance. Something, therefore, _is_ inherited.
+And my suggestion is this: That the gregarious instinct, the ancient
+origin of which we can infer from its manifestation in so many and
+diverse forms of life, supplies the material upon which evolution works;
+that variations of the initial impulse, at first slight and not in
+themselves of selection value, in so far as they coincide in direction
+with modifications of procedure due to experience or tradition, are
+preserved; and that, in the process of time, they are so accumulated as
+to form a specific congenital endowment determining a definite mode of
+behaviour.
+
+
+  FOOTNOTES:
+
+  [1] June 1915, R. M. Barrington.
+
+  [2] _Dictionary of Birds_, p. 556.
+
+  [3] _Social Psychology._
+
+  [4] _Manual of Psychology._
+
+  [5] _Ibis_, April 1918.
+
+  [6] _Zoologist_, 1912, p. 327.
+
+
+
+
+  INDEX
+
+
+  Acquired experience, 300
+
+  Adjustments, transitory, of distribution, 275
+
+  Alarm notes, 119
+
+  Arrival, advantages and disadvantages of late, 33-44
+
+  Assemblies in winter, 262, 263
+
+  Assembly grounds, 173
+
+  Attainment of reproduction, 171
+
+
+  Barrington, R. M., on the sex of migrants, 25
+
+  Battle between two male Cuckoos, 82
+
+  ---- between two Moor-Hens, 86, 92, 93, 94
+
+  ---- ---- Pied Wagtails, 86
+
+  ---- ---- Raven and Buzzard, 217
+
+  ---- ---- Raven and Peregrine, 216
+    law of, 13,19
+
+  Behaviour routine, 262
+
+  ---- sexual, 3
+
+  Bickerings, 96
+
+  Birthplace, return to, 43, 50
+
+  Blackbird, 87, 182, 222, 244
+
+  Blackcap, 81, 156, 224, 230
+
+  Black Grouse, 63
+
+  Black-tailed Godwit, 53
+
+  Boundaries, 1, 5
+
+  ---- conflicts for retention of, 7, 62
+
+  ---- disputes as to, 1
+
+  Brambling, 124
+
+  Breeding ground, search for appropriate, 270, 271
+
+  ---- range, extension of, 291-92
+
+  ---- site, acquirement of, 3
+
+  ---- stations, evolution of, 15-19
+
+  ---- ---- repeatedly visited long before nesting-time, 64
+
+  ---- territory, 2, 3, 7
+
+  ---- ---- evolution of, 18
+
+  ---- ---- foundation of, 7
+
+  ---- ---- innate capacity to return to former, 279-81
+
+  Bridled Guillemot, 64
+
+  Brooding, 180
+
+  ---- impulse, 191
+
+  Bunting, Cirl, 28, 140
+
+  ---- Corn, 28
+
+  ---- Reed, 28, 68, 69, 85, 104, 132, 158, 160, 244
+
+  ---- Yellow, 28, 30, 47, 64, 140, 159, 162, 183, 187, 188, 189,
+    235, 236, 286
+
+  Buzzard, 217
+
+
+  Capacity, innate, to return to former breeding territory, 279-81
+
+  Carrion Crow, 226
+
+  Chaffinch, 28, 31, 32, 33, 45, 87, 103, 156, 159, 235, 236, 244
+
+  ---- Donegal, 160
+
+  Change of breeding quarters owing to unsuitableness, 50
+
+  Chiffchaff, 49, 51, 80, 139, 140, 221, 224, 244
+
+  Cirl Bunting, 28, 140
+
+  Clarke, W. Eagle, _Studies in Bird Migration_, 24
+
+  Cleanliness of nest, 180
+
+  Cliff-breeding species, 63
+
+  Climatic changes, alteration of routine, due to, 284
+
+  ---- changes, food dependent on, 283
+
+  ---- conditions, influence of, 20
+
+  Communities, 202
+
+  ---- birds after breeding-season remain in, 265-67
+
+  Competition, female, for males, 13
+
+  Complexity of strife, 84-85
+
+  Conflicts between males during the mating period, 74, 86
+
+  ---- between males during the nesting period, 87
+
+  ---- for areas, 10, 11, 13, 62
+
+  ---- of Ruff, 54
+
+  ---- sexual, 10
+
+  Congenital disposition, 135
+
+  Contests between males for possession of females, 80
+
+  Coot, 61
+
+  Corn-Bunting, 28
+
+  Corncrake, 39
+
+  Crow, Carrion, 226, 227
+
+  Crow, Hooded, 202
+
+  Cuckoo, 52, 82, 144, 296
+
+  ---- restricted breeding area, 52
+
+  Curlew, 119, 138, 140, 250, 262, 263, 265, 273
+
+
+  Danger warnings, 269
+
+  Darwin, C., _Descent of Man_, 35
+
+  ---- on the arrival of males before females, 35
+
+  Defence of territory, 6
+
+  Development, sexual, 6
+
+  Disposition, congenital, 135
+
+  ---- functioning of, 74
+
+  ---- inherited, 5
+
+  ---- to defend the territory, 73-118
+
+  ---- to mate, 27
+
+  ---- to remain in a particular place in a particular environment, 6
+
+  ---- to secure a territory, 6, 20-72
+
+  Distribution, adjustment of, 275
+
+  Dove, Turtle, 126, 232
+
+  Dunlin, 250
+
+
+  Emotional behaviour, 53, 82, 114
+
+  ---- manifestation, 90, 283
+
+  ---- response, 26
+
+  Enemies, 282
+
+  Energy, waste of, 219
+
+  Environment, 6
+
+  ---- and food, 56
+
+  ---- changes of, 283
+
+  ---- external, conditions in, 279, 282
+
+  Equipment, hereditary, 6
+
+  Evolution of breeding stations or territory, 15, 19
+
+  ---- of the territory, 176
+
+  ---- of the voice, 163
+
+  Existence, struggle for, 294
+
+  Experience, acquired, 300
+
+  Experiments, removal of nests for, 181, 185, 190, 213, 214
+
+  Exposure, its effect on nestlings, 180
+
+  External environment, conditions in, 279, 282
+
+
+  Falcon, 48, 71
+
+  Feeding grounds, neutral, 125 in communities, 70
+
+  Females, fighting amongst, 109-118
+
+  ---- sexual impulse of, 13
+
+  Fieldfare, 124
+
+  Fighting instinct, 79, 82
+
+  Flight, emotional behaviour of Godwit during, 53
+
+  Flocks, in winter, birds collect together in, 262
+
+  Flycatcher, 244
+
+  Food, procuring of, 5
+
+  ---- abundance, or scarcity of, its relation to prosperity of young,
+         15, 16
+
+  ---- its bearing, on the movement of flocks, 262
+
+  ---- rearing of young dependent on rapid and regular, 179, 195
+
+  ---- supply, proximity to, necessary for rearing young, 179, 195
+
+  Fortuitous mating, 174
+
+  Fowler, Ward, on the value of communities, Rooks, 202
+
+  Fulmar, 121, 247
+
+  Functional activity, 259
+
+  ---- instinct of Reeve, 173
+
+  Functioning of the disposition, 275
+
+  ---- of the primary dispositions, 100
+
+
+  Garden Warbler, 223, 225, 230
+
+  Gätke, H., _Birds of Heligoland_, 24
+
+  ---- on the absence of song in birds on Heligoland, 124
+
+  ---- on the early arrival of Guillemots on Heligoland, 64
+
+  Godwit, emotional behaviour of, during flight, 53
+
+  ---- Black-tailed, 53
+
+  Grasshopper Warbler, 39, 131, 139, 153, 155, 187, 244
+
+  Greenfinch, 28, 33, 140, 235, 236
+
+  Gregarious instinct, 20, 61, 141, 265-66, 269, 276, 289, 290, 291,
+    296, 300
+
+  Grouse, Black, 63
+
+  Guillemot, Bridled, 64
+
+  ---- Common, 63, 64, 121, 192, 195, 206, 211, 247
+
+  ---- Ringed, 64
+
+  Gull, Common, 119
+
+  ---- Herring, 210, 278
+
+
+  Habit formation, law of, 8, 62, 65, 66, 67, 205
+
+  Hawfinch, 28
+
+  Headquarters, 176, 206, 207, 274
+
+  ---- restricted, 8, 9, 30, 50, 58, 64, 127
+
+  Hedge-Sparrow, 213, 221, 244
+
+  Hereditary equipment, 6
+
+  Herring-Gull, 210, 278
+
+  Hooded-Crow, 202
+
+  Hostility and territory, relationship between, 242
+
+  House-Sparrow, 218
+
+
+  Imitation, vocal, powers of, 156, 157, 161
+
+  Impulse, internal, 279
+
+  ---- to brood, 191
+
+  Inherited disposition, 5
+
+  Instinct, fighting, 79-82
+
+  ---- gregarious, 20, 61, 141, 265, 266, 269, 276, 289, 290, 291, 296,
+         300
+
+  ---- migratory, 37
+
+  ---- of song related to establishment of territory, 125
+
+  ---- sexual, reawakening of, 4, 18
+
+  Instinctive response, 180
+
+  Instincts susceptible to stimulation, 259
+
+  Internal impulse, 279
+
+  Internal stimulation, 62, 123
+
+  Interpretation of battles, 75
+
+  Intolerance of other birds, 218, 219
+
+  Intrusion resented, 274
+
+  Isolation, impulse to seek, 288
+
+  ---- of male, 12, 62, 65, 73, 81
+
+  ---- of male during breeding season, 267, 272, 273, 275, 281
+
+
+  Jay, 87, 156, 283
+
+
+  Kestrel, 228
+
+  Kittiwake, 116, 200, 247
+
+
+  Lapwing, 58, 59, 61, 62, 64, 84, 103, 104, 126, 189, 190, 220, 251, 284
+
+  Lapwing, life-history of, 58-61
+
+  Late arrival, advantages and disadvantages of, 33-44
+
+  Law of battle, 74, 75, 86
+
+  Lesser Whitethroat, 230, 244
+
+  Linnet, 156
+
+
+  M'Dougall, Dr, _Social Psychology_, 77
+
+  Magpie, 219, 283
+
+  Males arrive before advent of females, 24
+
+  Marsh-Warbler, 39, 40, 52, 81, 132, 140, 153, 155, 156, 165, 225
+
+  Martin, 201, 218
+
+  Mating, difficulties of, 172
+
+  ---- fortuitous, 174
+
+  Maximum number supportable in a given locality, 49
+
+  Meadow-Pipit, 188
+
+  Meeting places for antics, 54, 63
+
+  Mental Image, 77
+
+  Merlin, 227
+
+  Migration, 3-4
+
+  ---- distance no criterion, 279
+
+  ---- its relation to territory, 259
+
+  Migration, origin of, 260, 277
+
+  ---- phenomenon of, 277
+
+  Migratory instinct, 37
+
+  ---- species more highly specialised than resident species, 56
+
+  Missel-Thrush, 21
+
+  Mobility of the land and stability of the water, 260
+
+  Moor-hen, 61, 85, 103, 218, 250, 251
+
+  Morgan, Professor Lloyd, on instinctive behaviour, 74
+
+  ---- on emotional behaviour, 114
+
+
+  Nest, cleaning of, 180
+
+  ---- construction of, 3
+
+  Nests, removal of, for experiments, 181, 185, 190, 213, 214
+
+  Neutral feeding grounds, 62, 125
+
+  ---- ground, 98
+
+  Newton, E., on the arrival at breeding stations of males before female,
+    24, 35
+
+  Nightingale, 39, 156
+
+  Notes of alarm, 119
+
+  ---- of anger, 119
+
+  ---- of recognition, 139
+
+  ---- of warning, 119, 139, 141, 145, 151, 153
+
+
+  Offspring, rearing of, 3, 4
+
+  Organic change, sexual, 92, 123
+
+  ---- changes, 65
+
+  ---- condition of Reeve, 173
+
+  Owl, Wood, 156
+
+
+  Paired for life, 55-56
+
+  Parental instinctive response, failure of, 185
+
+  Partridge, 87, 218
+
+  Persecution, Carrion Crow and Magpie, 226
+
+  Persecution, Carrion Crow and Rook, 227
+
+  ---- House Sparrow and Martin, 218
+
+  ---- Lapwing and Snipe, 220
+
+  ---- Raven and Buzzard, 217
+
+  ---- ---- and Peregrine, 216
+
+  ---- Starling and Woodpecker, 218, 237
+
+  Persistency to remain in territory, 68
+
+  Pied-Wagtail, 86, 155
+
+  Pigeon, Wood, 219
+
+  Pipit, Meadow, 188
+
+  ---- Tree, 51, 188, 189, 222, 244, 278
+
+  Polyandrous females, 144
+
+  Predatory species, 268
+
+  Promiscuous pairing of Ruffs, 172
+
+  Proximity to food-supply necessary for rearing young, 179, 195
+
+  _Psychology, Manual of_, 1
+
+  Puffin, 63, 116, 200
+
+  Pugnacious instinct, 87-109
+
+  Pugnacity, 11, 62
+
+  ---- of females to obtain mates, 109-118
+
+  ---- of males, prior to mating-season, 77-81
+
+  ---- of Moor-Hen, 218
+
+
+  Racial preparation, 41, 43, 46, 67, 205, 206, 266
+
+  Rail, Water, 218
+
+  Raven, 48, 202, 216
+
+  Razor-bill, 63, 64, 200, 247
+
+  Readjustment of territory, 146
+
+  Rearing of offspring, 3, 4
+
+  Red-backed Shrike, 39, 50, 51, 156
+
+  Redbreast, 47
+
+  Redshank, 139
+
+  Redwing, 124
+
+  Redstart, 230, 244
+
+  Reed-Bunting, 28, 68, 69, 85, 104, 132, 156, 158, 160, 244, 246, 273
+
+  Reed-Warbler, 49, 51, 68, 81, 132, 140, 152, 153, 211, 225
+
+  Reeve, 171
+
+  Relation of song to the territory, 119-68
+
+  ---- of territory to migration, 259
+
+  ---- of territory to the system of reproduction, 169-214
+
+  Relationship to a territory, 169
+
+  Reproduction, 14, 15
+
+  ---- and territory, 169-214
+
+  ---- attainment of, 2, 6, 37
+
+  ---- goal of, 6
+
+  Ringed Guillemot, 64
+
+  Robbery of territory, 104-107
+
+  Rock-formation, suitability for Guillemots nesting on, 196
+
+  Rook, 202, 227
+
+  Routine behaviour, 262
+
+  Ruff, 54, 63, 172
+
+  ---- meeting places for conflicts, 54
+
+  Ruffs, promiscuous pairing of, 172
+
+
+  Savi's Warbler, 139
+
+  Sedge-Warbler, 25, 44, 152, 226, 244
+
+  Selous, E., on the life-history of Ruffs and Reeves, 172
+
+  ---- on meeting places for conflicts and antics, 54
+
+  ---- on the meeting places of Black Grouse, 63
+
+  Service, Robert, on flocks of unmated Sedge-Warblers, 44, 45
+
+  Sexual behaviour, 3
+
+  ---- conflicts, 10
+
+  ---- development, 6
+
+  ---- function, discharge of, 2, 3, 26
+
+  ---- impulse of females, 13
+
+  Sexual instinct in the migratory male, 26
+
+  ---- of Reeve, 173
+
+  ---- ---- reawakening of, 4, 18
+
+  ---- life of birds, 1
+
+  ---- maturity, males arrive at, before females, 36
+
+  ---- organic change, 92, 123
+
+  ---- selection, 166
+
+  Shag, 121
+
+  Shrike, Red-backed, 39, 50, 51, 156
+
+  Skylark, 188, 236, 244
+
+  Snipe, 153, 156, 219, 220
+
+  Sociability when not paired, 125, 126
+
+  Song, as an aid in searching for a mate, 12
+
+  ---- its influence on mating, 167
+
+  ---- origin of, 138
+
+  ---- relation to reproduction, 123
+
+  ---- relation to territory, 119-168
+
+  ---- volume of, influenced by age, seasonal sexual development,
+         or isolation, 166
+
+  Song-Thrush, 222, 244
+
+  Sparrow, House, 218
+
+  Sparrow-Hawk, 269
+
+  Spring, at approach of, birds lose their shyness, 138
+
+  Stability of the water and mobility of the land, 260
+
+  Starling, 217, 218, 237, 251
+
+  Stimulation, internal, 62, 123
+
+  ---- question of, 284
+
+  Stonechat, 87 187, 188, 189, 222, 233, 234
+
+  Stout, Dr, _Manual of Psychology_, 1, 77
+
+  Struggle for existence, 294
+
+  Susceptibility to position, 96
+
+  Swallow, 21, 156, 278
+
+
+  Territory, 1, 5
+
+  ---- adjustment of, 10
+
+  Territory and reproduction, 169-214
+
+  ---- breeding, 2, 3, 7
+
+  ---- dates of acquisition of, 33
+
+  ---- defence of, 6
+
+  ---- desertion of, after rearing young, 276
+
+  ---- disposition to defend, 73-118
+
+  ---- disposition to secure, 6, 20-72
+
+  ---- establishment of, 74, 285
+
+  ---- evolution of, 176
+
+  ---- failure to secure, 286
+
+  ---- fights for, 10, 11, 13, 62
+
+  ---- ownership of, 189
+
+  ---- possession of, a stimulus to song, 136
+
+  ---- its relation to migration, 259
+
+  ---- its relation to reproduction, 169-214
+
+  ---- readjustment of, 147
+
+  ---- restriction of, advantageous for mating, 172
+
+  ---- restricted, 8, 9, 30, 50, 58, 64
+
+  ---- separate for male and female Cuckoo, 144
+
+  ---- song, its relation to the, 119-68
+
+  ---- temporary desertion of, 28, 35, 58, 59
+
+  ---- and hostility, relationship between, 242
+
+  Thrush, Song, 222, 244
+
+  Tit, Blue, 221, 226
+
+  ---- Great, 221
+
+  ---- Long-tailed, 226
+
+  Tradition, 300
+
+  Tree-Pipit, 51, 188, 189, 222, 232, 244, 278
+
+  Turtle-Dove, 126, 232
+
+
+  Union of sexes, 12
+
+  Ussher, H. B., on the hostility between Choughs and Hooded Crows
+    and Choughs and Ravens, 227
+
+
+  Vocal Imitation, 156, 157, 161
+
+  Voice calls of Curlew, 263
+
+
+  Wagtail, Pied, 86, 155
+
+  ---- Yellow, 278
+
+  Wanderings from land, Guillemots, 193
+
+  Warbler, Garden, 223, 225, 230
+
+  ---- Grasshopper, 39, 131, 139, 155, 187, 244
+
+  ---- Marsh, 39, 40, 52, 81, 132, 140, 155, 156, 225
+
+  ---- Reed, 49, 51, 68, 81, 132, 140, 152, 153, 211, 225
+
+  ---- Savi's, 139
+
+  ---- Sedge, 25, 44, 152, 226, 244
+
+  ---- Willow, 25, 47, 50, 51, 80, 91, 140, 187, 211, 232, 244, 273
+
+  ---- Wood, 50, 51, 132, 221
+
+  Warfare between different species and its relation to the territory,
+    215-58
+
+  Warning notes, 119
+
+  ---- of danger, 269
+
+  Water Rail, 218
+
+  Wheatear, 25, 51
+
+  Whimbrel, 140
+
+  Whinchat, 39, 50, 51, 81, 222, 232, 233, 234, 244
+
+  Whitethroat, 25, 50, 68, 69, 124, 140, 182, 187, 189, 190, 213, 230,
+    244
+
+  ---- Lesser, 230, 244
+
+  Wild Duck, 250
+
+  Will, the, to fight, 102
+
+  Willow-Warbler, 25, 47, 50, 51, 80, 91, 140, 187, 211, 232, 244, 273
+
+  Winter assemblies, 262-63
+
+  Witherby, H. F., in _British Birds_, on the return to former
+    breeding-ground, 281
+
+  Wood-Owl, 156
+
+  Wood-Pigeon, 219
+
+  Wood-Warbler, 50, 51, 132, 221
+
+  Woodpecker, Lesser Spotted, 237
+
+  ---- Great Spotted, 237, 238
+
+  ---- Green, 20, 71, 156, 208, 218, 237
+
+  Wren, 244
+
+
+  Yellow Bunting, 28, 30, 47, 64, 140, 159, 162, 183, 187, 188, 189,
+    235, 236, 286
+
+  Young die in nest from exposure, 184, 185
+
+
+
+PRINTED BY OLIVER AND BOYD, EDINBURGH, SCOTLAND
+
+
+
+
+
+End of Project Gutenberg's Territory in Bird Life, by H. Eliot Howard
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+Bird Life
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+
+The Project Gutenberg EBook of Territory in Bird Life, by H. Eliot Howard
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: Territory in Bird Life
+
+Author: H. Eliot Howard
+
+Illustrator: G. E. Lodge
+             H. Grönvold
+
+Release Date: April 14, 2010 [EBook #31987]
+
+Language: English
+
+Character set encoding: UTF-8
+
+*** START OF THIS PROJECT GUTENBERG EBOOK TERRITORY IN BIRD LIFE ***
+
+
+
+
+Produced by Chris Curnow, Turgut Dincer, Joseph Cooper and
+the Online Distributed Proofreading Team at
+https://www.pgdp.net
+
+
+
+
+
+
+</pre>
+
+<p>&nbsp;</p>
+<div class="box">
+<p>TRANSCRIBER'S NOTE:<br />
+There are a large number of compound words in
+this book including bird names which occur joined,
+spaced and hyphenated. No attempt has been made to
+correct these discrepancies as these are mostly
+alternative spellingd of thw same word. In the case of bird names it
+is difficult to decide as ornithologists are
+still debating on this subject.</p>
+</div>
+
+
+<h3><br />TERRITORY IN BIRD LIFE</h3>
+
+<div class="figcenter" style="width: 500px;"><a name="f004" id="f004"></a><img src="images/fig004.jpg" width="500" height="808"
+alt="A pair of Lesser Spotted Woodpeckers
+attacking a Great Spotted Woodpecker." title="A pair of Lesser Spotted Woodpeckers
+attacking a Great Spotted Woodpecker" /></div>
+
+<h1>
+TERRITORY IN<br />
+BIRD LIFE</h1>
+
+<h3>BY H. ELIOT HOWARD</h3>
+
+
+<h4>WITH ILLUSTRATIONS BY<br />
+G. E. LODGE AND H. GR&Ouml;NVOLD</h4>
+
+<h5>NEW YORK<br />
+<big>E. P. DUTTON AND COMPANY</big><br />
+1920</h5>
+
+<p><span class='pagenum'><a name="Page_v" id="Page_v">v</a></span></p>
+<hr />
+<h3>PREFACE</h3>
+
+
+<p>When studying the Warblers some twenty
+years ago, I became aware of the fact that
+each male isolates itself at the commencement
+of the breeding season and exercises dominion
+over a restricted area of ground. Further investigation,
+pursued with a view to ascertaining
+the relation of this particular mode of behaviour
+to the system of reproduction, led to my studying
+various species, not only those of close affinity,
+but those widely remote in the tree of avian
+life. The present work is the outcome of
+those investigations. In it I have endeavoured
+to interpret the prospective value of the behaviour,
+and to trace out the relationships in
+the organic and inorganic world which have
+determined its survival. Much is mere speculation;
+much with fuller knowledge may be
+found to be wrong. But I venture to hope
+that a nucleus will remain upon which a more
+complete territorial system may one day be
+established.<span class='pagenum'><a name="Page_vi" id="Page_vi">vi</a></span></p>
+
+<p>I have to thank Mr. G. E. Lodge and Mr.
+H. Gr&ouml;nvold for the trouble they have taken
+in executing my wishes; I also want to record
+my indebtedness to the late E. W. Hopewell;
+and to Professor Lloyd Morgan, F.R.S., I am
+beholden more than I can tell.</p>
+<hr />
+<p><span class='pagenum'><a name="Page_vii" id="Page_vii">vii-viii</a></span></p>
+<h3>CONTENTS</h3>
+
+<table width="100%" summary="toc" border="0">
+<tr>
+<td class="left">&nbsp;</td>
+<td class="right"><small>PAGE</small></td>
+</tr><tr>
+<td class="center50" colspan="2">CHAPTER I</td>
+</tr><tr>
+<td class="left"><p class="indent"><span class="smcap">Introduction</span></p></td>
+<td class="right"><a href="#Page_1">1</a></td>
+</tr><tr>
+<td class="center50" colspan="2">CHAPTER II</td>
+</tr><tr>
+<td class="left"><p class="indent"><span class="smcap">The Disposition to Secure a Territory</span></p></td>
+<td class="right"><a href="#Page_20">20</a></td>
+</tr><tr>
+<td class="center50" colspan="2">CHAPTER III</td>
+</tr><tr>
+<td class="left"><p class="indent"><span class="smcap">The Disposition to Defend the Territory</span></p></td>
+<td class="right"><a href="#Page_73">73</a></td>
+</tr><tr>
+<td class="center50" colspan="2">CHAPTER IV</td>
+</tr><tr>
+<td class="left"><p class="indent"><span class="smcap">The Relation of Song to the Territory</span></p></td>
+<td class="right"><a href="#Page_119">119</a></td>
+</tr><tr>
+<td class="center50" colspan="2">CHAPTER V</td>
+</tr><tr>
+<td class="left"><p class="indent"><span class="smcap">The Relation of the Territory to the System of
+Reproduction</span></p></td>
+<td class="right"><a href="#Page_169">169</a></td>
+</tr><tr>
+<td class="center50" colspan="2">CHAPTER VI</td>
+</tr><tr>
+<td class="left"><p class="indent"><span class="smcap">The Warfare between Different Species and its
+Relation to the Territory</span></p></td>
+<td class="right"><a href="#Page_215">216</a></td>
+</tr><tr>
+<td class="center50" colspan="2">CHAPTER VII</td>
+</tr><tr>
+<td class="left"><p class="indent"><span class="smcap">The Relation of the Territory to Migration</span></p></td>
+<td class="right"><a href="#Page_259">259</a></td>
+</tr><tr>
+<td class="left"><p class="indent"><span class="smcap">Index</span></p></td>
+<td class="right"><a href="#Page_302">302</a></td>
+</tr></table>
+<hr />
+<p><span class='pagenum'><a name="Page_ix" id="Page_ix">ix</a></span></p>
+
+<h3>LIST OF ILLUSTRATIONS</h3>
+
+<table width="100%" summary="illustrations" border="0">
+<tr>
+<td class="left">&nbsp;</td>
+<td class="right2"><i>Faces page</i></td>
+</tr><tr>
+<td class="left"><p class="indent2">A pair of Lesser Spotted Woodpeckers attacking a Great
+Spotted Woodpecker</p></td>
+<td class="right2"><a href="#f004"><i>Frontispiece</i></a></td>
+</tr><tr>
+<td class="left"><p class="indent2">Territorial flight of the Black-tailed Godwit</p></td>
+<td class="right2"><a href="#f073">54</a></td>
+</tr><tr>
+<td class="left"><p class="indent2">Competition for territory is seldom more severe than
+individual Razorbills to secure positions on the
+among cliff-breeding seabirds, and the efforts of
+crowded ledges lead to desperate struggles</p></td>
+<td class="right2"><a href="#f089">64</a></td>
+</tr><tr>
+<td class="left"><p class="indent2">Male Blackbirds fighting for the possession of territory.
+The bare skin on the crown of the defeated bird shows
+the nature of the injuries from which it succumbed.</p></td>
+<td class="right2"><a href="#f101">74</a></td>
+</tr><tr>
+<td class="left"><p class="indent2">Male Cuckoos fighting before the arrival of a female</p></td>
+<td class="right2"><a href="#f111">82</a></td>
+</tr><tr>
+<td class="left"><p class="indent2">Two pairs of Pied Wagtails fighting in defence of their
+territories</p></td>
+<td class="right2"><a href="#f117">86</a></td>
+</tr><tr>
+<td class="left"><p class="indent2">Long-tailed Tit: males fighting for the possession of
+territory. The feathers have been torn from the crown
+of the defeated and dying rival</p></td>
+<td class="right2"><a href="#f129">96</a></td>
+</tr><tr>
+<td class="left"><p class="indent2">A battle between two pairs of Jays</p></td>
+<td class="right2"><a href="#f141">106</a></td>
+</tr><tr>
+<td class="left"><p class="indent2">The Female Chaffinch shares in the defence of the territory
+and attacks other females</p></td>
+<td class="right2"><a href="#f147">110</a></td>
+</tr><tr>
+<td class="left"><p class="indent2">Peregrine Falcon attacking a Raven</p></td>
+<td class="right2"><a href="#f255">216</a></td>
+</tr><tr>
+<td class="left"><p class="indent2">A battle between a pair of Green Woodpeckers and a
+Great Spotted Woodpecker for the possession of a hole
+in an oak-tree</p></td>
+<td class="right2"><a href="#f281">238</a></td>
+</tr>
+</table>
+<hr />
+<table width="100%" summary="illustrations" border="0">
+<tr>
+<td class="left"><p class="indent2">Plans of the Water-meadow showing the Territories
+occupied by Lapwings in 1915 and 1916</p></td>
+<td class="right2"><a href="#f080"><i>Between</i>&nbsp;58&nbsp;and&nbsp;59</a></td>
+</tr>
+</table>
+
+<hr />
+
+<p><span class='pagenum'><a name="Page_xi" id="Page_xi">x-xi</a></span></p>
+
+<h3>SCIENTIFIC NAMES OF BIRDS<br />
+MENTIONED IN THE TEXT<br /><br /></h3>
+
+<table width="100%" summary="scientific names" border="0">
+<tr>
+<td class="left50">Raven</td>
+<td class="left50"><i>Corvus corax.</i></td>
+</tr><tr>
+<td class="left50">Carrion-Crow</td>
+<td class="left50"><i>Corvus corone.</i></td>
+</tr><tr>
+<td class="left50">Hooded Crow</td>
+<td class="left50"><i>Corvus cornix.</i></td>
+</tr><tr>
+<td class="left50">Rook</td>
+<td class="left50"><i>Corvus frugilegus.</i></td>
+</tr><tr>
+<td class="left50">Magpie</td>
+<td class="left50"><i>Pica pica.</i></td>
+</tr><tr>
+<td class="left50">Jay</td>
+<td class="left50"><i>Garrulus glandarius rufitergum.</i></td>
+</tr><tr>
+<td class="left50">Chough</td>
+<td class="left50"><i>Pyrrhocorax pyrrhocorax.</i></td>
+</tr><tr>
+<td class="left50">Starling</td>
+<td class="left50"><i>Sturnus vulgaris.</i></td>
+</tr><tr>
+<td class="left50">Greenfinch</td>
+<td class="left50"><i>Chloris chloris.</i></td>
+</tr><tr>
+<td class="left50">Hawfinch</td>
+<td class="left50"><i>Coccothraustes coccothraustes.</i></td>
+</tr><tr>
+<td class="left50">House-Sparrow</td>
+<td class="left50"><i>Passer domesticus.</i></td>
+</tr><tr>
+<td class="left50">Chaffinch</td>
+<td class="left50"><i>Fringilla c&#339;lebs.</i></td>
+</tr><tr>
+<td class="left50">Brambling</td>
+<td class="left50"><i>Fringilla montifringilla.</i></td>
+</tr><tr>
+<td class="left50">
+Linnet</td><td class="left50"><i>Acanthis cannabina.</i></td>
+</tr><tr>
+<td class="left50">
+Corn-Bunting</td><td class="left50"><i>Emberiza calandra.</i></td>
+</tr><tr>
+<td class="left50">
+Yellow Bunting</td><td class="left50"><i>Emberiza citrinella.</i></td>
+</tr><tr>
+<td class="left50">
+Cirl Bunting</td><td class="left50"><i>Emberiza cirlus.</i></td>
+</tr><tr>
+<td class="left50">
+Reed-Bunting</td><td class="left50"><i>Emberiza sch&#339;niclus.</i></td>
+</tr><tr>
+<td class="left50">
+Sky-Lark</td><td class="left50"><i>Alauda arvensis.</i></td>
+</tr><tr>
+<td class="left50">
+Pied Wagtail</td><td class="left50"><i>Motacilla lugubris.</i></td>
+</tr><tr>
+<td class="left50">
+Tree-Pipit</td><td class="left50"><i>Anthus trivialis.</i></td>
+</tr><tr>
+<td class="left50">
+Meadow-Pipit</td><td class="left50"><i>Anthus pratensis.</i></td>
+</tr><tr>
+<td class="left50">
+Great Titmouse</td><td class="left50"><i>Parus major newtoni.</i></td>
+</tr><tr>
+<td class="left50">
+Blue Titmouse</td><td class="left50"><i>Parus c&#339;ruleus obscurus.</i></td>
+</tr><tr>
+<td class="left50">
+Long-tailed Titmouse</td><td class="left50"><i>&AElig;githalus caudatus roseus.</i></td>
+</tr><tr>
+<td class="left50">
+Red-backed Shrike</td><td class="left50"><i>Lanius collurio.</i></td>
+</tr><tr>
+<td class="left50">
+Whitethroat</td><td class="left50"><i>Sylvia communis.</i></td>
+</tr><tr>
+<td class="left50">
+<span class='pagenum'><a name="Page_xii" id="Page_xii">xii</a></span>
+Lesser Whitethroat</td>
+<td class="left50"><i>Sylvia curruca.</i></td>
+</tr><tr>
+<td class="left50">
+Blackcap</td>
+<td class="left50"><i>Sylvia atricapilla.</i></td>
+</tr><tr>
+<td class="left50">
+Grasshopper-Warbler</td>
+<td class="left50"><i>Locustella n&#339;via.</i></td>
+</tr><tr>
+<td class="left50">
+Savi's Warbler</td>
+<td class="left50"><i>Locustella luscinioides.</i></td>
+</tr><tr>
+<td class="left50">
+Reed-Warbler</td>
+<td class="left50"><i>Acrocephalus scirpaceus.</i></td>
+</tr><tr>
+<td class="left50">
+Marsh-Warbler</td>
+<td class="left50"><i>Acrocephalus palustris.</i></td>
+</tr><tr>
+<td class="left50">
+Sedge-Warbler</td>
+<td class="left50"><i>Acrocephalus sch&#339;nob&aelig;nus.</i></td>
+</tr><tr>
+<td class="left50">
+Willow-Warbler</td>
+<td class="left50"><i>Phylloscopus trochilus.</i></td>
+</tr><tr>
+<td class="left50">
+Wood-Warbler</td>
+<td class="left50"><i>Phylloscopus sibilatrix.</i></td>
+</tr><tr>
+<td class="left50">
+Chiffchaff</td><td class="left50"><i>Phylloscopus collybita.</i></td>
+</tr><tr>
+<td class="left50">
+Song-Thrush</td>
+<td class="left50"><i>Turdus musicus clarkii.</i></td>
+</tr><tr>
+<td class="left50">
+Redwing</td>
+<td class="left50"><i>Turdus iliacus.</i></td>
+</tr><tr>
+<td class="left50">
+Blackbird</td>
+<td class="left50"><i>Turdus merula.</i></td>
+</tr><tr>
+<td class="left50">
+Redstart</td>
+<td class="left50"><i>Ph&#339;nicurus ph&#339;nicurus.</i></td>
+</tr><tr>
+<td class="left50">
+Redbreast</td><td class="left50"><i>Erithacus rubecula melophilus.</i></td>
+</tr><tr>
+<td class="left50">
+Nightingale</td>
+<td class="left50"><i>Luscinia megarhyncha.</i></td>
+</tr><tr>
+<td class="left50">
+Stonechat</td>
+<td class="left50"><i>Saxicola rubicola.</i></td>
+</tr><tr>
+<td class="left50">
+Whinchat</td><td class="left50"><i>Saxicola rubetra.</i></td>
+</tr><tr>
+<td class="left50">
+Wheatear</td><td class="left50"><i>&#338;nanthe &#339;nanthe.</i></td>
+</tr><tr>
+<td class="left50">
+Hedge-Sparrow</td>
+<td class="left50"><i>Accentor modularis.</i></td>
+</tr><tr>
+<td class="left50">
+Wren</td>
+<td class="left50"><i>Troglodytes troglodytes.</i></td>
+</tr><tr>
+<td class="left50">
+Spotted Flycatcher</td>
+<td class="left50"><i>Muscicapa striata.</i></td>
+</tr><tr>
+<td class="left50">
+Swallow</td>
+<td class="left50"><i>Hirundo rustica.</i></td>
+</tr><tr>
+<td class="left50">
+Martin</td>
+<td class="left50"><i>Delichon urbica.</i></td>
+</tr><tr>
+<td class="left50">
+Sand-Martin</td>
+<td class="left50"><i>Riparia riparia.</i></td>
+</tr><tr>
+<td class="left50">
+Great Spotted Woodpecker</td><td class="left50"><i>Dryobates major anglicus.</i></td>
+</tr><tr>
+<td class="left50">
+Lesser Spotted Woodpecker</td><td class="left50"><i>Dryobates minor.</i></td>
+</tr><tr>
+<td class="left50">
+Green Woodpecker</td><td class="left50"><i>Picus viridis.</i></td>
+</tr><tr>
+<td class="left50">
+Cuckoo</td><td class="left50"><i>Cuculus canorus.</i></td>
+</tr><tr>
+<td class="left50">
+Tawny Owl</td><td class="left50"><i>Strix aluco.</i></td>
+</tr><tr>
+<td class="left50">
+Buzzard</td><td class="left50"><i>Buteo buteo.</i></td>
+</tr><tr>
+<td class="left50">
+Sparrow-Hawk</td><td class="left50"><i>Accipiter nisus.</i></td>
+</tr><tr>
+<td class="left50">
+Peregrine Falcon</td><td class="left50"><i>Falco peregrinus.</i></td>
+</tr><tr>
+<td class="left50">
+Merlin</td><td class="left50"><i>Falco &aelig;salon.</i></td>
+</tr><tr>
+<td class="left50">
+Kestrel</td><td class="left50"><i>Falco tinnunculus.</i></td>
+</tr><tr>
+<td class="left50">
+<span class='pagenum'><a name="Page_xiii" id="Page_xiii">xiii</a></span>
+Shag</td><td class="left50"><i>Phalacrocorax graculus</i>.</td>
+</tr><tr>
+<td class="left50">
+Wild Duck</td><td class="left50"><i>Anas boschas</i>.</td>
+</tr><tr>
+<td class="left50">
+Snipe</td><td class="left50"><i>Gallinago gallinago</i>.</td>
+</tr><tr>
+<td class="left50">
+Dunlin</td><td class="left50"><i>Tringa alpina</i>.</td>
+</tr><tr>
+<td class="left50">
+Ruff</td><td class="left50"><i>Machetes pugnax</i>.</td>
+</tr><tr>
+<td class="left50">
+Redshank</td><td class="left50"><i>Totanus totanus</i>.</td>
+</tr><tr>
+<td class="left50">
+Black-tailed Godwit</td><td class="left50"><i>Limosa limosa</i>.</td>
+</tr><tr>
+<td class="left50">
+Curlew</td><td class="left50"><i>Numenius arquata</i>.</td>
+</tr><tr>
+<td class="left50">
+Whimbrel</td><td class="left50"><i>Numenius ph&aelig;opus</i>.</td>
+</tr><tr>
+<td class="left50">
+American Golden Plover</td><td class="left50"><i>Charadrius dominicus</i>.</td>
+</tr><tr>
+<td class="left50">
+Lapwing</td><td class="left50"><i>Vanellus vanellus</i>.</td>
+</tr><tr>
+<td class="left50">
+Oyster-Catcher</td>
+<td class="left50"><i>H&aelig;matopus ostralegus</i>.</td>
+</tr><tr>
+<td class="left50">
+Herring-Gull</td>
+<td class="left50"><i>Larus argentatus</i>.</td>
+</tr><tr>
+<td class="left50">
+Kittiwake</td>
+<td class="left50"><i>Rissa tridactyla</i>.</td>
+</tr><tr>
+<td class="left50">
+Razorbill</td><td class="left50"><i>Alca torda</i>.</td>
+</tr><tr>
+<td class="left50">
+Guillemot</td>
+<td class="left50"><i>Uria troille</i>.</td>
+</tr><tr>
+<td class="left50">
+Puffin</td>
+<td class="left50"><i>Fratercula arctica</i>.</td>
+</tr><tr>
+<td class="left50">
+Fulmar</td><td class="left50"><i>Fulmarus glacialis</i>.</td>
+</tr><tr>
+<td class="left50">
+Water-Rail</td><td class="left50"><i>Rallus aquaticus</i>.</td>
+</tr><tr>
+<td class="left50">
+Corn-Crake</td><td class="left50"><i>Crex crex</i>.</td>
+</tr><tr>
+<td class="left50">
+Moor-Hen</td>
+<td class="left50"><i>Gallinula chloropus</i>.</td>
+</tr><tr>
+<td class="left50">
+Coot</td>
+<td class="left50"><i>Fulica atra</i>.</td>
+</tr><tr>
+<td class="left50">
+Wood-Pigeon</td><td class="left50"><i>Columba palumbus</i>.</td>
+</tr><tr>
+<td class="left50">
+Turtle-Dove</td><td class="left50"><i>Streptopelia turtur</i>.</td>
+</tr><tr>
+<td class="left50">
+Partridge</td>
+<td class="left50"><i>Perdix perdix</i>.</td>
+</tr><tr>
+<td class="left50">
+Black Grouse</td>
+<td class="left50"><i>Lyrurus tetrix britannicus</i>.</td>
+</tr><tr>
+<td class="left50">Red Grouse</td>
+<td class="left50"><i>Lagopus scoticus</i>.</td>
+</tr>
+</table>
+<hr />
+<p><span class='pagenum'><a name="Page_1" id="Page_1">1</a></span></p>
+
+<h2>TERRITORY IN BIRD LIFE</h2>
+
+<h3>CHAPTER I</h3>
+
+<h4>INTRODUCTION</h4>
+
+
+<p>In his <i>Manual of Psychology</i> Dr Stout reminds
+us that "Human language is especially constructed
+to describe the mental states of human
+beings, and this means that it is especially
+constructed so as to mislead us when we attempt
+to describe the working of minds that differ in
+a great degree from the human."</p>
+
+<p>The use of the word "territory" in connection
+with the sexual life of birds is open to
+the danger which we are here asked to guard
+against, and I propose, therefore, before attempting
+to establish the theory on general grounds,
+to give some explanation of what the word is
+intended to represent and some account of the
+exact position that representation is supposed to
+occupy in the drama of bird life.</p>
+
+<p>The word is capable of much expansion.
+There cannot be territories without boundaries
+of some description; there cannot well be
+boundaries without disputes arising as to those
+boundaries; nor, one would imagine, can there
+be disputes without consciousness as a factor
+entering into the situation; and so on, until by<span class='pagenum'><a name="Page_2" id="Page_2">2</a></span>
+a simple mental process we conceive of a state
+in bird life analogous to that which we know
+to be customary amongst ourselves. Now,
+although the term "breeding territory," when
+applied to the sexual life of birds, is not altogether
+a happy one, it is difficult to know
+how otherwise to give expression to the facts
+observed. Let it then be clearly understood that
+the expression "securing a territory" is used to
+denote a process, or rather part of a process,
+which, in order to insure success to the individual
+in the attainment of reproduction, has
+been gradually evolved to meet the exigencies
+of diverse circumstances. Regarded thus, we
+avoid the risk of conceiving of the act of securing
+a territory as a detached event in the life of a
+bird, and avoid, I hope, the risk of a conception
+based upon the meaning of the word when
+used to describe human as opposed to animal
+procedure.</p>
+
+<p>Success in the attainment of reproduction is
+rightly considered to be the goal towards which
+many processes in nature are tending. But
+what is meant by success? Is it determined by
+the actual discharge of the sexual function?
+So many and so wonderful are the contrivances
+which have slowly been evolved to insure this
+discharge, that it is scarcely surprising to find
+attention focused upon this one aspect of the
+problem. Yet a moment's reflection will show
+that so limited a definition of the term "success"
+can only be held to apply to certain forms of
+life; for where the young have to be cared for,<span class='pagenum'><a name="Page_3" id="Page_3">3</a></span>
+fostered, and protected from molestation for
+periods of varying lengths, the actual discharge
+of the sexual function marks but one stage in a
+process which can only succeed if all the contributory
+factors adequately meet the essential
+conditions of the continuance of the species.</p>
+
+<p>Securing a territory is then part of a process
+which has for its goal the successful rearing
+of offspring. In this process the functioning
+of the primary impulse, the acquirement of a
+place suitable for breeding purposes, the advent
+of a female, the discharge of the sexual function,
+the construction of the nest, and the
+rearing of offspring follow one another in
+orderly sequence. But since we know so little
+of the organic changes which determine sexual
+behaviour, and have no means of ascertaining
+the nature of the impulse which is first
+aroused, we can only deal with the situation
+from the point at which the internal organic
+changes reflect themselves in the behaviour to
+a degree which is visible to an external observer.
+That point is reached when large numbers of
+species, forsaking the normal routine of existence
+to which they have been accustomed for
+some months, suddenly adopt a radical change
+in their mode of behaviour. How is this change
+made known to us? By vast numbers of
+individuals hurrying from one part of the globe
+to another, from one country to another, and
+even from mid-ocean to the coasts; by detachments
+travelling from one district to another;
+by isolated individuals deserting this place for<span class='pagenum'><a name="Page_4" id="Page_4">4</a></span>
+that; by all those movements, in fact, which
+the term migration, widely applied, is held to
+denote. Now the impulse which prompts these
+travelling hosts must be similar in kind whether
+the journey be long or short; and it were better,
+one would think, to regard such movements as
+a whole than to fix the attention on some one
+particular journey which fills us with amazement
+on account of the magnitude of the distance
+traversed or the nature of the difficulties overcome.
+For, after all, what does each individual
+seek? There may be some immature birds which,
+though they have not reached the necessary
+stage of development, happen to fall in with
+others in whom the impulse is strong and are
+led by them&mdash;they know not where. But the
+majority seek neither continent nor country,
+neither district nor locality is their aim, but a
+place wherein the rearing of offspring can be
+safely accomplished; and the search for this
+place is the earliest visible manifestation in many
+species of the reawakening of the sexual instinct.</p>
+
+<p>The movements of each individual are then
+directed towards a similar goal, namely, the
+occupation of a definite station; and this
+involves for many species a distinct change in
+the routine of behaviour to which previously they
+had been accustomed. Observe, for example,
+one of the numerous flocks of Finches that
+roam about the fields throughout the winter.
+Though it may be composed of large numbers
+of individuals of different kinds, yet the various
+units form an amicable society actuated by<span class='pagenum'><a name="Page_5" id="Page_5">5</a></span>
+one motive&mdash;the procuring of food. And since
+it is to the advantage of all that the individual
+should be subordinated to the welfare
+of the community as a whole there is no dissension,
+apart from an occasional quarrel here
+and there.</p>
+
+<p>In response, however, to some internal organic
+change, which occurs early in the season,
+individuality emerges as a factor in the developing
+situation, and one by one the males betake
+themselves to secluded positions, where each
+one, occupying a limited area, isolates itself from
+companions. Thereafter we no longer find that
+certain fields are tenanted by flocks of greater
+or less dimensions, while acres of land are
+uninhabited, but we observe that the hedgerows
+and thickets are divided up into so many territories,
+each one of which contains its owner.
+This procedure, with of course varying detail,
+is typical of that of many species that breed in
+Western Europe. And since such a radical
+departure from the normal routine of behaviour
+could scarcely appear generation after generation
+in so many widely divergent forms, and still be
+so uniform in occurrence each returning season,
+if it were not founded upon some congenital
+basis, it is probable that the journey, whether it
+be the extensive one of the Warbler or the short
+one of the Reed-Bunting, is undertaken in
+response to some inherited disposition, and
+probable also that the disposition bears some
+relation to the few acres in which the bird
+ultimately finds a resting place. Whilst for<span class='pagenum'><a name="Page_6" id="Page_6">6</a></span>
+the purpose of the theory I shall give expression
+to this behaviour in terms of that
+theory, and speak of it as a disposition to
+secure a territory, using the word disposition,
+which has been rendered current in recent discussion,
+for that part of the inherited nature
+which has been organised to subserve a specific
+biological purpose&mdash;strict compliance with the
+rules of psychological analysis requires a simpler
+definition; let us therefore say "disposition to
+remain in a particular place in a particular
+environment."</p>
+
+<p>But even granting that this disposition
+forms part of the hereditary equipment of
+the bird, how is the process of reproduction
+furthered? The mere fact of remaining in or
+about a particular spot cannot render the attainment
+of reproduction any less arduous, and may
+indeed add to the difficulties, for any number
+of individuals might congregate together and
+mutually affect one another's interests. A
+second disposition comes, however, into functional
+activity at much the same stage of sexual
+development, and manifests itself in the male's
+intolerance of other individuals. And the two
+combined open up an avenue through which
+the individual can approach the goal of reproduction.
+In terms of the theory I shall
+refer to this second disposition as the one
+which is concerned with the defence of the
+territory.</p>
+
+<p>Broadly speaking, these two dispositions may
+be regarded as the basis upon which the breed<span class='pagenum'><a name="Page_7" id="Page_7">7</a></span>ing
+territory is founded. Yet inasmuch as the
+survival value of the dispositions themselves
+must have depended upon the success of the
+process as a whole, it is manifest that peculiar
+significance must not be attached to just the
+area occupied, which happens to be so susceptible
+of observation; other contributory factors
+must also receive attention, for the process is
+but an order of relationships in which the
+various units have each had their share in
+determining the nature and course of subsequent
+process, so that, as Dr Stout says, when they
+were modified, it was modified.</p>
+
+<p>Now the male inherits a disposition which
+leads it to remain in a restricted area, but the
+disposition cannot determine the extent of that
+area. How then are the boundaries fixed?
+That they are sometimes adhered to with
+remarkable precision, that they can only be
+encroached upon at the risk of a conflict&mdash;all of
+this can be observed with little difficulty. But
+if we regard them as so many lines definitely
+delimiting an area of which the bird is cognisant,
+we place the whole behaviour on a different
+level of mental development, and incidentally
+alter the complexion of the whole process. It
+would be a mistake, I think, to do this. Though
+conscious intention as a factor may enter the
+situation, there is no necessity for it to do so;
+there is no necessity, that is to say, for the bird
+to form a mental image of the area to be
+occupied and shape its course accordingly. The
+same result can be obtained without our having<span class='pagenum'><a name="Page_8" id="Page_8">8</a></span>
+recourse to so complex a principle of explanation,
+and that by the law of habit formation.
+In common with other animals, birds are
+subject to this law in a marked degree. An
+acquired mode of activity becomes by repetition
+ingrained in the life of the individual, so that
+an action performed to-day is liable to be
+repeated to-morrow so long as it does not prejudice
+the existence or annul the fertility of the
+individual.</p>
+
+<p>Let us see how this may have operated in
+determining the limits of the area acquired, and
+for this purpose let us suppose that we are
+observing a male Reed-Bunting recently established
+in some secluded piece of marsh land.
+Scattered about this particular marsh are a
+number of small willows and young alder trees,
+each one of which is capable of providing plenty
+of branches suitable for the bird to perch upon,
+and all are in a like favourable position so far as
+the outlook therefrom is concerned. Well, we
+should expect to find that each respective tree
+would be made use of according to the position
+in which the bird happened to find itself. But
+what actually do we find&mdash;one tree singled out
+and resorted to with ever-increasing certainty
+until it becomes an important point in relation
+to the occupied area, a headquarters from
+which the bird advertises its presence by song,
+keeps watch upon the movements of its
+neighbours, and sets out for the purpose of
+securing food. We then take note of its
+wanderings in the immediate vicinity of the<span class='pagenum'><a name="Page_9" id="Page_9">9</a></span>
+headquarters, especially as regards the direction,
+frequency, and extent of the journeys; and
+we discover not only that these journeys proceed
+from and terminate in the special tree,
+but that there is a sameness about the actual
+path that is followed. The bird takes a short
+flight, searches a bush here and some rushes
+there, returns, and after a while repeats the
+performance; we on our part mark the extreme
+limits reached in each direction, and by continued
+observation discover that these limits
+are seldom exceeded, that definition grows more
+and more pronounced, and that by degrees
+the movements of the bird are confined within
+a restricted area. In outline, this is what
+happens in a host of cases. By repetition
+certain performances become stereotyped, certain
+paths fixed, and a routine is thus established
+which becomes increasingly definite as
+the season advances.</p>
+
+<p>But while it would be quite untrue to say
+that this routine is never departed from, and
+equally profitless to attempt to find a point
+beyond which the bird will under no circumstances
+wander, yet there is enough definition
+and more than enough to answer the purpose
+for which the territory has, I believe, been
+evolved, that is to say the biological end of
+reproduction. Again, however, the process of
+adjustment is a complex one. Habit plays its
+part in determining the boundaries in a rough
+and ready manner, but the congenital basis,
+which is to be found in the behaviour adapted<span class='pagenum'><a name="Page_10" id="Page_10">10</a></span>
+to a particular environment, is an important
+factor in the situation. For example, if instead
+of resting content with just a bare position
+sufficient for the purpose of reproduction, the
+Guillemot were to hustle its neighbours from
+adjoining ledges, the Guillemot as a species
+would probably disappear; or if instead of
+securing an area capable of supplying sufficient
+food both for itself and its young, the Chiffchaff
+were to confine itself to a single tree, and,
+after the manner of the Guillemot, trust to
+spasmodic excursions into neutral ground for
+the purpose of obtaining food, the Chiffchaff as
+a species would probably not endure. All such
+adjustments have, however, been brought about
+by relationships which have gradually become
+interwoven in the tissue of the race.</p>
+
+<p>The intolerance that the male displays
+towards other individuals, usually of the same
+sex, leads to a vast amount of strife. Nowhere
+in the animal world are conflicts more frequent,
+more prolonged, and more determined than in
+the sexual life of birds; and though they are
+acknowledged to be an important factor in the
+life of the individual, yet there is much difference
+of opinion as to the exact position they
+occupy in the drama of bird life. Partly
+because they frequently happen to be in
+evidence, partly because they are numerically
+inferior, and partly, I suppose, because the
+competition thus created would be a means of
+maintaining efficiency, the females, by common
+consent, are supposed to supply the condition<span class='pagenum'><a name="Page_11" id="Page_11">11</a></span>
+under which the pugnacious nature of the
+male is rendered susceptible to appropriate
+stimulation. And so long as the evidence
+seemed to show that battles were confined
+to the male sex, so long were there grounds
+for hoping that their origin might be traced
+to such competition. But female fights with
+female, pair with pair, and, which is still
+more remarkable, a pair will attack a single
+male or a single female; moreover, males that
+reach their destination in advance of their
+prospective mates engage in serious warfare.
+How then is it possible to look upon the
+individuals of one sex as directly responsible for
+the strife amongst those of the other, or how
+can the female supply the necessary condition?
+As long as an attempt is made to explain it in
+terms of the female, the fighting will appear to
+be of a confused order; regard it, however, as part
+of a larger process which demands, amongst
+other essential conditions of the breeding
+situation, the occupation of a definite territory,
+and order will reign in place of confusion.</p>
+
+<p>But even supposing that the male inherits
+a disposition to acquire a suitable area, even
+supposing that it inherits a disposition which
+results indirectly in the defence of that area,
+how does it obtain a mate? If the female
+behaved in a like manner, if she, too, were to
+isolate herself and remain in one place definitely,
+that would only add to the difficulties of mutual
+discovery. We find, however, in the migrants,
+that the males are earlier than the females<span class='pagenum'><a name="Page_12" id="Page_12">12</a></span>
+in reaching the breeding grounds, and, in
+resident species, that they desert the females
+and retire alone to their prospective territories,
+so that there is a difference in the behaviour
+of the sexes at the very commencement of
+the sexual process. What is the immediate
+consequence? Since the male isolates itself,
+it follows, if the union of the sexes is to be
+effected, that the discovery of a mate must
+rest largely with the female. This of course
+reverses the accepted course of procedure.
+But after all, what reason is there to suppose
+that, the male seeks the female, or that a
+mutual search takes place; what reason to
+think that this part of the process is subject
+to no control except such as may be supplied
+by the laws of chance?</p>
+
+<p>Now, clearly, much will depend upon the
+rapidity with which the female can discover a
+male fit to breed; for if the course of reproduction
+is to flow smoothly, there must be neither
+undue delay nor waste of energy incurred in the
+search&mdash;some guidance is therefore necessary,
+some control in her external environment.
+Here the song, or the mechanically produced
+sound, comes into play, and assists in the attainment
+of this end. Nevertheless if every male
+were to make use of its powers whether it were
+in occupation of a territory or not, if the
+wandering individual had an equal chance of
+attracting a mate, then it would be idle to
+attempt to establish any relation between
+"song" on the one hand, and "territory" on<span class='pagenum'><a name="Page_13" id="Page_13">13</a></span>
+the other, and impossible to regard the voice as
+the medium through which an effectual union of
+the sexes is procured. But there is reason to
+believe that the males utilise their powers of
+producing sound only under certain well-defined
+conditions. For instance, when they are on
+their way to the breeding grounds, or moving
+from locality to locality in search of isolation, or
+when they desert their territories temporarily,
+as certain of the residents often do, they are
+generally silent; but when they are in occupation
+of their territories they become vociferous&mdash;and
+this is notoriously the case during the
+early hours of the day, which is the period of
+maximum activity so far as sexual behaviour is
+concerned. So that just at the moment when
+the sexual impulse of the female is most susceptible
+to stimulation, the males are betraying
+their positions and are thus a guide to her
+movements. Nevertheless, even though she
+may have discovered a male ready to breed,
+success is not necessarily assured to her; for
+with multitudes of individuals striving to procreate
+their kind, it would be surprising if there
+were no clashing of interests, if no two females
+were ever to meet in the same occupied territory.
+Competition of this kind is not uncommon, and
+the final appeal is to the law of battle, just as an
+appeal to physical strength sometimes decides
+the question of the initial ownership of a
+territory.</p>
+
+<p>I shall try to make clear the relations
+of the various parts to the whole with the<span class='pagenum'><a name="Page_14" id="Page_14">14</a></span>
+assistance of whatever facts I can command.
+I shall do so not only for the purposes of the
+theory, but because one so often finds the
+more important features of sexual behaviour
+regarded as so many distinct phenomena requiring
+separate treatment, whereas they are mutually
+dependent, and follow one another in ordered
+sequence. I spoke of the process as a series
+of relationships. Some of these relationships
+have already been touched upon; others will
+become apparent if we consider for a moment
+the purposes for which the territory has been
+evolved. Indirectly its purpose is that of the
+whole process, the rearing of offspring. But
+inasmuch as a certain measure of success could
+be attained, and that perhaps often, without all
+the complications introduced by the territory,
+there are manifestly advantages to be gained
+by its inclusion in the scheme. The difficulties
+which beset the path of reproduction are by no
+means always the same&mdash;all manner of adjustments
+have to be made to suit the needs of
+different species. There are direct relationships,
+such as we have been speaking of, which are
+essential to the every-day working of the
+process, and others which are indirect, though
+none the less important for they must have
+exercised an influence throughout the ages.
+These latter are furnished by the physical&mdash;the
+inorganic world, by climate, by the supply of
+the particular kind of breeding stations, by the
+scarcity or abundance of the necessary food
+and by the relative position of the food supply<span class='pagenum'><a name="Page_15" id="Page_15">15</a></span>
+to the places suitable for breeding. Why does
+the Reed-Bunting cling so tenaciously to an
+acre or more of marshy ground, while the
+Guillemot rests content with a few square feet
+on a particular ledge of rock? The answer is
+the same in both cases&mdash;to facilitate reproduction.
+But why should a small bird require
+so many square yards, whilst a very much
+larger one is satisfied with so small an area?
+The explanation must be sought in the conditions
+of existence. The Reed-Bunting has
+no difficulty in finding a position suitable for
+the construction of its nest; there are acres
+of waste land and reedy swamps capable of
+supplying food for large numbers of individuals,
+and the necessary situations for countless nests.
+But its young, like those of many another
+species, are born in a very helpless state. For
+all practical purposes they are without covering
+of any description and consequently require
+protection from the elements, warmth from
+the body of the brooding bird, and repeated
+supplies of nourishment. A threefold burden
+is thus imposed upon the parents: they must
+find food for themselves, they must afford
+protection to the young by brooding, and they
+must supply them with the necessary food at
+regular intervals. And their ability to do all
+this that is demanded of them will be severely
+taxed by the brooding which must perforce
+curtail the time available for the collection
+of food.</p>
+
+<p>Let us then suppose that the Reed-Buntings<span class='pagenum'><a name="Page_16" id="Page_16">16</a></span>
+inhabiting a certain piece of marsh are divided
+into two classes, those which are pugnacious
+and intolerant of the approach of strangers, and
+those which welcome their presence. The nests
+of the former will be built in isolation, those
+of the latter in close proximity. In due course
+eggs will be laid and incubation performed,
+and thus far all alike will probably be successful.
+Here, however, a critical point is reached. If
+the young are to be freed from the risk of
+exposure, the parents must find the necessary
+supply of food rapidly. But manifestly all
+will not be in a like satisfactory position to
+accomplish this, for whereas the isolated pairs
+will have free access to all the food in the
+immediate vicinity of the nest, those which
+have built in proximity to one another, meeting
+competition in every direction, will be compelled
+to roam farther afield and waste much
+valuable time by doing so; and under conditions
+which can well be imagined, even this slight
+loss of time will be sufficient to impede the
+growth of the delicate offspring, or to lead
+perhaps to still greater disaster. If any one
+doubts this, let him first examine one of the
+fragile offspring; let him then study the conditions
+under which it is reared, observing the
+proportion of time it passes in sleep and the
+anxiety of the parent bird to brood; and finally
+let him picture to himself its plight in a wet
+season if, in order to collect the necessary food,
+the parents were obliged to absent themselves
+for periods of long duration.</p>
+
+<p><span class='pagenum'><a name="Page_17" id="Page_17">17</a></span>Now take the case of the Guillemot. Its
+young at birth are by no means helpless in the
+sense that the young Reed-Bunting is, and food
+is readily procured. But breeding stations are
+scarce, for although there are many miles of
+cliff-bound coast, yet not every type of rock
+formation produces the fissures and ledges upon
+which the bird rests. Hence vast stretches of
+coast-line remain uninhabited, and the birds are
+forced to concentrate at certain points, where
+year after year they assemble in countless
+numbers from distant parts of the ocean. If,
+then, different individuals were to jostle one
+another from adjoining positions, and each one
+were to attempt to occupy a ledge in solitary
+State, not only would the successful ones gain
+no advantage from the additional space over
+which they exercised dominion, but inasmuch as
+many members that were fitted to breed would
+be precluded from doing so, the status of the
+species as a whole would be seriously affected.
+The amount of space occupied by each individual
+is therefore a matter of urgent importance. A
+few square feet of rock sufficient for the immediate
+purpose of incubation is all that can be
+allowed if the species is to maintain its position
+in the struggle for existence.</p>
+
+<p>Our difficulty in estimating the importance
+of the various factors that make for success or
+failure arises from our inability to see more than
+a small part of the scene as it slowly unfolds
+itself. The peculiar circumstances under which
+these cliff-breeding forms dwell does, however,<span class='pagenum'><a name="Page_18" id="Page_18">18</a></span>
+enable us to picture, on the one hand, the
+precarious situation of an individual that was
+incapable of winning or holding a position at
+the accustomed breeding station, and, on the
+other, the plight of the species as a whole if
+each one exercised authority over too large an
+area. With the majority of species it is difficult
+to do this. So many square miles of suitable
+breeding ground are inhabited by so few Reed-Buntings
+that, even supposing certain members
+were to establish an ascendency over too wide
+an area, it would be impossible to discover
+by actual observation whether the race as a
+whole were being adversely affected. Competition
+doubtless varies at different periods and
+in different districts according to the numerical
+standing of the species in a given locality and
+according to the numerical standing of others
+that require similar conditions of existence; at
+times it may even be absent, just as at any
+moment it may become acute. These examples
+show how profoundly the evolution of the
+breeding territory may have been influenced by
+relationships in the inorganic world, and they
+give some idea of the intricate nature of the
+problem with which we have to deal.</p>
+
+<p>I mentioned that the first visible manifestation
+of the revival of the sexual instinct
+was to be found in the movements undertaken
+by the males at the commencement
+of the breeding season. Such movements are
+characterised by a definiteness of purpose,
+whether they involve a protracted journey of<span class='pagenum'><a name="Page_19" id="Page_19">19</a></span>
+some hundreds of miles or merely embrace a
+parish or so in extent, and that purpose is the
+acquirement of a territory suitable for rearing
+offspring. They are thus directly related to the
+territory, and the question arises as to whether
+their origin may not be traced to such relatedness.
+So long as we fix our attention solely
+upon the magnitude of the distance traversed
+the suggestion may seem a fanciful one. Nevertheless,
+if the battles between males of the
+same species <i>are</i> directly related to the occupation
+of a position suitable for breeding purposes,
+if those which occur between males of closely
+related forms <i>can</i> be traced to a similar source,
+if the females take their share in the defence
+of the ground that is occupied, if, in short, the
+competition is as severe as I believe it to be,
+and is wholly responsible for the strife which
+is prevalent at the commencement of the
+breeding season&mdash;then such competition must
+have introduced profound modifications in the
+distribution of species; it must have even
+influenced the question of the survival of
+certain forms and the elimination of others;
+and since the powers of locomotion of a bird
+are so highly developed it must have led to
+an extension of breeding range, limited only
+by unfavourable conditions of existence.</p>
+<hr />
+<p><span class='pagenum'><a name="Page_20" id="Page_20">20</a></span></p>
+<h3>CHAPTER II</h3>
+
+<h4>THE DISPOSITION TO SECURE A TERRITORY</h4>
+
+
+<p>Those who have studied bird life throughout
+the year are aware that the distribution of
+individuals changes with the changing seasons.
+During autumn and winter, food is not so
+plentiful and can only be found in certain places,
+and so, partly by force of circumstances and
+partly on account of the gregarious instinct
+which then comes into functional activity,
+different individuals are drawn together and
+form flocks of greater or less dimensions, which
+come and go according to the prevailing climatic
+conditions. But with the advent of spring a
+change comes over the scene: flocks disperse,
+family parties break up, summer migrants begin
+to arrive, and the hedgerows and plantations are
+suddenly quickened into life. The silence of
+the winter is broken by an outburst of song
+from the throats of many different species, and
+individuals appear in their old haunts and vie
+with one another in advertising their presence
+by the aid of whatever vocal powers they
+happen to possess&mdash;the Woodpecker utters its
+monotonous call from the accustomed oak; the<span class='pagenum'><a name="Page_21" id="Page_21">21</a></span>
+Missel-Thrush, perched upon the topmost
+branches of the elm, persistently repeats its few
+wild notes; and the Swallow returns to the barn.</p>
+
+<p>All of this we observe each season, and our
+thoughts probably travel to the delicate piece of
+architecture in the undergrowth, or to the hole
+excavated with such skill in the tree trunk; to
+the beautifully shaped eggs; to the parent birds
+carrying out their work with devoted zeal&mdash;in
+fact, to the whole series of events which complete
+the sexual life of the individual; and the attachment
+of a particular bird to a particular spot is
+readily accounted for in terms of one or other
+of the emotions which centre round the human
+home.</p>
+
+<p>But if this behaviour is to be understood
+aright; if, that is to say, the exact position it
+occupies in the drama of bird life is to be
+properly determined, and its biological significance
+estimated at its true value, it is above all
+things necessary to refrain from appealing to
+any one of the emotions which we are accustomed
+to associate with ourselves, unless our
+ground for doing so is more than ordinarily
+secure. I shall try to show that, in the case of
+many species, the male inherits a disposition to
+secure a territory; or, inasmuch as the word
+"secure" carries with it too much prospective
+meaning, a disposition to remain in a particular
+place when the appropriate time arrives.</p>
+
+<p>If the part which the breeding territory
+plays in the sexual life of birds is the important
+one I believe it to be, it follows that the<span class='pagenum'><a name="Page_22" id="Page_22">22</a></span>
+necessary physiological condition must arise at
+an early stage in the cycle of events which
+follow one another in ordered sequence and
+make towards the goal of reproduction, and that
+the behaviour to which it leads must be one of
+the earliest visible manifestations of the seasonal
+development of the sexual instinct. When does
+this seasonal development occur? For how
+long does the instinct lie dormant? In some
+species there is evidence of this first step in the
+process of reproduction early in February; there
+is reason to believe that in others the latter part
+of January is the period of revival; and the
+possibility must not be overlooked of still earlier
+awakenings, marked with little definiteness,
+though nevertheless of sufficient strength to call
+into functional activity the primary impulse in
+the sexual cycle. Here, then, we meet with a
+difficulty so far as direct observation is concerned,
+for the duration of the period of
+dormancy and the precise date of revival vary
+in different species; and, if accurate information
+is to be obtained, the study of the series of
+events which culminate in the attainment
+of reproduction ought certainly to begin the
+moment behaviour is influenced by the internal
+changes, whatever they may be, which are
+responsible for the awakening of the sexual
+instinct.</p>
+
+<p>In considering how this difficulty might be
+met, the importance of migratory species as a
+channel of information was gradually borne in
+upon me; for it seemed that the definiteness<span class='pagenum'><a name="Page_23" id="Page_23">23</a></span>
+with which the initial stage in the sexual process
+was marked off, as a result of the incidence of
+migration, would go far towards removing much
+of the obscurity which appeared to surround the
+earlier stages of the breeding problem in the
+case of resident species. Recent observation
+has shown that I exaggerated this difficulty, and
+that it is generally possible to determine with
+reasonable accuracy the approximate date at
+which the internal changes begin to exert an
+influence on the behaviour of resident species
+also. Nevertheless, the specialised behaviour of
+the migrants furnished a clue, and pointed out
+the direction which further inquiry ought to
+take.</p>
+
+<p>Those who are accustomed to notice the
+arrival of the migrants are aware that the woods,
+thickets, and marshes do not suddenly become
+occupied by large numbers of individuals, but
+that the process of "filling up" is a gradual
+one. An individual appears here, another there;
+then after a pause there is a further addition,
+and so on with increasing volume until the tide
+reaches its maximum, then activity wanes, and
+the slowly decreasing number of fresh arrivals
+passes unnoticed in the wealth of new life that
+everywhere forces itself upon our attention. If
+now, instead of surveying the migrants as a
+whole, our attention be directed to one species
+only, this gradual arrival of single individuals in
+their accustomed haunts will become even more
+apparent; and if the investigation be pursued
+still further and these single individuals observed<span class='pagenum'><a name="Page_24" id="Page_24">24</a></span>
+more closely, it will be found that in nearly
+every case they belong to the male sex. Males
+therefore arrive before females. This does not
+mean, however, that the respective times of
+arrival of the males and females belonging to
+any one species are definitely divided, for males
+continue to arrive even after some of the females
+have reached their destination; and thus a certain
+amount of overlapping occurs. A truer
+definition of the order of migration would be as
+follows:&mdash;Some males arrive before others, and
+some females arrive before others, but on the
+average males arrive before females. This fact
+has long been known. G&auml;tke refers to it in his
+<i>Birds of Heligoland</i>. "Here in Heligoland," he
+says, "the forerunners of the spring migration
+are invariably old males; a week or two later,
+solitary old females make their appearance; and
+after several weeks, both sexes occur mixed, <i>i.e.</i>,
+females and younger males; while finally only
+young birds of the previous year are met with."
+Newton alludes to it as follows:&mdash;"It has been
+ascertained by repeated observation that in the
+spring movement of most species of the northern
+hemisphere, the cock birds are always in the van
+of the advancing army, and that they appear some
+days, or perhaps weeks, before the hens"; and
+Dr Eagle Clarke, in his <i>Studies in Bird Migration</i>,
+makes the following statement:&mdash;"Another
+characteristic of the spring is that the males,
+the more ardent suitors, of most species, travel
+in advance of the females, and arrive at their
+meeting quarters some days, it is said in some<span class='pagenum'><a name="Page_25" id="Page_25">25</a></span>
+cases even weeks, before their consorts." Some
+interesting details were given in <i>British Birds</i><a name="FNanchor_1_1" id="FNanchor_1_1"></a><a href="#Footnote_1_1" class="fnanchor">1</a>
+in regard to the sex of the migrants that were
+killed by striking the lantern at the Tuskar
+Rock, Co. Wexford, on the 30th April 1914. In
+all, there were twenty-four Whitethroats, nine
+Willow-Warblers, eight Sedge-Warblers, and six
+Wheatears; and on dissection it was found that
+twenty Whitethroats, seven Willow-Warblers,
+eight Sedge-Warblers, and one Wheatear were
+males.</p>
+
+<p>What a curious departure this seems from
+the usual custom in the animal world! Here
+we have the spectacle afforded us of the males,
+in whom presumably the sexual instinct has
+awakened, deserting the females just at the
+moment when we might reasonably expect their
+impulse to accompany them would be strongest;
+and this because of their inherited disposition
+to reach the breeding grounds. If, in order
+to attain to reproduction, the male depended
+primarily upon securing a female&mdash;whether by
+winning or fighting matters not at the moment&mdash;if
+her possession constituted the sole difference
+in his external environment between success and
+failure, then surely one would suppose that an
+advantage must rest with those individuals
+which, instead of rushing forward and inflicting
+upon themselves a life of temporary isolation,
+remained with the females and increased
+their opportunities for developing that mutual
+appreciation which, by some, is held to be a
+<span class='pagenum'><a name="Page_26" id="Page_26">26</a></span>
+necessary prelude to the completion of the
+sexual act, and to which close companionship
+would tend to impart a stimulus.</p>
+
+<p>In thus speaking, however, we assume that
+the revival of the sexual instinct in the migratory
+male is coincident in time with its return to the
+breeding quarters; and we do so because the
+act of migrating is believed to be the first step
+in the breeding process. But it is well to bear in
+mind just how much of this assumption is based
+upon fact, and how much is due to questionable
+inference. All that can be definitely asserted is
+this, that appropriate dissection reveals in most
+of the migrants, upon arrival at their destination,
+unquestionable evidence of seasonal increase in
+the size of the sexual organs. Beyond this there
+is nothing to go upon. Yet if the term "sexual
+instinct" is held to comprise the whole series of
+complex relationships which are manifest to us
+in numerous and specialised modes of behaviour,
+which ultimately lead to reproduction, and which
+have gradually become interwoven in the tissue
+of the race, there can be little doubt that the
+assumption is a reasonable one. To some, the
+term may recall the fierce conflicts which are
+characteristic of the season; to others, emotional
+response; to not a few, perhaps, the actual
+discharge of the sexual function&mdash;all of these, it
+is true, are different aspects of the one instinct;
+but at the same time each one marks a stage in
+the process, and the different stages follow one
+another in ordered sequence. However, we are
+not concerned at the moment with the term in<span class='pagenum'><a name="Page_27" id="Page_27">27</a></span>
+its wider application; we wish to know the
+precise stage at which the disposition to mate
+influences the behaviour of the male. Is the
+female to him, from the moment the seasonal
+change in his sexual organs takes place, a goal
+that at all costs must be attained? Or is it only
+when the cycle of events which leads up to
+reproduction is nearing completion that she
+looms upon his horizon? One would like to be
+in a position to answer these questions, but
+there is nothing in the way of experimental
+evidence to go upon; and if I say that there is
+reason to believe that, in the earlier stages, the
+female is but a shadow in the external environment
+of the male, it must be taken merely as
+an expression of opinion, though based in some
+measure upon a general observation of the
+behaviour of various species.</p>
+
+<p>Before attempting to explain the difference
+in the times of arrival of the male and female
+migrant, let us examine the behaviour of some
+resident species at a corresponding period.
+My investigations have been made principally
+amongst the smaller species&mdash;the Finches and
+the Buntings&mdash;which often pass the winter in
+or near the localities wherein they brought up
+offspring or were reared. It is true that they
+wander from one field to another according to
+the abundance or scarcity of food; it is also true
+that, if the weather is of a type which precludes
+the possibility of finding the necessary food,
+these wanderings may become extensive or even
+develop into partial migrations. But under the<span class='pagenum'><a name="Page_28" id="Page_28">28</a></span>
+normal climatic conditions which prevail in
+many parts of Britain, these smaller resident
+species seem to find all that they require
+without travelling any great distance from
+their breeding haunts. Flocks composed of
+Yellow Buntings, Cirl Buntings, Corn-Buntings,
+Chaffinches, Greenfinches, etc., can be observed
+round the farmsteads or upon arable land; small
+flocks of Reed-Buntings take up their abode on
+pieces of waste land and remain there until the
+supply of food is exhausted, deserting their
+feeding ground only towards evening when
+they retire to the nearest reed-bed to pass the
+night; flocks of Hawfinches visit the same holly-trees
+day after day so long as there is an
+abundance of berries on the ground beneath;
+and so on.</p>
+
+<p>I have mentioned the Reed-Bunting; let us
+take it as our first example and try to follow its
+movements when the influence exerted by the
+internal secretions begins to be reflected on the
+course of its behaviour. First, it will be
+necessary to discover the exact localities in any
+given district to which the species habitually
+returns for the purpose of procreation; otherwise
+the earlier symptoms of any disposition to
+secure a territory may quite possibly be overlooked
+in the search for its breeding haunts.</p>
+
+<p>In open weather Reed-Buntings pass the
+winter either singly, in twos or threes, or in
+small flocks, on bare arable ground, upon seed
+fields, or in the vicinity of water-courses; but
+in the breeding season they resort to marshy<span class='pagenum'><a name="Page_29" id="Page_29">29</a></span>
+ground where the <i>Juncus communis</i> grows in
+abundance, to the dense masses of the common
+reed (<i>Arundo phragmites</i>), and such like places.
+During the winter, the male's routine of existence
+is of a somewhat monotonous order, limited
+to the necessary search for food during the few
+short hours of daylight and enforced inactivity
+during the longer hours of darkness. But
+towards the middle of February a distinct
+change manifests itself in the bird's behaviour.
+Observe what then happens. When they leave
+the reed-bed in the morning, instead of flying
+with their companions to the accustomed feeding
+grounds, the males isolate themselves and scatter
+in different directions. The purpose of their
+behaviour is not, however, to find fresh feeding
+grounds, nor even to search for food as they
+have been wont to do, but rather to discover
+stations suitable for the purpose of breeding;
+and, having done so, each male behaves in a
+like manner&mdash;it selects some willow, alder, or
+prominent reed, and, perching thereon, leads
+a quiet life, singing or preening its feathers.
+Now if the movements of one particular male
+are kept in view, it will be noticed that only
+part of its time is spent in its territory. At
+intervals it disappears. I do not mean that one
+merely loses sight of it, but that it actually
+deserts its territory. As if seized with a sudden
+impulse it rises into the air and flies away, often
+for a considerable distance and often in the same
+direction, and is absent for a period which may
+vary in length from a few minutes to an hour<span class='pagenum'><a name="Page_30" id="Page_30">30</a></span>
+or even more. But these periodical desertions
+become progressively less and less frequent in
+occurrence until the whole of its life is spent
+in the few acres in which it has established
+itself.</p>
+
+<p>The behaviour of the Yellow Bunting is
+similar. In any roadside hedge two or more
+males can generally be found within a short
+distance of one another, and in such a place
+their movements can be closely and conveniently
+followed. Under normal conditions the ordinary
+winter routine continues until early in February;
+but the male then deserts the flock, seeks a
+position of its own, and becomes isolated from
+its companions. Now the position which it
+selects does not, as a rule, embrace a very large
+area&mdash;a few acres perhaps at the most. But
+there is always some one point which is singled
+out and resorted to with marked frequency&mdash;a
+tree, a bush, a gate-post, a railing, anything in
+fact which can form a convenient perch, and
+eventually it becomes a central part of the
+bird's environment. Here it spends the greater
+part of its time, here it utters its song persistently,
+and here it keeps watch upon intruders. The
+process of establishment is nevertheless a
+gradual one. The male does not appear in its
+few acres suddenly and remain there permanently
+as does the migrant; at first it may not even
+roost in the prospective territory. The course
+of procedure is somewhat as follows:&mdash;At dawn
+it arrives and for a while utters its song, preens
+its feathers, or searches for food; then it vanishes,<span class='pagenum'><a name="Page_31" id="Page_31">31</a></span>
+rising into the air and flying in one fixed
+direction as far as the eye can follow, until
+it becomes a speck upon the horizon and is
+ultimately lost to view. During these excursions
+it rejoins the small composite flocks which still
+frequent the fields and farm buildings. For a
+time the hedgerow is deserted and the bird
+remains with its companions. But one does not
+have to wait long for the return; it reappears
+as suddenly as it vanished, flying straight back
+to the few acres which constitute its territory,
+back even to the same gate-post or railing,
+where it again sings. This simple routine may
+be repeated quite a number of times during the
+first two hours or so of daylight, with, of course,
+a certain amount of variation; on one occasion
+the bird may be away for a few minutes only,
+on another for perhaps half an hour, whilst
+sometimes it will fly for a few hundred yards,
+hesitate, and then return&mdash;all of which shows
+clearly enough that these few acres possess
+some peculiar significance and are capable of
+exercising a powerful influence upon the course
+of its behaviour. And so the disposition in
+relation to the territory becomes dominant in
+the life of the bird.</p>
+
+<p>Or take the case of the Chaffinch. In
+winter large or small flocks can be found in
+many varied situations. But in the latter part
+of February, or the early days of March, these
+flocks begin to disperse. At daylight males
+can then be observed in all kinds of situations,
+either calling loudly, uttering their spring note,<span class='pagenum'><a name="Page_32" id="Page_32">32</a></span>
+or exercising their vocal powers to the full;
+and it will be found that, in the majority of
+instances, these males are solitary individuals,
+that they pass the early hours of the morning
+alone, and that their normal routine of calling,
+singing, or searching for food, is only interrupted
+by quarrels with their neighbours. The same
+locality is visited regularly&mdash;not only the same
+acre or so of ground, but even the same elm
+or oak, has, as its daily occupant, the same cock
+Chaffinch. And temporary desertions from the
+territory occur also, much like those referred to
+in the life of the Bunting, but perhaps not so
+frequently. One has grown so accustomed
+during the dark days of winter to the sociable
+side of Chaffinch behaviour&mdash;to the large flocks
+searching for food, to the endless stream of
+individuals returning in the evening to roost
+in the holly-trees, to the absence of song&mdash;that
+this radical departure from the normal
+routine comes as something of a surprise; for
+the days are still short, the temperature is still
+low, the nesting season is still many weeks
+ahead, and yet for part of the day, and for just
+that part when the promptings of hunger must
+be strongest, the male, instead of joining the
+flock, isolates itself and expends a good deal of
+energy in insuring that its isolation shall be
+complete. And in place of the silence we
+hear from all directions the cheerful song
+uttered with such marked persistency that it
+almost seems as if the bird itself must be
+aware that by doing so it was advertising the<span class='pagenum'><a name="Page_33" id="Page_33">33</a></span>
+fact of its occupation of a territory. This
+is surely a remarkable change, and the females
+in the meantime continue their winter routine.</p>
+
+<p>One other example. The monotonous call
+of the Greenfinch is probably familiar to all.
+In winter these birds accompany other Finches
+and form with them flocks of varying sizes, but
+in the spring the flocks disperse, and the Greenfinch,
+in common with other units of the flock,
+alters its mode of life. But whereas the
+Chaffinch or the Bunting begins to acquire
+its territory in February, the Greenfinch only
+does so in April. When the organic changes
+do at length begin to make themselves felt,
+the male seeks a position of its own, and
+having found one remains there, uttering its
+characteristic call. But owing probably to the
+fact that it is much later than the aforementioned
+species in acquiring a territory,
+temporary desertions are not so much in evidence.
+The species is so very plentiful, and
+the bird is so prone to nest in gardens and
+shrubberies surrounding human habitations, that
+this seasonal change in its routine of existence
+cannot fail to be noticed. One can hear its
+call in every direction, one can watch the
+same individual in the same tree; and it is
+the male that is thus seen and heard, the
+female appears later. Thus the behaviour falls
+into line with that of the Bunting or the
+Chaffinch.</p>
+
+<p>The behaviour of these resident species
+throws some light upon the early arrival of the<span class='pagenum'><a name="Page_34" id="Page_34">34</a></span>
+males which we are endeavouring to explain in
+the case of the migrants. Let us see how their
+actions compare. The male resident deserts the
+female early in the year and establishes itself in
+a definite position, where it advertises its presence
+by song; the male migrant travels from a great
+distance, arrives later, and also establishes itself
+in a definite position, where it, too, advertises its
+presence by song. The male resident passes
+only the earlier part of the day in its territory at
+the commencement of the period of occupation;
+the male migrant remains there continuously
+from the moment it arrives. The male resident
+deserts its territory at intervals, even in the
+morning; the male migrant betrays no inclination
+to do so. Thus there is a very close
+correspondence between the behaviour of the
+two, and what difference there is&mdash;slight after
+all&mdash;cannot be said to affect the main biological
+end of securing territory. One is apt to think
+of the problem of migration in terms of the
+species instead of in terms of the individual.
+One pictures a vast army of birds travelling
+each spring over many miles of sea and land,
+and finally establishing themselves in different
+quarters of the globe; and so it comes about,
+I suppose, that a country or some well-defined
+but extensive area is regarded as the destination,
+the ultimate goal, of the wanderers. But the
+resident male has a journey to perform, short
+though it may be; it, too, has a destination
+to reach, neither a country nor a locality, but
+a place wherein the rearing of offspring can<span class='pagenum'><a name="Page_35" id="Page_35">35</a></span>
+be safely accomplished, and it, too, arrives in
+that place in advance of the female.</p>
+
+<p>With these facts at our disposal, we will
+endeavour to find an explanation. It is unlikely
+that specialised behaviour would occur in generation
+after generation under such widely divergent
+conditions, and, moreover, expose the birds to
+risk of special dangers, if it were but an
+hereditary peculiarity to which no meaning
+could be attached. Hence the appearance of
+the males in their breeding haunts ahead of the
+females becomes a fact of some importance, and
+suggests that the extensive journey in the one
+case, and the short journey in the other, may
+both have a similar biological end to serve.</p>
+
+<p>Darwin evidently attached importance to
+this difference between the males and the
+females in their times of arrival. In the
+<i>Descent of Man</i> he referred to it as follows:
+"Those males which annually first migrated in
+any country, or which in spring were first ready
+to breed, or were the most eager, would leave
+the largest number of offspring; and these
+would tend to inherit similar instincts and
+constitutions. It must be borne in mind that
+it would have been impossible to change very
+materially the time of sexual maturity in the
+females without at the same time interfering
+with the period of the production of the young&mdash;a
+period which must be determined by the
+season of the year." Newton suggested the
+following explanation<a name="FNanchor_2_2" id="FNanchor_2_2"></a><a href="#Footnote_2_2" class="fnanchor">2</a>: "It is not difficult to
+<span class='pagenum'><a name="Page_36" id="Page_36">36</a></span>
+imagine that, in the course of a journey prolonged
+through some 50&deg; or 60&deg; of latitude,
+the stronger individuals should outstrip the
+weaker by a very perceptible distance, and it
+can hardly be doubted that in most species
+the males are stouter, as they are bigger
+than the females." Granting that the males
+are the stronger, how can this account for their
+outstripping the females by a week, ten days,
+or even a fortnight, in a journey of perhaps
+1500 miles? To expect the birds to accomplish
+such a distance in seven days is surely
+not estimating their capabilities too highly,
+and any slight inequality in the power of
+flight or endurance could give the males an
+advantage of a few hours only. But this explanation,
+based upon inequalities in the power
+of flight and endurance on the one hand, and
+the magnitude of the distance traversed on the
+other, cannot afford a solution of the behaviour
+of the resident males, and is less likely, therefore,
+to be a true solution of that of the
+migrants.</p>
+
+<p>There is another theory, simple enough in its
+way, which will probably occur to many. It is
+based on the assumption that the males reach
+sexual maturity before the females; and it is
+contended that the functioning of the instincts
+which contribute towards the biological end of
+reproduction depend upon the organic changes
+which the term "sexual maturity" is held to
+embrace, and that, inasmuch as the migratory
+instinct belongs to the group of such instincts,<span class='pagenum'><a name="Page_37" id="Page_37">37</a></span>
+the males must be the first to leave their winter
+quarters.</p>
+
+<p>What is meant by the "migratory instinct"?
+To speak of it as one of the instincts concerned
+in reproduction is not enough. Reproduction
+involves the actual discharge of the sexual
+function, which involves the females; but the
+first visible manifestation of organic change in
+the male is its desertion of the females. Yet
+this is the behaviour which is referred to as the
+"migratory instinct," and which comes into play,
+according to this theory, because the bird has
+reached sexual maturity. Manifestly we must
+have some clear understanding as to what these
+terms represent. That organic changes determine
+the functioning of certain definite instincts
+at certain specified times there can be no doubt;
+that these changes may occur at a somewhat
+earlier date in the male than in the female is
+more than probable, but that this explains the
+behaviour in question I do not believe. One
+wants to know why the changes should occur
+earlier in the male, what disposition it is which
+first comes into functional activity, and to what
+such disposition is related.</p>
+
+<p>It may, however, be urged that, after all,
+this apparent eagerness to reach the breeding
+grounds is but a modification of hereditary procedure
+under the guiding hand of experience.
+What more likely result would follow from the
+enjoyment associated with previous success in
+the attainment of reproduction than a craving to
+repeat the experience? What stronger incentive<span class='pagenum'><a name="Page_38" id="Page_38">38</a></span>
+to a hurried return could be imagined? It must
+be admitted that there are certain facts which
+might be used in support of an appeal to
+experience as a reasonable explanation. For
+example, the first males to arrive often display
+that richness of colouring which is generally
+supposed to indicate a fuller maturity. G&auml;tke
+even speaks of the "most handsome old birds
+being invariably the first to hasten back to their
+old homes." But if experience is a factor, if
+some dim recollection of the past is held to
+explain the hurried departure of the male
+migrant, one wants to know with what such
+recollection is associated. Is it associated with
+the former female, or with the former breeding
+place, or with both? I take it that any recollection,
+no matter how vague, must be primarily
+associated with the particular place wherein
+reproduction had previously been accomplished;
+and I grant that if the first individuals to
+appear were invariably the older and experienced
+birds, their early return might be explained on
+the basis of such an association. But if there
+is reason to believe that a proportion are young
+birds on the verge of carrying out their instinctive
+routine for the first time, then we cannot
+appeal to past experience in explanation of their
+behaviour.</p>
+
+<p>The age of a bird is difficult to determine.
+Experience leads me to believe that some of
+the males that arrive before the females are
+birds born the previous season; one finds, for
+instance, individuals with plumage of a duller hue,<span class='pagenum'><a name="Page_39" id="Page_39">39</a></span>
+which denotes immaturity, amongst the first
+batch of arrivals. But though plumage may
+sometimes be a satisfactory guide, yet to rely
+upon it alone, or upon a more perfect development
+of feather, is to exceed the limits of
+safety. How, then, can we ascertain whether
+all the males that arrive before the females have
+had some previous experience of reproduction?
+Well, we take a particular locality and note the
+migrants that visit it year after year, and we
+find that the respective numbers of the different
+species are subject to wide annual fluctuations.
+Not every species lends itself to an inquiry of
+this kind: some are always plentiful and fluctuation
+is consequently difficult to discern; others
+are scarce and variation is easily determined.
+Those which are of local distribution but conspicuous
+by their plumage, or easily traced by
+the beauty or the peculiarity of their song,
+afford the more suitable subjects for investigation.
+For example, the Grasshopper-Warbler,
+Marsh-Warbler, Nightingale, Corncrake, Red-backed
+Shrike, or Whinchat have each some
+distinctive peculiarity which makes them conspicuous,
+and each one is subject to marked
+fluctuation in numbers. The small plantation or
+wooded bank may hold a Nightingale one year,
+but we miss its song there the next; the
+osier bed or gorse-covered common which vibrates
+with the trill of the Grasshopper-Warbler one
+April is deserted the following season; the
+plantation which is occupied by a host of
+common migrants this summer may be enlivened<span class='pagenum'><a name="Page_40" id="Page_40">40</a></span>
+next year by the song of the rarer Marsh-Warbler
+also; and so on. The fluctuation is
+considerable: we observe desertion on the one
+hand, appropriation on the other, and yet males
+appear before females whether the particular
+plantation, osier bed, or swamp had been inhabited
+or not the previous season. This fact is
+not without significance. It shows that similar
+conditions prevail both amongst the males that
+appropriate breeding grounds new to them, and
+amongst those that return to some well-established
+haunt; and on the assumption that
+the earlier arrivals are experienced males, the
+same birds evidently do not return to the same
+place year after year. Granting, then, that the
+males which appropriate new breeding-grounds
+are young birds, how can their earlier arrival
+be explained in terms of past experience; and
+granting that they are old, and therefore
+experienced, how can it be explained in terms of
+association?</p>
+
+<p>Again, it may be urged that if there is some
+biological end to be furthered by this hurried
+return, and if recollection of past experience is a
+means towards that end, such recollection need
+not necessarily be associated with a definite
+place, but only in a vague way with the whole
+series of events leading up to reproduction&mdash;in
+which series the migratory journey may even
+have acquired meaning. Whether there be any
+recollection of a previous journey or of a nest
+with young, I do not know. But the young
+bird is capable of performing its journey, of<span class='pagenum'><a name="Page_41" id="Page_41">41</a></span>
+building its nest, and of rearing its young antecedent
+to experience&mdash;racial preparation has
+fitted it thus far; why then exclude the other
+event in the series, the earlier departure of the
+male, from hereditary equipment? If the
+journey were a casual affair without any goal
+attaching to it, if the males upon arrival
+wandered about in search of a mate, there would
+be some ground for thinking that a vague
+recollection of the whole former experience was
+sufficient to explain the hurried return; but
+since the pleasurable effect of association,
+founded upon previous experience of a definite
+place, cannot well be established, and since it is
+so difficult to study the objective aspect of the
+behaviour in question without coming to the
+conclusion that the journey is related to the
+appropriation of a place suitable for the rearing
+of offspring, one is tempted to ask whether the
+hurried return may not also be so related.</p>
+
+<p>Now the males of some of the migratory
+species, especially of those which are accustomed
+to return to their breeding haunts early
+in the season, are called upon to face greater
+dangers and have a greater strain imposed
+upon their strength by starting forth upon their
+journey ten days or a fortnight before their
+prospective mates. The blizzards which so often
+sweep across the northern parts of Europe in
+the latter half of March, destroying in their
+course the all too scanty supply of insect life,
+may take toll of their numbers; or the westerly
+gales, which are not infrequent at that period,<span class='pagenum'><a name="Page_42" id="Page_42">42</a></span>
+may meet them in mid-ocean and add to the
+perils of their journey; or the temperature of
+the previous weeks may have been sufficiently
+low to arrest the development of insect life&mdash;and
+yet males are annually exposed to these
+risks in hurrying to their breeding grounds.
+For what purpose? The answer will largely
+depend upon the way in which we regard those
+few acres wherein a resting place is ultimately
+found. For myself, I believe that they are
+of importance, inasmuch as the securing of a
+place suitable for the rearing of offspring is
+a primary condition of success in the attainment
+of reproduction; and if this be so, it is
+evident that the interests of the race will be
+better served by the males making good this
+first step before the females are ready to pair,
+otherwise they might oscillate between two
+modes of behaviour, created by the premature
+functioning of conflicting impulses.</p>
+
+<p>The different steps in the process seem to
+follow one another in ordered sequence. The
+male inherits a disposition&mdash;which for us, of
+course, has prospective meaning&mdash;to seek the
+appropriate breeding ground and there to
+establish itself; and as early a functioning of
+this disposition as possible, consonant with the
+conditions of existence in the external environment,
+may have been evolved for the following
+reasons&mdash;firstly, the earlier individuals will
+meet with less interference wherever they may
+settle, every locality will be open to them,
+every acre free, their only need being that<span class='pagenum'><a name="Page_43" id="Page_43">43</a></span>
+particular environment for which racial preparation
+has fitted them. In the second place,
+being already established when other males
+appear upon the scene, and advertising their
+presence by song, they will be less liable to
+molestation; thirdly, in those cases in which
+a long journey is undertaken, they will have
+ample time to recover from the fatigue, and,
+if attacked by later arrivals, will thus be in a
+better position to defend their territories; and
+lastly, a greater uniformity in their distribution
+will be insured before the females begin their
+search.</p>
+
+<p>There is, besides, another good reason for
+thinking that the earlier males will have an
+advantage. We will assume&mdash;and from the
+abundant evidence supplied by the marking
+of birds, it is quite a reasonable assumption&mdash;that
+there is a tendency, generally speaking,
+for individuals to return to the neighbourhood
+of their birthplace, or to the place in which
+they had previously reared their offspring.
+Now the earlier arrivals will have no difficulty
+in securing territories; those that come later
+may have to search more diligently, still they
+will gain all that they require so long as any
+available space remains. Then comes the point
+when all suitable ground is occupied, and yet
+there are males to be provided for. What
+will be the position of these males? Urged by
+their inherited nature, they will leave the district
+and possibly continue their search into those
+adjoining, only, however, to add to the diffi<span class='pagenum'><a name="Page_44" id="Page_44">44</a></span>culties
+of the males there similarly situated;
+and even allowing that they are at length
+successful in establishing themselves, what
+are their prospects of securing mates? Since
+the earlier females will not extend their wanderings
+farther than is absolutely necessary, but
+will pair whenever the opportunity for doing
+so arises, it is to the later females, forced
+onwards by competition, that the late males
+must look for mates; so that when at length
+pairing does take place, much valuable time
+will have been lost.</p>
+
+<p class="tb">The disadvantages which the late arrivals
+have to face are therefore great, and it is
+probable that the percentage which attain to
+reproduction will on the average be somewhat
+lower than the percentage in the case of the
+earlier arrivals. The district in which my
+observations have been made lies well within
+the limits of the breeding range of most of
+our common species, and it is not surprising
+that I should have met with little evidence
+of failure to breed as a result of failure to
+secure territory. Some interesting information
+was supplied to me, however, by the late
+Robert Service. He found, in certain seasons
+in Dumfriesshire, flocks of from ten to fifty
+unmated Sedge-Warblers, which, from the time
+of their arrival in May until the middle of
+July, haunted reed-filled spaces along stagnant
+streams. These flocks appeared to him to be
+composed of loosely-attached individuals of
+a migrant flock that had failed to find things<span class='pagenum'><a name="Page_45" id="Page_45">45</a></span>
+congenial enough to entice them to disperse.
+But may they not have been composed of
+males that had failed to secure territories, or
+of females that had failed to discover males in
+possession of territories, or of both?</p>
+
+<p>We have seen that, in the case of many
+species, each male establishes itself in a
+particular place at the commencement of the
+breeding season, even though this may mean a
+partial or perhaps a complete severance from
+former companions. We must now discuss
+this fact in greater detail because it is opposed
+to the views often held regarding the sexual
+behaviour of birds, and is manifestly of importance
+when considering the theory of breeding
+territory.</p>
+
+<p>First, however, there is a point which
+requires some explanation. I speak of the <i>same</i>
+male being in the <i>same</i> place. How can I prove
+its identity? In the first place it is highly
+improbable that a bird which roams about
+within the same small area of ground, makes
+regular use of a certain tree and a certain
+branch of that tree, and observes a similar
+routine day after day, can be other than the
+same individual. But, apart from this general
+consideration, are there any means by which
+individuals of the same species can be identified?
+Well, there is variation in the plumage.
+Supposing we take a dozen cock Chaffinches
+and examine them carefully, we shall find slight
+differences in pattern and in colour&mdash;more grey<span class='pagenum'><a name="Page_46" id="Page_46">46</a></span>
+here or a duller red there, as the case may be&mdash;and
+though these differences may not be
+sufficient to enable us to pick out a bird at
+a distance, they are nevertheless conspicuous
+when it is close at hand. Then again there is
+variation in the song; and the more highly
+developed the vocal powers the greater scope
+there is for variation. But even the phrases of
+a simple song can be split up and recombined
+in different ways. If one were asked casually
+whether the different phrases of the Reed-Bunting's
+song always followed one another in
+the same sequence, the answer would probably
+be that they certainly did so, whereas the bird is
+capable of combining the few notes it possesses
+in a surprising number of different ways. And
+lastly, there are differences in just the particular
+way in which specific behaviour, founded upon
+a congenital basis, is adapted by each individual
+to its own special environment. Racial preparation
+determines behaviour as a whole, but
+the individual is allowed some latitude in the
+execution of details which are in themselves of
+small moment&mdash;the selection of a particular tree
+as a headquarters and a particular branch upon
+that tree, the direction of the distant excursion,
+and the direction of the limited wanderings
+within the small area surrounding the headquarters
+which in the course of time determine
+the extent of the territory, are matters for
+each individual to decide when the occasion
+for doing so arises. Moreover instances of
+abnormal coloration or abnormal song are not<span class='pagenum'><a name="Page_47" id="Page_47">47</a></span>
+rare, and they are valuable since they place
+the identity of the individual beyond dispute.
+I can recall the case of a Willow-Warbler whose
+song was unlike that of its own or any other
+species, and of a Redbreast whose voice puzzled
+me not a little. I can recollect also a male Yellow
+Bunting whose foot was injured or deformed.
+Of this bird's behaviour I kept a record for two
+months or so; and inasmuch as it inhabited a
+roadside hedge, and was of fearless disposition,
+the deformed foot could plainly be seen whenever
+it settled upon the road to search for food.
+Identification is not, therefore, a difficulty.
+There is always some small difference in colour
+or in song, or some well-defined routine which
+makes recognition possible.</p>
+
+<p>Owing to their great powers of locomotion,
+birds have generally been regarded as wanderers
+more or less; anything in the nature of a fixed
+abode, apart from the actual nest, having been
+accounted foreign to their mode of life; and
+even the locality immediately surrounding the
+nest has not been apprehended as possessing any
+meaning for the owner of that nest. No doubt
+the supply of food determines their movements
+for a considerable part of the year; they seek
+it where they can find it, here to-day, there
+to-morrow&mdash;in fact few species fail to move
+their quarters at one season or another, so that
+there is much truth in the notion that birds
+are wanderers. Yet to suppose that every
+individual one sees or hears&mdash;every Lapwing
+on the meadow, or Nightingale in the withy<span class='pagenum'><a name="Page_48" id="Page_48">48</a></span>
+bed&mdash;is in that particular spot just because it
+happens to alight there as it roams from place to
+place, is to take a view which the observed facts
+do not support. For as soon as the question
+of reproduction dominates the situation, a new
+condition arises, and the habits formed during
+the previous months are reversed, and the males,
+avoiding one another, or even becoming actively
+hostile, prefer a life of seclusion to their former
+gregariousness&mdash;all of which occurs just at the
+moment when we might reasonably expect them
+to exhibit an increased liveliness and restlessness
+as a result of their endeavour to secure mates;
+and so universal is the change that it might
+almost be described as an accompaniment of the
+sexual life of birds generally.</p>
+
+<p>That the Raven and certain birds of prey
+exert an influence over the particular area which
+they inhabit has long been known, and it has
+been recognised more especially in the case of
+the Peregrine Falcon, possibly because the bird
+lives in a wild and attractive country, and,
+forcing itself under the notice of naturalists, has
+thus had a larger share of attention devoted to its
+habits. Moreover, when a species is represented
+by comparatively few individuals, and each pair
+occupies a comparatively large tract of country,
+it is a simple matter to trace the movements
+and analyse the behaviour of the birds. There
+is a rocky headland in the north-west of
+Co. Donegal comprising some seven miles or
+so of cliffs, where three pairs of Falcons and two
+pairs of Ravens have nested for many years.<span class='pagenum'><a name="Page_49" id="Page_49">49</a></span>
+Each year the different pairs have been more
+or less successful in rearing their young; each
+year the young can be seen accompanying their
+parents up to the time when the sexual instinct
+arises; and yet the actual number of pairs is on
+the whole remarkably constant, and there is no
+perceptible increase. It seems as if the numbers
+of three and two respectively were the maximum
+the headland could maintain. But this
+is no exceptional case; it represents fairly the
+conditions which obtain as a rule amongst
+those species, granting, of course, a certain
+amount of variation in the size of each territory
+determined by the exigencies of diverse
+circumstances.</p>
+
+<p>If we take a given district, and devote our
+attention to the smaller migrants that visit
+Western Europe each returning spring for the
+purpose of procreation, we shall find that the
+movements of the males are subject to a very
+definite routine. This, however, is not true of
+every male; some may be wending their way to
+breeding grounds at a distance; others may be
+seeking the particular environment to which
+they may be adapted; others again, having found
+their old haunts destroyed, may consequently
+be seeking new.</p>
+
+<p>Of all this there is evidence. Small parties
+of Chiffchaffs pass through a district on their
+way to other breeding grounds, flitting from
+hedge to hedge as they move in a definite
+direction with apparently a definite purpose;
+Reed-Warblers settle in a garden or plantation,<span class='pagenum'><a name="Page_50" id="Page_50">50</a></span>
+eminently unsuited to their requirements, and
+disappear; Wood-Warblers arrive in some old
+haunt, and finding it no longer suitable for
+their purpose, seek new ground. So that plenty
+of individuals are always to be found, which, for
+the time being at least, are wanderers.</p>
+
+<p>In the district which I have in mind, the
+wandering males form only a small part of the
+incoming bird population. The majority of
+individuals that fall under observation are those
+that have made this particular district their
+destination; and in doing so, they may possibly
+have been guided by their experience as owners
+or inmates of former nests, for it cannot be
+doubted that a return to the neighbourhood of
+the birthplace would lead to a more uniform
+distribution and therefore be advantageous, and
+the tendency to do so might consequently have
+become interwoven in the tissue of the race.
+How, then, do they behave? A certain amount
+of movement, an interchanging of positions, even
+though restricted to an area defined, let us say,
+by experience, might be expected under the
+circumstances&mdash;that, however, is not what we
+find; we observe the available situations plotted
+out into so many territories, each one of which
+is occupied by a male who passes the whole of
+his time therein. Take whatever species we
+will&mdash;Whitethroat, Whinchat, Willow-Warbler,
+Red-backed Shrike, it matters not which, for
+there is no essential difference in the general
+course of procedure&mdash;this condition will be
+found to prevail. Generally speaking, the<span class='pagenum'><a name="Page_51" id="Page_51">51</a></span>
+behaviour in relation to the territory can be
+studied more conveniently where a number of
+individuals of the same species have established
+themselves in proximity to one another. Such
+species as the Chiffchaff, Willow-Warbler, or
+Wood-Warbler are often sufficiently common to
+allow of three or more of their respective males
+being kept in view at the same time; and the
+disposition to occupy a definite position can be
+readily observed. The Reed-Warbler is a suitable
+subject for an investigation of this kind;
+for since it is restricted by its habits to localities
+wherein the common reed (<i>Arundo phragmites</i>)
+grows in abundance, and since such localities
+are none too plentiful and often limited in
+extent, the area occupied by each individual is
+necessarily small&mdash;if it were not so the species
+would become extinct. Hence it is a simple
+matter to study the routine of the different
+individuals and to mark the extent of their
+wanderings.</p>
+
+<p>In this way the males of all the Warblers
+that breed commonly in Great Britain establish
+themselves, each one in its respective station at
+the respective breeding ground; so, too, do
+those of many other migrants&mdash;for example, the
+Whinchat, Wheatear, Tree-Pipit, and Red-backed
+Shrike. All of these, it is true, are
+common species&mdash;numbers of individuals can
+often be found in close proximity&mdash;and therefore
+it may be argued that they keep to one position
+more from pressure of population than from any
+inherited disposition working towards that end.<span class='pagenum'><a name="Page_52" id="Page_52">52</a></span>
+But the rarer species behave similarly. Districts
+frequented by the Marsh-Warbler and offering
+plenty of situations of the type required by the
+bird are often inhabited by a few members only,
+and yet the disposition to remain in a definite
+position is just as marked.</p>
+
+<p>You will say, however, that these smaller
+migrants have no exceptional powers of flight;
+that they have besides just completed a long
+and arduous journey; and you will ask why
+they should be expected to wander, whether it
+is not more reasonable to expect that, in order
+to overcome their fatigue, they should remain
+where they settle. The Cuckoo is a wanderer
+in the wider sense of the term, and is gifted with
+considerable powers of flight. Upon arrival the
+male flies briskly from field to field, showing but
+little signs of weariness; yet we have only to
+follow its movements for a few days in succession
+to assure ourselves that the bird is no longer
+a wanderer; for just as the Warbler or the Chat
+moves only within a definitely delimited area,
+so the male Cuckoo, strange as it may seem,
+restricts itself to a particular tract of land.
+The area over which it wanders is often considerable
+and consequently it is not possible to
+keep the bird always in view, but inasmuch
+as the variation in the voices of different
+individuals is quite appreciable, identification is
+really a simple matter. If we cannot keep the
+bird in sight, we can trace its movements by
+sound and mark the extent of its wanderings,
+which by repetition become more and more<span class='pagenum'><a name="Page_53" id="Page_53">53</a></span>
+defined, until a belt of trees here, or an orchard
+there, mark a rough and rarely passed boundary
+line.</p>
+
+<p>Let us take another example from the larger
+migrants&mdash;the Black-tailed Godwit, a bird
+common enough in the Dutch marshes but no
+longer breeding in this country. On suitable
+stretches of marsh land, numbers will be found
+in proximity one to another after the manner
+of the Lapwing, each male occupying a definite
+space of ground wherein it passes the time
+preening, searching for food, or in sleep&mdash;though
+at the same time keeping a strict watch
+over its territory. Now the preference shown
+for a particular piece of ground, and the determination
+with which it is resorted to, is the
+more remarkable when we take into consideration
+the specific emotional behaviour arising
+from the seasonal sexual condition. This
+behaviour is expressed in a peculiar flight. The
+bird rises high in the air, circles round with
+slowly beating wings above the marsh, and
+utters a call which, as far as my experience goes,
+is characteristic of the performance. The air
+is often full of individuals circling thus even
+beyond the confines of the marsh, for a male
+does not limit its flight to a space immediately
+above its territory; but nevertheless careful
+observation will show how unerringly each one
+returns to its own position on the breeding
+ground, no matter how extensive the aerial
+excursion may have been. And so, when the
+males of the smaller migrants confine their<span class='pagenum'><a name="Page_54" id="Page_54">54</a></span>
+movements to an acre of ground at the completion
+of their long journey, they are acting no
+more under the influence of fatigue than the
+Cuckoo, which keeps within certain bounds yet
+flies about briskly, or the Godwit which, though
+holding to its few square yards on the ground,
+executes most tiring and extensive flights above
+the marsh.</p>
+
+<p>Of all the migrants, however, the behaviour
+of the Ruff is perhaps the most strange, and
+though it has long been known that these birds
+have their special meeting places where they
+perform antics and engage in serious strife, yet
+it is only within recent years that the primary
+purpose of these gatherings has been ascertained&mdash;that
+purpose being the actual discharge of
+the sexual function. Mr. Edmund Selous has
+carried out some exhaustive investigations into
+their activities at the meeting places, and he
+makes it clear that each bird has its allotted
+position. He says, for example, that "It begins
+to look as though different birds had little
+seraglios of their own in different parts of the
+ground," that "each Ruff has certainly a place
+of its own," or again that "this Ruff indeed,
+which I think must be a tender-foot, does not
+seem to have a place of its own like the others."
+Nevertheless it is only at the meeting places
+that they have their special positions; there is
+no evidence to show that each one has a special
+territory, wherein it seeks its food, as the
+Warbler has, and therefore some may think that
+we are here confronted with behaviour of a<span class='pagenum'><a name="Page_55" id="Page_55">55</a></span>
+different order. But we must bear in mind that
+the process has been adjusted to meet the
+requirements of different species: the size of the
+territory, the period of its daily occupation, the
+purpose which it serves&mdash;these all depend upon
+manifold relationships and do not affect the
+principle. Why it has been differentiated in
+different circumstances we shall have occasion
+to discuss later; for the moment it is enough
+that at the end of its migratory journey each
+Ruff occupies one position on the meeting
+ground.</p>
+
+<div class="figcenter" style="width: 500px;"><a name="f073" id="f073"></a><img src="images/fig073.jpg" width="500" height="404"
+alt="Territorial flight of the Black-tailed Godwit." title="Territorial flight of the Black-tailed Godwit." /></div>
+
+<p>Now birds that are paired for life, whose
+food-supply is not affected by alternations of
+climate, have no occasion to desert the locality
+wherein they have reared their offspring, and so
+their movements, being subject to a routine
+which would tend to become increasingly
+definite, must in the course of time and according
+to the law of habit formation become
+organised into the behaviour we observe. Is it
+necessary, therefore, to seek an explanation of
+their tendency to remain in one place in anything
+so complex as an inherited disposition?
+Again, since we have to confess to so very much
+ignorance on so many points connected with the
+whole phenomenon of migration, may there not
+be some condition, hitherto shrouded in mystery,
+which might place so different a complexion on
+the corresponding aspect of migrant behaviour
+as to rid us, in their case also, of the necessity
+of appealing to an inherited disposition? Such
+questions are justifiable. And if the life-histories<span class='pagenum'><a name="Page_56" id="Page_56">56</a></span>
+of other species gave no further support
+to our interpretation, if, in short, the evidence
+were to break down at this point, then we
+should be forced to seek some other explanation
+more in keeping with the general body of
+facts.</p>
+
+<p>But far from placing any obstacle in the way
+of an interpretation in terms of inherited disposition,
+the behaviour of many of those residents
+which are not paired for life gives us even surer
+ground for that belief. Moreover in their case
+the initial stages in the process are more accessible
+to observation. I will endeavour to explain
+why. In the process of reproduction the
+environment has its part to play&mdash;whether in the
+manner here suggested, or indirectly through
+the question of food-supply, matters not at the
+moment. Now, migratory species are more
+highly specialised than resident species as
+regards food, and are affected more by variations
+of temperature, so that they can live for only a
+part of the year in the countries which they visit
+for the purpose of procreation. Hence the
+organic changes, which set the whole process in
+motion, must be coincident in time with the
+growth of appropriate conditions in the environment;
+for if it were not so, if the internal
+organic changes were to develop prematurely,
+the bird would undertake its journey only to
+find an insufficiency of food upon its arrival, and
+this would scarcely contribute towards survival.
+Definite limitations have therefore been imposed
+upon the period of organic change. But in the<span class='pagenum'><a name="Page_57" id="Page_57">57</a></span>
+case of many resident species the conditions are
+somewhat different, for they remain in the same
+locality throughout the year, and a gradual
+unfolding of the reproductive process cannot
+therefore have a similarly harmful effect. Thus
+it comes about that the behaviour of the
+migrant, when it arrives at the breeding ground
+and first falls under observation, represents a
+stage in the process which, in the case of the
+resident, is only reached by slow degrees; and
+by closely observing the behaviour as it is
+presented to us in the life of the resident male,
+we not only gain a better insight into the
+changes in operation, but can actually witness
+the breaking down of the winter routine, stereotyped
+through repetition, by the new disposition
+as it arises.</p>
+
+<p>The first visible manifestations, even though
+they may be characterised by a certain amount
+of vagueness, are therefore of great importance
+if the behaviour is to be interpreted aright; and
+in order to insure that none of these earlier
+symptoms shall be missed, it is necessary to
+begin the daily record of the bird's movements
+at an early date in the season. As a rule the
+second week in February is sufficiently early for
+the purpose, but the date varies according to the
+prevailing climatic conditions. Even in species
+widely remote there is great similarity of procedure,
+and the behaviour of the Buntings is
+typical of that of many. With the rise of the
+appropriate organic state the male resorts at
+daybreak to a suitable environment, occupies a<span class='pagenum'><a name="Page_58" id="Page_58">58</a></span>
+definite position, and singling out some tree or
+prominent bush, which will serve as a headquarters,
+advertises its presence there by song.
+At first the bird restricts its visits, which though
+frequent in occurrence are of short duration, for
+the most part to the early hours of the morning;
+it disappears as suddenly as it appeared, and
+one can trace its flight to the feeding grounds&mdash;a
+homestead or perhaps some newly sown
+field. But by degrees the impulse to seek the
+society of the flock grows less and less pronounced,
+the visits to the territory are more
+and more prolonged, and the occupation of
+it then becomes the outstanding feature of
+the bird's existence. This in outline is the
+course of procedure as it appears to an external
+observer.</p>
+
+<p>But although much can be learnt from the
+lives of these smaller species, there is no gain-saying
+the fact that a great deal of patient
+observation is required, and the process is apt
+to become tedious. There are others, however,
+which are more readily observed, whilst their
+life-histories afford just as clear an insight into
+the effect produced by the new disposition
+upon the developing situation; and among these
+the Lapwing takes a prominent position, because
+it is plentiful and inhabits open ground where
+it is easily kept in view.</p>
+
+<div class="figcenter2" style="width: 500px;"><a name="f080" id="f080"></a><a href="images/fig080z.jpg"><img src="images/fig080.jpg" width="500" height="342" alt="Plan of the
+water meadow showing the territories occupied by Lapwings in the year
+1915." title="Plan of the water meadow showing the territories occupied
+by Lapwings in the year 1915." /></a></div>
+
+<p class="caption">Plans of the Water-meadow showing the Territories occupied by Lapwings in 1915.</p>
+
+<div class="figcenter2" style="width: 500px;"><a name="f081" id="f081"></a><a href="images/fig081z.jpg"><img src="images/fig081.jpg" width="500" height="333" alt="Plan of the
+water meadow showing the territories occupied by Lapwings in the year
+1915." title="Plan of the water meadow showing the territories occupied
+by Lapwings in the year 1915." /></a></div>
+
+<p class="caption">Plans of the Water-meadow showing the Territories occupied by Lapwings in 1916</p>
+
+<p>There is a water meadow with which I am
+familiar, where large numbers resort annually
+for the purpose of procreation. Here they
+begin to arrive towards the end of February,<span class='pagenum'><a name="Page_59" id="Page_59">59</a></span>
+and at first collect in a small flock at one end
+of the meadow. A male, here and there, can
+then be seen to break away from the flock, and
+to establish itself in a definite position upon the
+unoccupied portion of the ground, where it
+remains isolated from its companions. Others
+do likewise until the greater part of the meadow
+is divided into territories. Six of these territories
+I kept under observation for approximately
+two months in the year 1915. The occupant
+of the one marked No. 6 upon the 1915 plan
+was a lame bird, a fortunate occurrence as it
+enabled me to follow its movements with some
+accuracy; and though it maintained its position
+for some weeks, it ultimately disappeared, as a
+result, I believe, of the persistent attacks of
+neighbouring males. The behaviour of the
+males during the first fortnight or so after
+they broke away from the flock was interesting.
+Though they retired to their territories and
+remained in them for the greater part of their
+time, yet it was only by degrees that they
+finally severed their connection with the flock,
+for so long as a nucleus of a flock remained,
+so long were they liable to desert their
+territories temporarily and to rejoin their
+companions.</p>
+
+<p>Lapwings, as is well known, collect in flocks
+during the winter months, and these flocks,
+which sometimes reach vast proportions, are
+to be found on tidal estuaries, water meadows,
+arable land, and such like places, according to
+the prevailing climatic conditions. This flocking<span class='pagenum'><a name="Page_60" id="Page_60">60</a></span>
+may contribute towards survival, and may
+therefore be the result of congenital dispositions
+which have been determined on biological
+grounds. On the other hand, since food at
+that season is only to be obtained in a limited
+number of situations, the birds may be simply
+drawn together by accident. In the former
+case the behaviour would be instinctive, in
+the latter, though accidental at first, recurrent
+repetition would tend to make it habitual; but
+in either case the impulse to accompany the
+flock must be a powerful one, for on the one
+hand it would depend upon inherited, and on
+the other hand upon acquired, connections in
+the nervous system. Now observe that soon
+after the flock arrived in the meadow, single
+males detached themselves; there was no
+hesitation, they just retired from their companions
+and settled in their respective territories.
+They were not expelled, for if their leaving had
+been compulsory much commotion would have
+preceded their departure, and their return
+would certainly not have been welcomed. A
+reference to the plan will make the position
+clearer; the neutral zone inhabited by the
+flock is there shown as situated in one corner
+of the meadow, the territories that fell under
+observation are plotted out as far as possible
+to scale, and the more important zones of
+conflict are also marked.</p>
+
+<p>The males spent part of their time in their
+respective territories and part with the flock,
+so long as it remained in existence. When a<span class='pagenum'><a name="Page_61" id="Page_61">61</a></span>
+male was in its territory it avoided companions
+and was openly hostile to intruders; when it
+was with the flock it wandered about with
+companions in search of food. The contrast
+between the two modes of behaviour was very
+marked, and it was evident that the gregarious
+instinct was gradually yielding its position of
+importance to the new factor&mdash;the territory.
+If there had been no flock, if a few solitary
+individuals had appeared here and there and
+had established themselves in different parts of
+the meadow, one would have had no definite
+evidence of the strength of the impulse in the
+male to seek a position of its own, one could
+only have argued from the general fact of males
+flocking in the winter and isolating themselves
+in spring that something more than accident
+was required to explain so radical a change.
+But since the birds returned in a flock to the
+ground upon which they intended to breed, and
+since the flock occupied temporarily part of
+the ground whilst the partitioning of the
+remainder was still proceeding, it was possible
+to gauge the strength of the impulse, which was
+forcing the males to isolate themselves in
+particular areas of ground, by comparing it
+with the impulse to accompany the flock&mdash;and
+the measure of its intensity was the rapidity
+with which the latter impulse yielded its position
+of importance.</p>
+
+<p>Like the Lapwing, the Coot and Moor-Hen
+are easily kept under observation, and since
+many individuals often breed in proximity,<span class='pagenum'><a name="Page_62" id="Page_62">62</a></span>
+more than one can be watched at the same
+moment; moreover the area occupied by each
+male generally embraces an open piece of
+water as well as part of the fringe of reeds,
+so that the movements of the bird can be
+followed without much difficulty. Under favourable
+conditions manifestations of the developing
+situation become visible at a comparatively
+early date in the season&mdash;the middle or the
+latter part of February&mdash;and these manifestations
+resemble those of other species. But
+the Moor-Hen passes summer and winter alike
+in the same situation, and being therefore in
+a position to respond at once to internal stimulation,
+however vague, the change from the one
+state to the other is gradual. This, however,
+is a matter of detail; the main consideration
+lies in the fact that the impulse to retire to
+a definite position, to avoid companions, and
+to live in seclusion, is strongly marked, and
+produces a type of behaviour similar on the
+whole to that of the Lapwing. First of all
+there is the appropriation of a certain position,
+the limits of which are fixed according to the
+law of habit formation, and according to the
+pressure exerted by neighbouring individuals;
+then there is the neutral ground over which
+the birds wander amicably in search of food;
+and finally there is the contrast between the
+pugnacity of the male whilst in its territory,
+and its comparative friendliness when upon
+neutral ground.</p>
+
+<p>Evidence of similar behaviour is to be found<span class='pagenum'><a name="Page_63" id="Page_63">63</a></span>
+in the life of the Black Grouse, a bird which has
+always excited the curiosity of naturalists on
+account of the special meeting places to which
+both sexes resort in the spring. Mr. Edmund
+Selous watched these birds in Scandinavia,
+where he kept a daily record at one of the
+meeting places. In various passages he refers
+to the appropriation of particular positions by
+particular males, and concludes thus: "It would
+seem from this that, like the Ruffs, each male
+Blackcock has its particular domain on the
+assembly ground, though the size of this is in
+proportion to the much greater space of the
+whole. On the other mornings, too, the same
+birds, as I now make no doubt they are,
+have flown down into approximately the same
+areas."</p>
+
+<p>The cliff-breeding species&mdash;Guillemots, Razorbills,
+and Puffins&mdash;are difficult to investigate
+because individuals vary so little, and the sexes
+resemble one another so closely; yet, despite
+these difficulties, we can gain some idea of the
+general purport of their activities. But when
+the ledges are crowded and the air is filled with
+countless multitudes, how is it possible to keep
+a single bird in view for a sufficient length of
+time to understand its routine? The difficulty
+is not an insuperable one. The flights, undertaken
+seemingly for no particular purpose, are
+often of short duration and are completed before
+the strain of observation becomes too great;
+moreover an individual sometimes possesses a
+special mark or characteristic which serves to<span class='pagenum'><a name="Page_64" id="Page_64">64</a></span>
+make it conspicuous. For example, there is a
+well-marked variety of the Common Guillemot,
+the Ringed or Bridled Guillemot of science,
+distinguished by an unusual development of
+white round the eye and along the furrow
+behind it. One such individual I was fortunate
+in discovering upon a crowded cliff, and, as in
+the case of the Lapwing with the broken
+leg or the Yellow Bunting with the injured
+foot, the identity of the bird was beyond dispute,
+and one could observe that it appropriated
+to itself a particular position upon a particular
+ledge.</p>
+
+<p>Guillemots and Razorbills return at intervals
+to the breeding stations early in the season, and
+these visits are repeated with growing frequency
+until the birds are finally established. I have
+witnessed these periodic returns during March
+in the south of England, and during April in
+the north-west of Ireland, and I am informed
+that in the latter district such visits may occur
+as early as February. G&auml;tke, who had ample
+opportunity of observing the birds in Heligoland,
+puts their return at an even earlier date. "They
+visit their breeding places," he says, "in flocks
+of thousands at the New Year, often even as
+early as December, as though they wanted to
+make sure of their former haunts being well
+preserved and ready for their reception." Such
+visits, however, are irregular in occurrence; the
+birds arrive, and, after spending a short time
+upon the ledges, disappear. And since there is
+not the same evidence in their coming and going<span class='pagenum'><a name="Page_65" id="Page_65">65</a></span>
+of that method which we observe in the
+periodical returns of the Bunting or the Finch,
+it may be thought that needless importance
+is being attached to an episode in their lives
+which is quite intelligible in terms of a feeble
+response determined by a dawning organic
+change. While it may be quite intelligible in
+such terms it is not thereby explained; for
+every response must have as its antecedent an
+inherited connection in the nervous system
+determined on biological grounds. Besides,
+these early periodic returns conform in general
+to the type of behaviour displayed by other
+species, the males of which return to their breeding
+grounds many weeks before the real business
+of reproduction begins. Are we then justified in
+regarding them as accidents of the developing
+situation? Are we not rather bound to admit
+that they have some definite biological end to
+serve?</p>
+
+<div class="figcenter" style="width: 500px;"><a name="f089" id="f089"></a><img src="images/fig089.jpg" width="500" height="866"
+alt="Competition for territory is seldom more severe than
+amongst cliff-breeding sea birds, and the efforts of
+individual Razorbills to secure positions on the
+crowded ledges lead to desperate struggles.." title="Competition for territory is seldom more severe than
+amongst cliff-breeding sea birds, and the efforts of
+individual Razorbills to secure positions on the
+crowded ledges lead to desperate struggles." /></div>
+
+<p class="tb">These examples show that the males of many
+species reverse their mode of life at the commencement
+of the breeding season and proceed
+to isolate themselves, each one in a definitely
+delimited area.</p>
+
+<p>There are three ways in which we may
+attempt to interpret this particular mode of
+male behaviour. We may regard it as an
+accidental circumstance, nowise influencing the
+course of subsequent procedure; or, appealing
+to the law of habit formation, we may
+regard it as an individual acquirement; or<span class='pagenum'><a name="Page_66" id="Page_66">66</a></span>
+again, we may invest it with a deeper significance
+and seek its origin in some specific
+congenital disposition determined on purely
+biological grounds.</p>
+
+<p>Which of these three shall we choose? The
+first by itself requires but little consideration;
+for though it might explain the initial visit, it
+cannot account for the persistency with which
+the plot of ground is afterwards resorted to.
+Supposing, however, that we combine the first
+and the second; supposing, that is to say, we
+assume, for the purpose of argument, that the
+initial visit is fortuitous, and that constancy is
+supplied by habit formation&mdash;would that be a
+satisfactory interpretation? It is a simple one,
+inasmuch as it only requires that a male shall
+alight by chance in a particular place for a few
+mornings in succession in order that the process
+may be set in motion. Now an essential condition
+of habit formation is recurrent repetition;
+given this repetition and, it is true, any mode of
+activity is liable to become firmly established.
+But how can we explain the repetition? Even
+if we are justified in assuming that the initial
+visit is purely an accidental occurrence, we
+cannot presume too far upon the laws of chance
+and assume that the repetition, at first, is also
+fortuitous.</p>
+
+<p>So that we come back to the congenital
+basis, the last of our three propositions. And it
+will, I think, be admitted that the facts give us
+some grounds for believing that the securing of
+the territory has its root in the inherited con<span class='pagenum'><a name="Page_67" id="Page_67">67</a></span>stitution
+of the bird. In comparing the behaviour
+of the migratory male with that of the resident,
+attention was drawn to the manner in which
+the occupation of a territory was effected: the
+former bird, it may be remembered, established
+itself without delay, whereas the latter did so
+only by degrees, and the difference was attributed
+to the incidence of migration which required
+a closer correspondence between organic process
+and external environment. But the significance
+for us just now lies in the fact that the definiteness,
+which accompanies the initial behaviour of
+the migratory male in relation to the territory,
+cannot have been acquired by repetition; for
+this reason, that when the male occupies its
+space of ground at the end of its long and
+arduous journey, it does so without preparation
+or experiment, even without hesitation, as if
+aware that it was making good the first step in
+the process of reproduction. No doubt, if it
+happened to be an individual that had already
+experienced the enjoyment of reproduction, it
+might be aware of the immediate results to be
+achieved and act accordingly. But among the
+hosts of migrants that one observes, there must
+be many males which have not previously mated;
+and yet, upon arrival, they all behave in a
+similarly definite manner&mdash;so that experience
+cannot well be the primary factor in the situation.
+If, then, the essential condition of habit
+formation is absent and experience is eliminated,
+there is nothing left but racial preparation to fall
+back upon.</p>
+
+<p><span class='pagenum'><a name="Page_68" id="Page_68">68</a></span>Nevertheless, it is true that many resident
+males seem to pass through a period of indecision
+before they establish themselves permanently
+in their respective territories; they come and
+go, their visits grow more and more prolonged,
+and only after the lapse of some
+considerable time does the process of establishment
+attain that degree of completeness which
+is represented in the initial behaviour of the
+migratory male. Their whole procedure seems
+therefore to bear the stamp of individual acquirement;
+and, if it stood alone, we might be
+content to construe it thus, but the example
+of the migratory male necessitates our looking
+elsewhere for the real meaning of the
+indecision.</p>
+
+<p>Let me first of all give some instances of the
+persistence with which a male remains in one
+spot, and this despite the fact that it has
+no mate.</p>
+
+<p>A Reed-Bunting occupied a central territory
+in a strip of marshy ground inhabited annually
+by four or five males of this species. Throughout
+April, May, and until the 19th June, it
+clung to its small plot of ground, tolerated no
+intrusion, and sang incessantly.</p>
+
+<p>Two Whitethroats arrived at much the
+same time&mdash;the 30th April approximately&mdash;and
+occupied the corner of a small plantation;
+the one obtained a mate the day following
+its arrival, the other remained unpaired for a
+fortnight.</p>
+
+<p>A Reed-Warbler established itself amongst<span class='pagenum'><a name="Page_69" id="Page_69">69</a></span>
+some willows and alders adjoining a reed-bed
+and made its headquarters in a small willow
+bush. Not more than fifteen yards away, on the
+edge of the main portion of the reeds, another
+male was established and was paired on the 22nd
+May. Each morning the single male behaved
+in much the same way, singing continuously
+whilst perched upon the bush. And so the
+days passed by until it seemed improbable
+that it would ever secure a mate, but one
+appeared on the 20th June, and a nest was built
+forthwith.</p>
+
+<p>Now it is difficult to believe that a chance
+visit, even though repeated for a few mornings
+in succession, could have accounted for the
+Reed-Bunting remaining so persistently in the
+marsh, or the Whitethroat in one corner of the
+osier bed, or the Reed-Warbler in that one
+particular willow. Not only so, but if a habit of
+such evident strength can be acquired so readily,
+we have a right to ask why it should only be
+acquired in the spring&mdash;why not at every season?
+Considerations such as these lead to the belief
+that there must be some congenital basis to
+account for such persistent endeavour; the more
+so since it is difficult not to be impressed with
+the conative aspect of the male's behaviour. To
+a stranger, unacquainted with its previous
+history, the bird might appear to be leading a
+life of hesitation, whereas, if carefully watched,
+its whole attitude will be found to betray
+symptoms of a striving towards some end; and
+the frequent departure and return, which might<span class='pagenum'><a name="Page_70" id="Page_70">70</a></span>
+be pointed to as the material from which a
+definite mode of procedure would be likely to
+emerge, is in reality behaviour of a determinate
+sort.</p>
+
+<p>My interpretation, then, of the apparent
+indecision in the behaviour of the resident male
+is this. During the winter most species live in
+societies, together they seek their food and
+together they retire in the evening to the
+accustomed roosting places; and the association
+of different individuals confers mutual benefits
+upon the associates. The movements of these
+societies are dominated by the question of food;
+all else is subservient, and the supply of the
+necessary sustenance may, under certain conditions,
+become a difficulty which can only be
+met by energy and resource. After the long
+night the sensation of hunger is strong, and the
+birds, on awakening, fly to the accustomed
+feeding grounds, returning again in the evening
+to the selected spot, and by frequent repetition
+a routine becomes established. Thus
+the behaviour of each individual is determined
+not only by the powerful gregarious impulse
+but also by the habits formed in connection
+therewith during many weeks in succession.
+Now with the rise of the appropriate organic
+state, the disposition to seek the breeding
+ground and there to establish itself becomes
+dominant in the male. But the process is a
+gradual one. There is no need, as happens
+amongst the migrants, for the period of organic
+change to conform rigidly to the growth of<span class='pagenum'><a name="Page_71" id="Page_71">71</a></span>
+any particular condition in the environment,
+and hence for a time the bird oscillates between
+two modes of behaviour&mdash;between that one
+organised by frequent repetition and that one
+determined by the functioning of this new
+disposition.</p>
+
+<p>To look at the matter broadly, it is scarcely
+likely that so definite a mode of behaviour would
+recur with such regularity, generation after
+generation, in the individuals belonging to so
+many widely divergent forms, if it had no root
+in the inborn constitution of the bird. But the
+law of habit formation has its part to play also.
+By itself it is inadequate; yet it probably does
+assist very materially in adding still greater
+definition, and it probably is responsible in a
+large measure for determining the limits of
+the territory according to the conditions of
+existence of the species&mdash;thus the Falcon
+seeks its prey over wide tracts of land, and,
+by hunting over certain ground repeatedly,
+establishes a routine, which broadly fixes the
+area occupied; the Woodpecker cannot find
+food upon every tree, and every forest does
+not contain the necessary trees, and therefore
+the bird regulates its flight according to the
+position of the trees; and the Warbler, finding
+food close at hand, does not need to travel
+far, and the area it occupies is consequently
+small.</p>
+
+<p>So that the most likely solution of the
+problem will be found in a combination of our
+second and third propositions; that is to say, in<span class='pagenum'><a name="Page_72" id="Page_72">72</a></span>
+an initial responsive behaviour provided for in
+the inherited constitution of the nervous system,
+and in a definiteness acquired by repetition and
+determined by relationships in the external
+environment.</p>
+<hr />
+<p><span class='pagenum'><a name="Page_73" id="Page_73">73</a></span></p>
+<h3>CHAPTER III</h3>
+
+<h4>THE DISPOSITION TO DEFEND THE TERRITORY</h4>
+
+
+<p>In the previous chapter I endeavoured to show
+that each male establishes a territory at the
+commencement of the breeding season, and there
+isolates itself from members of its own sex.
+And further I gave my reasons for believing
+that this particular mode of behaviour is determined
+by the inherited nature of the bird, and
+that we are justified in speaking of it as "a
+disposition to secure a territory" because we can
+perceive its prospective value. But the act of
+establishment is only one step towards "securing."
+By itself it can achieve nothing; for any number
+of different individuals might fix upon the same
+situation, and if there were nothing in the
+inherited constitution of the bird to prevent
+this happening, where would be the security, or
+how could any benefit accrue to the species?</p>
+
+<p>In withdrawing from its companions in the
+spring, the male is breaking with the past, and
+this action marks a definite change in its routine
+of existence. But the change does not end in
+attempted isolation; it is carried farther and
+extends to the innermost life and affects what,<span class='pagenum'><a name="Page_74" id="Page_74">74</a></span>
+humanly speaking, we should term its emotional
+nature, so that the bird becomes openly hostile
+towards other males with whom previously it
+had lived on amicable terms.</p>
+
+<p>The seasonal organic condition is responsible
+for the functioning of the disposition which
+results in this intolerance, just as it is for
+the functioning of the disposition which leads
+to the establishment of the territory; and the
+effect of these two dispositions is that a space of
+ground is not only occupied but made secure
+from intrusion. The process is a simple one.
+There is no reason to believe, there is no
+necessity to believe, that any part of the procedure
+is conditioned by anticipatory meaning;
+the behaviour is "instinctive" in Professor
+Lloyd Morgan's definition of the word, since it
+is of a "specific congenital type, dependent upon
+purely biological conditions, nowise guided by
+conscious experience though affording data for
+the life of consciousness."</p>
+
+<p>That the males of many animals are apt to
+become quarrelsome during the mating period is
+notorious. Darwin collected a number of facts,
+many of which related to birds, showing the
+nature and extent of the strife when the sexual
+instinct dominated the situation. And pondering
+over these facts, he deduced therefrom a "law of
+battle," which, he believed, bore a direct relation
+to the possession of a female. And it must
+be admitted that he had excellent ground for his
+conclusion in the fact not only that the conflicts
+occur mainly during the pairing season, but that
+<span class='pagenum'><a name="Page_75" id="Page_75">75</a></span>
+the female is often a spectator and seems even to
+pair with the victor. I accepted it, therefore, as
+the most reasonable interpretation of the facts.
+But, as time passed by, incidents of a conflicting
+character led me to think that after all there
+might be another solution of the problem. And
+when it was no longer possible to doubt that
+there was a widespread tendency to establish
+territories, it at once became manifest that the
+battles might have an important part to play in
+the whole scheme. But how was this to be
+proved? What sort of evidence could show
+whether the proximate end for which the males
+were fighting had reference to the female or to
+the territory? Clearly nothing but a complete
+record of the whole series of events leading up
+to reproduction could supply the necessary data
+upon which a decision might rest. In the
+present chapter I shall give, in the first place,
+the reasons which lead me to think that the
+origin of the fighting cannot be traced to the
+female; afterwards, the evidence which seems to
+show that it must be sought in the territory;
+and finally, I shall make a suggestion as to the
+part the female may play in the whole scheme.</p>
+
+<div class="figcenter" style="width: 500px;"><a name="f101" id="f101"></a><img src="images/fig101.jpg" width="500" height="426"
+alt="Male Blackbirds fighting for the possession of territory.
+The bare skin on the crown of the defeated bird shows the
+nature of the injuries from which it succumbed." title="Male Blackbirds fighting for the possession of territory.
+The bare skin on the crown of the defeated bird shows the
+nature of the injuries from which it succumbed." /></div>
+
+<p>The facts upon which the "law of battle"
+was founded were ample to establish the truth of
+its main doctrine. But the evidence upon which
+the interpretation of the battles was based was
+somewhat superficial. It was based mainly upon
+the general observation that one or more females
+could frequently be observed to accompany the
+combatants; and if this were the sole condition<span class='pagenum'><a name="Page_76" id="Page_76">76</a></span>
+under which the fighting occurred, one must
+admit that this view would have much to
+recommend it. But it is not merely a question
+of males disputing in the presence of a female;
+for males fight when no female is present, pair
+attacks pair, or a male may even attack a female&mdash;in
+fact there is a complexity of strife which is
+bewildering.</p>
+
+<p>In attributing the rivalry to the presence
+of the female, it is assumed that males are in
+a preponderance, and that consequently two or
+more are always ready to compete for a mate.
+Her presence is presumably the condition under
+which his pugnacious nature is rendered susceptible
+to its appropriate stimulus, the stimulus
+being, of course, supplied by the opponent.
+There would be nothing against this interpretation
+if it were in accord with the facts; but it
+can, I think, be shown that the males are just
+as pugnacious and the conflicts just as severe
+even when the question of securing a mate
+is definitely excluded; and I shall now give the
+evidence which has led me to this conclusion.</p>
+
+<p>In the previous chapter we had occasion to
+refer to the difference in the times of arrival
+of the male and female migrants, and we
+came to the conclusion, it may be remembered,
+that this was a fact of some importance,
+because it gave us a clue to the meaning
+of much that was otherwise obscure in their
+behaviour. But it is also of importance in
+connection with the particular aspect of the
+problem which we now have in view, for if it<span class='pagenum'><a name="Page_77" id="Page_77">77</a></span>
+can be shown that males, when they first reach
+their breeding grounds, are even then intolerant
+of one another's presence, if their actions and
+attitudes betray similar symptoms of quasi-conation,
+if disputes are rife and the struggles
+of a kind to preclude all doubt as to their
+reality, then it is manifest that in such cases
+their intolerance cannot be due to the presence
+of the female.</p>
+
+<p>Here, however, I must refer to a view which
+is held by some psychologists, namely, that
+amongst the higher animals, even on the
+occasion of the first performance of an instinctive
+act, there is some vague awareness of the
+proximate end to be attained. Discussing the
+nature of instincts, Dr M'Dougall<a name="FNanchor_3_3" id="FNanchor_3_3"></a><a href="#Footnote_3_3" class="fnanchor">3</a> says, "Nor
+does our definition insist, as some do, that the
+instinctive action is performed without awareness
+of the end towards which it tends, for this,
+too, is not essential; it may be, and in the case
+of the lower animals no doubt often is, so
+performed, as also by the very young child,
+but in the case of the higher animals some
+prevision of the immediate end, however vague,
+probably accompanies an instinctive action that
+has often been repeated." A similar view seems
+to be held by Dr Stout.<a name="FNanchor_4_4" id="FNanchor_4_4"></a><a href="#Footnote_4_4" class="fnanchor">4</a> "As I have already
+shown," he says, "animals in their instinctive
+actions do actually behave from the outset as
+if they were continuously interested in the
+development of what is for them one and the
+same situation or course of events; they actually
+<span class='pagenum'><a name="Page_78" id="Page_78">78</a></span>behave as if they were continuously attentive,
+looking forward beyond the immediately present
+experience in preparation for what is to come.
+They apparently watch, wait, search, are on the
+alert. They also behave exactly as if they
+appreciated a difference between relative success
+and failure, trying again when a certain perceptible
+result is not attained and varying their
+procedure in so far as it has been unsuccessful.
+All these characters are found in the first nest-building
+of birds as well as in the second; they
+are found also in courses of conduct which occur
+only once in the lifetime of the animal." Both
+these writers would, I imagine, contend that,
+even when a female is absent, the idea of the
+female, as the end in view throughout, is
+present; and they would argue that the fact
+of her absence during the fighting in no way
+disposes of the belief that she is the condition
+under which the pugnacious instinct of the
+male is rendered susceptible to stimulation.
+What reason is there to think that this interpretation
+is applicable to the case under consideration?
+When a female is present, we
+observe that the males are pugnacious, and,
+when she is absent, that they still continue to
+be hostile&mdash;that is to say, they behave <i>as if</i> she
+were present. Now, as far as I can ascertain,
+the "<i>as if</i>" is the only ground there is for
+supposing that the female is represented in
+imaginal form&mdash;there is no evidence of the
+fact, if fact it be. On the contrary, the behaviour
+of the male affords some fairly conclusive evidence<span class='pagenum'><a name="Page_79" id="Page_79">79</a></span>
+that no such image is the primary factor in
+exciting the instinctive reaction. For if it be
+the actual presence of the female, or, in the
+absence of such, a mental image, that renders
+the pugnacious nature of the male responsive;
+provided the usual stimulus were present, the
+instinct ought surely to respond, not only under
+one particular circumstance, but under all
+circumstances. Yet, as we shall presently see,
+a male is by no means consistently intolerant
+of other males. It may be sociable at one
+moment or pugnacious at another, but the
+pugnacity is always peculiar to a certain
+occasion&mdash;the occupation of a territory. What
+shall we say then&mdash;that a mental image is a
+situational item only when the territory is
+occupied? It may be so; it may be that the
+fact of occupation gives rise to the mental image
+which, in its turn, renders the fighting instinct
+explosive, which again renders the possession
+of the territory secure. That such an interpretation
+is possible we must all admit. But
+if it were true, though it would not affect
+the main consideration, namely, whether the
+fighting has reference to the possession of a
+particular female, or to the protection of the
+territory, it would make further discussion as
+to which of these is the condition of the fighting
+unprofitable, for each would have its part to
+play in the process, the territory remaining,
+however, the principal factor in the situation.</p>
+
+<p>Now the difference in the times of arrival
+of the male and female migrant varies in<span class='pagenum'><a name="Page_80" id="Page_80">80</a></span>
+different species from a few days to a fortnight
+or even more. It is most marked in those that
+return to their breeding grounds early in the
+season, and the greater the margin of difference
+the greater scope is there for observation. In
+my records for the past twelve years, there are
+frequent references to these initial male contests in
+the life of the Willow-Warbler and of the Chiffchaff;
+and in the district which I have in mind,
+these two species arrive early in the season, the
+males preceding the females by a week or even
+as much as a fortnight. Suppose, then, that two
+Chiffchaffs establish themselves in adjoining
+territories; or suppose that a male settles in a
+territory already occupied; what is the result?
+Well, scenes of hostility soon become apparent;
+as the birds approach one another they become
+more and more restive, their song ceases, they
+no longer search for food in the usual methodical
+manner, but instead their movements are hurried
+and their call-notes are uttered rapidly&mdash;all of
+which betrays a heightened emotional tone.
+Then the climax is reached, there is a momentary
+fluttering of tiny wings, a clicking of bills, and
+for the time being that may be all. But unless
+one or other of the combatants retires, this scene
+may be repeated many times in the course of a
+few hours, and repeated with varying degrees of
+severity. Yet the fighting, even in the most
+extreme form, when the birds locked together
+fall slowly to the ground, is seldom of an
+impressive kind, and one has to bear in mind
+the capabilities of the actors, remembering that<span class='pagenum'><a name="Page_81" id="Page_81">81</a></span>
+the most severe struggle might readily be interpreted
+as a game if it were not for certain
+symptoms which reveal its inner nature.</p>
+
+<p>The males of many other migrants can frequently
+be observed to fight when there was
+every reason to believe that females had still
+to arrive. The Blackcap is notoriously pugnacious,
+but not more so than the Marsh-Warbler
+or the Whinchat. Here in Worcestershire, the
+<i>Arundo phragmites</i> grows mainly on certain
+sheets of water which are comparatively few
+and far between, and the Reed-Warbler is
+consequently restricted to isolated and more or
+less confined areas. The males arrive early in
+May before the new growth of reeds has
+attained any considerable height, and each one
+has its own position in the reed-bed, sings there,
+and throughout the whole period of reproduction
+actively resists intrusion on the part of other
+males. I have kept watch upon a small area
+of reeds daily from the date of the first arrival;
+each individual was known to me, and as the
+growing reeds were only a few inches in height,
+a female could scarcely have escaped detection.
+Yet time and again disputes arose, and males
+pursued and pecked one another, striving to
+attain that isolation for which racial preparation
+had fitted them.</p>
+
+<p>But on account of their violence, or their
+novelty, or because the absence of a female was
+beyond question, some battles stand out in one's
+memory more prominently than others. An
+instance of this was a struggle between two<span class='pagenum'><a name="Page_82" id="Page_82">82</a></span>
+Whitethroats which happened in the latter part
+of April and lasted for three successive days.
+The scene of its occurrence was more or less the
+same on each occasion, and the area over which
+the birds wandered was comparatively small.
+The fighting was characterised by persistent
+effort and was of a most determined kind, and
+so engrossed did the assailants become that they
+even fluttered to the ground at my feet. No
+trace of a female was to be seen at any time
+during these three days, nor, during the pauses
+in the conflict, was the emotional behaviour of
+a kind which led me to suppose that a female
+was anywhere in the vicinity. And, if she had
+been near, she must have made her presence
+known, for the belief that she is a timid creature,
+skulking on such occasions in the undergrowth,
+is by no means borne out by experience.</p>
+
+<p>Even more impressive was a battle between
+two male Cuckoos. It occurred high up in the
+air above the tops of some tall elm-trees which
+roughly marked the boundary line between their
+respective areas, and the actions of the birds
+were plainly visible. At the moment of actual
+collision the opponents were generally in a
+vertical position, and wings, feet, and beaks were
+made use of in turn; one could plainly see them
+strike at one another with their feet, and one
+could observe the open bill which generally
+denotes exhaustion, but may of course have been
+due to anger, or used as a means of producing
+terror. Yet no female appeared in the locality until
+six days after the occurrence of this struggle&mdash;and<span class='pagenum'><a name="Page_83" id="Page_83">83</a></span>
+she certainly is not easily overlooked, for her
+note is unmistakable even when the behaviour of
+the male does not betray her arrival.</p>
+
+<div class="figcenter" style="width: 500px;"><a name="f111" id="f111"></a><img src="images/fig111.jpg" width="500" height="756" alt="Male Cuckoos
+fighting before the arrival of a female." title="Male Cuckoos fighting
+before the arrival of a female." /></div>
+
+<p>That the actual presence of the respective
+females exercised any influence on the course of
+these struggles is more than doubtful. Not only
+did one fail to detect them, but one's failure to
+do so was confirmed by the knowledge that they
+had not yet arrived in those particular localities.
+Hence the fact of the male preceding the female
+is a valuable aid to the interpretation of subsequent
+behaviour; and one appreciates it the
+more after having experienced the difficulty of
+deciding whether she is present during the
+conflicts between resident males, for no matter
+how carefully we may observe the conditions
+which lead up to, and which accompany, such
+conflicts, or how closely we may scrutinise the
+surrounding trees, undergrowth, or ground, there
+always remains the possibility that she may,
+after all, have been overlooked. But this must
+not be taken to imply that in such cases direct
+observation alone can lead to no serviceable
+result, or that the evidence gained therefrom is
+worthless. Far from it. Failure to detect a
+female is so very common an occurrence that,
+even if we lacked the corroborative evidence
+supplied in the life of the migratory male, it
+would still be unreasonable to suppose that it
+were solely due to mistaken observation. We
+mark her absence during the conflicts between
+the respective males of many common species&mdash;the
+Finches, Buntings, and Thrushes that occupy<span class='pagenum'><a name="Page_84" id="Page_84">84</a></span>
+their territories early in the season when the
+hedgerows and trees are still bare; but more frequently
+amongst those that inhabit open ground,
+because the movements of the birds are there
+more accessible to observation. For instance,
+half a dozen or more Lapwings can be kept in
+view at the same time, and as they stand at dawn
+in solitary state, keeping watch upon their respective
+territories, they are conspicuous objects on
+the short, frosted grass; no stranger can enter the
+arena without the observer being aware of it, no
+commotion can occur but one detects it, no
+movement however small need be missed. And
+so they fight, in a manner which leaves no doubt
+as to the reality of the struggle, when their
+prospective mates are absent not only from the
+particular territories in which the conflicts take
+place, but absent too from those adjoining.</p>
+
+<p>If the fact that males fight before they are
+paired and in the absence of a female could be
+placed beyond all question, it would no longer
+be possible to regard her possession as the end
+for which they are contending, and consequently
+there would be no need to produce further
+evidence. But the examples which I have given
+refer, of course, to only a few migrants and a few
+residents&mdash;and moreover it must be admitted
+that a female <i>is</i> often conspicuous during the
+battles&mdash;so that by themselves they must
+be regarded, and rightly so, as inconclusive.
+We must therefore pass on to consider evidence
+of a somewhat different character.</p>
+
+<p>I spoke of the complexity of the strife. By<span class='pagenum'><a name="Page_85" id="Page_85">85</a></span>
+this I mean that it is not merely a matter of
+disputes between adjoining males, but that it
+is a far more comprehensive business involving
+both sexes. Thus female fights with female and
+pair with pair, or a male will attack a female, or,
+again, a pair will combine against a single male
+or a single female. And from all this complexity
+of strife we gain much valuable evidence
+in regard to the question immediately before us.
+For when one pair attacks another, or males
+that are definitely paired fight with one another,
+or an unpaired male attacks either sex of a
+neighbouring pair indiscriminately, there is
+surely little ground for supposing that the
+possession of a mate is the reason of it all.</p>
+
+<p>The battles between pairs of the same species
+are by no means uncommon. Observe, for
+example, the central pair of three pairs of Reed-Buntings
+occupying adjoining territories, and
+keep a daily record of the routine of activity
+practised by both sexes during the early hours
+of the morning; then, at the close of the season,
+summarise all the fighting under different headings,
+and it will be found that the number of
+occasions upon which the central pair attacked,
+or was attacked by, neighbouring pairs will form
+a considerable portion of the whole.</p>
+
+<p>Or watch the Moor-Hen, and for the purpose
+choose some sheet of water large enough to
+accommodate three or more pairs, and so situated
+that the birds can always be kept in view.
+Early in February the pool will be haunted
+by numbers of individuals of both sexes, all<span class='pagenum'><a name="Page_86" id="Page_86">86</a></span>
+swimming about together, and, if the pool is
+surrounded by arable land, wandering over that
+land subject to no territorial restrictions, apparently
+free to seek food where they will. But as
+time goes by, their number gradually decreases
+until a few pairs only remain, and these will
+occupy definite areas. If careful watch is then
+kept and the relations of the pairs closely
+studied, there will be no difficulty in observing
+the particular kind of warfare to which I
+am alluding, and it will be noticed that the
+encounters are of a particularly violent description.
+Thus two pairs approach one another,
+and, when they meet, throw themselves upon
+their backs, each bird striking at its adversary
+with its feet or seizing hold of it with its beak;
+and though, in the commotion that ensues, it is
+almost impossible to determine what exactly is
+happening, there is reason to believe that the
+sexes attack one another indiscriminately.</p>
+
+<p>A struggle between two pairs of Pied Wagtails
+is worth mentioning. It impressed itself
+upon my memory because of the unusual vigour
+with which it was conducted. The battle lasted
+for fifteen minutes or more, and the four birds,
+collecting together, pursued and attacked one
+another&mdash;at one moment in the air, at another
+upon the roof of a house where they would
+alight and flutter about on the slates, uttering
+their call-note without ceasing&mdash;until finally
+they disappeared from view, still, however, continuing
+the struggle.</p>
+
+<div class="figcenter" style="width: 500px;"><a name="f117" id="f117"></a><img src="images/fig117.jpg" width="500" height="756" alt="Two pairs of Pied Wagtails fighting
+in defence of their territories." title="Two pairs of Pied Wagtails fighting
+in defence of their territories." /></div>
+
+<p>Such is the nature of the warfare which<span class='pagenum'><a name="Page_87" id="Page_87">87</a></span>
+prevails between neighbouring pairs, and which
+can be observed in the life of many other
+species&mdash;the Chaffinch, Stonechat, Blackbird,
+Partridge, Jay, to mention but a few.</p>
+
+<p>The conflicts between males that are
+definitely paired are of such common occurrence
+that it is scarcely necessary to mention specific
+instances. But the occasions on which a male
+attacks either sex of a neighbouring pair indiscriminately,
+or on which a pair combine to
+attack a female, are less frequent.</p>
+
+<p>Now if it be true that males fight for no other
+purpose than to gain possession of a mate, what
+meaning are we to attach to the battles between
+the pairs, or what explanation are we to give
+of the fact that paired males are so frequently
+hostile? Those who hold this view will probably
+argue thus: "The presence of the female
+is the condition under which the pugnacious
+instinct of the male is rendered susceptible
+to appropriate stimulation, and the stimulus
+is supplied by a rival male; we admit that
+all the fighting which occurs after pairing has
+taken place has nothing to do strictly speaking
+with gaining a mate, but, inasmuch as the
+fact of possession is always liable to be challenged&mdash;and
+no male can differentiate between a paired
+and an unpaired intruder&mdash;we contend that it
+would add to the security of possession if the
+pugnacious instinct remained susceptible to
+stimulation so long as there were any possibility
+of challenge from an unpaired male; and we
+think that the waste of energy involved in<span class='pagenum'><a name="Page_88" id="Page_88">88</a></span>
+the struggles between paired birds, and which
+we grant is purposeless, would be more than
+balanced by the added security." This is a
+possible explanation and requires consideration.
+It cannot account for all the diverse ways in
+which the sexes are mixed up in the fighting&mdash;it
+cannot, for instance, explain the fact that an
+unpaired male will attack either sex of an
+adjoining pair indiscriminately&mdash;but nevertheless
+it appears at first sight to be a reasonable
+explanation of some of them. We must
+remember, however, that fighting continues
+throughout the whole period of reproduction.
+Even after the discharge of the sexual function
+has ceased, and the female is engaged in incubation
+or in tending her young, the male is still
+intolerant of intruders; and it is difficult to
+believe that, at so late a stage in the process, a
+female could be any attraction sexually to an
+unpaired male. But apart from any theoretical
+objection, there remains the fact&mdash;namely that
+there is no evidence that a male, after having
+once paired, is liable to be robbed of its mate.
+And in support of this fact I have only to state
+that I have met with no single instance of
+failure to obtain and hold a mate when once a
+territory had been secured. Bearing in mind
+then that both sexes participate in the fighting,
+and that individuals of the opposite sex frequently
+attack one another; that all such
+conflicts are characterised by persistent effort,
+and that they are not limited to just the
+particular period when the sexual instinct is<span class='pagenum'><a name="Page_89" id="Page_89">89</a></span>
+dominant but continue throughout the breeding
+season; bearing in mind that in at least one
+form of this promiscuous warfare the influence
+of the female can be definitely excluded, and
+that, in the remaining forms, the evidence which
+is required to link them up with the biological
+end of securing mates is lacking&mdash;can it be
+denied that the complexity of the strife makes
+against the view that the possession of a female
+is the proximate end for which the males are
+fighting?</p>
+
+<p class="tb">We started with the most simple aspect of
+the whole problem, the fighting of two males in
+the presence of one female&mdash;the aspect upon
+which attention has usually been fixed. And if
+it remained at that, if observation failed to
+disclose any further development in the situation,
+then there would be no need to probe the
+matter deeper, there would be no reason to
+doubt the assertion that the quarrel had direct
+reference to the female. But assuredly no one
+can ponder over the diversity of battle and
+still believe that the possession of a mate
+furnishes an adequate solution of the mystery.
+Clearly such an hypothesis cannot cover all
+the known facts; there are conflicts between
+separate pairs, and there are conflicts between
+males when females are known to be absent and
+when their mates are even engaged in the work
+of incubation&mdash;these cannot be due to an
+impulse in a member of one sex to gain or keep
+possession of one of the other sex. So that
+taking all these facts into consideration, we are<span class='pagenum'><a name="Page_90" id="Page_90">90</a></span>
+justified, I think, in hesitating to accept this
+view, and must look elsewhere for the real
+condition under which the pugnacious nature of
+the male is rendered susceptible to appropriate
+stimulation.</p>
+
+<p>What then is the meaning of all this
+warfare? The process of reproduction is a
+complex one, built up of a number of different
+parts forming one inter-related whole; it is
+not merely a question of "battle," or of
+"territory," or of "song," or of "emotional
+manifestation," but of all these together. The
+fighting is thus one link in a chain of events
+whose end is the attainment of reproduction;
+it is a relationship in an inter-related process,
+and to speak of it as being even directly related
+to the territory is scarcely sufficient, for it
+is intimately associated with the disposition
+which is manifested in the isolation of the
+male from its companions, and forms therewith
+an <i>imperium in imperio</i> from which our
+concept of breeding territory is taken. But
+let me say at once that it is no easy matter to
+prove this, for since so many modes of behaviour,
+which can be interpreted as lending support to
+this view, are likewise interpretable on the view
+that the presence of a female is a necessary condition
+of the fighting, it is difficult to find just
+the sort of evidence that is required. Nevertheless,
+after hearing the whole of the evidence and
+at the same time keeping in mind the conclusion
+which we have already reached, I venture to<span class='pagenum'><a name="Page_91" id="Page_91">91</a></span>
+think that the close relationship between the
+warfare on the one hand and the territory on the
+other will be fully admitted.</p>
+
+<p>Formerly I deemed the spring rivalry to
+be the result of accidental encounters, and I
+believed that an issue to a struggle was only
+reached when one of the combatants succumbed
+or disappeared from the locality, a view which
+neither recognised method nor admitted control.
+Recent experience has shown, however, that I
+was wrong, and that there is a very definite
+control over and above that which is supplied by
+the physical capabilities of the birds.</p>
+
+<p>Let us take some common species, the
+Willow-Warbler being our first example; and,
+having found three adjoining territories occupied
+by unpaired males, let us study the conflicts
+at each stage in the sexual life of the three
+individuals, observing them before females have
+arrived upon the scene, again when one or two
+of the three males have secured mates, and yet
+again when all three have paired. Now we
+shall find that the conditions which lead up
+to and which terminate the conflicts are remarkably
+alike at each of these periods. A male
+intrudes, and the intrusion evokes an immediate
+display of irritation on the part of the owner
+of the territory, who, rapidly uttering its song
+and jerking its wings, begins hostilities. Flying
+towards the intruder, it attacks viciously, and
+there follows much fluttering of wings and
+snapping or clicking of bills. At one moment
+the birds are in the tree-tops, at another in the<span class='pagenum'><a name="Page_92" id="Page_92">92</a></span>
+air, and sometimes even on the ground, and
+fighting thus they gradually approach and
+pass beyond the limits of the territory. Whereupon
+a change comes over the scene; the male
+whose territory was intruded upon and who all
+along had displayed such animosity, betrays
+no further interest in the conflict&mdash;it ceases to
+attack, searches around for food, or sings, and
+slowly makes its way back towards the centre
+of the territory.</p>
+
+<p>Scenes of this kind are of almost daily
+occurrence wherever a species is so common,
+or the environment to which it is adapted so
+limited in extent, that males are obliged to
+occupy adjacent ground. The Moor-Hen abounds
+on all suitable sheets of water, and it is a bird
+that can be conveniently studied because, as
+a rule, there is nothing, except the rushes that
+fringe the pool, to hinder us from obtaining a
+panoramic view of the whole proceedings, and
+moreover the area occupied by each individual
+is comparatively small. Towards the middle of
+February, symptoms of sexual organic change
+make themselves apparent, and the pool is then
+no longer the resort of a peaceable community;
+quarrels become frequent, and as different
+portions of the surface of the water are gradually
+appropriated, so the fighting becomes more
+incessant and more severe. Each individual
+has its own particular territory, embracing a
+piece of open water as well as a part of the rush-covered
+fringe, within which it moves and lives.
+But in the early part of the season, when the<span class='pagenum'><a name="Page_93" id="Page_93">93</a></span>
+territories are still in process of being established,
+and definiteness has still to be acquired, trespassing
+is of frequent occurrence, and the
+conflicts are often conspicuous for their severity.</p>
+
+<p>Now these conflicts are not confined to
+unpaired individuals, nor to one sex, nor to
+one member of a pair&mdash;every individual that
+has settled upon the pool for the purpose of
+breeding will at one time or another be involved
+in a struggle with its neighbour. If then we
+single out certain pairs and day by day observe
+their actions and their attitude towards intruders,
+we shall notice that, instead of their routine of
+existence consisting, as a casual acquaintance
+with the pool and its inmates might lead us
+to believe, of an endless series of meaningless
+disputes, the behaviour of each individual is
+directed towards a similar goal&mdash;the increasing
+of the security of its possession; and further,
+if we pay particular attention to the circumstances
+which lead up to the quarrels and the
+circumstances under which such quarrels come
+to an end, we shall find, when we have accumulated
+a sufficient body of observations, that the
+disputes always originate in trespass, and that
+hostilities always cease when the trespasser
+returns again to its own territory. By careful
+observation it is possible to make oneself
+acquainted with the boundaries&mdash;I know not
+what other term to use&mdash;which separate this
+territory from that; and it is the conduct of the
+birds on or near these boundaries to which
+attention must be drawn. A bird may be<span class='pagenum'><a name="Page_94" id="Page_94">94</a></span>
+feeding quietly in one corner of its territory
+when an intruder enters. Becoming aware of
+what is happening it ceases to search for food,
+and approaching the intruder, at first swimming
+slowly but gradually increasing its pace, it
+finally rises and attacks with wings and beak,
+and drives its rival back again beyond the
+boundary. Thereupon its attitude undergoes
+a remarkable change; ceasing to attack, but
+remaining standing for a few moments as if
+still keeping guard, it betrays no further interest
+in the bird with which a few seconds previously
+it was fighting furiously. On one occasion I
+watched a trespasser settle upon a conspicuous
+clump of rushes situated near the boundary.
+The owner, who was at the moment some
+distance away, approached in the usual manner,
+and, having driven off the trespasser, returned
+immediately to the clump, where it remained
+erect and motionless.</p>
+
+<p>A feature which marks all the fighting, and
+which we cannot afford to disregard, is the
+conative aspect of the behaviour of the owner of
+the territory. The bird attacks with apparent
+deliberation <i>as if</i> it were striving to attain some
+definite end. I recollect an incident which was
+interesting from this point of view. A pair of
+Reed-Buntings were disturbed by a Weasel
+which had approached their nest containing
+young. Both birds betrayed symptoms of
+excitement; as the Weasel threaded its way
+amongst the rushes, so they fluttered from
+clump to clump or clung to the stems, uttering<span class='pagenum'><a name="Page_95" id="Page_95">95</a></span>
+a note which is peculiar to times of distress, and
+followed it thus until finally it disappeared in
+a hedge. The rapidly uttered note and the
+excitement of the birds caused some commotion,
+and the male from an adjoining territory
+approached the scene. Now one would have
+expected that the presence of this bird, and
+possibly its aid in driving away a common
+enemy, would have been welcomed; one would
+have thought that all else would have been
+subservient to the common danger, and that
+so real a menace to the offspring would have
+evoked an impulse in the parent powerful enough
+to dominate the situation and subordinate all the
+activities of the bird to the attainment of its end.
+But what happened? Three times during this
+incident, the male, whose young were in danger,
+abandoned the pursuit of the Weasel and
+pursued the intruder. It was not merely that
+he objected to the presence of this neighbouring
+male in a passive way, nor even that he had
+a momentary skirmish with it, but that he
+determinedly drove the intruder beyond the
+boundary and only then returned to harass the
+Weasel.</p>
+
+<p>Thus it seems clear that the proximate end to
+which the fighting is directed is not necessarily
+the defeat of the intruder, but its removal from a
+certain position. And inasmuch as this result
+will be obtained whether the retreat is brought
+about by fear of an opponent or by physical
+exhaustion, it is manifest that too much significance
+need not be attached to the amount of<span class='pagenum'><a name="Page_96" id="Page_96">96</a></span>
+injury inflicted. It is necessary to bear this in
+mind, because it is held by some, who have
+carefully observed the actions of various species,
+that overmuch importance is attached to the
+conflicts, that in a large number of instances
+they are mere "bickerings" and lead to nothing,
+and that they are now only "formal," which
+means, I suppose, that they are vestigial&mdash;fragments
+of warfare that determined the survival
+of the species in bygone ages. But if the
+conclusion at which we have just arrived be
+correct, if we can recognise a single aim passing
+through the whole of the warfare&mdash;and that one
+the removal of an intruder from a certain
+position, then we need no longer concern ourselves
+as to the degree of severity of the battles&mdash;we
+see it all in true perspective. Neither
+exhaustion nor physical inability are the sole
+factors which determine the nature and extent of
+the fighting; there is a more important factor
+still&mdash;position. According, that is to say, to the
+position which a bird occupies whilst fighting is
+in progress, so its pugnacious nature gains or
+loses susceptibility, and it is this gain or loss of
+susceptibility which I refer to when I speak of
+the fighting as being controlled.</p>
+
+<p>What we have then to consider is the relation
+of "susceptibility" to "position." We can
+explain the relationship in two ways. We can
+say that the part of the nature of the male which
+leads to the occupation of a territory, and is
+partly hereditary and partly acquired, is stronger
+than the part which leads the bird to fight, and<span class='pagenum'><a name="Page_97" id="Page_97">97</a></span>
+which is conditioned by the presence of a female,
+and that consequently when the male passes the
+boundary, the impulse to return asserts itself and
+the conflict ceases; or we can say that the
+occupation of a territory is the condition under
+which the pugnacious instinct is rendered susceptible
+to stimulation, that the stimulus is
+supplied by the intruder, and that when the male
+passes outside the accustomed area its instinct is
+no longer so susceptible and it therefore retires
+from the conflict.</p>
+
+<div class="figcenter" style="width: 500px;"><a name="f129" id="f129"></a><img src="images/fig129.jpg" width="500" height="409"
+alt="Long-tailed Tit
+Males fighting for possession of territory. The feathers
+have been torn from the crown of the defeated and dying rival." title="Long-tailed Tit
+Males fighting for possession of territory. The feathers
+have been torn from the crown of the defeated and dying rival." /></div>
+
+<p>Of these explanations, the first is not altogether
+satisfactory. It requires the presence of
+a female and, as we have seen, a female is by
+no means always present. Then it attributes to
+the one side of the inherited nature an influence
+which is not borne out by the facts, for in the
+ordinary routine of existence, without the incentive
+of battle, every individual is liable to wander
+occasionally beyond its boundary and to intrude
+temporarily upon its neighbours; and this it
+could scarcely do, providing its nature to remain
+within the territory were powerful enough to
+dominate its movements and curtail its activities
+even during the excitement of an encounter.
+But there is nothing inherently improbable in
+the alternative hypothesis, nor anything that
+is at all inconsistent with the behaviour as
+observed; on the contrary, if it is admitted, the
+facts become connected together and exhibit a
+meaning which they otherwise would not have
+possessed.</p>
+
+<p>So much for the controlling influence of<span class='pagenum'><a name="Page_98" id="Page_98">98</a></span>
+"position," which alone seems to me sufficient
+ground for believing that the fighting has reference
+to the territory. But it is not the whole of
+the evidence.</p>
+
+<p>Now if it were possible to demonstrate by
+actual observation that those males which had
+not established territories were not pugnacious,
+we should have something in the nature of proof
+of the correctness of this view. Demonstrative
+evidence of this kind is, however, unattainable.
+Yet we can come very near to obtaining it by
+reason of a peculiar feature which marks the process
+of acquiring territory&mdash;the neutral ground.
+The Lapwing will serve as an illustration. In
+the previous chapter I referred to the small flocks
+that appeared in the accustomed water meadow
+early in February, and I described how they
+settled day after day in that meadow, but only
+in a limited part of it, where they passed their
+time in rest, in preening their feathers, or in
+running this way and that lazily searching for
+food; and how, at length, the flock dwindled by
+reason of individuals breaking away in order to
+secure positions on the remaining part of the
+meadow. Here the neutral ground is adjacent
+to the territories, and, while still occupied by
+the flock, is resorted to by the males that had
+deserted that flock in order to establish those
+territories.</p>
+
+<p>Suppose now that we have the whole
+meadow in view from some point of vantage.
+In front of us are the territories, in the distance
+the neutral ground; and in each territory there<span class='pagenum'><a name="Page_99" id="Page_99">99</a></span>
+is a solitary male, while on the neutral ground
+a number of individuals of both sexes are
+assembled, and move about freely one amongst
+another. So that the scene presented to view
+is somewhat as follows: a flat meadow, at one
+end of which, and at fairly regular intervals,
+a few solitary individuals are dotted about, each
+one keeping at a distance from its neighbours;
+while at the other end a number of individuals
+are collected together in a comparatively small
+space, apparently deriving some satisfaction from
+their close association. That surely is a very
+remarkable contrast. But let us continue our
+investigation, first fixing our attention upon the
+solitary individuals; one is standing preening its
+feathers, another is squatting upon the ground,
+a third runs a few yards in this direction then a
+few yards in that, stimulated apparently by the
+sight of food, and so on. Moreover, each one
+keeps strictly to a well-defined area and makes
+no attempt to associate with its fellows. One of
+the males, however, whilst roaming backwards
+and forwards approaches the limit of its territory,
+and this brings the neighbouring bird, whose
+boundary is threatened, rapidly to the spot. In
+an upright position both stand face to face, and
+the battle then begins; with their wings they
+attempt to beat one another about the body,
+with their beaks they aim blows at the head,
+and in the m&ecirc;l&eacute;e wings and legs seem to be
+inextricably mixed; whilst at intervals, driven
+backwards by the force of the collision, they are
+compelled to separate, only, however, to return to<span class='pagenum'><a name="Page_100" id="Page_100">100</a></span>
+the charge&mdash;and the sound of beating wings and
+the feathers that float in the air are tokens of
+earnestness. Such scenes are of frequent occurrence;
+but the conflicts vary in intensity, and
+the circumstances under which they occur vary
+too, and females come and go without leaving
+any clue as to their ultimate intentions.</p>
+
+<p>Turning now to the flock one is impressed
+with the friendship that seems to exist between
+the various members. There are, it is true,
+occasional displays of pugnacity which never
+seem to develop into anything very serious; for
+instance, one bird will fly at another, and a
+momentary scuffle is followed by a short pursuit
+but nothing more&mdash;nothing, that is to say, in
+the least comparable with the battle previously
+described. Of what is the flock composed?
+Of members of both sexes. There is no difficulty
+in assuring oneself that this is so. But is it
+entirely composed of individuals in whom development
+has not reached a stage adequate for the
+functioning of the primary dispositions? No,
+not entirely; for it will be observed that its
+number is a fluctuating one, that birds come
+and go, and, if a close watch is kept upon the
+different individuals as they leave, it will be
+noticed that some at least are inmates of the
+territories at the opposite end of the meadow&mdash;the
+solitary members whose behaviour we were
+recently watching. This fact is an important
+one. We were impressed, it may be remembered,
+with the contrast between the general behaviour
+of the birds at the opposite ends of the meadow.<span class='pagenum'><a name="Page_101" id="Page_101">101</a></span>
+But now it appears as if the contrast were not
+between this individual and that, but between
+the behaviour of the same one under different
+circumstances. The male, that is to say, which,
+while in its territory, tolerates the approach of
+no other male, flies to the flock and is there
+welcomed by the very individuals with whom a
+short time previously it had been engaged in
+serious conflict.</p>
+
+<p>But if the conditions are reversed and the
+flock happens to settle in an occupied territory,
+the attitude of the owner towards the flock is
+very different. In the year 1916 an incident
+of this kind occurred in the meadow to which
+reference has already been made. The weather
+had been exceptionally severe&mdash;very cold easterly
+and north-easterly winds, frost, and frequent
+falls of snow had affected the behaviour of the
+Lapwings, and seemed to have checked the
+normal development of their sexual routine.
+The males would attempt to establish themselves,
+and then, when the temperature fell and
+the ground was covered with snow, would collect
+again in flocks and follow their winter routine.
+It was on the 9th March, during one of the spells
+of milder weather, that the flock on the neutral
+ground was disturbed and settled mainly in
+the territory marked No. 3 on the 1916 plan,
+but partly on that marked No. 2. The owners
+thereupon began to attack the different members
+of the invading flock. Fixing attention upon a
+particular bird whilst ignoring the remainder,
+the No. 3 male drove it away, and then after<span class='pagenum'><a name="Page_102" id="Page_102">102</a></span>
+a pause drove another away, and so on until
+by degrees all the invaders were banished, and
+the No. 2 male did likewise. The interest of
+this incident lies, however, in the behaviour of
+the different individuals of which the flock
+was composed; when attacked they made no
+real show of resistance, but accepted the situation
+and left. The will to fight was clearly lacking,
+yet their presence was a source of annoyance to
+the owners of the territories. A short time
+previously a female had accompanied one of
+the males and was at that time somewhere in
+the vicinity, but beyond this there was no
+evidence to show that either of them were
+paired, and even if the presence of the female
+were the reason of the pugnacity of the one,
+it could not well account for that of the
+other.</p>
+
+<p>The neutral ground does not always happen
+to be so close at hand as in the case of the
+meadow referred to. Sometimes the birds will
+resort to a particular field, attracted probably
+by a plentiful supply of food, and here they
+collect and behave as they do during the winter,
+running this way and that as the fancy takes
+them, meeting together by accident at one
+moment, parting at another, according to the
+direction in which they happen to wander.
+Of animosity there is little sign; the season
+might be the middle of winter instead of the
+middle of March for all the indication there
+is of sexual development, and yet one knows
+that they will behave differently when they<span class='pagenum'><a name="Page_103" id="Page_103">103</a></span>
+leave this ground, as presently they will, and
+return to their territories in the surrounding
+neighbourhood, and that there each one will
+fight if necessary to preserve its acre from
+intrusion.</p>
+
+<p>It would seem, then, from this that the
+fighting must bear some relation to the
+particular area of ground in which it occurs;
+and unless it can be shown that there is some
+other factor in the external environment of
+the male, that is the direction in which we
+must look for the condition under which the
+instinct is rendered susceptible. One's thoughts
+turn, of course, to the female, but she too passes
+backwards and forwards between the territories
+and the neutral ground, and if her presence
+were really a <i>conditio sine qua non</i> of the strife,
+one would like to know why, when she leaves
+those territories and joins the flock and the
+males do likewise, similar conflicts should not
+prevail there also.</p>
+
+<p>Other species have their neutral ground, but
+the environment seldom affords such facilities
+for observation as does that of the Lapwing.
+Even though the Moor-Hens, who are so
+conspicuously intolerant upon the pool, <i>do</i> feed
+together amicably upon the meadows adjoining;
+and the Chaffinch that is so pugnacious in the
+morning, <i>does</i> seek out the flock later in the
+day; yet their conditions of existence prevent
+our obtaining a panoramic view of the whole
+proceeding, and we have to study each scene
+separately before discovering that the relation<span class='pagenum'><a name="Page_104" id="Page_104">104</a></span>ship
+between intolerance and the territory
+on the one hand, and friendship and the
+neutral ground on the other, is just as strong
+a feature as it is in the behaviour of the
+Lapwing.</p>
+
+<p>I shall now give a brief account of the
+conduct of a male Reed-Bunting which by
+persistent effort established itself late in the
+season, and I shall do so because its behaviour
+tends to confirm much that has been said in
+the preceding pages.</p>
+
+<p>Early in March three male Reed-Buntings
+occupied a small water meadow overgrown
+with the common rush, and by the third week
+all of them were paired. On the 30th March
+two of the males were unusually pugnacious,
+and on the following day fighting continued
+and at times was very severe. Now I knew
+that the occupants of the ground in which
+the fighting was taking place were paired,
+and not doubting that the combatants were
+the owners of two territories marked for
+convenience sake Nos. 1 and 2, I was at a
+loss to understand the meaning of so determined
+and persistent a struggle. My attention, however,
+was presently drawn to a third bird, which
+also joined in the conflict and made the whole
+situation still more perplexing. This bird, as
+it soon became clear, was none other than the
+owner of No. 2 territory, and the one that
+I had previously regarded as such was a new
+arrival. On the following day, the 1st April,
+fighting continued, and in my record for that<span class='pagenum'><a name="Page_105" id="Page_105">105</a></span>
+day there is a note to the effect that "No. 2
+female seems to be of no interest to No. 5
+male (the new arrival); its purpose seems to be
+to drive away intruders." On the 2nd April
+and subsequent days, this bird attacked every
+other male that approached, and not only
+maintained its position but ultimately succeeded
+in securing a mate. Here then we have two
+territories occupied by two males, both of
+which had obtained a mate. The relation of
+these two birds was normal, a month's routine
+had defined their boundaries, and conflicts were
+less frequent than formerly. But upon this
+comparatively peaceful scene a strange male
+intrudes. Observe the manner of the intrusion.
+The stranger does not wander about first in
+this direction and then in that, but acts <i>as if</i>
+it had some definite end in view, and establishing
+itself in a small alder bush which it
+uses as a base or headquarters, it gradually
+extends its dominion, gains the mastery over
+the surrounding ground, part of which belonged
+to No. 1 male and part to No. 2, and finally
+drives a wedge, so to speak, between the two
+territories.</p>
+
+<p>How is its behaviour to be explained, and
+why did its presence cause such commotion?
+No one could have watched the gradual unfolding
+of this incident day by day and not have been
+impressed by the persistent endeavour with
+which this male maintained its position in one
+small part of the meadow. This is the first and
+most important consideration. Then there is<span class='pagenum'><a name="Page_106" id="Page_106">106</a></span>
+the attitude, also significant, which it adopted
+towards the females; for I take it that, apart
+from the question of territory, the explanation of
+its intrusion must be sought in the necessity for
+securing a mate&mdash;that it was attracted by the
+presence of the females, and that the proximate
+end of its behaviour was the possession of one of
+them. But if there is one thing that emerges
+from the facts more clearly than another it is
+that the course of its behaviour was in no way
+influenced by the presence or absence of either
+of the females. My reasons for saying so are
+the following: in the first place, it made no
+attempt to pursue or to thrust its attention upon
+either one or the other of them; secondly, it
+even went so far as to attack and drive them
+away when they approached too closely; and in
+the third place, when an unpaired female did at
+length appear, it adopted a different attitude and
+forthwith paired. And bearing in mind that
+these two females had already been with their
+respective mates for some considerable time, and
+that there was reason to believe that coition had
+actually taken place, is it likely that any counter-attraction
+would have proved successful in
+tempting either of them away from its mate, or
+probable, if they were the sole attraction, that
+the intruding male would have been so persistent
+in remaining? How very much simpler it is to
+fit the pieces together, if for the time being we
+ignore the female and fix our attention upon the
+territory. Each item of behaviour then falls
+into its proper place, and the fighting which<span class='pagenum'><a name="Page_107" id="Page_107">107</a></span>
+seemed so perplexing and meaningless becomes
+a factor of prime importance. First of all the
+male arrives; then it establishes itself in a small
+alder bush and advertises its presence by song;
+next, by persistent effort in attacking the
+neighbouring males, it frees a piece of ground
+from their dominion; and finally, in proper
+sequence, a female arrives, pairing takes place,
+and reproduction is secured.</p>
+
+<div class="figcenter" style="width: 500px;"><a name="f141" id="f141"></a><img src="images/fig141.jpg" width="500" height="792" alt="A battle between
+two pairs of Jays." title="A battle between two pairs of Jays." /></div>
+
+<p>How then does the whole matter stand? If
+it were males only that engaged in serious
+conflict, and if they fought only in the presence
+of a female, the problem would resolve itself into
+one simply of obtaining mates. But the warfare
+extends in a variety of directions, it is not
+confined to one sex, nor to unpaired individuals,
+nor need the opponents necessarily be of the
+same sex; it involves both sexes alike singly or
+combined. Now the view that the biological
+end of battle is, in its primary aspect, related
+to the female, cannot, as we have seen, apply
+to the conflicts between different pairs, and
+only by much stretching of the imagination
+can it be held responsible for the hostility that
+males frequently display towards females or <i>vice
+versa</i>. It is valid only for a certain form of
+warfare. But that form represents, you will say,
+a large proportion of the whole, which is true;
+and so long as we ignore the remainder, we
+might rest content in the belief that we had
+solved the major part of the problem. But can
+we ignore the remainder? Can we say that the
+conflicts between paired males, for example, are<span class='pagenum'><a name="Page_108" id="Page_108">108</a></span>
+simply offshoots of the pugnacious disposition,
+and have no part to play in the process of
+reproduction? They recur with marked persistency
+season after season and generation after
+generation; they are to be found in species
+widely remote; they are frequent in occurrence;
+and no one who had observed them and noted
+the vigour with which they are conducted, could,
+I think, conclude that they were meaningless&mdash;and
+be satisfied. They must somehow be
+explained. So that if anyone thinks fit to
+maintain that possession of a mate is an adequate
+explanation of part of the hostilities, it is clearly
+impossible to regard all the fighting as a
+manifestation of one principle directed towards
+a common biological end.</p>
+
+<p class="tb">But wherever we extend our researches, we
+find that the facts give precision to the view that
+the occupation of a territory is the condition
+under which the pugnacious instinct is rendered
+susceptible to stimulation. The Lapwing, when
+in its territory, displays hostility towards other
+males of its own species, but when upon neutral
+ground, treats them with indifference; the Chiffchaff
+pursues its rival up to the boundary and is
+then apparently satisfied that its object has been
+achieved; the cock Chaffinch in March permits
+no other male to intrude upon its acre or so of
+ground during the early hours of the morning,
+but for the rest of the day it joins the flock
+and is sociable; the Herring-Gull resents the
+approach of strangers so long as it occupies its
+few square feet of cliff, but welcomes companions<span class='pagenum'><a name="Page_109" id="Page_109">109</a></span>
+whilst it is following the plough&mdash;all of which
+points to a relation between the territory and the
+fighting. And this view has at least one merit&mdash;it
+accounts for all the fighting no matter what
+degree of severity may be reached or in what
+way the sexes may be involved. The complexity
+of the strife presents no obstacle; for if the
+biological end of the fighting is to render the
+territory, which has already been established,
+secure from intrusion, each sex will have its
+allotted part to play at the allotted time: thus
+the battles between the males before females
+appear on the scene will decide the initial
+question of ownership; those between the
+females will give an advantage to the more
+virile members and insure an even distribution
+of mates for the successful males; the constant
+struggles between paired males will roughly
+maintain the boundaries and prevent such
+encroachment as might hamper the supply of
+food for the young; and the co-operation of
+male and female in defence of the territory will
+be an additional safeguard. Each form of battle
+will contribute some share towards the main
+biological function of reproduction.</p>
+
+<p>Hitherto we have dealt principally with the
+male. We have referred, it is true, to the fact
+that the female co-operates with her mate in
+order to drive away intruders, but beyond this,
+we have made no attempt to trace what part, if
+any, she plays in the whole scheme. We must
+do so now.<span class='pagenum'><a name="Page_110" id="Page_110">110</a></span></p>
+
+<p>The various steps by which the territory is
+not only established but made secure from
+invasion, imply an inherited nature nicely
+balanced in many directions&mdash;first of all the male
+must be so attuned as to be ready to search for
+a territory at the right moment; then it must
+be capable of selecting a suitable environment;
+and, having established itself, it must be prepared
+to defend its area from a rival, and to resist
+encroachment by its neighbours&mdash;and if it failed
+in any one of these respects, it would run the
+risk of failure in the attainment of reproduction.
+Each individual has therefore to pass, so to
+speak, through a number of sieves&mdash;the meshes
+of which are none too wide&mdash;before it can have
+a reasonable prospect of success. This being so,
+we ask, in the first place, whether the female,
+too, may not have an eliminating test to pass;
+and in the second place, whether she may not
+also assist in furthering the biological end of
+securing the territory.</p>
+
+<p>Now the answer to the first of these
+questions will be found to be in the affirmative.
+Just as, in the securing of a territory, the ultimate
+appeal is to the physical strength of the male,
+so, in the course of her search for a mate, the
+female may be called upon to challenge, or may
+be challenged by a rival, and the issue is decided
+by force. My attention was first drawn to this
+fact by a struggle between two female Whitethroats,
+which I have described elsewhere. The
+scene of its occurrence was the corner of a small
+osier bed occupied by one male, and the females<span class='pagenum'><a name="Page_111" id="Page_111">111</a></span>
+that took part in it had only recently arrived,
+but the male, an unpaired bird, had been in
+possession of its territory for some days. The
+sequel to this struggle, which was protracted and
+severe, was the disappearance of both females,
+the male being left without a mate for a further
+ten days.</p>
+
+<div class="figcenter" style="width: 500px;"><a name="f147" id="f147"></a><img src="images/fig147.jpg" width="500" height="932" alt="The female Chaffinch shares in the defence
+of the territory and attacks other females." title="The female Chaffinch shares in the defence
+of the territory and attacks other females." /></div>
+
+<p>Numerous instances have since come under
+my notice. Hen Chaffinches become so absorbed
+that they fall to the ground and there continue
+the struggle. Seizing hold of one another by
+the feathers of the head, they roll from side to
+side, and then, without relaxing their grip, lie
+exhausted&mdash;the quickened heart-beat, altered
+respiration, tightly compressed feathers and
+partially expanded wings betraying the intensity
+of the conflict.</p>
+
+<p>As the breeding season approaches, hen
+Blackbirds grow more pugnacious. Individuals
+that early in the year have frequented the same
+spot daily and have even shown every sign of
+friendship, become openly hostile. For two
+years in succession I had an opportunity of
+observing females under such conditions, and
+of studying the gradual change in their relationship.
+Each morning at break of day and for
+some hours afterwards they could be seen in the
+same place, one following the other as they
+searched for food first in this direction and then
+in that, as if they derived some special pleasure
+from the fact of their companionship. Then a
+change began to manifest itself. Indications of
+animosity became apparent; one would run<span class='pagenum'><a name="Page_112" id="Page_112">112</a></span>
+towards the other in a threatening attitude
+and, in a half-hearted manner, peck at it; and
+gradually the hostility grew, until the tentative
+pecking developed into a scuffle and the scuffle
+into a conflict.</p>
+
+<p>Much fighting also occurs between the
+females of the Reed-Bunting, and likewise
+between those of the Moor-Hen, and because
+these two species are not only common but
+inhabit respectively open stretches of marshy
+ground or large sheets of water, the fighting can
+be readily observed.</p>
+
+<p>Why do the females fight before they are
+definitely paired? To obtain mates? This
+certainly seems to be the obvious explanation
+because any question of securing territory can
+be excluded; yet if it be true that their sex is
+numerically inferior, it is difficult to understand
+the necessity for such strenuous competition.
+But what is the condition under which the
+pugnacious instinct of the female is rendered
+susceptible to stimulation? It cannot be merely
+the presence of a male ready to breed, for then
+there would be endless commotion amongst the
+flocks of Chaffinches or of Lapwings which in
+March are composed of both sexes, including
+even males that have secured territories. There
+must be some other circumstance; and, judging
+by experience, it is to be found in the territory&mdash;a
+male, that is to say, in occupation of one, is
+the condition under which the inherited nature
+of the female is allowed free play. We must
+bear in mind, however, that the competition<span class='pagenum'><a name="Page_113" id="Page_113">113</a></span>
+between the males is very severe, that large
+numbers probably fail to pass even this preliminary
+test, and that only a proportion are in
+a position to offer to the female the condition
+under which her process can successfully run its
+course; so that the presumption is&mdash;though it is
+incapable of demonstration&mdash;that there is a competition
+for such males each recurring season,
+and that, on the average, the weaker females fail
+to procreate their kind.</p>
+
+<p>But apart from any direct assistance she may
+give in driving away intruders, does she in any
+way help to further the biological end of reproduction?
+This is a difficult question to answer,
+and the suggestion I have to make can only
+apply in those cases in which the territory is
+occupied throughout the breeding season.
+Much of the fighting between the males occurs
+in her presence, and it must be admitted&mdash;though
+it is difficult to speak with any degree of
+certainty&mdash;that such fighting, taken as a whole,
+bears the stamp of exceptional determination.
+Let us then grant that the excitement of a male
+does, under these circumstances, reach a higher
+level of intensity, and let us see how this will
+add to the security of the territory. The fact
+that the male has established itself and obtained
+a mate is not alone sufficient to accomplish the
+end for which the territory has been evolved.
+During the period between the initial discharge
+of the sexual function and the time when
+incubation draws to a close, much may happen
+to prejudice the future of the offspring; there<span class='pagenum'><a name="Page_114" id="Page_114">114</a></span>
+is always the possibility of invasion by an
+individual whose development is backward or
+which has been unsuccessful in making good
+the first step, and, as we saw in the case of the
+Reed-Bunting, a portion of the ground won
+may be lost; there is always the danger of
+gradual encroachment by neighbouring owners;
+and there is even a possibility that a pair may be
+so persistently harassed by more virile neighbours
+as to forsake the locality permanently. If then
+a male is to attain a full measure of success it
+must be capable of keeping its boundaries intact
+up to the time when the young are able to fend
+for themselves, and consequently it is important
+that its intolerant nature should remain susceptible
+to stimulation throughout the greater part
+of the season.</p>
+
+<p>Does the presence of a female serve to
+promote this end? Now we know very little of
+the influence exerted by one sex upon the other.
+Professor Lloyd Morgan has suggested that the
+male raises the emotional tone of the female, a
+suggestion which seems to me in accordance
+with the facts. There is reason to believe, however,
+that the converse is also true&mdash;namely that
+the excitement of the male reaches a higher level
+of intensity when a female is present. Granting
+then that his emotional tone is raised, how will
+this affect the question? So great is the
+difference of opinion as to the part that the
+emotions play in furthering the life of the
+individual that one hesitates to accept any
+particular one. But it seems to be generally<span class='pagenum'><a name="Page_115" id="Page_115">115</a></span>
+admitted that emotion adds to the efficacy of
+behaviour, and this is the view of Professor
+Lloyd Morgan. "Whatever may be the exact
+psychological nature of the emotions, it may be
+regarded," he says, "as certain that they introduce
+into the conscious situation elements which
+contribute not a little to the energy of behaviour.
+They are important conditions to vigorous and
+sustained conation." Therefore, if it be true
+that the female raises the emotional tone of the
+male, the result will be an increased flow of
+energy into all the specific modes of behaviour
+connected with reproduction, amongst which
+those directly concerned in the securing and
+defence of the territory will receive their share;
+so that instead of a progressive weakening of
+just those elements in the situation which make
+for success, the level of their efficiency will be
+maintained as a result of such reinforcement.
+But the female becomes intolerant of her own
+sex when she has discovered a male ready to
+breed, and, later, assists her mate in resisting
+intrusion; and by raising her emotional tone, he
+may be the means of furthering more strenuous
+behaviour on her part. Each member of the
+pair would in this way contribute towards the
+energy of behaviour of its mate, and hence add
+indirectly to the security of the territory.</p>
+
+<p class="tb">It may be well to illustrate the foregoing
+remarks. Suppose that there is a small piece of
+woodland barely sufficient to hold three pairs of
+Willow-Warblers, and suppose that the male and
+female in the middle territory did not respond to<span class='pagenum'><a name="Page_116" id="Page_116">116</a></span>
+one another's influence quite as readily as the
+adjoining males and females, what would be the
+result? The emotional tone of the central pair
+would stand at a lower level of intensity; and,
+since their congenital dispositions would lack the
+necessary reinforcement, the birds would tend
+to become less and less punctilious in keeping
+their boundaries intact, whereas the adjoining
+pairs, always on the alert and meeting with little
+opposition, would encroach more and more and
+gradually extend their dominion. And so, by
+the time the young were hatched, the parents
+would be in occupation of an area too limited in
+extent to insure the necessarily rapid supply of
+food, and would be compelled to intrude upon
+the adjoining ground. But knowing how
+routine becomes ingrained in the life of the
+individual, knowing that for weeks this pair had
+submitted to their neighbours, can we believe
+that they would be capable of asserting their
+authority and that the young would be properly
+cared for? Or suppose that different pairs of
+Kittiwake Gulls on the crowded ledges, or
+different pairs of Puffins in the crowded burrows,
+varied in like manner, would they all have
+equal chances of rearing their offspring? The
+struggle for reproduction is nowhere more severe
+than amongst the cliff-breeding sea birds; it is
+not for nothing that one sees Kittiwake Gulls,
+locked together, fall into the water hundreds of
+feet below and struggle to the point of exhaustion,
+or, as has been reported, to the point of
+death; it is not for nothing that Puffins fight<span class='pagenum'><a name="Page_117" id="Page_117">117</a></span>
+with such desperation. And surely success will
+be attained by that pair whose emotional tone
+stands high and whose impulse to fight is therefore
+strong, rather than to the ill-assorted couple.</p>
+
+<p>The argument, then, is briefly this. In the
+spring, a marked change takes place in the
+character of the males of very many species;
+instead of being gregarious they either avoid one
+another and become hostile, or, if their conditions
+of existence require that they shall
+still live together, they become irritable and
+pugnacious. This change is made known to us
+by the battles of varying degrees of severity
+which are such a feature of bird life in the
+spring; and since a female can commonly be
+observed to accompany the combatants, the
+possession of a mate appears at first sight to be
+the proximate end for which the males are
+contending. But when the circumstances which
+lead up to the quarrels are investigated closely,
+the problem becomes more difficult; for it is
+not merely a question of males fighting in the
+presence of a female, as is generally supposed to
+be the case, but on the contrary there is a complexity
+of strife which is bewildering&mdash;males
+attack females or <i>vice versa</i>; female fights
+with female; or a pair combine to drive
+away another pair, or even a solitary individual
+no matter of which sex. This complexity of
+strife makes against the view that the possession
+of a mate is the reason of the fighting. But an
+even stronger objection is to be found in the fact<span class='pagenum'><a name="Page_118" id="Page_118">118</a></span>
+that males are hostile when no female is present&mdash;and
+hence we must seek elsewhere for the true
+explanation.</p>
+
+<p>Now if the behaviour of a male be closely
+observed, it will be found that its pugnacious
+instinct gains or loses susceptibility according to
+the position which it happens to occupy&mdash;when
+its ground is trespassed upon, the impulse to
+fight is strong; but when it crosses the boundary
+it seems to lose all interest in the intruder.
+Moreover, in some species, the male rejoins
+the flock at intervals during the early part
+of the season and for a time leads a double
+existence, passing backwards and forwards
+between its territory and the neutral ground.
+Its behaviour under these circumstances affords
+some valuable evidence, for the bird displays
+little if any hostility when accompanying the
+flock, yet when it returns to the ground over
+which it exercises dominion, no male can
+approach without being attacked. The conclusion,
+therefore, seems to be inevitable, namely
+that the actual occupation of a territory is the
+condition under which the pugnacious nature of
+the male is rendered susceptible to appropriate
+stimulation.</p>
+<hr />
+<p><span class='pagenum'><a name="Page_119" id="Page_119">119</a></span></p>
+<h3>CHAPTER IV</h3>
+
+<h4>THE RELATION OF SONG TO THE TERRITORY</h4>
+
+
+<p>If we listen to the voices of the Waders as,
+in search of food, they follow the slowly ebbing
+tide, we shall notice that each species has a
+number of different cries, some of which are
+uttered frequently and others only occasionally.
+Not only so, but if we study the circumstances
+under which they are uttered, we shall in time
+learn to associate certain specific notes with
+certain definite situations.</p>
+
+<p>The Curlew, when surprised, utters a cry
+with which most of us, I suppose, are familiar;
+but when with lowered head it drives away
+another individual from the feeding ground,
+it gives expression to its feelings by a low,
+raucous sound, which again is different from
+its cry when a Common Gull steals the <i>arenicola</i>
+that has been drawn out of the mud with such
+labour.</p>
+
+<p>Thus we come to speak of "alarm notes,"
+"notes of anger," "warning notes"&mdash;naming
+each according to the situations which normally
+accompany their utterance. And so, all species,<span class='pagenum'><a name="Page_120" id="Page_120">120</a></span>
+or at least a large majority of them, have, in
+greater or lesser variety, cries and calls which
+are peculiar to certain seasons and certain
+situations; and since on many occasions we
+have indisputable evidence of the utility of
+the sound produced&mdash;as when, upon the alarm
+being given by one individual, the flock of
+Lapwing rises, or when, in response to a
+particular note of the parent, the nestling
+Blackcap ceases to call&mdash;so are we bound to
+infer that all the cries are, in one way or
+another, serviceable in furthering the life of
+the individual.</p>
+
+<p>But besides these call-notes, birds produce
+special sounds during the season of reproduction&mdash;some
+by instrument, others by voice,
+others again by the aid of mechanical device.
+And not only is this the case, but many
+accompany their songs with peculiar flights,
+such as soaring to a great height, or circling,
+or floating in the air upon outstretched wings.
+These special sounds and special flights are
+those with which I now propose to deal,
+including under the heading "song" all sounds
+whether harsh or monotonous or beautiful, and
+whether vocally or otherwise produced; and I
+shall endeavour to show not only that they are
+related to the "territory," but that they contribute
+not a little to the successful attainment
+of reproduction.</p>
+
+<p>The vocal productions are infinite in variety
+and combination. At the one extreme we
+have songs composed of a single note repeated<span class='pagenum'><a name="Page_121" id="Page_121">121</a></span>
+slowly or rapidly as the case may be, whilst at
+the other we have the complex productions
+of the Warblers; and between these two
+extremes, notes and phrases are combined and
+recombined in ways innumerable. And just as
+there is a rich variety of combination, so
+there is a very wide variation in the purity
+and character of the notes&mdash;some are harsh,
+others melodious, some flute-like, others more
+of a whistle, and others again such as can
+only be likened to the notes of a stringed
+instrument. Hence in variety of phrase combination
+added to variety in the character of
+the note, there is a possibility of infinite modes
+of expression.</p>
+
+<p>If, in the latter part of May, we take up
+a position at dawn in some osier bed, we listen
+to songs which have reached a high degree
+of specialisation, songs, moreover, which appeal
+to us on account of their beauty; if, on the
+other hand, we climb down the face of the
+sea cliff, we hear an entirely different class of
+songs&mdash;harsh, guttural, weird, monotonous
+sounds, which, appeal to us though they may,
+lack the music of the voices in the osier bed.
+And just as, in the osier bed, we can recognise
+each species by its voice, so we can distinguish
+the "cackle" of the Fulmar, the "croak" of
+the Guillemot, or the "grunt" of the Shag.
+In the osier bed, however, there is considerable
+variation in the song of different individuals
+of the same species, so much so that we can
+recognise this one from that; whereas on the<span class='pagenum'><a name="Page_122" id="Page_122">122</a></span>
+cliff we cannot distinguish between the voices
+of different individuals. And the more highly
+developed the song, the greater the range of
+variation appears to be; but notwithstanding
+this&mdash;notwithstanding the fact that the pitch
+may differ, the phrase combination may differ,
+and the timbre may differ&mdash;the song remains
+nevertheless specific. So that the two principal
+features of "song," broadly speaking, are
+"diversity" and "specific character."</p>
+
+<p>In contrast with the call-notes, the majority
+of which can be heard at all times of the year,
+the song is restricted as a rule to one season,
+and that one the season of reproduction. It
+is true, of course, that some birds sing during
+the autumn, and, if the climatic conditions are
+favourable, in the winter also, just as others
+betray, in the autumn, symptoms of emotional
+manifestation peculiar to the spring; but just as
+the manifestation of the latter is feeble and
+vestigial, so, too, does the song of the former
+lack the vigour and persistency which is characteristic
+of the spring. Again, in contrast with
+the call-notes, which are common alike to both
+sexes, song is confined to one sex&mdash;a peculiar
+property of the males.</p>
+
+<p>Now all, I think, will agree that it must
+serve some biological purpose&mdash;this at least
+seems to be the conclusion to be drawn from the
+two outstanding features of "diversity" and
+"specific character"; and since the voices of
+different individuals of the same species vary, it
+has been suggested that, by creating a more<span class='pagenum'><a name="Page_123" id="Page_123">123</a></span>
+effective pairing situation, it is serviceable in
+furthering the life of the individual. I do not
+propose at the moment to enquire whether this
+doctrine be true, but rather to direct attention
+to other ways in which the song may be
+useful.</p>
+
+<p>Is the instinct susceptible to stimulation
+under all conditions during the season of reproduction,
+or only under some well-defined
+condition? This is the question to which we
+will first direct inquiry.</p>
+
+<p>Song in its full development belongs, as we
+have seen, to the season of reproduction; it is
+heard at the dawn of the seasonal sexual process,
+and is the most conspicuous outward manifestation
+of the internal organic changes which
+ultimately lead to reproduction. These changes
+would appear, at first sight, to be the primary
+condition which renders the instinct susceptible
+to appropriate stimulation. But while this is
+true up to a point, in so far, that is to say, as
+organic changes are a necessary antecedent of
+all behaviour connected with the attainment
+of reproduction, closer acquaintance with the
+circumstances under which the instinct is allowed
+full play leads to the belief that they are not
+alone sufficient to account for the facts as
+observed. In order to arrive at a decision we
+must seek out the specific factors in the external
+environment with which "song" is definitely
+related.</p>
+
+<p>Some birds cross whole continents on their
+way to the breeding grounds, others travel many<span class='pagenum'><a name="Page_124" id="Page_124">124</a></span>
+miles, others again find suitable accommodation
+in a neighbouring parish&mdash;nearly all have a
+journey to perform, it may be short or it may be
+long. The flocks of Finches gradually decrease
+and we observe the males scattering in different
+directions in search of territories; we watch the
+summer migrants on their way&mdash;small parties
+halting for a few hours in the hedgerows and
+then continuing their journey, single individuals
+alighting on trees and bushes and resting there
+for a few minutes, and the constant passage of
+flocks of various dimensions at various altitudes;
+and we see Fieldfares, Redwings, and Bramblings
+slowly making their way from the south and
+the west to their homes in the far north.
+Occasionally we hear their song, not the
+emotional outburst customary at this season,
+but, except in isolated cases, a weak and tentative
+performance. G&auml;tke speaks of the absence
+of song on the Island of Heligoland, and refers
+to the Whitethroat as one of the few migrants
+that enliven that desolate rock with their melody.
+On the other hand, many migrants that rest
+temporarily on the Isle of May sing vigorously.<a name="FNanchor_5_5" id="FNanchor_5_5"></a><a href="#Footnote_5_5" class="fnanchor">5</a>
+But on the whole there is, I think, no question
+that the male whilst travelling to its breeding
+grounds, and, even after its arrival, whilst in
+search of a territory, sings but little&mdash;and that
+little lacks the persistency characteristic of
+the period of sexual activity. Yet, when a
+suitable territory is eventually secured, the
+nature of the bird seems to change; for, instead
+<span class='pagenum'><a name="Page_125" id="Page_125">125</a></span>
+of being silent and retiring, as if aware of some
+end not fully attained, it not only makes itself
+conspicuous but advertises its presence by a
+song uttered with such perseverance as to
+suggest that that end is at length attained.
+Hence, in a general way, the instinct of song
+seems to be related to the establishment of a
+territory.</p>
+
+<p>Now the subsequent course of behaviour
+tends to confirm this view. We have already
+had occasion to refer to the fact that the males
+of some species desert their territories temporarily
+and join together on ground which is regarded
+by the birds that associate there as neutral, and
+that they do so not merely for the purpose of
+securing food but because they derive some
+special pleasure from the act of association, and
+we shall find that the altered behaviour of the
+male when it leaves its territory to seek food or
+to join the flock is an important point for us
+just now.</p>
+
+<p>Buntings desert their territories temporarily
+and collect in flocks on the newly sown fields of
+grain. Some of the males are single, others are
+paired, and accompanied, it may be, by their
+mates; they wander over the ground in search
+of food, uttering their call-notes from time to
+time, or, settling upon the hedges and trees
+surrounding the field, rest there and preen their
+feathers. But even though a male may be
+surrounded by other males, even though it may
+occupy a position where it is conspicuous to all
+around, even though, that is to say, it is<span class='pagenum'><a name="Page_126" id="Page_126">126</a></span>
+apparently in contact with just those stimulating
+circumstances which will evoke a response when
+it returns to its territory, yet it makes no attempt
+to sing.</p>
+
+<p>Lapwings, when they resort to the neutral
+ground, run this way and that in full enjoyment
+of one another's companionship, behaving
+as they do when they flock in autumn
+and winter. Specific emotional manifestation
+is, however, absent, and their actions seem to
+be in nowise affected by the powerful impulse
+which only a few minutes previously determined
+their conduct, for of the characteristic
+flight with its accompanying cry there is no
+sign.</p>
+
+<p>Early in the season Turtle Doves often
+collect from the surrounding country at certain
+spots where their favourite food is abundant.
+The croak of this Dove&mdash;its true song&mdash;is a
+familiar sound during the summer, but in
+addition the bird has a sexual note characteristic
+of the race. I watched a flock of upwards of
+one hundred on some derelict ground approximately
+eight acres in extent. Here, in May,
+the birds were attracted by the seeds of <i>Stellaria
+media</i> which was growing in profusion. After
+5 <span class="smcaplc">A.M.</span> there was continuous traffic between this
+piece of ground and the surrounding neighbourhood,
+a constant arrival and departure of single
+individuals or pairs; and, as they fed, the sexual
+note could be heard in all directions. Now some
+of the males occupied territories close at hand,
+and one could watch their passage to and fro;<span class='pagenum'><a name="Page_127" id="Page_127">127</a></span>
+yet in no single instance did I hear the true song
+uttered on the feeding ground, although the
+moment a male returned to its territory its
+monotonous croak could be heard, uttered moreover
+with that persistence which is so marked
+a feature of all song or of the sounds that
+correspond to it.</p>
+
+<p>Thus it will be seen that, even after the
+internal organic changes have taken place,
+the instinct of song is not susceptible to
+stimulation at all times and under all circumstances,
+but only at certain specified times
+and under special circumstances which can be
+observed to correspond with the occupation of
+the territory.</p>
+
+<p>In many species each male singles out
+within its territory some prominent position
+to which it resorts with growing frequency.
+This position is an important feature of the
+territory, and exercises a dominating influence
+on the life of the bird. I have referred to it
+as the "headquarters," and it may be a solitary
+tree or bush, an outstanding mound or
+mole hillock, a gatepost or a railing&mdash;anything
+in fact that supplies a convenient
+resting place so long as it fulfils one condition,
+namely that the bird when it is there is conspicuous.
+It need not, however, be a tree or a
+mound or indeed anything upon which the
+bird can perch, for there is reason to think
+that the soaring flight undertaken at this
+season by so many males, since it is generally
+accompanied by the specific sexual sound,<span class='pagenum'><a name="Page_128" id="Page_128">128</a></span>
+answers the same purpose as the topmost branch
+of a tree.</p>
+
+<p>Now there is nothing in the external
+environment to which the song is more
+definitely related than to the "headquarters"&mdash;this
+at least is the conclusion to be drawn from
+the behaviour, and I will indicate the sort of
+evidence upon which such conclusion is based.
+There is, first of all, the persistency with which
+the male resorts to the same tree, even to the
+same branch, and, as it seems, solely for the
+purpose of advertisement. We know by
+experience the approximate routine of the
+male's behaviour; we know where to seek it,
+where to hear it, and when once we have
+discovered its headquarters, we know that there
+it will sing day after day for weeks or it may
+be for months together&mdash;perhaps the most
+striking feature of its behaviour at this season.
+Next, we find that other trees, though made use
+of, are not made use of to a similar extent for
+the purpose of song. The area occupied varies
+much according to the nature of the environment;
+it is sometimes extensive, and seldom less
+than half an acre or so in extent; but in most
+instances it contains plenty of trees and bushes
+which could, one would imagine, serve the
+purpose of a "headquarters" just as well as the
+particular one selected, and yet the bird, when
+there, betrays no inclination to sing at all comparable
+with that which can be observed when
+it occupies its accustomed perch. Further
+evidence is afforded in the behaviour of those<span class='pagenum'><a name="Page_129" id="Page_129">129</a></span>
+species that make temporary excursions from
+their territories. The male, on its return, flies
+as a rule direct to its special tree and sings.
+Sometimes, however, it settles upon the ground,
+not unfrequently accompanied by the female,
+and while there remains silent; but presently
+rising from the ground and deserting its mate,
+it flies to the headquarters and sings. Again,
+nearly every male at one time or another in the
+course of the season is aroused to action by the
+intrusion of a rival. The emotional tone of the
+owner of the territory is then raised, and the
+intruder is pursued and attacked; but this alone
+is not sufficient, it seems as if the chain of
+instinctive activities, when once aroused by
+appropriate stimulation, must pursue its course
+to the end&mdash;and the end in such a case is only
+reached and complete satisfaction only gained
+when the bird has not merely returned to his
+"headquarters" but has given vocal expression
+to his emotion. Finally, we must bear in mind
+these two facts, that the "headquarters" is
+occupied solely by the male&mdash;it forms no part of
+the life of the female&mdash;and that it is the male
+only that sings.</p>
+
+<p>Many such subtle incidents of behaviour as
+the foregoing can be perceived but not readily
+described, and trifling though they may seem
+to be in themselves, yet in the aggregate they
+yield full assurance of a close relationship.</p>
+
+<p>The distant song of a male, or the presence
+of an intruding male, have also stimulating
+effects, though in somewhat different ways.<span class='pagenum'><a name="Page_130" id="Page_130">130</a></span>
+The former evokes the normal reply, that is to
+say the bird, if silent, is liable to utter a corresponding
+reply; the latter arouses hostility into
+which is infused much feeling tone, the bird
+sings hurriedly while in pursuit of its rival,
+and, which is more remarkable still, even in the
+midst of an encounter. Both the normal reply
+and the emotional song must be similar in
+origin&mdash;different aspects of the same situation&mdash;and
+both are clearly related to the other
+male.</p>
+
+<p>The arrival of a female may also be followed
+by an emotional outburst which can be heard
+at intervals for some days; on the other hand,
+the song may continue as before or, for a time,
+entirely cease.</p>
+
+<p>To take the emotional outburst first. This
+would appear to be susceptible of explanation
+on the hypothesis that the voice contributes to
+a more effective pairing situation; an hypothesis
+which admittedly, at first sight, gains some
+support from the fact that a second or a third
+male is frequently present. But, in truth, the
+presence of a second male makes the situation,
+so far as the relationship between the song and
+the female is concerned, all the more perplexing;
+for, as we have already seen, the instinct of
+pugnacity, when aroused by the appearance of
+an intruder, is also liable to be accompanied by
+a similarly extravagant song. On each occasion
+the vocal effort is infused with much feeling
+tone, and it would be impossible to point to
+any one feature which is peculiar to only one<span class='pagenum'><a name="Page_131" id="Page_131">131</a></span>
+occasion. The question therefore arises as to
+whether the emotional outburst which we are
+attributing to the arrival of a female may not
+after all be due to the presence of an intruding
+male. It may be so. But although I can recall
+no single instance in which the presence of an
+intruder could be definitely excluded, yet I
+should hesitate to base upon this any broad
+generalisation.</p>
+
+<p>When the normal course of the song is not
+interrupted by the arrival of a female, when,
+that is to say, the male still pursues the routine
+to which he has all along been accustomed,
+and still sings at stated intervals in stated
+places with a voice that betrays no heightened
+emotional tone, even though the song may
+convey some meaning to the delicate perceptual
+powers of the female, we have nothing to lay
+hold upon which can be construed as an indication
+of direct relationship between the song
+and the presence of the female.</p>
+
+<p>The partial or complete suspension of the
+song after pairing has taken place is the most
+interesting, as it is the most noticeable, feature.
+Not that it is by any means universal&mdash;if it
+were so, some of the difficulties that beset the
+path of interpretation would be removed, but
+it is sufficiently widespread to demand explanation.
+In nearly every case it is, however,
+only temporary, the period during which the
+male is silent varying from a few days to a
+few weeks. The male Grasshopper-Warbler,
+when it first reaches us, sings persistently, but<span class='pagenum'><a name="Page_132" id="Page_132">132</a></span>
+when it is joined by a female a change becomes
+apparent; instead of the incessant trill, there
+are spasmodic outbursts of short duration, and
+in the course of a few days the bird lapses into
+a silence which may be broken for a short while
+at dawn, or late in the evening, but is often
+complete. More striking still is the change in
+the case of the Marsh-Warbler, and the sudden
+deterioration, or even suspension, of strains so
+beautiful and so varied, at a moment, too, when
+it might least be expected, at once arrests the
+attention. The Reed-Warbler that had its
+headquarters in a willow sang vigorously from
+the middle of May until a female arrived on
+the 20th June, when its voice was hushed, except
+for occasional outbursts which lacked force
+and were of short duration. When the Wood-Warbler
+secures a territory it repeats its sibilant
+trill with unwearying zeal, yet no sooner does
+a mate appear than its emotion is manifested
+in other directions. The Reed-Bunting is
+vociferous during February and March; but
+when a female arrives, periods of silence are
+frequent and the instinct of the bird becomes
+progressively less susceptible to stimulation.
+After the manner of the race the male makes
+temporary excursions from its territory accompanied
+by his mate, and it is noteworthy that
+when he returns and she is absent he sings,
+but that the moment she joins him, or even
+comes into sight, he is silent. In fact, in greater
+or less degree, a change is noticeable in the
+song of many resident and migratory species<span class='pagenum'><a name="Page_133" id="Page_133">133</a></span>
+under similar circumstances, a deterioration so
+marked that we learn by experience to regard
+it as a certain indication of the arrival of a
+mate.</p>
+
+<p>Thus it becomes clear that there are certain
+specific factors in the external environment with
+which the instinct can be definitely related,
+and in the order of their importance they are
+(1) the territory as a whole; (2) the headquarters;
+(3) an intruding male; (4) the female.</p>
+
+<p>To what extent are these relationships interrelated?
+Are they all mutually dependent upon
+one another, or is there one which conditions the
+remainder?</p>
+
+<p>In the first place it is evident that if a male
+were not to establish a territory, no opportunity
+would be afforded for making use of any special
+post or for acquiring a habit in relation to it,
+and so without further consideration we may
+say that the connection between the song and
+the headquarters, whatever it may be, is
+primarily dependent upon the establishment of
+a territory.</p>
+
+<p>Next, we have the fact that the distant voice,
+or still more so the presence, of another male
+has an exciting influence and evokes a corresponding
+reply. Here we have a direct relationship,
+and one which at first sight appears to
+be exclusive of cross-correlation. But is it really
+so; does no circumstance arise under which even
+the proximity of a rival fails to evoke response?
+The reply is not doubtful. Such a circumstance
+<i>does</i> arise&mdash;when a male for one reason or another<span class='pagenum'><a name="Page_134" id="Page_134">134</a></span>
+passes outside the limits of its accustomed area.
+This aspect of behaviour has already been fully
+discussed in connection with the question of
+hostility, and everyone, I imagine, must by
+now be pretty well familiar with the facts.
+However, it does not often happen that we
+are given such an aid to interpretation as is
+vouchsafed to us in the altered behaviour of
+the male when it joins the flock, and if, as
+I believe, song and hostility are intimately
+associated, forming part of an inter-related
+whole which, for biological interpretation, has,
+as its end, the attainment of reproduction, it
+is not surprising that circumstances which lead
+to the modification of the one should likewise
+affect the other; I offer no apology, therefore,
+for adverting to this aspect of behaviour once
+again.</p>
+
+<p>Now a male may leave its territory for three
+reasons&mdash;to pursue an intruder, to join the flock
+on neutral ground, or to find the necessary means
+of subsistence on other feeding grounds. On
+each of these occasions it hears the song of, and
+is in close contact with, other males; and if the
+relationship of which we are speaking be really
+exclusive of cross-correlation, its instinct ought
+to respond with the customary freedom. But
+what happens? A male pursues its rival,
+betraying much emotion and singing extravagantly,
+until the boundary is passed, when
+emotion subsides and it is silent; or, it flies to
+the flock on neutral ground, and, although
+surrounded by the very males that a short time<span class='pagenum'><a name="Page_135" id="Page_135">135</a></span>
+previously evoked response, is there unresponsive;
+or again, it goes in search of food and collects
+with other males bent on a similar errand, and
+in presence of what we know would be an
+exciting influence under other circumstances,
+it nevertheless remains silent. Hence the
+relationship between the song and a male rival
+seems, as in the case of the headquarters, to
+depend in the first instance upon the occupation
+of a territory.</p>
+
+<p>So that the relationship between the song
+and the territory as a whole is clearly of a
+different order from that which obtains between
+the song and the headquarters, or the song and a
+male rival; for the first, as far as can be judged
+by observation, is exclusive of, whilst the second
+and the third involve, cross-correlation. How
+are these facts to be explained? We have
+already seen that it belongs to the nature of the
+male during the season of reproduction to
+establish itself in a definite place, and this action
+is just as much a part of its hereditary nature as
+the building of the nest is of that of the female,
+and it is just as necessary for the successful
+attainment of reproduction. What exactly the
+stimulus is to this mode of behaviour we do
+not know; we can go no further back than
+the internal organic changes which are known
+to occur and which we assume, not without
+some reason, are responsible for its initiation.
+Granting, then, that there is this congenital
+disposition, what relation does it bear to the
+song? Without a doubt the song is likewise<span class='pagenum'><a name="Page_136" id="Page_136">136</a></span>
+founded upon a congenital basis; it is truly
+instinctive, and as such requires appropriate
+stimulation; furthermore the male sings only
+when in occupation of its territory. Having
+regard to these two facts we might say that
+the territory is the stimulus to the song. But
+this can scarcely be a true interpretation, for
+inasmuch as the stimulus would be relatively
+constant, a relatively constant response ought to
+follow, and even a slight acquaintance with the
+daily round of behaviour will furnish plenty of
+evidence to the contrary, seeing that the song,
+though persistent, is never continuous&mdash;in fact
+there are long periods of silence during the
+daytime, and only in the morning and the
+evening does the male become really vociferous.
+What then is the stimulus? Through awareness
+of something in the environment the male
+responds to stimulation, and the only reply we
+can give is that the headquarters, or a distant
+song, or the proximity of another male&mdash;with
+all of which, as we have seen, the instinct is
+definitely related&mdash;are the specific factors which
+normally evoke response&mdash;and experience teaches
+us that the periods of quiescence are just those
+when life is at its lowest ebb and these stimulating
+factors less in evidence. Bearing this in
+mind, bearing in mind the fact that when a male
+joins the flock or crosses the boundary its
+instinct ceases to respond, bearing in mind,
+that is to say, that there is evidence of relationship
+between these specific factors and the
+song only when the territory is actually occu<span class='pagenum'><a name="Page_137" id="Page_137">137</a></span>pied,
+the conclusion seems inevitable that we
+have here the determining condition which
+renders the instinct susceptible to appropriate
+stimulation.</p>
+
+<p>There remains the female. I place her last
+in order of importance, not because I regard her
+influence as of small consequence, but because
+the evidence is of a varied and complex kind,
+so much so that it is difficult to ascertain by
+observation just how far she is a situational item.
+It will be remembered that the only direct
+evidence we had of such influence was a
+deterioration or, in some instances, a complete
+cessation of vocal manifestation. Clearly then
+we are confronted with a relationship of a
+different kind from that which we have been
+discussing; for not only is anything in the
+nature of stimulation absent, but, and this is a
+remarkable fact, the other items in the environment
+which formerly evoked response no longer
+do so in quite the same way. Is there any
+awareness on the part of the male of the relation
+between his voice and the mate that is to be, or
+is it merely that as the sexual situation increases
+in complexity some inhibiting influence comes
+into play? These are questions which lead up
+to difficult problems. But it is no part of my
+task to discuss the psychological aspect of the
+behaviour; my purpose is merely to show that
+the situation on the arrival of a female undergoes
+marked modification, that the instinct of the
+male is then less susceptible to stimulation, and
+that the factors in the external environment<span class='pagenum'><a name="Page_138" id="Page_138">138</a></span>
+which formerly elicited response become relatively
+neutral.</p>
+
+<p>Hence the appearance of the female on the
+scene marks the opening of a new stage in the
+life-history of the male, and, to judge by the
+course of events, it would seem as if the song
+with its network of relationships had now served
+its main biological purpose.</p>
+
+<p>And now, what is the purpose, and what the
+origin, of song? Is it, as some naturalists have
+conceived, a means of raising the emotional tone
+of the female, of creating a more effective pairing
+situation, and so of removing a barrier to the
+successful discharge of the sexual function; or,
+is the emphasis here too much upon the
+emotional, too little upon the strictly utilitarian,
+aspect? All, I think, will agree that it must
+serve some biological purpose, and the position
+we have so far reached is that the determining
+condition of its manifestation is not merely the
+establishment, but the actual occupation of a
+territory, and that there are no factors in the
+external environment which can evoke response
+in the absence of such condition. This being so,
+the further questions arise as to whether it
+contributes towards the attainment of the end
+for which the whole territorial system has been
+built up, and what precisely is the way in which
+it does so.</p>
+
+<p>Everyone knows that in the spring the
+shyest of birds no longer practise the art of
+concealment. The Curlew soars to a great
+height, and upon outstretched wings hovers in<span class='pagenum'><a name="Page_139" id="Page_139">139</a></span>
+the air whilst uttering its plaintive wail; the
+cock Grouse, as if dissatisfied with its "crowing,"
+springs into the air and becomes a conspicuous
+object of the moor; the wary Redshank, poised
+on flickering wings, forgets its mournful alarm
+cry, and finds again its melodious song; and
+even the secretive Grasshopper-Warbler crawls
+out of the midst of the thicket in order to "reel,"
+just as, for a similar reason, Savi's Warbler
+climbs to the top of a tall reed. In fact the
+males of most species, when they are finally
+established on the breeding grounds, make
+themselves as conspicuous as possible by sight
+and by sound. And since the sounds produced
+by no two species are exactly alike, the females
+are able to recognise their prospective mates,
+and the males that are still in search of ground
+have ample warning if that upon which they are
+treading is already occupied. So that you see,
+from the remarkable development of the vocal
+powers in the male, there follow two important
+results&mdash;"recognition" and "warning."</p>
+
+<p>We here turn from song as the expression of
+an instinctive disposition, and the question of
+what calls forth this expression, to the impression
+produced by the song on the hearer.</p>
+
+<p>Most birds have a call-note or a number of
+call-notes, which, generally speaking, are specifically
+distinct. But to the human ear they are not
+always so, perhaps because our power of hearing
+is less sensitive than that of a bird, and unable to
+appreciate delicate differences of tone. Be this
+as it may, however, the fact remains that we<span class='pagenum'><a name="Page_140" id="Page_140">140</a></span>
+often find it difficult, and in not a few cases
+impossible, to recognise a bird merely by its call.
+The plaintive notes of the Willow-Warbler and
+of the Chiffchaff are to our ears very closely
+akin, so, too, are those of the Marsh-Warbler
+and of the Reed-Warbler, and there is a great
+resemblance between the hissing sound produced
+by the two Whitethroats. In Co. Donegal I
+have been deceived by the spring-call of the
+Chaffinch which, owing possibly to the humidity
+of the atmosphere, is, there, almost indistinguishable
+from the corresponding note of the
+Greenfinch. The Yellow Bunting and the Cirl
+Bunting frequently make use of a similar note,
+so do the Curlew and the Whimbrel. In fact,
+numberless instances could be quoted in which
+notes appear to us identical, and, as a rule, the
+more closely related the species, the more difficult
+it becomes to distinguish the sounds&mdash;alike in
+plumage, alike in behaviour, alike in emotional
+manifestation, it would be surprising if they were
+not alike in voice. But the moment we pass
+from the call-notes to a consideration of the
+songs we are faced with a very remarkable fact,
+for not only are these readily distinguished, but
+in many cases they bear no resemblance in any
+single characteristic. What could be more unlike
+than the songs of the Willow-Warbler and of
+the Chiffchaff, of the Marsh-Warbler and the
+Reed-Warbler, or of the Yellow Bunting and
+the Cirl Bunting?</p>
+
+<p>Now when different individuals collect in
+flocks at certain seasons, they assist one another<span class='pagenum'><a name="Page_141" id="Page_141">141</a></span>
+in finding food, and afford mutual protection by
+giving timely warning of the approach of a
+common enemy, and the gregarious instinct is
+thus of great advantage to the species; but no
+matter how powerful the impulse to flock might
+be, if there were no adequate means of communication,
+the different units would frequently
+fail to discover their neighbours. Here the
+specific cries and calls come into play, enabling
+them as they move about in search of food, or
+change their feeding grounds, or whilst they are
+on migration, to keep constantly in touch with
+one another; and hence one purpose that these
+call-notes serve is that of recognition. Moreover,
+they convey their meaning to individuals of other
+species and are acted upon, and are thus in every
+sense socially serviceable; but on the other hand,
+whilst there is much evidence to show that the
+song is of great individual value, there is none
+to show that it is in any like manner of direct
+advantage to the community.</p>
+
+<p>If, then, there is in the call-notes an adequate
+means of communication and of recognition, why
+do I suggest that the song has also been evolved
+primarily for the purpose of recognition?</p>
+
+<p>What, first of all, are the conditions in the
+life behaviour during the season of reproduction
+that make the intervention of the voice a consideration
+of such importance? The general
+result of our investigation might be summed up
+thus: we found that the male inherits a disposition
+to secure a territory, that at the proper
+season this disposition comes into functional<span class='pagenum'><a name="Page_142" id="Page_142">142</a></span>
+activity and leads to its establishment in a
+definite place, and that it cannot search for a
+mate because its freedom of action in this respect
+is forbidden by law; that the female inherits no
+such disposition, that she is free to move from
+place to place, free to satisfy her predominant
+inclination, and to seek a mate where she wills;
+and, since the appropriate organic condition
+which leads to pairing must coincide with
+appropriate conditions in the environment, that
+the union of the sexes must be accomplished
+without undue delay. Furthermore we found
+that a territory is essential if the offspring are to
+be successfully reared; that, since the available
+breeding ground is limited, competition for it is
+severe, and that the male is precluded from
+leaving the ground which he has selected, and
+is obliged, in order to secure a mate, to make
+himself conspicuous. That was our general
+result. Now there are two ways by which the
+male can make himself conspicuous&mdash;by occupying
+such a position that he can be readily seen, or
+by producing some special sound which will be
+audible to the female and direct her to the spot.
+The former, by itself, is insufficient; in the dim
+light of the early dawn, when life is at its highest,
+and mating proceeds apace, what aid would it be
+for a male to perch on the topmost branch of a
+tree, how slender a guide in the depth of the
+forest? But whether in the twilight or in the
+dark, in the thicket or the jungle, on the mountain
+or on the moor, the voice can always be
+heard&mdash;and the voice is the principal medium<span class='pagenum'><a name="Page_143" id="Page_143">143</a></span>
+through which the sexes are brought into
+contact.</p>
+
+<p>Well now, we come back to the question,
+why, if all species have a serviceable recognition
+call, that call should not be sufficient for the
+purpose, just as, without a doubt, it is adequate
+for all purposes at other seasons? The answer
+is, I think, clear. The recognition call is not
+confined to one sex, nor only to breeding birds;
+it is the common property of all the individuals
+of the species, and if the female were to rely
+upon it as a guide she might at one moment
+pursue another female, at another a non-breeding
+male; she might even be guided to a
+paired female or to a paired male, and time
+would be wasted and much confusion arise. So
+that no matter how much a male might advertise
+himself by cries and calls which were common
+alike to all the individuals of the species, it
+would not assist the biological end which we
+have in view. Something else is therefore
+required to meet the peculiar circumstances,
+some special sound bearing a definite meaning
+by which the female can recognise, amongst the
+host of individuals of no consequence to her,
+just those particular males in a position to breed
+and ready to receive mates. Hence the vocal
+powers, the power of producing sounds instrumentally,
+and the power of flight, have been
+organised to subserve the biological end of
+"recognition."</p>
+
+<p>And this view is strengthened, it seems to
+me, by the erratic behaviour of certain species,<span class='pagenum'><a name="Page_144" id="Page_144">144</a></span>
+more particularly by one remarkable case, the
+case of the Cuckoo. The male, after having
+established himself, utters his call persistently
+from the day of arrival until approximately the
+middle of June; but, in contrast with the
+large majority of species, the female has a
+characteristic call which she, too, utters at
+frequent intervals. The female is polyandrous
+and has a sphere of influence embracing the
+territories of a number of males; she wanders
+from place to place, is often silent, and not
+unfrequently is engaged in dealing with her egg
+or in searching for a nest in which to deposit it,
+and therefore she is not always in touch with a
+male, still less with any particular one. Now
+there is much evidence to show that the
+discharge of the sexual function amongst birds
+is subject to control, and that this control
+operates through the female&mdash;through her
+physiological state becoming susceptible to
+stimulation only at certain periods. So that we
+have these considerations, that the female is
+polyandrous, that she has a territory distinct
+from that of the male, and that her sexual
+impulse is periodical; and the further consideration
+that the impulse, since it is periodical, is of
+limited duration and must receive immediate
+satisfaction. Such being the circumstances of
+the case, would the voice of the male serve to
+insure the union of the sexes at the appropriate
+moment? Well, the fact that she is polyandrous
+implies that every male in her sphere of
+influence is not always capable of satisfying her<span class='pagenum'><a name="Page_145" id="Page_145">145</a></span>
+sexual instinct. Is, then, the male's call an
+indication of his readiness to yield to stimulation?
+Without a doubt it is an index of the
+general physiological state which generates the
+sexual impulse, without a doubt it denotes a
+general preparedness to breed, but there is no
+evidence to show that it denotes the degree of
+ardour of the male at any particular moment,
+and much that proves the contrary. So that
+only by the female producing some special
+sound which will attract the males that are
+eager and bring them rapidly to the spot where
+she happens to be, only thus is it possible to
+insure the consummation of the sexual act.
+This, it seems to me, is the purpose of the
+peculiar call of the female&mdash;a call which, so far
+as biological interpretation is concerned, is just
+as much a song as the melody of the Marsh-Warbler&mdash;and
+its interest for us just now lies in
+this, that here we have a special case in which
+the sexes have separate territories, the female is
+polyandrous, and the voice of the male is not
+sufficient by itself to bring to pass the union
+of the sexes; and in which, consequently, if
+the purpose of song be that of recognition,
+we should expect to find, as we do find, that
+the female had a distinct and penetrating
+call.</p>
+
+<p>We now come to the question of "warning,"
+by no means the least important purpose of
+song. I pointed out that one of the chief
+differences between the call-notes and the song
+was that the former were socially serviceable,<span class='pagenum'><a name="Page_146" id="Page_146">146</a></span>
+whereas the latter was only serviceable to
+certain individuals; and in making this statement,
+I had in mind the direct benefits to the
+community which proceeded from an appreciation
+of sounds having a mutually beneficial
+meaning, not the indirect, though none the less
+beneficial, consequences to the species as a
+whole. Biologically considered, song, if it acts
+as a warning and thereby leads in one way or
+another to more complete success in the rearing
+of offspring, may be spoken of as socially
+serviceable; but it is legitimate to draw a
+distinction between the prospective value of
+remote relationships which we can foresee,
+and the mutual assistance which the individuals
+of a community derive from their close
+association.</p>
+
+<p>If there were always sufficient breeding
+ground to support the offspring of all the
+individuals of each species, if the individuals
+were always so distributed that there was no
+possibility of overcrowding in any particular
+area, and if the conditions of existence of
+different species were so widely divergent that
+the presence of this one in no way affected the
+interests of that, no opportunity would be
+afforded for the development of so complex a
+system as is involved in the "territory" and all
+that appertains to it. But the available breeding
+ground is by no means unlimited. The
+supply of food, which is a determining factor
+in the environment, is always fluctuating according
+to the climate and according to the changes<span class='pagenum'><a name="Page_147" id="Page_147">147</a></span>
+in the earth's surface; and so the distribution of
+the bird population in any given area, though it
+may be suitably adjusted for one year or even
+for a period of years, is bound in the course of
+time to require readjustment. Now there
+cannot be readjustment without competition,
+nor competition without combat. But the
+appeal to physical force is only a means to an
+end, and, since no male can endure incessant
+warfare and the perpetual strain of always being
+on the alert, without experiencing such physical
+exhaustion as might affect his power of reproduction,
+its direct effect upon the combatants
+cannot be otherwise than harmful&mdash;in fact it is
+a necessary evil which for the good of the
+species must be kept strictly within bounds.
+Bearing in mind, then, these two facts, namely
+that the distribution of the males is never stable
+and that overmuch fighting may defeat the end
+in view, we can appreciate the importance of
+any factor which will lead to a more uniform
+distribution and at the same time insure security
+by peaceable means.</p>
+
+<p>The proximate end of the male's behaviour is
+isolation&mdash;how is it to be obtained? If, after
+having occupied a territory, the bird were to
+remain silent, it would run the risk of being
+approached by rivals; if, on the other hand, it
+were merely to utter the recognition call of the
+species, it would but attract them. In neither
+case would the end in view be furthered, and
+isolation would solely depend upon alertness and
+the capacity to eject intruders. Supposing,<span class='pagenum'><a name="Page_148" id="Page_148">148</a></span>
+however, that the song, just as it serves to
+attract the females, serves to repel other males,
+a new element is introduced deserving of recognition;
+for those males that had established
+themselves would not only be spared the
+necessity of many a conflict, but they would be
+spared also the necessity of constant watchfulness,
+and so, being free to pursue their normal routine&mdash;to
+seek food, to rest, and, if migrants, to
+recover from the fatigue of the journey, they
+would be better fitted to withstand the strain of
+reproduction; and those that were still seeking
+isolation in an appropriate environment, instead
+of settling first here and then there only to find
+themselves forestalled, would avoid and pass by
+positions that were occupied, establishing themselves
+without loss of time in those that were
+vacant. Without the aid of something beyond
+mere physical encounter to regulate dispersal,
+it is difficult to imagine how in the
+short time at disposal anything approaching
+uniformity of distribution could be obtained.
+Hence, both in the direction of limiting combat,
+of insuring accommodation for the maximum
+number of pairs in the minimum area, and of
+conserving energy, the song, by conveying a
+warning, plays an important part in the whole
+scheme.</p>
+
+<p>And if this be so, if the song repels instead
+of attracting, it follows that the more distinct
+the sounds, the less likelihood will there be of
+confusion; for supposing that different species
+were to develop similar songs, whole areas might<span class='pagenum'><a name="Page_149" id="Page_149">149</a></span>
+be left without their complement of pairs just
+because this male mistook the voice of that,
+and avoided it when there was no necessity for
+doing so. So that just as from the point of
+view of "recognition" each female must be able
+to distinguish the voice of its own kind, so
+likewise the warning can only be adequate
+providing that the sounds are specifically distinct.
+A point, however, arises here in regard to
+closely related forms. Some species require
+similar food and live under similar conditions of
+existence; they meet in competition and fight
+with one another; and, if they did not do so, the
+food-supply of a given area would be inadequate
+to support the offspring of all the pairs inhabiting
+that area. Generally speaking, the more closely
+related the forms happen to be, the more severe
+the competition tends to become; and it may be
+argued that in such cases a similar song would
+contribute to more effective distribution and in
+some measure provide against the necessity of
+physical encounter; that, in fact, it would stand
+in like relation to the success of all the
+individuals concerned, as does the song to the
+individuals of the same species. But we must
+bear in mind that the primary purpose of song
+is to direct the females to those males that
+are in a position to breed; and to risk the
+possibility of prompt recognition in order that
+the males of closely related species should fight
+the less, would be to sacrifice that which is
+indispensable for a more remote and less
+important advantage.</p>
+
+<p><span class='pagenum'><a name="Page_150" id="Page_150">150</a></span>What meaning does the song convey to a
+male that is unestablished? Does the bird
+recognise that it is forestalled; does it foresee
+and fear the possibility of a conflict, and
+conclude that the attempt to settle is not worth
+while? I do not imagine that it thinks about it
+at all. How then does the warning warn?
+We will endeavour to answer this question, but,
+in order to do so, we must review the stages by
+which a territory is secured.</p>
+
+<p>We take as our starting point the internal
+organic changes which are known to occur.
+These changes are correlated with other changes,
+manifested by a conspicuous alteration in
+behaviour&mdash;to wit, the disappearance of sociability
+and its replacement by isolation. Having
+found a station which meets the requirements of
+its racial characteristics, the male establishes
+itself for a season, becomes vociferous, displays
+hostility towards others of its kind, and in due
+course is discovered by a female. The whole is
+thus an inter-related whole, a chain of activities
+which follow one another in ordered sequence.
+Now we have seen that it is neither pugnacious
+nor vociferous until the territory is actually
+occupied; we have seen that the fact of occupation
+is the condition under which the instincts of
+pugnacity and of song are rendered susceptible
+to appropriate stimulation; we have discussed
+the nature of the stimulus in each case, and we
+wish to know the sort of meaning that the song
+conveys to an individual which is still in the
+preliminary stage of seeking a station. In<span class='pagenum'><a name="Page_151" id="Page_151">151</a></span>
+sequential order we have the following: (1)
+internal organic changes which lead to isolation,
+(2) the appropriate environment which gives rise
+to an impulse to remain in it, (3) the occupation
+of a territory which is the condition under which
+the instincts are rendered susceptible to stimulation,
+(4) the various stimuli. Each is dependent
+upon that which precedes it, and no part can be
+subtracted without failure of the biological end
+in view, neither can the different stages be
+combined in different order. So that, in
+considering the significance of song to an
+unestablished male, we are dealing with the
+situation at a point at which all the latent
+activities have not been fully felt, for all that so
+far has occurred is the change from sociability to
+isolation determined by internal organic changes.
+The bird has not established a territory because
+it has not come into contact with the appropriate
+environment, and it is not pugnacious because
+the condition which renders its instinct susceptible
+is absent; and so, as it wanders from place
+to place and hears the voices of males here or
+males there, it merely behaves in accordance
+with that part of its nature which predominates
+just at that particular moment&mdash;the impulse to
+avoid them.</p>
+
+<p>But given the appropriate environment,
+given, that is to say, just that combination of
+circumstances which might bring into functional
+activity all the latent instincts of the intruder,
+and no matter how vociferous the occupant of
+a territory might be, it would not be preserved<span class='pagenum'><a name="Page_152" id="Page_152">152</a></span>
+from molestation. The advantage of the song,
+biologically considered, is then this, that it will
+often prove just sufficient to preclude males
+in search of isolation from coming into contact
+with the environmental conditions adequate to
+supply the stimulus to their latent activities
+and to convert them into rivals.</p>
+
+<p>If this interpretation be correct, if we are
+right in attributing the withdrawal solely to
+the fact that the first stage only in the relational
+series has been reached, it follows that the
+effect of song upon males that have reached
+subsequent stages in that series must be of a
+very different kind. We have dealt with the
+male when in the preliminary stage of seeking
+isolation, we must deal with it now when
+eventually it occupies a territory. How does
+it behave when it hears, as it is bound to do,
+the voices of rivals in its neighbourhood? You
+may remember that some allusion was made
+to the fact that an outburst of song from one
+individual was followed, not unfrequently, by a
+similar outburst on the part of other individuals
+in the immediate locality. For example, silence
+may reign in the reed-bed except for an occasional
+note of the Reed-Warbler or Sedge-Warbler.
+Suddenly, however, a dispute arises between two
+individuals, accompanied by a violent outburst
+of song, and forthwith other males in the
+vicinity begin to sing excitedly and continue
+doing so for some minutes in a strangely
+vigorous manner, the tumult of voices affording
+a striking contrast to the previous silence.<span class='pagenum'><a name="Page_153" id="Page_153">153</a></span>
+Spasmodic outbursts of this kind, stimulated
+by an isolated utterance, are by no means
+uncommon. But not only does song stimulate
+song; under certain conditions it has the still
+more remarkable effect of arousing hostility.
+The boundary that separates two adjoining
+territories is by no means a definite line, but
+rather a fluid area wandered over by this
+owner at one moment, by that at another.
+Now so long as the bird is silent while in this
+area, the probability is that it will escape
+detection and remain unmolested; let it however
+sing&mdash;it often does so&mdash;and it will not merely
+be approached but attacked, and consequently
+this area is the scene of much strife. The point
+to be noticed here is that the song brings about
+no withdrawal; it elicits a response, attracts
+instead of repelling, and, in short, arouses the
+impulse that is always predominant in the
+nature of the male when eventually it occupies
+a territory&mdash;the impulse of self-assertiveness.
+Therefore it seems clear that the different stages
+in the process of reproduction mark the appearance
+of different conditions, each of which
+renders some new impulse susceptible to
+stimulation, and that the significance of song
+depends upon the stage which happens to
+have been reached. Hence when we speak
+of song acting as a "warning," we do not
+mean that it arouses any sensation of fear; it
+is but a stimulus to that part of the inherited
+nature of the hearer which predominates at the
+moment.</p>
+
+<p><span class='pagenum'><a name="Page_154" id="Page_154">154</a></span>Are we then justified in the use of such
+terms as "warning," "significance," or even
+"meaning," when it is but a matter of stimulus
+and response? In what does the impulse to
+avoid other males consist? There is no reason
+to suppose that there is any sensation of fear
+in the first stage, and the course of behaviour
+demonstrates that there is none in the later
+stages. But it is difficult to conceive of an
+impulse which has, as its end, the isolation
+of the individual from members of its own
+sex and kind, without some feeling-tone, the
+reverse of pleasurable, entering into the situation;
+just as it is difficult to believe that the
+female experiences no pleasurable sensation
+when she hears the voice of the male that
+directs her search. So that the song may be
+actually repellent in the one case and attractive
+in the other; and it is none the less repellent
+when, as in the later stages, it attracts a
+neighbouring male, for the attraction is then
+of a different order, determined by the presence
+of the condition which renders the pugnacious
+nature susceptible and leads to attack. In a
+sense, therefore, we can speak of "meaning"&mdash;though
+not perhaps of "significance"&mdash;and
+of "warning," when we refer to the prospective
+value of the behaviour.</p>
+
+<p>So much for the purpose of "song"; there
+still remains the more difficult question&mdash;the
+question of origin. Let me make clear what
+I mean by origin. As we have already seen,
+there is infinite diversity in the sexual voice<span class='pagenum'><a name="Page_155" id="Page_155">155</a></span>
+of different species; some are harsh and others
+monotonous, and some strike the imagination
+by their novelty whilst others are melodious;
+and to the naturalist each, in its particular
+way and in a particular degree, probably makes
+some appeal according to the associations that
+it arouses. But just why a Marsh-Warbler
+is gifted with a voice that is so beautiful and
+varied, whilst the Grasshopper-Warbler must
+perforce remain content with a monotonous
+trill; just why the tail feathers of the Snipe
+have developed into an instrument, whilst the
+Pied Woodpecker has developed muscles which
+enable it to make use of a decayed branch as
+an instrument&mdash;we know no more than we do
+of the nature of the forces which lead the Reed-Warbler
+to weave its nest to reeds, or the
+caterpillar of the Elephant Hawk Moth to
+assume so peculiar an attitude when disturbed.
+When therefore I speak of the origin, I do
+not refer to the mode of origin of variation;
+I take for granted that variations somehow
+arise, and I seek to ascertain whether there
+is anything in the phenomena which we have
+explored which might reasonably be held to
+determine the survival of this one in preference
+to that.</p>
+
+<p>When we reflect upon the problem of song
+and consider the numerous and diverse forms
+in which it is manifested, we are apt to draw
+a comparison between the sounds we hear
+and those produced by musical instruments,
+and hence to conclude that each bird is gifted<span class='pagenum'><a name="Page_156" id="Page_156">156</a></span>
+with a special instrument in virtue of which
+it produces its characteristic melody. But there
+is a very remarkable phenomenon connected
+with the singing of birds which shows that this
+is really not the case&mdash;I mean the phenomenon
+of imitation. There are plenty of good imitators
+amongst our native species, and the power of
+imitation is not the exclusive property of those
+which have reached a high degree of vocal
+development, nor, for the matter of that, of
+song-birds at all. Even the Jay, than which
+few birds have a more raucous voice, that
+"hoots" like the Wood-Owl, or copies the
+sounds produced by the tail feathers of the
+Snipe, will occasionally imitate the most
+melodious strains of some other species; and
+the Red-backed Shrike, whose sexual call is
+principally a few harsh notes rapidly repeated,
+bursts at times into perfect imitations of the
+song of the Swallow, Linnet, or Chaffinch.
+Nevertheless it is amongst such typical songsters
+as the Warblers that we find the greatest volume
+of imitation, and no limit seems to be placed
+upon their capacity. The Marsh-Warbler can
+utter the call of the Green Woodpecker, or sing
+as the Nightingale does, with as much facility
+as it sings its own song; and the Blackcap is
+well-nigh as proficient in copying the cries
+and melodies of surrounding species&mdash;and so,
+if it were necessary, we might proceed to add
+to the list.</p>
+
+<p>These examples demonstrate that different
+songs are not represented by a corresponding<span class='pagenum'><a name="Page_157" id="Page_157">157</a></span>
+number of different physiological contrivances;
+for if the difference were really attributable to
+some structural peculiarity, then the range of
+sounds embraced in the call-notes and the sexual
+call of any given species, must be the measure
+of the capacity of its instrument; and no matter
+how great its power of imitation may be, it
+follows that it will only be capable of copying
+those sounds which fall within that range.
+There is plenty of evidence to show that the
+power of imitation is almost unlimited, at all
+events that it is not confined within such
+narrow limits as are here demanded. Hence
+it seems clear that the diversity of song is
+not to be sought in structure, but in some
+innate capacity to play one tune in preference
+to another; and if this be so, and if
+out of the same instrument, which has been
+primarily evolved to further the biological end
+of intercommunication, all manner of diverse
+sounds can be made to proceed, the problem
+of the origin of song is to that extent
+simplified.</p>
+
+<p>We must next inquire into the nature of
+song, and endeavour to ascertain whether all
+the individuals of a species are alike proficient,
+or, failing this, whether there is any quality
+which can be observed to be constant under
+all conditions. I watch the Reed-Buntings in
+a marsh and find that there are three males
+occupying adjoining territories. Two of them
+are fully mature and their plumage is bright:
+that is to say the crown is black, the collar<span class='pagenum'><a name="Page_158" id="Page_158">158</a></span>
+and breast are white, the flanks are dull white
+spotted with black, and the mantle is reddish-brown.
+The third is immature: the crown,
+instead of being black, is suffused with brown;
+the collar, instead of being white, is mottled with
+brown; and the flanks are more heavily streaked
+with brown. These three birds take up their
+positions in February, and, as is their wont,
+sing incessantly each day at daybreak. The
+song of the first two is normal, including the
+usual number of phrases which flow in no
+definite sequence, but are combined and recombined
+in different order, and the tone is
+pure; that of the third, the immature bird,
+is, however, very different; for just as in
+comparison its plumage is dull, so the phrases
+of its song are limited and reiterated with
+great monotony, the tone is impure, and the
+whole performance is dull and to our ears
+unmusical. I watch them from February to
+June, and observe the order in which they are
+mated&mdash;first a mature male; next, after a short
+interval, the immature male; and finally, after
+a still longer interval, the remaining bird gets
+a mate. As the season advances, still keeping
+watch on the development of the plumage
+and of the voice of the immature male, I
+observe that no very definite change takes
+place&mdash;that the colours remain dull, that
+there is a conspicuous absence in the song of
+certain phrases, and that the notes lack purity
+of tone.</p>
+
+<p>If now, instead of Reed-Buntings in a marsh,<span class='pagenum'><a name="Page_159" id="Page_159">159</a></span>
+I watch Yellow Buntings on a furze-covered
+common, I find that, establishing themselves
+early in February, they sing persistently, and
+in a few weeks are paired. But what arrests
+my attention more particularly is the quality
+of the song; for although the voice is unmistakably
+the voice of the Yellow Bunting,
+yet it is incomplete and lacks the variety of
+phrases and musical notation which we customarily
+associate with the bird. Nevertheless, as
+the season advances, there is a progressive
+development in both these directions, and by
+the end of March or the beginning of April the
+song possesses all those qualities which appeal
+to us so forcibly.</p>
+
+<p>There is one other fact to which attention
+must be drawn&mdash;the variation in the song of
+the same species in different districts. As an
+illustration let us take the case of the Chaffinch.
+In Worcestershire the bird sings what I imagine
+to be a normal song&mdash;the notes are clear and
+the phrases are distinct and combined in
+numerous ways. With the notes fresh in
+mind I leave them and go to the west of
+Donegal, where I am at once conscious of a
+difference; not a subtle difference that perplexes
+the mind and is difficult to trace, but
+a change so remarkable that one is conscious
+of a passing doubt as to whether after all the
+voice is the voice of the Chaffinch; the song
+is pitched in a lower key, certain phrases are
+absent, the notes lack tone and are sometimes
+even harsh, and the bird seems wholly in<span class='pagenum'><a name="Page_160" id="Page_160">160</a></span>capable
+of reaching the higher notes to which
+I am accustomed.</p>
+
+<p>Now the immature Reed-Bunting, though to
+our ears its song is but a poor representation
+of that of the adult, gains a mate; the Yellow
+Bunting pairs, and the discharge of the sexual
+function may even have taken place before its
+voice attains what we judge to be its full
+development; and there are no grounds for
+supposing that the Donegal Chaffinch, with its
+less musical notes, has on that account any
+the less chance of procreating its kind&mdash;facts
+which demonstrate that the biological value
+of song is neither to be sought in the purity
+of tone, nor in the variety and combination of
+phrases, nor, indeed, in any of those qualities
+by which the human voice gains or loses merit,
+and which leave us with no alternative but to
+dismiss from our minds all &aelig;sthetic considerations
+in the attempt to estimate its true
+significance.</p>
+
+<p>What, then, determines its value? Are
+there any qualities which, whether the bird is
+mature or immature, whether it is untrained
+or has acquired fuller expression by practice,
+whether it inhabits this district or that, are
+alike constant? Well, no matter how great
+the variation, no matter how much this voice
+falls below or exceeds the standard, judged
+from the human standpoint, attained by that,
+even we, with our duller perception, have no
+difficulty in recognising the species to which
+the owner of the voice belongs; in other<span class='pagenum'><a name="Page_161" id="Page_161">161</a></span>
+words, the song is always specific, and this is
+the most noticeable, as it is the most remarkable,
+characteristic.</p>
+
+<p>There is still, however, another quality to
+which I would draw attention&mdash;that of loudness.
+The sounds produced are on the
+whole alike penetrative, and the individuals
+of any given district, even though the climate
+by affecting their vocal muscles may
+have modified the character of the song, are
+at no disadvantage in this respect; neither are
+the females on the same account the less likely
+to hear the undeveloped voice of the immature
+male.</p>
+
+<p>We have then the following considerations:
+firstly, there is the widespread and remarkable
+phenomenon of imitation, from which we can
+infer that the diversity of song is not due to
+structural differences but must be sought in
+some innate capacity to play one tune in
+preference to another; secondly, not all the
+individuals of the same species play a similar
+tune&mdash;we find that there is in certain directions
+a noticeable variation which nevertheless does
+not seem to affect the question of success or
+failure in the attainment of reproduction; in
+the third place, in contrast with this variation,
+we can observe a striking uniformity in two
+important particulars, namely in the specific
+character and penetrative power of the song&mdash;qualities
+which we know are essential for the
+purposes of "recognition" and "warning"; and
+finally, from the general course of our investi<span class='pagenum'><a name="Page_162" id="Page_162">162</a></span>gation,
+we can infer that if a male had no
+certain means of advertising its position, the
+territory would not be brought into useful
+relation in its life. Have we here sufficient
+ground on which to construct a theory of
+origin; in other words, has the evolution of
+song been incidental to, and contributory to,
+the evolution of the territory?</p>
+
+<p>We have all along spoken of the song and
+of the call-notes as if they were manifestations
+of separate emotional states having their respective
+and well-defined spheres of usefulness;
+and while, speaking generally, this is a true
+statement of the case, there is much evidence
+to show that the relationship between them
+is nevertheless very close. There are, for
+example, quite a number of cases in which a
+particular call-note is uttered with unusual
+energy during sexual emotion, and is attached
+to the song, of which it may be said to form a
+part; but a still closer connection can be traced
+in many simple melodies which are merely
+compositions of social and family calls repeated
+many times in succession, and even in some
+of the more complex productions there will
+be found indications of a similar construction.
+And since this is so, since moreover,
+in the seasonal vocal development of such a
+bird as the Yellow Bunting, we can observe
+the gradual elaboration from simple to complex&mdash;from
+the repetition of single notes to
+phrases and from phrases to the complete
+melody&mdash;we have every reason to suppose that<span class='pagenum'><a name="Page_163" id="Page_163">163</a></span>
+it is along these lines that the evolution of
+the voice has proceeded.</p>
+
+<p>In all probability there was a time when
+vocal expression was limited to primitive social
+and family cries which would be called into play
+with special force during times of excitement,
+more particularly during the sexual season
+which is the period of maximum emotional
+excitement. But the excitement would express
+itself in all the congenital modes of behaviour
+peculiar to the season, and thus the repetition
+of these cries would become associated with
+combat, with extravagant feats of flight, and
+with other forms of motor response. Now the
+more emotional individuals would be the more
+pugnacious, and all the more likely therefore to
+secure territory and so to procreate their kind;
+and, being of an excitable disposition, they
+would at the same time be the more vociferous.
+Hence variations of the hereditary tendency to
+vocal expression, even though in themselves
+they were not of survival value, would be
+fostered and preserved, so long as they were not
+harmful, in virtue of their association with
+pugnacity. But if, instead of being neutral,
+they helped to further the biological end of
+combat, the relationship between the voice and
+pugnacity would be of a mutually beneficial
+kind; and those individuals in which variation
+in both directions happened to coincide, would
+have a better chance of success in the attainment
+of reproduction.</p>
+
+<p>A territorial system, closely corresponding<span class='pagenum'><a name="Page_164" id="Page_164">164</a></span>
+to that which we have discussed, forms part of
+the life behaviour of certain mammals, and of
+its existence much lower in the scale of life
+evidence is not wanting; from which we can
+infer that it is not of recent origin, but that
+the conditions in the external environment
+demanded such a system at a remote period of
+avian development. Now even in its incipient
+stages the system must have involved a separation
+of the sexes, and howsoever slight the
+degree of separation may have been in comparison
+with that which can be observed to-day,
+inasmuch as the power of locomotion was then
+less highly developed, mating could only have
+proceeded satisfactorily providing that males fit
+to breed had some adequate means of disclosing
+their positions. Thus there is reason to think
+that from the very commencement of the
+process variations of emotional disposition
+expressed through the voice would have been of
+survival value.</p>
+
+<p>But expressed in what direction, in loudness
+and persistency of utterance, these are the
+qualities which, I imagine, would have been
+more likely to have facilitated the search of the
+female? Yet if she were uncertain as to the
+owner of the voice, neither loudness nor persistent
+repetition would avail much; and as
+species multiplied and the competition for the
+means of living became increasingly severe, so
+the necessity of a territory would have become
+intensified, and so, too, with the extension of
+range, would the separation of the sexes have<span class='pagenum'><a name="Page_165" id="Page_165">165</a></span>
+been an ever-widening one; and as with their
+multiplication, irregularities and delays in
+mating, arising from the similarity of the calls,
+would have increased in frequency, so a distinctive
+call, which would have tended to minimise
+these risks, would have come to possess
+biological value.</p>
+
+<p>Here we have a theory of origin, but origin
+of what? Of certain characteristics of song&mdash;nothing
+more; and therefore to suppose that it
+furnishes a complete explanation, which satisfies
+all the requirements of scientific logic, of so
+wonderful an intonation as that, for example, of
+the Marsh-Warbler, or that no other relationships,
+except that of the territory, enter into the
+total emotional complex, simplifying here or
+elaborating there to meet the exigencies of
+diverse circumstances&mdash;to suppose this would be
+foolish. That there are many relationships
+which even to-day are leading to modifications
+in important particulars, but which at the
+present time are beyond our cognisance, of this
+there can be no doubt.</p>
+
+<p>There is one process by which song may
+have attained a fuller development, and which
+would account in some measure for the elaboration,
+inexplicable merely in terms of "recognition."
+It is this: the effect of the sexual call
+upon the female cannot well be neutral, it must
+be either pleasurable or the reverse&mdash;it must, that
+is to say, be accompanied by some suggestiveness,
+and by suggestion I mean the arousing of some
+emotion akin to that of the male; and if there<span class='pagenum'><a name="Page_166" id="Page_166">166</a></span>
+are degrees of suggestiveness, which well there
+may be, some males will mate sooner than others
+and some will remain mateless&mdash;this is the
+theory of sexual selection. The question to be
+decided here is whether the biological emphasis
+is on loudness, or specific distinctness, or pitch,
+or modulation, or the manner in which the
+phrases are combined&mdash;that is, on some qualities
+in preference to others&mdash;or whether the emphasis
+is on the whole. We have already seen, and it
+is well known, that there is much variation in
+the voices of different individuals of the same
+species, and thus the first condition of the theory
+is fulfilled. Now the conditions which lead to
+variation are threefold&mdash;immaturity, seasonal
+sexual development, and isolation. Of the
+three, the variation in the case of the immature
+bird is the most instructive; the tone is not so
+pure, the combination of phrases is incomplete,
+and elaboration is imperfect, and yet, notwithstanding
+all these imperfections, we can observe
+that the bird pairs as readily as does the adult.
+But even if we lacked this demonstrative
+evidence, we should still be justified in assuming
+that such must be the case, for we know from
+experience in the preservation of game, where
+there is no surer way of reducing the stock than
+by leaving too high a percentage of old cocks,
+that for the young bird to be at any disadvantage
+in competition with the adult is detrimental, if
+not disastrous, to the species. So that while
+there is plenty of evidence of variation in those
+particular qualities which appeal to our &aelig;sthetic<span class='pagenum'><a name="Page_167" id="Page_167">167</a></span>
+faculties, there is at the same time evidence
+which demonstrates that such variations exercise
+no influence on the course of mating; and
+inasmuch as it is difficult to conceive of
+any voice departing more from the normal
+type in these particular qualities than the
+immature does from the adult, if there be
+degrees of suggestive influence, we must seek
+it in some other direction. There remain the
+two other characteristics which we found to
+be constant under all circumstances, namely,
+loudness and specific distinctness; and if, in
+addition to serving the purpose of disclosing
+the positions of the males, they serve to
+evoke some emotion in the female, which
+helps to further the biological end of mating,
+so much the more reason is there for their
+survival.</p>
+
+<p>There can be no question that this ingenious
+and attractive theory, if it were true in its
+special application to song, would immensely
+simplify interpretation, and moreover that
+preferential mating would contribute not a little
+to the success of the whole territorial system.
+No one can deny the strength of the argument:
+that the sexual instinct, like all other instincts,
+must require a stimulus of an appropriate kind;
+that the effect of the sexual call upon the
+female cannot be neutral; and hence the probability
+that stimulation varies too; no one, I
+say, can question the strength of this evidence,
+and, one might add, of the evidence derived
+from the analogy of the human voice. But<span class='pagenum'><a name="Page_168" id="Page_168">168</a></span>
+when we have said this, we have said all;
+and our acceptance of the hypothesis, so far
+as song is concerned, must remain provisional
+so long as the evidence remains but secondary
+evidence.</p>
+<hr />
+<p><span class='pagenum'><a name="Page_169" id="Page_169">169</a></span></p>
+<h3>CHAPTER V</h3>
+
+<h4>THE RELATION OF THE TERRITORY TO THE
+SYSTEM OF REPRODUCTION</h4>
+
+
+<p>In the first two chapters I tried to show that
+the inherited nature of the male leads it to
+remain in a definite place at a definite season
+and to become intolerant of the approach of
+members of its own sex, and that a result is
+thus attained which the word "territory" in
+some measure describes. But the use of this
+word is nevertheless open to criticism, for it
+denotes a human end upon which the highest
+faculties have been brought to bear, and consequently
+we have to be on our guard lest our
+conception of the "territory" should tend to
+soar upwards into regions which require a level
+of mental development not attained by the
+bird. It is necessary to bear this in mind
+now we have come to consider the meaning
+of the territory, or rather the position that it
+occupies in the whole scheme of reproduction.</p>
+
+<p>Relationship to a territory within the interrelated
+whole of a bird's life serves more than
+one purpose, and not always the same purpose
+in the case of every species. We have only<span class='pagenum'><a name="Page_170" id="Page_170">170</a></span>
+to glance at the life-histories of divergent forms
+to see that the territory has been gradually adjusted
+to suit their respective needs&mdash;limited in
+size here, expanded there, to meet new conditions
+as they arose. Now some may think that the
+theory would be more likely to be true if the
+territory had but one purpose to fulfil, and
+that one the same for every species; and they
+may see nothing but weakness in the multiplication
+of ways in which I shall suggest it may
+be serviceable. But such an objection, if it
+were raised, would arise from a mistaken conception,
+a conception which, instead of starting
+with a relationship and working up to the
+"territory," sees in the "territory" something
+of the bird's own selection and thence works
+back to its origin. Holding the view that it
+is nothing but a term in a complex relationship
+which has gradually become interwoven in
+the history of the individual, I see no reason
+why the fact of its serving a double or a treble
+purpose should not be a stronger argument
+for its survival. I now propose to examine
+the various ways in which the territory may
+have been of use in furthering the life of the
+individual, and the circumstances in the inorganic
+world which have helped to determine its
+survival.</p>
+
+<p>The purpose that it serves depends largely
+upon the conditions in the external environment&mdash;the
+climate, the supply of food, the
+supply of breeding-stations, and the presence
+of enemies. Hence its purpose varies with<span class='pagenum'><a name="Page_171" id="Page_171">171</a></span>
+varying conditions of existence. But before
+we proceed to examine the particular ways
+in which it has been modified to suit the needs
+of particular classes of species, and the reason
+for such modifications, we must inquire whether
+there is not some way in which it has been
+serviceable alike to every species, or at least
+to a large majority of them.</p>
+
+<p>Success in the attainment of reproduction
+depends upon the successful discharge of the
+sexual function; and the discharge of the sexual
+function depends primarily upon an individual
+of one sex coming into contact with one of the
+opposite sex at the appropriate season and
+when its appropriate organic condition arises.
+Now the power of locomotion is so highly
+developed in birds that it may seem unreasonable
+to suppose that males and females would
+have any difficulty in meeting when their
+inherited nature required that they should do
+so, still less reasonable to suggest that this
+power might even act as a hindrance to
+successful mating. Nevertheless, if we try to
+picture to ourselves the conditions which would
+obtain if the movements of both sexes were in
+no wise controlled, and mating were solely
+dependent upon fortuitous gatherings, we shall
+come, I fancy, to no other conclusion than that
+much loss of valuable time and needless waste
+of energy would often be incurred in the search,
+and that many an individual would fail to
+breed just because its wanderings took it into
+districts in which, at the time, there happened<span class='pagenum'><a name="Page_172" id="Page_172">172</a></span>
+to be too many of this sex or too few of that.
+And as the power of locomotion increased
+and the distribution of the sexes became more
+and more irregular, so the opportunity would
+be afforded for the development of any variation
+which would have tended to facilitate the
+process of pairing, and by so doing have conferred
+upon the individuals possessing it, some
+slight advantage over their fellows.</p>
+
+<p>What would have been the most likely
+direction for variation to have taken? Any
+restriction upon the freedom of movement of
+both sexes would only have added to the
+difficulties of mating; but if restriction had
+been imposed upon one sex, whilst the other
+had been left free to wander, some order would
+have been introduced into the process. That
+the territory serves to restrict the movements
+of the males and to distribute them uniformly
+throughout all suitable localities, there can be
+no question; and since the instinctive behaviour
+in relation to it is timed to appear at a very
+early stage in the seasonal sexual process, the
+males are in a position to receive mates before
+the impulse to mate begins to assert itself
+in the female.</p>
+
+<p>We will take the Ruff as an example.
+According to Mr. Edmund Selous, pairing, in
+this species, is promiscuous&mdash;the Ruffs are
+polygamous, the Reeves polyandrous. Suppose,
+then, that upon this island of some few
+miles in circumference, whereon his investigations
+were made, the movements of neither Ruff<span class='pagenum'><a name="Page_173" id="Page_173">173</a></span>
+nor Reeve were subject to control, that the
+birds wandered in all directions, and that the
+union of the sexes were fortuitous, would the
+result have been satisfactory? We must
+remember that the Reeve requires more than
+one Ruff to satisfy her sexual instinct; we must
+also bear in mind the possibility that the
+functioning of her instinct may be subject to
+some periodicity, and we ask whether, under
+these circumstances, accidental gatherings would
+meet all the requirements of the situation.
+Now, manifestly, she must be in a position to
+find males when her appropriate organic condition
+arises. But in the absence of any system in the
+distribution of the sexes, how could delay be
+avoided, or how could a uniform discharge of
+the sexual function be assured? There is,
+however, a system. In the first place, there
+are the assembly grounds to which the birds
+repair season after season; and then, on the
+assembly grounds, there are the territories,
+represented, as Mr. Selous tells us, by depressions
+where the grass by long use has been worn
+away, and each depression is owned by one
+particular Ruff. The assembly grounds have
+the effect of splitting up and scattering the
+birds, and the number of Ruffs at any one particular
+meeting place is limited by the territories;
+with the result that Ruffs fit to breed are evenly
+distributed and always to be found in certain
+definite places, and the Reeves know by experience
+where to find them.</p>
+
+<p>The advantage of this territorial system is<span class='pagenum'><a name="Page_174" id="Page_174">174</a></span>
+therefore apparent. Instead of this district
+being overcrowded and that one deserted;
+instead of there being too many of one sex
+here and too few of the other sex there; instead
+of a high percentage of individuals failing to
+procreate their kind, just because circumstances
+over which they have no control prevent their
+discovering one another at the appropriate time&mdash;each
+sex has its allotted part to play, each
+district has its allotted number of inhabitants,
+and the waste of energy and the loss of time
+incurred in the process of mating is reduced to
+a minimum.</p>
+
+<p>Let us return again to the question of
+fortuitous mating, and consider the position of
+a male and female that have discovered one
+another by accident and have paired; what will
+be the subsequent course of their behaviour?
+We are assuming, of course, that a territory
+forms no part of their life-history. If the
+discharge of the sexual function takes place
+immediately and the ovaries of the female are
+in an advanced state of seasonal development,
+the construction of the nest will proceed without
+delay&mdash;and the nest will answer the same
+purpose as the territory in so far as it serves to
+restrict the movements of the birds and tends to
+make them remain in, or return to, its vicinity;
+but if not, there will be an interval during which
+both sexes will continue to wander as before,
+guided only by the scarcity or abundance of
+food. In the first case, there will be the
+attraction of the nest to prevent any untimely<span class='pagenum'><a name="Page_175" id="Page_175">175</a></span>
+separation; in the second, there will be nothing
+in the external environment to induce them to
+remain in any particular spot. Now if we turn
+to any common species and observe the sequence
+of events in the life of different pairs, we shall
+find that pairing is seldom followed by an
+immediate attempt to build; that an interval
+of inactivity is the rule rather than the exception,
+and that this interval varies in different
+species, in different individuals, and in different
+seasons. Our imaginary male and female will
+therefore be faced with considerable difficulty;
+for with nothing in the external environment to
+attract them and with no restriction imposed
+upon the direction or extent of their flight, their
+union will continue to be, as it began by being,
+fortuitous. Next, let us consider their position
+were a disposition to establish a territory to
+form part of the inherited nature of the male.
+Each one will then be free to seek food when
+and where it wills and to associate with other
+individuals without the risk of permanent
+separation from its mate; and, no matter how
+long an interval may elapse between mating and
+nest-building, each one will be in a position to
+find the other when the appropriate moment for
+doing so arrives. Hence, while preserving
+freedom of movement for each individual, the
+territory will render their future, as a pair,
+secure.</p>
+
+<p>No doubt the course of behaviour, as we
+observe it to-day in the lives of many species, is
+the outcome of, rather than the condition which<span class='pagenum'><a name="Page_176" id="Page_176">176</a></span>
+has led to, the evolution of the territory. Thus,
+in many cases, we find that early mating is the
+rule rather than the exception; we find that the
+sexes frequently separate to seek their food, and
+fly away temporarily in different directions;
+and, under exceptional climatic conditions, we
+find that they even revert to their winter routine
+and form flocks; only, however, to return to
+their territories, as pairs, under more congenial
+conditions. Yellow Buntings, for example, pair
+comparatively early in the season&mdash;some in the
+latter part of February, others in March, and
+others again in April; and some build their
+nests in April, others in May. There is a gorse-covered
+common which I have in mind, a
+favourite breeding resort of this species.
+Between this common and the surrounding
+country, the birds constantly pass to and fro.
+If you watch a particular male you will observe
+that it sings for a while in its territory, that it
+then rises in the air and disappears from view,
+and finally that it returns to the tree, bush, or
+mound which constitutes its headquarters, where
+it again sings. Meanwhile the female, with
+which there is every reason to believe that this
+male has paired, behaves similarly; she, too, flies
+to the surrounding country and in time returns
+with equal certainty. Sometimes male and
+female accompany one another&mdash;that is, they
+leave simultaneously and likewise return; at
+other times, though they depart together, the
+male returns alone; or the male may disappear
+in one direction whilst the female does so in<span class='pagenum'><a name="Page_177" id="Page_177">177</a></span>
+another&mdash;and, on the whole, there is a sameness
+in the direction of flight taken by the same pairs
+on different occasions. An interval of nearly
+two months may thus elapse between mating
+and nest-building, during which the sexes are
+not only often apart but often separated by a
+considerable distance.</p>
+
+<p>What does this species gain by the
+individuals belonging to it mating so early in
+the season? If the appropriate condition which
+leads the females to seek males were to arise
+in each individual at a late date, the first stage
+in the process&mdash;mating&mdash;would not be completed
+before the second&mdash;the discharge of the
+sexual function&mdash;were due to begin. Thus,
+instead of having ample time, the females
+would have but a short period in which to
+discover males; and this in some cases might
+lead to delay, in others to failure, and in
+others again to needlessly severe competition,
+entailing physical exhaustion at a critical
+moment in their lives. Hence those females
+in which the appropriate organic condition
+developed early in the season would not only
+be more likely to find males, but would be
+in a position to rear more broods than those
+in which it developed late; and they would
+have a better chance of leaving offspring,
+which, in their turn, would reproduce the
+peculiarities of their parents. Moreover, within
+certain limitations, the more these successful
+females varied in the date of their development,
+the less severe would be the competition, and<span class='pagenum'><a name="Page_178" id="Page_178">178</a></span>
+the more uniformly successful would the mating
+of all the individuals in a given district tend
+to become. But all of this renders an interval
+of sexual inactivity unavoidable; an interval
+which must constitute a danger unless there
+were something in the external environment
+to prevent the male and female from drifting
+apart. Inasmuch, then, as the occupation of
+a territory serves to remove all possibility of
+permanent separation, I suggest that its evolution
+has afforded the condition under which
+this beneficial procedure has developed&mdash;free
+to mate when they will, free to seek food
+where they will, free to pursue their normal
+routine of existence, and to meet all exigencies
+as they arise in their ordinary daily life&mdash;whilst
+free to do this, their future, as a pair,
+is nevertheless secure.</p>
+
+<p>Thus far we have considered the territory
+in its relation to the discharge of the sexual
+function. In many of the lower forms of life,
+the success or the failure of reproduction, so
+far as the individual is concerned, may be said
+to end with the completion of the sexual act&mdash;the
+female has but to deposit her eggs in a
+suitable environment and then her work is done,
+because in due course and under normal conditions
+of temperature the young hatch out, and
+from the first are able to fend for themselves.
+And so, when we come to consider the question
+of reproduction in the higher forms of life, we
+are apt to focus attention too much upon the
+sexual function and too little upon the con<span class='pagenum'><a name="Page_179" id="Page_179">179</a></span>tributory
+factors, the failure of any one of
+which would mean failure of the whole. For
+a bird, success in the attainment of reproduction
+does not merely imply the successful discharge
+of the sexual function; much more is demanded;
+it must find somewhere to build its nest and
+to lay its eggs, it must shield its young from
+extremes of temperature and protect them from
+enemies, and it must be in a position to supply
+them with food at regular intervals. And,
+consequently, every situation is not equally
+favourable for rearing young; there must be a
+plentiful supply of food of the right kind in
+the immediate vicinity of the nest, and it must
+be in greatest abundance just at the moment
+when it is most urgently needed&mdash;that is to
+say, during the first few weeks after the birth
+of the young. Success, therefore, depends upon
+manifold relationships which centre in the
+station, and these relationships vary in intensity
+with the conditions of existence.</p>
+
+<p>First, then, let us examine the problem from
+the point of view of the food-supply. There
+are many species whose success in rearing
+offspring is largely dependent upon the rapidity
+with which they can obtain food; and it makes
+but little difference which species we choose
+out of many&mdash;Finch, Bunting, Warbler, or
+Chat. I shall choose the Buntings, as their
+life-history in broad outline conforms to the
+general type, and, moreover, their behaviour
+is fresh in my mind. The young are born in a
+very helpless state; they are without covering<span class='pagenum'><a name="Page_180" id="Page_180">180</a></span>
+&mdash;fragile organisms, ill-fitted, one would think, to
+withstand extremes of temperature, and wholly
+incapable of protecting themselves from enemies
+of any description. For the first three days
+after they are hatched the female spends much
+of her time in brooding them, and, when she
+is thus occupied, the male sometimes brings
+food to her, which she proceeds to distribute
+or swallows. But all the young cannot be fed,
+neither are they ready to be fed, at the same
+moment; and the parents have besides to find
+food for themselves, and the nest has to be
+cleaned&mdash;all of which necessitates the young
+being exposed to the elements at frequent
+intervals. Now it is impossible to observe the
+instinctive routine of the parents, when the
+young need attention, without being impressed
+with the conative aspect of their behaviour.
+Why, we ask, are the movements of the female
+so brisk; why does she seek food and clean
+the nest so hurriedly; why, if her instinctive
+routine is interrupted, do her actions and her
+attitude betray such bewilderment? I take it
+that the only answer we can give to these
+questions is that the part of her inherited
+nature which predominates just at this particular
+time is to brood. But why is brooding
+of such importance? Partly to maintain the
+young at the proper temperature, and thereby
+to induce sleep&mdash;and sleep for offspring newly
+hatched is as important as food&mdash;and partly to
+protect them from the risk of exposure to
+extremes of temperature. This latter danger<span class='pagenum'><a name="Page_181" id="Page_181">181</a></span>
+is no imaginary one. Examine a young bird
+that has recently left the egg; observe its
+nakedness; and consider what it has to withstand&mdash;a
+temperature that may rise to 70&deg; F.
+or may fall to 40&deg; F., the tropical rain of a
+thunderstorm or the persistent drizzle of many
+hours' duration, the scorching effect of a
+summer sun or the chilling effect of a cold
+north-easterly wind, and, constantly, the sudden
+change of temperature each time that the
+parent leaves the nest. One marvels that
+it ever does survive; one marvels at the
+evolution of a constitution sufficiently elastic
+to withstand such changes. But, however
+much the constitution may give us cause to
+wonder, it is clear that much depends upon
+the parents. A slight inefficiency of the
+instinctive response which the presence of the
+young evokes, a little slowness in searching
+for food or sluggishness in returning to the
+nest, might lead to exposure and prove fatal.
+And, however much is demanded of the parents,
+it is clear that much also depends upon the
+relationships in the external environment; for
+no matter how sensitive or how well attuned
+the instinctive response of the parent may be,
+it will avail but little in the presence of
+unfavourable conditions in the environment.</p>
+
+<p>Everything turns upon the question of the
+effect of exposure. And in order to ascertain
+how far extremes of temperature are injurious,
+I removed the nests of various species containing
+newly hatched young, and, placing them<span class='pagenum'><a name="Page_182" id="Page_182">182</a></span>
+in surroundings that afforded the customary
+amount of protection from the elements, I made
+a note of the temperature and the atmospheric
+conditions and then observed the condition of
+the young at frequent intervals. Details of
+these experiments will be found at the end of
+the chapter.</p>
+
+<p>The experiments with the Blackbirds and
+the Whitethroats gave the most interesting
+results. Both broods of each species were
+respectively of much the same age, yet one
+brood of Blackbirds survived for five, and the
+other only for two and a half hours, and one
+brood of Whitethroats lived for twelve hours
+whilst the other succumbed in a little over an
+hour. This difference is rather remarkable;
+and it seems clear that the power of resistance
+of the young diminishes rapidly when the
+temperature falls below 52&deg; F. It must be
+borne in mind, however, that the conditions
+under which the experiments were made were,
+on the whole, favourable&mdash;the weather was dry,
+the temperature was not unusually low, nor was
+the wind exceptionally strong or cold; and even
+in those cases in which the young succumbed so
+rapidly, the atmospheric conditions could by no
+means be regarded as abnormal.</p>
+
+<p>What, then, would happen in an unusually
+wet or cold breeding season? For how long
+would the young then survive? In the spring
+and early summer of the year 1916, I was
+fortunate in observing the effect of exposure
+under natural but inclement conditions. I<span class='pagenum'><a name="Page_183" id="Page_183">183</a></span>
+happened to be watching the Yellow Buntings
+on Hartlebury Common&mdash;200 acres of Upper
+Soft Red Sandstone, profusely overgrown with
+cross-leaved heath (<i>Erica tetralix</i>), ling (<i>Calluna
+vulgaris</i>), and furze (<i>Ulex</i>)&mdash;in one corner of
+which eight males had established adjoining
+territories covering some fifteen acres of ground.
+The males obtained mates towards the end of
+March or at the beginning of April; nests were
+built in the middle of May, and the successful
+pairs hatched out their young in June. On
+the 10th June the weather became exceptionally
+cold, and during the next ten days the temperature
+fell at times to 40&deg; F. during the daytime.
+Slight frosts were registered at night in the
+district, and the young bracken, which covered
+the Common in places, had the appearance of
+having been scorched and eventually withered
+away. At the coldest period of this cold spell
+the young were hatched in two of the nests&mdash;in
+the first one on the 10th June, and in the second
+a day or so later; and on the morning of the 10th
+June, having found a suitable position near the
+first nest, I began to watch the movements of
+the parents, with the intention of keeping some
+record of their behaviour each day so long as
+the young needed attention. An hour passed
+without their appearing, and on examining the
+young I found that they were cold, feeble, and
+unresponsive, but the female presently arrived
+and went to the nest. Later in the day the
+young were lively and responded freely when
+the nest was approached, but nevertheless I was<span class='pagenum'><a name="Page_184" id="Page_184">184</a></span>
+impressed with the length of time during which
+the parents were absent; for, judging by the
+experience of previous experiment, there seemed
+to be every likelihood of their losing their
+offspring in such abnormally cold weather,
+unless they brooded them more persistently.
+On the 11th June at 5.50 <span class="smcaplc">A.M.</span> neither parent was
+to be seen and the young could scarcely be made
+to respond; but shortly afterwards both male
+and female appeared, and, after remaining a
+few minutes, again disappeared without even
+approaching the nest. At 6.45 <span class="smcaplc">A.M.</span> no attempt
+had been made to brood and the young were
+then so feeble that they were scarcely able to
+open their mouths, and at 6 <span class="smcaplc">P.M.</span> one was still
+alive but the remaining three were dead. Yet
+the parents returned and the female went to the
+nest; and, from a distance of a few feet, I
+watched her brooding the living and the dead.
+At 5.45 <span class="smcaplc">A.M.</span> the following day the remaining
+young bird had succumbed, the temperature
+then being 49&deg; F.</p>
+
+<p>At the second nest, I was unable to watch
+the behaviour of the parents so closely. On the
+15th June the nest contained three young from
+three to four days old, and during the morning
+of that and the succeeding day nothing unusual
+occurred, with the exception that the period of
+exposure seemed, as in the former case, to be
+too long. On the 17th June at 3.10 <span class="smcaplc">A.M.</span> the
+young had collapsed and were stiff, but the
+parents were in their territory and anxious
+apparently to attend to their brood. At 9.15<span class='pagenum'><a name="Page_185" id="Page_185">185</a></span>
+<span class="smcaplc">A.M.</span> only two of the young were left in the
+nest, and though I searched amongst the undergrowth
+and in the gorse bush in which the nest
+was placed, no trace of the third bird was to be
+found. Of the two remaining young, one was
+alive and responsive but the other was dead,
+and though the female attended assiduously to
+the sole surviving offspring, yet it too had
+succumbed by the following morning.</p>
+
+<p>In a third territory, there was a nest containing
+four eggs. These eggs were due to
+hatch at much the same time as those in the
+two nests just referred to, but they failed to do
+so, and an examination showed that they contained
+well developed but dead chicks.</p>
+
+<p>To what can the death of the young and of
+the chicks in the eggs be attributed? Not to
+any failure in the instinctive response of the
+females, for they fed their young, they brooded
+them, they even brooded the dead as well as the
+living, and probably did all that racial preparation
+had fitted them to do. Yet the fact that
+the young in the second nest were lifeless and
+exposed at 3 <span class="smcaplc">A.M.</span> seems to betoken absence on
+the part of the parents during the night, and
+may be interpreted as a failure of the parental
+instinctive response. Let us return for a
+moment to the experiments. These showed, it
+will be remembered, that a rise or fall in the
+temperature of but a few degrees was sufficient
+to make an astonishing difference in the length
+of time that the young were able to survive
+without their parents; that when the tempera<span class='pagenum'><a name="Page_186" id="Page_186">186</a></span>ture
+reached 58&deg; F. the bodies of the young
+retained their warmth, and that under such
+conditions even a night's exposure had little, if
+any, effect; so that even supposing that the
+parents were absent during the night, the death
+of the young cannot be said to have been due to
+a failure of the parental instinct, because under
+normal conditions&mdash;and under such has their
+instinctive routine been evolved&mdash;their absence
+would not have prejudiced the existence of the
+offspring. I attribute the collapse of the young
+solely to the exceptional cold that prevailed at
+just the most critical time, and I base this
+conclusion partly on the experience gained from
+experiment, but mainly on their condition
+observed at different intervals; for during
+exposure they collapsed rapidly, their flesh
+became cold and their movements sluggish,
+their response grew weak, and gradually they
+became more and more feeble until they could
+scarcely close their bills after the mandibles had
+been forced asunder. Yet, even after having
+reached so acute a stage of collapse, the warmth
+from the body of the brooding bird was
+sufficient to restore them temporarily; once
+more they would become lively and responsive,
+only, however, to revert to the previous condition
+soon after the parent had again abandoned
+them. Doubtless their power of resistance
+grew less and less during each successive period
+of exposure.</p>
+
+<p>If the nestling Bunting is to be freed from
+the risk of exposure, it is evident that there<span class='pagenum'><a name="Page_187" id="Page_187">187</a></span>
+must be, in the vicinity of the nest, an adequate
+supply of food upon which the parents can draw
+liberally. Hence those pairs that exercise
+dominion over the few acres surrounding the
+nest, and are thus able to obtain food rapidly,
+will stand a better chance of rearing their
+offspring than others which have no certain
+supply to draw upon&mdash;and this, I believe, is one
+of the biological ends for which the territory has
+been evolved. But it must not be supposed
+that each pair finds, or even attempts to find,
+the whole of the food within its territory, or
+that it is necessary for the theory that it should
+do so; all that is required is that such overcrowding
+as might lead to prolonged absence on
+the part of the parents and inordinate exposure
+of the young shall be avoided. So that the
+problem has to be considered not merely from
+the point of view of the individual, but from the
+larger point of view of all the pairs inhabiting
+a given area.</p>
+
+<p>Now there were eight pairs of Yellow
+Buntings occupying the one corner of Hartlebury
+Common, and their territories in the
+aggregate covered some fifteen acres. The
+birds obtained part of their food-supply amongst
+the gorse and in some young scattered oak-trees,
+and part in an adjoining coppice and on
+the surrounding arable land. But they were
+not the sole occupants of this corner of
+the Common; other insectivorous species had
+territories there also&mdash;amongst which were
+Whitethroats, Grasshopper-Warblers, Willow-Warblers,<span class='pagenum'><a name="Page_188" id="Page_188">188</a></span>
+Whinchats, Stonechats, Meadow-Pipits,
+Tree-Pipits, and Skylarks. Suppose
+then that there had been sixteen pairs of Yellow
+Buntings instead of eight; that there had been
+other pairs, which assuredly there were, inhabiting
+the locality; that they had also resorted,
+which assuredly they did, to the coppice and
+arable ground for the purpose of securing food;
+and that their numbers had also been increased
+in a similar ratio&mdash;would a supply of food for
+all have been forthcoming with the necessary
+regularity and promptitude? Well, the parents
+might have had to travel a little farther; but
+even if they had been compelled to do so, their
+absence would only have been prolonged by so
+many minutes the more, and under normal
+conditions what harmful result to the offspring
+could possibly have followed? The question for
+us, however, is not what might have occurred
+under normal conditions, but whether the life
+behaviour is so adjusted as to meet the exigencies
+of diverse, and in this case of abnormal, circumstances.
+Now the capacity of the young to
+resist exposure diminishes very rapidly when the
+temperature falls below the normal&mdash;the danger
+zone seems to be reached at approximately
+52&deg; F., and the length of time during which they
+survive then becomes astonishingly short&mdash;and
+moreover the fall in the temperature would tend
+to decrease the supply of insect life upon which
+they depend, so that if the size of the territories
+had been reduced by one half, and the parents
+in consequence had been compelled to seek their<span class='pagenum'><a name="Page_189" id="Page_189">189</a></span>
+food at a greater distance, can it be doubted
+that the cumulative effect of even a few minutes
+of additional exposure would have been detrimental,
+if not disastrous, to the offspring?</p>
+
+<p>We speak, however, of the parents extending
+their journeys a little farther in this direction or
+a little farther in that, as though they could do
+so with impunity except in so far as it affected
+themselves, or their offspring, or the other
+Yellow Buntings inhabiting that particular area.
+But, most certainly, any extension would have
+meant so much encroachment upon the available
+means of support of other members of the
+species inhabiting adjoining areas, whose young
+in turn would have been liable to have been
+affected; and, with even greater certainty, the
+Whitethroats, the Stonechats, the Tree-Pipits,
+and the Willow-Warblers that had also
+established themselves in that one corner of
+the Common would have been hard pressed to
+find sufficient food with sufficient rapidity.</p>
+
+<p>Let me give another illustration of a somewhat
+different kind. Lapwings, as we saw in
+the previous chapters, establish territories and
+guard them from intrusion with scrupulous care.
+The young are able to leave the nest soon after
+they are hatched, and consequently the parents
+are not necessarily obliged to bring food <i>to</i>
+them&mdash;they can, if they so choose, lead them <i>to</i>
+the food. Whether each pair limits its search
+for food to its territory, I do not know. But
+even supposing that all ownership of territory
+were to lapse directly the young were hatched,<span class='pagenum'><a name="Page_190" id="Page_190">190</a></span>
+that the boundaries were to cease to exist, and
+that the birds were free to wander at will
+without fear of molestation, the end for which
+the territory had been evolved would none the
+less have been obtained; for inasmuch as the
+parents are accompanied by their young, it
+matters not in what part of the meadow they
+seek their food; all that matters is that the
+number of families shall not exceed the available
+supply of food. So far, then, as the Lapwing is
+concerned, the territory fulfils its purpose when
+once it limits the number of males, since, by
+doing so, it limits the number of families and
+prevents undue pressure upon the means of
+support.</p>
+
+<p>Nevertheless, there are many birds that
+seem to rely entirely upon the territory to
+supply them with all that is necessary. Each
+Warbler seeks its food within the precincts
+of its own particular domain, and, except in
+occasional instances, neither resorts to neutral
+ground nor makes excursions into the locality
+immediately surrounding the territory, as does
+the Bunting. Probably it would be disastrous
+if it attempted to do so, for since its young
+at birth are so delicate and so susceptible to
+changes of temperature, it cannot afford to
+be absent from them for long. Of the two
+experiments made with young Whitethroats,
+one was made under favourable and the other
+under unfavourable conditions. In this latter
+case the temperature was 50&deg; F., and the young,
+it may be remembered, only survived for a<span class='pagenum'><a name="Page_191" id="Page_191">191</a></span>
+little over one hour. Now exposure at that
+temperature is evidently dangerous, but it
+would be still more dangerous if the weather
+were wet instead of dry, and the temperature
+46&deg; F. instead of 50&deg; F.; and it is, I imagine,
+on this account that the impulse to brood is
+so strongly implanted in the female. No
+sooner, it seems, does she depart than she
+returns with a small quantity of food which
+she hurriedly distributes and immediately settles
+down to brood; and if forcibly prevented from
+returning, her attitude betrays symptoms of
+what, humanly speaking, we should term great
+distress. If, then, the conditions in the external
+environment were such as would make it
+difficult for the female to obtain food rapidly,
+what advantage would she derive from so
+strongly developed an impulse? Might it
+not be a disadvantage? Might it not mean
+that she would abandon the search too readily
+and be content to return with an insufficient
+supply, and might not that be as injurious to
+the young as prolonged exposure? Manifestly
+the impulse to brood could only have developed
+strength in so far as it fitted in with all the
+other factors that make for survival; and the
+principal factor in the external environment
+seems to be the territory. How could the
+young have been freed from the risk of
+exposure if the impulse to brood had not
+been so strongly implanted in the parent?
+How could the impulse to brood have been
+free to develop if a supply of food had not<span class='pagenum'><a name="Page_192" id="Page_192">192</a></span>
+been first insured? How could the supply
+of food have been insured if numbers of the
+same species had been allowed to breed in
+close proximity?</p>
+
+<p class="tb">From the foregoing facts it is clear that the
+young of many species are at birth susceptible
+to cold and unable to withstand prolonged
+exposure. The parents must therefore be in
+a position to obtain food rapidly, and consequently
+it is important that there should be
+an ample supply in the vicinity of the nest.
+This end the territory certainly serves to
+promote; it roughly insures that the bird
+population of a given area is in proportion to
+the available means of subsistence, and it
+thus reduces the risk of prolonged exposure
+to which the young are always liable.</p>
+
+
+<p>This leads on to a consideration of those
+cases in which the question of securing food
+is subordinate to the question of securing a
+station suitable for reproduction.</p>
+
+<p>I take the Guillemot as an example. In
+principle its behaviour is similar to that of the
+Bunting; the male repairs to a definite place,
+isolates itself, and becomes pugnacious. But
+the Guillemot is generally surrounded by other
+Guillemots, and the birds are often so densely
+packed along the ledges that there is scarcely
+standing room, so it seems, for all of them.
+Nevertheless the isolation of the individual
+is, in a sense, just as complete as that of the
+individual Bunting, for each one is just as<span class='pagenum'><a name="Page_193" id="Page_193">193</a></span>
+vigilant in resisting intrusion upon its few
+square feet as the Bunting is in guarding its
+many square yards, so that the evidence seems
+to show that that part of the inherited nature
+which is the basis of the territory is much
+the same in both species. What we have then
+to consider is, What is the biological value to
+the Guillemot of an inherited nature which,
+for the Bunting, has utility in relation to the
+supply of food for the young? Up to a point,
+the act of securing a territory has like value
+for each respective species, whether the area
+occupied be large or small&mdash;that is to say, it
+enables the one sex to discover the other with
+reasonable promptitude.</p>
+
+<p>For the greater part of the year, Guillemots
+live at sea; singly, in twos or threes, or in
+small parties, they move upon the face of the
+waters, extending their wanderings far away
+from land, out into the broad ocean, where
+for weeks together they face the gales and
+heavy seas of the Atlantic. But in due course
+and in response to internal organic changes,
+they return, like the Warbler, to their breeding
+grounds&mdash;rocky headlands or islands appropriately
+situated and affording the appropriate
+rock formation. During all these months of
+wandering, the majority seem to ignore the
+land, to pass away from it altogether, and to
+spread themselves over the surface of the ocean
+regardless of mainland or island. Some useful
+observations, which throw some light on the
+distance that Guillemots are accustomed to<span class='pagenum'><a name="Page_194" id="Page_194">194</a></span>
+wander from land, were made by Lieut. B. R.
+Stewart during a number of voyages between
+various ports in Great Britain and Ireland and
+ports in North America, principally New York
+and Quebec. Thus, on the 24th March, large
+numbers were seen in lat. 55&deg; N., long. 24&deg; W.,
+five hundred miles approximately from land,
+though on the following day&mdash;four hundred
+miles off Tory Island&mdash;they were not so plentiful.
+Again, on the 1st October, in lat. 53&deg; N., long.
+27&deg; W., seven hundred miles or so from land, one
+bird was seen, whilst on the following day, in
+lat. 52&deg; N., long. 21&deg; W., a single individual
+was washed on board by the heavy seas and
+seemed little the worse for the adventure.
+Within two hundred miles of the west coast
+of Ireland, he found them plentiful on various
+occasions. From this it is clear that the circumstances
+under which the bird lives for many
+months in succession must impose a considerable
+strain upon its constitution; and how it is able
+to withstand the buffeting of wind and water,
+to secure its food, and to endure, is a mystery.
+It is important, therefore, that the young bird
+should be properly nourished and protected
+from anything that might harm its constitution,
+and important, too, that the parents should be
+freed from any undue strain during the course
+of reproduction.</p>
+
+<p>The conditions which the breeding station
+has to fulfil are threefold: in the first place,
+it must be in proximity to the food-supply;
+secondly, it must provide the necessary shelter<span class='pagenum'><a name="Page_195" id="Page_195">195</a></span>
+for the egg and for the helpless offspring;
+and, in the third place, it must be so situated
+that the young can reach the water in safety.
+We will examine these conditions one by
+one.</p>
+
+<p>The proximity to the food-supply is a
+consideration of some importance. The life
+of the Guillemot during the winter is a
+strenuous one; we know that large numbers
+succumb in stormy weather, and we can infer
+that slight constitutional defects might make
+all the difference between failure and success;
+and, therefore, the less severely the constitution
+of the parent is taxed during reproduction,
+and the more securely the constitution of the
+offspring is built up, the greater prospect
+will both have of resisting the hardships of the
+winter successfully. Much, then, will depend
+upon the distance the parents have to travel
+in order to obtain food. The farther the
+breeding station is removed from the feeding
+ground the greater the physical strain which
+will be imposed upon the birds, and the greater
+the chance will there be of the offspring being
+improperly nourished. Now the food consists
+of small fish, largely of sand-eels, which are
+secured in deep water, and the abundance of
+which varies, possibly according to the nature
+of the currents. Hence cliffs which are situated
+away from the water, or from which the water
+recedes at low tide, or which are surrounded
+by an area of shallow water, and are thus not in
+proximity to the feeding ground, even though<span class='pagenum'><a name="Page_196" id="Page_196">196</a></span>
+they may fulfil the second and third condition,
+will not answer the requirements of a breeding
+station.</p>
+
+<p>Of no less importance is the type of rock-formation.
+Not every formation affords the
+necessary ledges upon which the egg can be
+deposited with safety&mdash;the face of the cliff may
+be too smooth, or too jagged, or the shelves
+may run at too acute an angle. Many of the
+large assemblages of Guillemots in the British
+Islands are found where the rock is quartzite,
+mica-schist, limestone, or chalk. The reason of
+this is that such rocks are weathered along the
+planes of stratification, of jointing, of cleavage,
+or of foliation&mdash;the strata being probably of
+unequal durability&mdash;with the result that innumerable
+shelves, ledges, and caverns, which
+are taken advantage of by the birds, form a
+network over the face of the cliff. But only
+those ledges can be made use of which are
+placed at a considerable height above the water,
+because, when the cliff faces the open sea, the
+lower ones are liable to be washed in stormy
+weather by the incoming swell and thus become
+untenable. There is a small cove in the midst
+of the most precipitous part of the breeding
+station at Horn Head, wherein the shingly
+shore shelves rapidly to the Atlantic and faces
+to the west. Here, towards the end of July,
+young Kittiwake Gulls can sometimes be found
+washed up on the beach&mdash;some living, but in
+every stage of exhaustion, others dead, and in
+every stage of decomposition; here is the young<span class='pagenum'><a name="Page_197" id="Page_197">197</a></span>
+bird, recently caught by the swell and thrown
+upon the shore, lying side by side with the
+remains of others that had previously succumbed
+to starvation&mdash;on every side evidence of the
+devastation wrought by the Atlantic. May not
+some of this destruction have been brought
+about by the nests having been placed upon
+the lower ledges within reach of an exceptionally
+heavy sea? Hence much depends upon the
+nature of the rock-formation, and many a
+mighty precipice, even though it may fulfil
+the first and third condition, is nevertheless
+valueless as a breeding station.</p>
+
+<p>Finally, the young bird must occupy a ledge
+from which it can reach the water in safety.
+There is much difference of opinion as to the
+manner in which it leaves the ledge, but all
+agree that it does so before it is capable of
+sustained flight. If, then, the face of the cliffs
+were made up of a series of broken precipices, or
+if the rocks at the base projected out into the
+water, or if detached rocks abounded in the
+waters beneath, the mortality amongst the chicks
+would no doubt be considerable.</p>
+
+<p>The coast-line of Co. Donegal will illustrate
+the foregoing remarks. On the southern and
+western side of the Slieve League promontory
+there is no real Guillemot station; only on the
+northern side&mdash;the quartzite in the vicinity of
+Tormore&mdash;are the birds to be found in large
+numbers. Northwards from here, a wild and
+rugged coast is passed over before other stations
+are reached&mdash;at the eastern end of Tory Island<span class='pagenum'><a name="Page_198" id="Page_198">198</a></span>
+and on Horn Head; and beyond this, to the
+east, there are none, not even on the old rocks
+that form the promontory of Inishowen. Why,
+we ask, do countless numbers crowd the ledges
+of Horn Head, whilst they are absent from the
+precipices of Slieve League; why, too, are they
+absent from the granite cliffs of Owey? The
+reason is not far to seek. Either the face of
+the cliff is made up of a series of broken
+precipices, or the face of the precipices is
+too smooth, or the otherwise suitable ledges
+are situated too near the water, or the water
+recedes from the base of the cliff at low tide.
+Many miles of rock-bound coast are thus useless
+for the purpose of reproduction.</p>
+
+<p>Now when we bear in mind how large an
+expanse of coast is formed of blown sand or of
+rocks of low altitude, and how many miles of
+cliff fail to supply the three essential conditions
+that we have been considering, we can see
+that suitable breeding stations must be limited
+both in number and extent. From a wide
+expanse of ocean hosts of individuals are therefore
+obliged to converge at certain definite
+points; and hence, each recurring season, there
+must arise a competition for positions at the
+station, just as there is competition between
+individual Buntings for positions in the marsh.
+And the ability to obtain a position upon a
+suitable ledge involves, in the first place,
+an impulse to search for it; in the second
+place, an impulse to dwell in it; and in the
+third place, an impulse to resist intrusion<span class='pagenum'><a name="Page_199" id="Page_199">199</a></span>
+upon it. It would be useless for an individual
+to be pugnacious if it had no fixed abode;
+equally useless for it to establish itself on a
+particular ledge if it had no power to defend it&mdash;all
+of which implies an inherited nature similar
+to that of the Bunting. But the proximate end
+to which the competition is directed is not alike
+in the case of both species. In the case of the
+Guillemot it has reference solely to the piece of
+rock whereon the egg is laid; in the case of the
+Bunting to a piece of ground capable of furnishing
+an adequate supply of food for the young;
+and the reason for the difference is this, that
+there is always an abundance of food in the
+water beneath the cliff, but breeding stations are
+scarce, whereas there is always an abundance of
+situations in the marsh in which the Bunting
+can place its nest, but the supply of food varies
+and at times can only be obtained with
+difficulty.</p>
+
+<p>If then the Guillemot were to behave after
+the manner of the Bunting and assign to itself a
+portion of the face of the cliff, or if it were only
+to occupy a few ledges, or an even lesser area&mdash;a
+single ledge&mdash;what would be the result? That
+it would attain to reproduction is beyond
+question; that the egg would be safely deposited
+there can be no manner of doubt; neither is
+there any reason to suppose that the offspring
+would not be successfully reared. But, indirectly,
+its behaviour would affect the Guillemot
+race. For if it be true, as the crowded ledges
+certainly seem to show, that there is a dearth of<span class='pagenum'><a name="Page_200" id="Page_200">200</a></span>
+suitable breeding ground, no greater calamity
+could befall the species than that some members
+should exercise dominion over too large an area
+of the habitable part of the cliff and thus
+prevent others from breeding. Under such
+conditions the race could not endure, since in
+this, as in every case, its survival must depend
+upon a close correspondence between the
+behaviour of the individual and the circumstances
+in the external environment.</p>
+
+<p>Scarcity of suitable cliffs is the principal
+reason of the ledges being so closely packed
+with Guillemots, just as it accounts for this
+part of the precipice being crowded with Kittiwake
+Gulls, that part with Herring-Gulls, and
+that part again with Razorbills and Puffins.
+Yet each individual preserves its few square
+feet of rock or soil from molestation, and the
+area each one occupies varies according to the
+conditions of existence of the species. Thus
+the Herring-Gull occupies a comparatively small
+area, although one many times larger than that
+of the Guillemot. It requires more space than
+the latter, owing to the fact that it not only
+builds a nest but rears four instead of a single
+offspring, and it can be allowed this, because,
+since its young remain in the nest until they are
+capable of sustained flight, it can make use of
+many miles of cliff from which the tide recedes
+at the base, or which have, at their base,
+rocks jutting out into the sea; but manifestly
+it cannot be allowed so much space as the
+Bunting.</p>
+
+<p><span class='pagenum'><a name="Page_201" id="Page_201">201</a></span>Martins build in close proximity to one
+another, owing probably to shortage of accommodation,
+and, in their case, the nests have to
+be so situated as to be sheltered from the wet.
+If water drips upon them for any length of
+time, the mud, of which they are composed,
+crumbles and large pieces fall away, with the
+result that the eggs or the young are precipitated
+to the ground. Consequently, not every
+house or perpendicular cliff will answer the
+purpose of a breeding station. A few pairs
+build their nests beneath the eaves close against
+the walls of my house, and year after year the
+result is much the same; after every downfall
+of rain, the water collects into rivulets, trickles
+down over the eaves, is absorbed by the mud
+and destroys the nests. Thereupon, the birds
+set to work and rebuild; but again the nest is
+destroyed, and again they rebuild, and so on
+throughout the summer, and only on rare
+occasions do they succeed in rearing offspring
+at the proper season. Similar conditions must
+prevail in many situations; but, clearly, the
+more binding and plastic the building material,
+the longer the nest will withstand the action of
+the dripping water and the greater chance will
+there be of the young being reared in safety.
+Observe, therefore, how far-reaching an effect so
+small a detail as the nature of the mud can have
+upon the status of the species in any given
+locality. Where the conditions are favourable,
+there the birds must congregate to breed, and,
+like the Guillemot, if each individual exercised<span class='pagenum'><a name="Page_202" id="Page_202">202</a></span>
+dominion over too large an area, the species as
+a whole would suffer.</p>
+
+<p>In all these examples, the fact of different
+individuals being in such close proximity may
+afford some protection from enemies both as
+regards the egg and the offspring, and in so far
+as there is a mutual advantage such assemblages
+may be spoken of as communities. A community,
+however, in the true sense of the word,
+is a collection of individuals brought together,
+not primarily as a result of shortage of breeding
+ground, but in consequence of advantages of
+communal ownership over individual ownership.
+A rookery is an example of a true community.
+Neither shortage of nesting accommodation nor
+scarcity of food can account for Rooks assembling
+together to breed; for if the different
+pairs which go to make up the rookery were to
+scatter throughout the surrounding neighbourhood,
+they would, as a rule, find plenty of trees
+in which to build their nests, and plenty of food.</p>
+
+<p>How, then, can the theory apply to a species
+that breeds under such conditions? What part
+can the territory play in furthering the life of
+the individual when large numbers of nests are
+built closely together in the same tree? There
+is much evidence to show that mutual protection
+is a necessary condition of the Rook's
+existence; many cases are on record of rookeries
+being destroyed by Carrion-Crows, Hooded
+Crows, and Ravens. For instance, Mr. Ward
+Fowler records a case in which a pair of Crows
+attacked a small rookery, ransacked the nests,<span class='pagenum'><a name="Page_203" id="Page_203">203</a></span>
+and destroyed the eggs, with the result that not
+a single pair of Rooks was left in the settlement.
+Each Rook must therefore secure a position
+within the precincts of the community if it is to
+have a chance of success in the attainment of
+reproduction. But every locality cannot supply
+sufficient trees of the right kind, appropriately
+situated and in suitable relation to the food
+supply, in which numbers of nests can be built
+in close proximity; so that if more than one
+community were to attempt to establish itself in
+a limited area, the supply of food or the supply
+of trees might become a pressing problem.
+Each community must therefore be prepared
+to defend its own interests, and each must be
+regarded as one unit and the area occupied
+as one territory within which are included a
+number of lesser territories. The individual
+may fail to establish itself within a community,
+but, even if it succeeds, the community may fail
+to establish the rights of communal ownership;
+hence it has to face a twofold possibility of
+failure, and if it lacked the inherited nature
+which leads the Guillemot to secure a position
+upon the ledge, or the Bunting to obtain a
+position in the marsh, the chances are that it
+would fail in the attainment of reproduction.</p>
+
+<p>The question now arises as to how it comes
+about that the area occupied by each individual
+conforms in broad outline to that which has
+proved beneficial for the welfare of the species
+as a whole. We shall find that up to a point
+the answer is a simple one. No one could study<span class='pagenum'><a name="Page_204" id="Page_204">204</a></span>
+the behaviour of animals without observing the
+important part that habit plays in the life of the
+individual; an action performed to-day is liable
+to be repeated to-morrow and the following day
+until it becomes ingrained in the life of the
+individual. This must not be taken to mean,
+however, that a particular action has to be
+performed for many days in succession before
+it becomes definitely fixed; if only it is repeated
+a number of times, even within the space of
+a few hours, it will acquire sufficient strength
+for its continuance; but continued repetition
+gives increased fixity, and, as time goes by, it
+becomes increasingly difficult for the creature to
+make a change unless the character of the
+situation necessitates readjustment.</p>
+
+<p>For example, when the organic condition
+which leads to nest-building becomes active,
+the bird tentatively collects some of the
+necessary material in its bill, flies round with
+it, and then drops it. After a while it collects
+some more, and this time leaves it perhaps in
+a bush. Later on it makes another attempt,
+and, meeting with a situation which calls forth
+the appropriate response, it thereupon lays the
+foundation of the structure. We will assume
+that the nest is placed in the midst of a tangled
+bush. Well, the bird lays the first strands of
+the foundation and then goes in search of more
+material. The next time it approaches the nest
+from the opposite side of the bush, and presently
+it finds yet a third entrance. But each entrance
+is not made use of in turn: one is employed<span class='pagenum'><a name="Page_205" id="Page_205">205</a></span>
+more frequently than the other two, and in the
+course of time becomes the sole highway to and
+from the nest. Suppose now that, when the
+young are hatched, I cut away the foliage from
+the bush on the opposite side from that on
+which the bird customarily enters, and by so
+doing leave the nest exposed, what is the result?
+The female arrives with food, threads her way
+through the bush, and, when beside the nest,
+pauses as if aware that some change had taken
+place, and then flies away through the new
+opening. In a short time she returns, flits from
+twig to twig on the outskirts of the bush,
+and comes upon the new opening&mdash;there she
+hesitates. But though the nest is in full view
+and within a few inches of her perch, and though
+the young stretch out their necks, yet so strong
+is the former habit that she is compelled to
+return to the opposite side and approach the
+nest by the usual circuitous route before she
+distributes the food amongst her offspring.</p>
+
+<p>Let us see how far this law of habit
+formation may have been effective in defining
+the extent of the area occupied. When a male
+Warbler arrives at its destination in the spring
+it seeks out a suitable environment, and, having
+found a place unoccupied by any other male,
+settles in it and remains there&mdash;its behaviour
+up to this point being determined by racial
+preparation. After the fatigue of the journey
+its movements are at first sluggish; hunger,
+however, asserts itself and a search is made for
+food; wandering away from the position in<span class='pagenum'><a name="Page_206" id="Page_206">206</a></span>
+which it first settled and which acts as a headquarters,
+it hunts through certain trees here or
+certain bushes there and returns, and presently
+it wanders away again, perhaps in another
+direction, but, as before, works its way back
+again to the headquarters. The journeys thus
+radiate outwards from the headquarters, and
+according to the success with which the bird
+meets, so, probably, it happens that some trees
+are searched more often than others and certain
+directions are taken more frequently than others,
+and by constant repetition a routine is established
+which limits the direction and scope of its
+wanderings.</p>
+
+<p>But in the case of the Guillemot the
+conditions of existence are reversed: food can
+be had in abundance but suitable breeding
+stations are scarce. The few square feet of
+ledge correspond to the tree or clump of bushes
+which acts as a headquarters for the Warbler,
+and the occupation of them is determined, as
+it is in the case of the Warbler, by racial
+preparation. Since, however, the ledge is only
+made use of for the immediate purpose of
+incubation and is in no way affected by
+questions relating to food, there is no occasion
+for the bird to wander along the ledge nor to
+encroach upon those adjoining. Hunger stimulates
+the Warbler to search the surrounding
+trees, and so to extend its area; but hunger
+takes the Guillemot down to the water, and
+hence the area which it primarily occupied
+remains unmodified.</p>
+
+<p><span class='pagenum'><a name="Page_207" id="Page_207">207</a></span>To sum up: the territory is useful in various
+ways, but not necessarily in the same way
+for every species. Reproduction would always
+have remained fortuitous, and the number of
+individuals that attained to it would seldom
+have reached the possible maximum unless some
+provision had been included in its system for
+insuring that the males and females could meet
+at the proper moment and afterwards remain in
+touch with one another, and that the number of
+pairs inhabiting a given area did not exceed the
+available means of support. I have tried to
+show that the inclusion of a disposition to secure
+a territory tends to remove these difficulties.
+In the first place, the disposition which leads to
+its occupation comes into functional activity (in
+the male) early in the season; and so, by the
+time that the appropriate pairing condition
+arises in the females, the process of acquiring
+territories is well advanced, and the males being
+regularly distributed, each in its respective
+position, are readily found by their prospective
+mates. The behaviour of each sex is thus
+adjusted to further the end of mutual discovery.
+Next, after mating has taken place, the position
+occupied by the male acts as a headquarters to
+which the birds can always repair, and becomes
+a bond of union which is serviceable in that it
+prevents any possibility of their drifting apart.
+And in the third place, the males become
+pugnacious and in this way secure for themselves
+areas which vary in size according to the
+conditions of existence of the species, so that<span class='pagenum'><a name="Page_208" id="Page_208">208</a></span>
+there is no possibility of too many congregating
+in this locality, and all the less likelihood of too
+few finding their way to that; and hence, on the
+average, different pairs are distributed throughout
+all suitable localities. Furthermore, owing
+to the fact of their having a headquarters, the
+male and female are allowed a freedom of
+movement which otherwise they would only
+possess when the construction of the nest had
+actually begun; they can seek their food
+independently, and, even though paired, they
+can if necessary continue their winter routine
+without risk of separation. This means that the
+organic condition which leads to pairing, is free
+to develop in the female earlier than would be
+the case if there were nothing in the external
+environment to attract the pair to a particular
+spot; and the longer the period over which the
+process of pairing can be spread, the greater
+chance will females have of discovering mates,
+the less severe will the competition tend to
+become, and, consequently, the smaller the
+percentage of individuals that fail to obtain
+suitable partners.</p>
+
+<p>In these ways the territory has been serviceable
+alike to a number of species. But much
+as the questions of mutual discovery and regular
+distribution may have influenced the course of
+its development, there can, I think, be little
+doubt that, on the one hand, the supply of
+the necessary accommodation for rearing offspring,
+and on the other, the necessity for an
+adequate supply of food in close proximity to<span class='pagenum'><a name="Page_209" id="Page_209">209</a></span>
+the nest, have been the main determining factors,
+and have led to a wide divergence in its function.
+At the one extreme the function is to insure
+a plentiful supply of food for the young; at the
+other, to insure a station suitable for rearing
+offspring. I took the Bunting and the Guillemot
+as types of the two extremes. The young of
+the former species are born in a very helpless
+state. They are susceptible to cold and unable
+to withstand prolonged exposure, and therefore
+it is essential that there should be an ample
+supply of food, upon which the parents can
+draw liberally, in the vicinity of the nest. But
+the nest is placed in a variety of situations, and
+accommodation in this respect may be said to
+be unlimited. The young of the latter species
+are not so susceptible to exposure, and moreover
+there is always an abundance of food in the
+waters beneath the cliff; but ledges of rock,
+upon which the egg can be securely deposited
+and the young successfully reared, are limited
+both in number and extent. The position then
+is as follows: there are situations in plenty in
+which hosts of Buntings can build their nests
+but the supply of food is a difficulty, and if the
+respective areas of different individuals were
+insufficient to supply them with the necessary
+food with the necessary rapidity, they would
+run the risk of losing their offspring and the
+species would not endure; on the other hand,
+cliffs upon which the Guillemot can rear its
+young are limited, but the supply of food
+presents no difficulty, and consequently the<span class='pagenum'><a name="Page_210" id="Page_210">210</a></span>
+smaller the area over which each individual
+exercises dominion, the greater the number
+that will attain to reproduction and the greater
+prospect the species will have of survival. The
+emphasis in the one case lies on the fact that
+the area occupied must be sufficiently large;
+on the other, on its being just sufficient and
+no more to accommodate the egg. Hence
+the difference in the function at the opposite
+extremes is brought about, not by modifications
+of the instinctive behaviour which leads to the
+establishment and defence of the territory, but
+solely by modifications in the size of the area
+occupied, in accordance with the conditions
+prevailing in the external environment. No
+doubt, if we had the life-histories of a sufficient
+number of species worked out, we should find
+that the gradations were complete from the
+one extreme to the other. We are justified
+in thinking that this must be so because in
+many directions we can not only observe
+differences in the size of the area occupied, but
+can recognise a close correspondence between
+those differences and the conditions of life of
+the species. Thus the Herring-Gull occupies
+a comparatively small area, though one which
+is many times larger than that of the Guillemot.
+It requires more space because it not only builds
+a nest but rears four instead of a single offspring,
+and it can be allowed more space because the
+young remain in the nest until they are capable
+of sustained flight, and consequently it can
+make use of many miles of cliff from which the<span class='pagenum'><a name="Page_211" id="Page_211">211</a></span>
+tide recedes at the base, and which on this
+account are denied to the Guillemot, but
+manifestly it cannot be allowed so much space
+as the Bunting, for then comparatively few
+individuals would attain to reproduction.</p>
+
+<p>Again, the Reed-Warbler inhabits swamps
+overgrown with the common reed, and in such
+places insect life is abundant just at the
+time when the young are hatched. But these
+swamps cover a comparatively small acreage in
+the breeding range of the bird, and if each pair
+were to attempt to establish dominion over an
+area equal, let us say, to that of the Willow-Warbler,
+the species would have but a poor
+chance in the struggle for existence. So that,
+in a case of this description, the supply of food
+and the comparative scarcity of breeding stations
+have been factors of like importance in the
+evolution of the territory.</p>
+
+<p>Finally we were led to inquire as to how
+it comes about that the extent of the area
+occupied by each individual is adapted to the
+circumstances in which the individual finds
+itself; and we came to the conclusion that the
+movements of the bird, subsequent to the
+initial act of establishing itself in a position,
+are regulated and defined by the law of habit
+formation. For example, the Warbler, in
+response to its inherited nature, takes up a
+position in an appropriate situation. It then
+proceeds to search for food; it makes short
+journeys first in this direction and then in
+that; it repeats these journeys, and gradually<span class='pagenum'><a name="Page_212" id="Page_212">212</a></span>
+forms a habit which compels it to remain
+within more or less well-defined boundaries.
+But the actual distance that it traverses on
+the occasion of its first attempt must be determined
+by the relative abundance or scarcity
+of the particular kind of insect life which it
+requires. So that, although habit defines and
+in some measure helps to determine the
+boundaries of the territory, it is clear that in
+the last resort they must depend upon the
+nature of the conditions in the external
+environment.</p>
+
+<p>We have, then, the congenital basis which
+leads to the occupation of a position, and to
+the enmity shown by the owner of the position
+towards other individuals; and this congenital
+basis is found alike in many widely divergent
+forms, living under equally widely divergent conditions;
+we have acquired accommodation; and
+we have relationships in the organic and inorganic
+world&mdash;and the outcome of it all is a system
+of behaviour which we, who can perceive the
+end to which such behaviour is tending, are
+justified in speaking of as "a disposition to
+secure a territory." In the development of
+this system a primary value must be ascribed
+to the conditions in the external environment,
+for they determine the direction of the variations
+of instinctive procedure and of acquired habit
+which work towards the same goal&mdash;that of
+adjustment to the conditions of life.</p>
+<hr />
+<p><span class='pagenum'><a name="Page_213" id="Page_213">213</a></span></p>
+<h3>NOTE</h3>
+
+
+<p class="tb2">The following are the experiments referred to on
+page 181:&mdash;</p>
+
+
+<p class="tb2">On the 14th May 1915, a nest of Blackbirds approximately
+four days old was removed at 6.45 <span class="smcaplc">A.M.</span> The
+temperature was considerably below the normal, and snow
+lay on all the high ground in the neighbourhood. In a
+short time the birds collapsed, and at 9.15 <span class="smcaplc">A.M.</span> were dead.
+On the 29th May, at 6 <span class="smcaplc">A.M.</span>, a second nest was removed,
+containing young of approximately the same age, and
+although the conditions were more normal, the temperature
+being 50&deg; F., the birds collapsed at 8 <span class="smcaplc">A.M.</span>, and an
+hour later one of the brood showed little signs of life.
+The wind, however, then changed to the west, and the
+temperature rose one degree, with the result that they
+were still living at 11 <span class="smcap">A.M</span>. A further experiment was
+made with Song-Thrushes on the 5th June. The wind was
+in the south and the temperature 63&deg; F. The young,
+approximately four days old, were removed at 7.25 <span class="smcaplc">A.M.</span>,
+but as they showed no signs of collapse at 1 <span class="smcaplc">P.M.</span> I replaced
+the nest in the original site.</p>
+
+
+<p class="tb2">On the 30th May, a nest of Whitethroats three days
+old was removed at 7.15 <span class="smcaplc">A.M.</span> The wind was northerly
+and the weather fine, but the temperature low&mdash;50&deg; F.
+At 8.15 <span class="smcaplc">A.M.</span> the birds showed no sign of life. A second
+experiment with this species was made on the 10th June
+under more favourable circumstances, for although the
+sky was overcast and the wind northerly, the temperature
+was 59&deg; F. In this case the young survived from 6.55 <span class="smcaplc">A.M.</span>
+to 7 <span class="smcaplc">P.M.</span></p>
+
+
+<p class="tb2">On the 27th May 1915, a nest of Hedge-Sparrows
+hatched the previous day was removed at 7 <span class="smcaplc">A.M.</span> The
+temperature was below the normal, being 49&deg; F. At<span class='pagenum'><a name="Page_214" id="Page_214">214</a></span>
+8 <span class="smcaplc">A.M.</span> the young were cold and in a state of collapse, but
+they survived nevertheless until 3.20 <span class="smcaplc">P.M.</span></p>
+
+
+<p class="tb2">On the 7th June 1915, a nest of young Skylarks three
+days old was removed at 7.15 <span class="smcaplc">A.M.</span> The temperature was
+62&deg; F., and the birds survived until 4 <span class="smcaplc">A.M.</span> the next day.</p>
+
+
+<p class="tb2">On the 6th June 1916, a nest of Linnets just hatched
+was removed at 6.47 <span class="smcaplc">A.M.</span> The temperature was 51&deg; F.
+At 7.50 <span class="smcaplc">A.M.</span> the birds were cold and in a state of collapse,
+and only survived until 8.50 <span class="smcaplc">A.M.</span></p>
+<hr />
+<p><span class='pagenum'><a name="Page_215" id="Page_215">215</a></span></p>
+<h3>CHAPTER VI</h3>
+
+<h4>THE WARFARE BETWEEN DIFFERENT SPECIES
+AND ITS RELATION TO THE TERRITORY</h4>
+
+
+<p>We have now considered the various ways in
+which the territory is useful in furthering the
+life of the individual. We have seen that, in
+some cases, there is competition for stations
+where the egg or eggs can be deposited and
+incubated in safety; that, in others, there is
+competition for stations capable of furnishing
+an adequate supply of food for the young;
+and that the establishment of "territories"
+not only renders the attainment of reproduction
+for the individual secure, but serves so to
+regulate the distribution of pairs that the
+maximum number can be accommodated in
+the minimum area. This being so, the question
+arises as to whether competition for territory
+is strictly limited to individuals of the same
+species, or whether it may not occur also
+between different kinds of birds, providing
+always that similar conditions of existence
+are required. First of all I shall relate a
+number of facts which will serve to show the
+nature and extent of the warfare, and I shall<span class='pagenum'><a name="Page_216" id="Page_216">216</a></span>
+then give the reasons which lead me to believe
+that the fighting not only bears some relation
+to the "territory," but that it is an important
+factor in contributing to the attainment of that
+which for biological interpretation is the end
+for which the whole territorial system has been
+evolved.</p>
+
+<p>Those who have studied wild life on one of
+the rocky headlands, which are so numerous
+round our coasts, will probably be familiar with
+the rivalry that exists between the Raven and
+certain birds of prey. Where the Raven finds
+shelter for its nest, there, too, the Peregrine
+has its eyrie&mdash;and so it happens that these two
+species are continually at war. Now the warfare
+occurs not only during the season of
+reproduction but continues throughout the
+greater part of the year, and can even be
+observed in the late summer or early autumn&mdash;the
+period when we should expect to find the
+instinct least susceptible to appropriate stimulation.
+But it is of a more determined kind
+early in the spring, and it is then that we often
+witness those remarkable exhibitions of flight,
+the skill of which excites our admiration. The
+Falcon rises above the Raven, stoops at it, and
+when it seems no longer possible for a collision
+to be avoided, or, one would imagine, for the
+Raven to escape destruction, the Raven skilfully
+turns upon its back and momentarily faces its
+opponent, and the Falcon with equal skill
+changes its course, passing upwards and away.
+The attack, however, is soon repeated, and<span class='pagenum'><a name="Page_217" id="Page_217">217</a></span>
+though no collision may actually take place, yet
+the fact that the Raven, when it turns to face
+its adversary, is obliged to drop the stick which
+it carries, is not only an indication of the
+character of the struggle, but it shows that a
+definite end is gained&mdash;that the efforts of the
+Raven to build in that particular locality are
+hampered. But the Falcon is not the only
+enemy that the Raven has to face; Buzzards
+are just as intolerant of the presence of Ravens
+in their neighbourhood as the Ravens are of
+them, and consequently there is incessant
+quarrelling wherever the same locality is
+inhabited. As a rule, the fighting occurs whilst
+the birds are on the wing; the Buzzard rises to
+a considerable height, and, closing its wings,
+stoops at the Raven below, and when within a
+short distance of its adversary, swerves upwards
+and gains a position from which it can again
+attack. The Buzzard, however, is by no means
+always the aggressor; I have watched one so
+persistently harassed by a Raven that at length
+it left the rock upon which it was resting and
+disappeared from view, still followed by its rival.
+Thus it seems as if they were evenly matched,
+and, when they occupy the same locality, it is
+interesting to notice how the initiative passes
+from the one to the other according to the
+position occupied by the birds in their respective
+territories.</p>
+
+<div class="figcenter" style="width: 500px;"><a name="f255" id="f255"></a><img src="images/fig255.jpg" width="500" height="450" alt="Peregrine Falcon
+attacking a Raven" title="Peregrine Falcon attacking a Raven." /></div>
+
+<p>That there is constant warfare between the
+Green Woodpecker and the Starling is well
+known, the purpose of the Starling being to<span class='pagenum'><a name="Page_218" id="Page_218">218</a></span>
+gain possession of the hole which the Woodpecker
+with much skill has drilled for itself.
+As far as my experience goes, the Starling is
+always the aggressor, and there is only too good
+reason to fear that, in the course of time, the
+Green Woodpecker will disappear as a result of
+the greater fertility and tenacity of its enemy.
+The Martin suffers a similar kind of persecution
+from the House-Sparrow, and here again there
+is reason to believe that the greater virility of
+the Sparrow will hasten the extinction of its
+rival. In cases of this description the purpose of
+the fighting is clear, and one can understand
+why such divergent species should be hostile to
+one another; yet others, equally remote in the
+scale of nature, are hostile when no such
+ostensible reason can be assigned for their
+hostility. Few birds are more pugnacious than
+the Moor-Hen, and the determined manner
+in which different individuals fight with one
+another is notorious. But the intolerance it
+displays towards other species is no less remarkable,
+and its pugnacious instinct seems to be
+peculiarly susceptible to stimulation by different
+individuals belonging to widely divergent forms.
+At one moment a Lapwing may be attacked,
+at another a Thrush or a Starling, harmless
+strangers that have approached the pool to
+drink; even a Water-Rail, as it threads its way
+through the rushes, may fail to escape detection;
+and, which is still more curious, a covey
+of Partridges will evoke response if they
+approach the pool too closely.</p>
+
+<p><span class='pagenum'><a name="Page_219" id="Page_219">219</a></span>Here is a curious instance of apparent waste
+of energy. A pair of Magpies built their nest
+in an ilex tree. Early one morning there was
+a commotion in the tree, much flapping of
+wings and a medley of sounds which told of
+large birds engaged in a struggle&mdash;the Magpies
+were attacking a pair of Wood-Pigeons. There
+was no question as to the genuineness of the
+struggle, nor any doubt as to the proximate end
+for which the Magpies were striving, for their
+efforts continued so long as the Wood-Pigeons
+remained in the tree, and only ceased when they
+had succeeded in driving them away.</p>
+
+<p>Turning next to species which are less
+distantly related, we find that instances of
+intolerance are more numerous and that a wider
+range of species is involved. The hostility that
+the Lapwing displays towards the Snipe calls
+for special remark. It often happens that the
+marshes or water meadows, that are such
+favourite haunts of the Lapwing, are also
+resorted to by Snipe for the purpose of securing
+food, or it may be even for the purpose of
+reproduction. In such places both species are
+often abundant; the meadow is divided up into
+Lapwings' territories, and early in the season the
+Snipe wander over it in small parties, singly, or
+in pairs. Now, if it were only on isolated
+occasions that the Lapwing paid heed to the
+Snipe, one would not perhaps attach any
+peculiar significance to the fact; but the
+pugnacious instinct of the bird responds to the
+presence of this intruder almost as freely as it<span class='pagenum'><a name="Page_220" id="Page_220">220</a></span>
+does to that of another Lapwing. Again and
+again, day after day, the Snipe are attacked and
+driven off in a manner which would be fittingly
+described as persistent persecution, for the Snipe
+has neither the physical capacity nor apparently
+any instinctive tendency to retaliate. Thus a
+Lapwing may come suddenly upon a small
+party of Snipe hidden from view in a dyke
+where they are probing the ground for food;
+the Snipe immediately rise and fly away and
+there is momentary confusion as the Lapwing
+darts first at this one, then at that; or, espying
+a Snipe at rest at the opposite end of its
+territory, it will first of all run rapidly towards
+it, and then fly after it, as, with twisting flight,
+it darts hither and thither a few feet above the
+ground; or again, it will attack and rapidly
+pursue solitary individuals as they skim across
+its territory and attempt to settle. Is this
+intolerance merely an exuberant expression of
+an instinct which is serviceable in another
+direction? The behaviour of the Lapwing
+scarcely justifies such a conclusion, for all its
+actions denote a striving towards some end
+which we can describe, and it seems to gain
+satisfaction only when the ejection of the
+intruder has been accomplished.</p>
+
+<p>Many of the Warblers display irritation
+when approached by other birds which we
+should scarcely expect would arouse their
+hostility. The Hedge-Sparrow, for example, is
+frequently regarded with suspicion, and it is
+by no means unusual to see it attacked by so<span class='pagenum'><a name="Page_221" id="Page_221">221</a></span>
+small a bird as the Chiffchaff. The Wood-Warbler
+is also pugnacious, and will even attack
+a pair of Chaffinches. Between the Tit family
+and some of the smaller Warblers there are
+constant exhibitions of hostility; even the Great
+Tit is liable to be driven away, but the Blue
+Tit is especially marked out for persecution,
+though doubtless it is well able to hold its own.</p>
+
+<p>The following incident will show how real is
+the antagonism between these two families.
+A Chiffchaff occupied the corner of a small
+osier bed, and was particularly aggressive
+towards other closely-related forms in its
+immediate neighbourhood. On two mornings
+in succession ten Blue Tits invaded its ground,
+passing from end to end of it as they wended
+their way from tree to tree in search of food.
+Their presence evoked the usual hostile response,
+yet, withal, aroused the fear of the Chiffchaff,
+which, at times, appeared to be swayed by
+conflicting impulses. Now, in attempting to
+interpret the nature of the instinct which was
+evoked, one has to be guided, in a case of this
+description, by the similarity of the response to
+that which can be observed on other occasions
+and in other situations when the intention of
+the bird is clear. And on this occasion the
+Chiffchaff betrayed all the symptoms which
+normally precede an attack; it spread its tail,
+quivered its wings, uttered its high-pitched note
+rapidly, hopped from twig to twig, or flew
+restlessly from tree to tree, and seemed to be
+prevented from attacking only by the number<span class='pagenum'><a name="Page_222" id="Page_222">222</a></span>
+of its opponents. This, indeed, was shown by
+its subsequent behaviour, for whenever a Tit
+became temporarily detached from its companions
+it hesitated no longer but forthwith
+attacked.</p>
+
+<p>There are other species which are no less
+aggressive than the Warblers&mdash;the Chats for
+example. The Stonechat regards with suspicion
+almost any bird of its own size, and will even
+pursue a Tree-Pipit if it approaches too closely.
+The same is true of the Whinchat, and one
+would scarcely expect to find this bird attacking
+Buntings as it sometimes does. A Whinchat
+that occupied some marshy ground was constantly
+at war with a pair of Reed-Buntings;
+their territories were adjacent and in some
+measure overlapped, and the Whinchat drove
+away either sex indiscriminately, and was not
+only always the aggressor but seemed to be
+master of the situation.</p>
+
+<p>Coming now to kindred forms, those, that
+is to say, which belong to the same family, we
+find that, both in intensity and extent, the
+warfare far exceeds anything that we have thus
+far considered. So frequent, indeed, are acts
+of intolerance, and so readily awakened into
+activity is the pugnacious nature of the bird,
+that the fighting will almost bear comparison
+in volume with that which occurs between
+individuals of the same species. Between the
+Thrush and the Blackbird there are incessant
+quarrels early in the year, and the initiative
+seems to pass from one to the other according to<span class='pagenum'><a name="Page_223" id="Page_223">223</a></span>
+the circumstances in which they are placed. If
+the territory of a Thrush is invaded the Thrush
+is the aggressor, and, conversely, if that of the
+Blackbird is threatened, the Blackbird becomes
+the aggressor; and so, when the territories of the
+two birds are adjacent or overlap, as frequently
+they do, there is constant friction, resulting in
+quarrels which attract attention on account of
+the noisiness of the birds.</p>
+
+<p>All the Warblers are exceedingly pugnacious,
+the fighting being especially severe between
+those that are very closely related. The Blackcap
+and the Garden-Warbler are constant rivals,
+and the scenes which can be witnessed when
+the two meet in competition are interesting
+from many points of view. The birds not only
+pursue and fight with one another, but their
+emotional behaviour reaches a high level of
+intensity&mdash;excitable outbursts of song are indulged
+in, tails are outspread, wings are slowly
+flapped, and feathers raised&mdash;in fact the attitudes
+assumed are similar in all respects to those
+which occur during the contests which are so
+frequent between the respective individuals of
+each species; and it would be difficult to point
+to any one item of behaviour which is not
+also manifest at one time or another during the
+battles between these rivals, and still more
+difficult to trace any difference in the intensity
+of the excitement. And if we are satisfied that
+the fighting in the one case is purposive, so, too,
+must we regard it as having some biological
+purpose to serve in the other. But the Garden-Warbler<span class='pagenum'><a name="Page_224" id="Page_224">224</a></span>
+is not the only bird that acts as a
+stimulus to the instinct of the Blackcap;
+Whitethroats are often attacked, and the Chiffchaff
+is a source of irritation. Even when a
+male Blackcap is engaged in incubation, it will
+leave its nest on the approach of a Chiffchaff,
+and, having driven away the intruder, proceed
+to sing excitedly. At other times both male
+and female will combine to attack this small
+intruder.</p>
+
+<p>But this does not mean that the Chiffchaff
+suffers persecution; it is itself most aggressive,
+as is shown by the fact that it will join in the
+Blackcap quarrels and attack the combatants
+indiscriminately. Its behaviour, however, requires
+further consideration, especially as regards
+its relations with its nearest of kin&mdash;the Willow-Warbler;
+for here we have a mutual intolerance
+which is somewhat remarkable, and evidence of
+it can be found wherever the birds occupy the
+same ground. Now it can be observed that the
+hostility is not limited merely to occasional acts
+of intolerance, but that there is organised
+warfare lasting, it may be, for many days in
+succession, and that the actions of the birds bear
+the stamp of a persistent striving towards some
+end. On one occasion the Willow-Warbler
+may be the aggressor, on another the Chiffchaff,
+and at times it is difficult to say which of
+the two is responsible for the quarrel. In size
+and in strength they are equal, and the "will to
+fight" is as strong in the one as in the other, so
+that it is seldom, if ever, possible to point to<span class='pagenum'><a name="Page_225" id="Page_225">225</a></span>
+this one as the victor and that one as the
+vanquished. Success or failure probably depends
+more upon the cumulative effect of many
+combats entailing physical exhaustion, than
+upon the issue of any one particular battle; and
+whilst observation might quite well fail to
+distinguish any resultant change in the relative
+positions of the birds, or any harmful effect
+upon their constitutions, yet the area occupied
+by this one might be sufficiently curtailed to
+prejudice the welfare of the young, or the
+vitality of that one might be seriously impaired&mdash;and
+we should be none the wiser.</p>
+
+<p>Neither the Marsh-Warbler nor the Reed-Warbler
+will tolerate strangers within the small
+space of ground over which they exercise
+dominion. Of the two, the Marsh-Warbler is
+perhaps the more pugnacious, and will attack
+any other Warbler that approaches too closely;
+Whitethroats are often pursued and driven
+away, and less frequently, Garden-Warblers.
+In one case, a male occupied the same ground
+as a Sedge-Warbler, and there was a constant
+feud between them; a willow-tree formed its
+headquarters, and this same tree seemed to be
+the headquarters of the Sedge-Warbler, so that
+they often met and whenever they did so they
+quarrelled. As a rule the Marsh-Warbler was
+the aggressor and had the mastery over its
+opponent, and when it attacked, it uttered a
+peculiar harsh scolding note, raised the feathers
+on its back, spread out its wings, and betrayed
+the usual symptoms of emotional excitement.</p>
+
+<p><span class='pagenum'><a name="Page_226" id="Page_226">226</a></span>On the other hand, the Sedge-Warbler is
+most aggressive towards other kindred species,
+and when a male happens to occupy the same
+ground as a Reed-Warbler, there are frequent
+battles between them and incessant commotion;
+they fly at one another and meet in the air with
+an audible clicking of bills, or pursue one
+another amongst the reeds, each one uttering
+its characteristic scolding note.</p>
+
+<p>The Tits, as a family, are notoriously
+pugnacious. I have seen a pair of Blue Tits
+attack a single Long-tailed Tit with great
+determination, and not only did they pursue it,
+but, flying at it, struck it with considerable
+force.</p>
+
+<p>In giving an account of the domestic
+economy of the Carrion-Crow, Mr. Edmund
+Selous refers to the hostility between this bird
+and the Magpie. "About a week ago," he
+says,<a name="FNanchor_6_6" id="FNanchor_6_6"></a><a href="#Footnote_6_6" class="fnanchor">6</a> "I saw a Crow busily engaged in chasing
+away several Magpies, not only from three or
+four tall slender trees close together, in one of
+which it had its nest, but also from various
+other trees, not far off, round about. In this
+the Crow had a good deal of trouble, as the
+Magpies were always returning. After a time
+it was joined by another crow, which however
+did not take so active a part in the drama, nor
+did I see either of the two actually go to the
+nest, though I could only explain their action by
+supposing it was their own. This morning I
+saw the same thing reversed, for a pair of
+<span class='pagenum'><a name="Page_227" id="Page_227">227</a></span>
+Magpies, with an undoubted nest, kept attacking
+a Crow that insisted on settling in one of a row
+of trees&mdash;also tall and slender&mdash;in which it was
+placed. Both were equally persevering&mdash;the
+Crow, though often chased away, always
+returning, and settling generally in the last
+tree of the row, where he would be left alone
+sometimes for a minute or two, but before long
+one of the Magpies flew at him, and put him to
+flight. The Crow defended itself, but not, it
+would seem, very successfully, and in the last
+attack upon him, made, with great spirit, in the
+air, a large black feather floated to the ground,
+which I made no doubt was his. Yet this did
+not drive him from the trees, and it was only on
+my approaching nearer that he finally left them.
+Thus we see that both species look upon the
+approach of the other to within a moderate
+distance of their nest as an intrusion."</p>
+
+<p>That the Rook suffers persecution from
+the Carrion-Crow is a well-established fact,
+and there is reason to believe that it has
+another dangerous enemy in the Hooded Crow.
+According to the late Mr. Ussher, Choughs will
+attack both Hooded Crows and Ravens. "I
+once saw," he says, "two Choughs energetically
+attacking a pair of Ravens; they shot up into
+the air and darted down on the latter, whose
+heavy flight made them helpless against their
+agile tormentors."</p>
+
+<p>Birds of prey are often hostile to one another.
+The Merlin is exceptionally pugnacious, and its
+boldness in attacking intruders is well known.<span class='pagenum'><a name="Page_228" id="Page_228">228</a></span>
+When, for example, a Kestrel approaches its
+territory, it leaves the tree, bush, or rock upon
+which it was resting, utters its characteristic
+cry, and soars rapidly upwards; then, rising to
+a considerable height, it swoops down upon the
+Kestrel, and by alternately stooping at and
+chasing its opponent, drives it away from the
+immediate neighbourhood.</p>
+
+<p>What we have, then, to consider is, Do these
+battles between different species contribute
+towards the attainment of the end for which
+the whole territorial system has been evolved?</p>
+
+<p>Let us take the individual and see whether
+we can establish any relation between the
+hostility it displays towards members of other
+species and its general disposition to secure
+a territory. We must remember that a male
+can have no knowledge of the prospective
+value of its behaviour, nor is it likely that it
+has any ulterior purpose in ejecting other males,
+beyond the pleasure it derives from satisfying
+its impulse to do so. The proximate end of
+its behaviour is to attack, nothing more, and
+this, of course, it can only do just in so far
+as the intruder evokes the appropriate instinct.</p>
+
+<p>Now the arguments we shall employ will,
+on the whole, be similar to those which we
+made use of in the second chapter, wherein
+we attempted to ascertain the conditions under
+which a male becomes intolerant of other
+males of its own species, and examined more
+especially the claims of the "territory" as
+opposed to those of the "female." But here<span class='pagenum'><a name="Page_229" id="Page_229">229</a></span>
+we start on firmer ground, because the one
+factor which introduced an element of uncertainty&mdash;the
+female&mdash;can be definitely excluded;
+at least it seems so to me, for granting even
+that her presence is the condition under which
+the pugnacious nature of the male is rendered
+susceptible to stimulation, it is difficult to see
+why a male of a different species should supply
+that stimulus, or what biological purpose could
+be served by its doing so.</p>
+
+<p>When dealing with the attitude of a male
+towards others of its kind, we attached considerable
+significance to the fact that its pugnacious
+nature gained or lost susceptibility according
+to the position which it happened to occupy.
+We found, it will be remembered, that the
+same bird that was pugnacious in its own
+territory took no further interest in its opponent
+when the boundary was passed; and, moreover,
+that if it happened to wander into an adjoining
+one, it made no real effort to defend itself
+when attacked, but returned forthwith to its
+own headquarters. It remains to be shown
+whether the rivalry between different kinds of
+birds is similarly related to the position which
+the opponents happen to occupy at the time.</p>
+
+<p>First, then, there is the general consideration,
+namely, that the enmity occurs for the most
+part just at the time when the territories are
+in process of being established. During autumn
+and winter, many birds of more or less close
+affinity assemble together in flocks, wherever
+the supply of food is abundant, and are then<span class='pagenum'><a name="Page_230" id="Page_230">230</a></span>
+not only sociable, but, so there is reason to
+believe, are mutually helpful both in discovering
+the necessary means of subsistence which are
+often none too plentiful, and in affording protection
+from enemies, which, on the contrary,
+are often numerous. That the different units
+of which these flocks are composed should live
+on amicable terms is therefore as necessary
+for the welfare of the whole community at
+this particular season as that the different
+individuals of the same species should do so.
+But just as the sociable relations, which obtain
+between these individuals throughout the winter,
+undergo a marked change at the commencement
+of the breeding season, so, too, do different
+species, which habitually associate together,
+suddenly become hostile to one another. This
+change is coincident in time with the rise of
+the organic condition which leads to the
+establishment of territories; and the hostility
+continues, though in diminishing degree,
+throughout the breeding season, and dies away
+the following autumn.</p>
+
+<p>For example, different Warblers resort to
+the elders (<i>Sambucus nigra</i>) in September, and
+there pass much time feeding on the fruit which
+is then ripe and often abundant. In the same
+bush there may be Blackcaps, Garden-Warblers,
+Whitethroats, and Lesser Whitethroats, some
+preening their feathers, others searching for
+the berries, others again, with feathers relaxed,
+making feeble attempts to sing. Occasionally
+there may be a scuffle, perhaps between a<span class='pagenum'><a name="Page_231" id="Page_231">231</a></span>
+Blackcap and a Lesser Whitethroat, or between
+a Garden-Warbler and a Blackcap, but it is
+of short duration and lacks vigour. Apart,
+however, from such temporary disturbances,
+there is no real rupture in their relations, and
+certainly nothing to lead one to suppose that
+the bickerings are determined by the functioning
+of any specific instinct. Yet only a few months
+previously some of them were constantly at
+war, and their quarrels betrayed symptoms of
+great persistence; and if we remember how
+the observed behaviour of the birds suggests
+the fact that they were striving to attain something
+definite, we shall understand the nature
+and extent of the change, and shall, I fancy,
+be in a better position to estimate its biological
+worth at its true value.</p>
+
+<p>We can find many similar examples&mdash;flocks
+are to be found on arable ground, on the water
+meadows, and on the mud-flats; here different
+kinds of Thrushes feed on the berries of the
+yew, there different kinds of Tits travel together
+in parties; hosts of Finches collect in the hollies
+to pass the night and Buntings roost together
+in the gorse; and, in fact, in whatever direction
+we choose to look in the autumn and winter,
+we find various birds assembled together and
+living on amicable terms. All of this changes
+in the spring, and the relationship undergoes
+a gradual but noticeable alteration; so much
+so that whereas the outstanding feature of bird
+life in the winter is sociability, that of the
+spring is hostility.<span class='pagenum'><a name="Page_232" id="Page_232">232</a></span></p>
+
+<p>So much, then, for the seasonal change of
+relationship; let us now turn to particular cases
+and attempt to trace the condition which
+accompanies such change.</p>
+
+<p>Many migrants in the spring seem to follow
+the course of the Severn during their journey
+northwards through Worcestershire; and where
+the river bends to the north-west at Lincombe
+Lock, there they leave it, or, rather, continue
+in a north-easterly direction which takes them
+across the southern end of Hartlebury Common.
+As I have already mentioned, this Common is
+overgrown with gorse, heather, and ling, and
+scattered here and there are a number of dwarf
+oak-trees and small elder-bushes. The situation
+is therefore an ideal one for the smaller migrants
+to rest for a brief time, and, from the point of
+view of the observer, very suitable because it is
+open and the movements of the birds can be
+traced for some distance. Turtle Doves pass
+over at a great height, or skim across a few
+feet above the gorse; Redstarts settle for a
+few minutes and then disappear; Tree-Pipits,
+Whinchats, and Willow-Warblers pass from
+tree to tree or flit from bush to bush&mdash;and all
+in a north-easterly direction. They do not
+sing, they are restless, and, judging by their
+behaviour, they are anxious to conceal their
+presence, not to make it known. Yet we know
+that when they reach their destination, as
+presently they will, all this will change; that
+each of them will employ every means at its
+disposal to make itself conspicuous; and that<span class='pagenum'><a name="Page_233" id="Page_233">233</a></span>
+each, as far as it is able, will resist intrusion on
+the part of other species.</p>
+
+<p>Now the southern end of the Common is
+always inhabited by individuals belonging to
+one of these species, or to others of close
+affinity; so that wherever these travellers settle
+whilst passing across it, the chances are that
+they will find the ground occupied&mdash;and their
+behaviour under such circumstances is no less
+interesting than the behaviour of the bird upon
+whose ground they are trespassing. We will
+take the case of the Whinchat. It arrives from
+the south-west, and, flying from bush to bush,
+works its way in a north-easterly direction. In
+doing so it intrudes upon the territory of
+a Stonechat; and the Stonechat, becoming
+excited, flies towards it, and it retires for a short
+distance in the direction from whence it came.
+Here again it is followed and attacked and
+again moves on, and then, flying in a circle as if
+to avoid the territory which blocked the path,
+resumes its former line of flight, though still
+followed by the Stonechat, which after continuing
+the pursuit for perhaps a quarter of a mile,
+suddenly turns in the air and returns to its
+headquarters.</p>
+
+<p>It is difficult to put oneself in the place of
+the Stonechat or of the Whinchat. But even
+after making due allowance for the danger
+inseparable from any attempt to do so, there
+remains the unquestionable fact that whereas
+the impulse to attack was strong in the one, the
+impulse to defend itself was wholly lacking in<span class='pagenum'><a name="Page_234" id="Page_234">234</a></span>
+the other. Yet a Whinchat, when it has
+established itself, is most pugnacious; it not
+only attacks every bird of a similar size that
+approaches its position, but its behaviour under
+such circumstances bears the impress of unusual
+determination; and if we were to take a male
+and place it in the position of the Stonechat, we
+should find that its nature would change, that
+the presence of the Stonechat would evoke a
+hostile response, and, conversely, that the
+instinct of the Stonechat would not be susceptible
+to stimulation. Hence it is clear that the
+nature of a bird when on migration is not quite
+the same as it is when its destination is reached;
+that the positions occupied from time to time
+during the journey carry no meaning, or, rather,
+are not brought into relation with its life in
+quite the same way as is the position which it
+finally occupies; and further, it is clear that the
+interest it displays in other species undergoes a
+somewhat remarkable transformation when at
+length its destination is reached.</p>
+
+<p>This altered nature of the migrant is a fact
+of some importance in relation to our present
+subject, but it does not stand alone&mdash;the same
+characteristic is observable in other phases of
+bird life. Some of the residents, the Buntings
+and the Finches for example, occupy their
+breeding ground very early in the year, and it
+often happens that the situations which they
+select are not capable of supplying them with
+food so early in the season, though at a later
+date food will be there in abundance; so that<span class='pagenum'><a name="Page_235" id="Page_235">235</a></span>
+they are compelled to resort to the surrounding
+neighbourhood, and since, even there, the
+available supply is sometimes scarce or, if
+plentiful, limited to certain areas, they are
+constrained from time to time to join together
+again in flocks. Thus, for part of the year,
+they may be said to lead a double existence;
+for just as the Whinchat, that is sociable on
+migration, betrays a changed nature when it
+reaches its destination, so too does the nature
+of these residents change from hour to hour
+according to whether they are seeking food or
+occupying the breeding ground.</p>
+
+<p>In the newly-sown fields of grain the birds
+frequently find a supply of food. Here Yellow
+Buntings, Greenfinches, and Chaffinches collect
+from the surrounding neighbourhood. The
+majority are somewhere in possession of territories,
+and not a few are paired. Between the
+territories and the feeding ground a highway is
+formed by individuals passing to and fro.
+Sometimes both members of the pair leave
+together in order to seek food, at other times
+they separate and the male may be in his
+territory whilst the female is with the flock.
+Apart from occasional manifestations of sexual
+emotion on the part of a male, there is nothing
+to disturb the harmony of the flock nor anything
+in the behaviour of the birds which would
+lead one to suspect that, when they return, their
+nature will change and that they will be no
+longer sociable; and, which is still more remarkable,
+no matter how great the provocation which<span class='pagenum'><a name="Page_236" id="Page_236">236</a></span>
+an individual, when in company with the flock,
+may be called upon to endure, its customary
+hostile response will fail to be elicited. An
+incident which happened in the spring of 1917
+will serve to make this clear. A flock of some
+thirty Yellow Buntings, Greenfinches, and
+Chaffinches were feeding in one corner of a
+field which had recently been sown with barley.
+As they sought their food they wandered
+outwards into the middle of the field, and in
+so doing, passed across the territory of a Skylark.
+Whereupon the Skylark became excited,
+uttered its call-note rapidly, and rising a few
+feet from the ground, attacked those members
+of the flock that were nearest, which happened
+to be the Yellow Buntings; and so determined
+were its onslaughts that the Yellow Buntings
+were forced to retire. The Skylark showed no
+discrimination as to sex, but attacked both males
+and females, and within a few minutes succeeded
+in driving away at least two pairs. One would
+have expected that the Yellow Buntings would
+have made some show of resistance; one would
+have thought that the fact of being violently
+attacked would have supplied a stimulus
+sufficiently strong to evoke a corresponding
+hostile response: yet there was no mistaking
+the lack of interest that they displayed in the
+contest&mdash;they made no effort to retaliate but
+seemed to accept the situation as unalterable
+and left.</p>
+
+<p>So far we have examined only those cases in
+which the pugnacious instinct was stimulated in<span class='pagenum'><a name="Page_237" id="Page_237">237</a></span>
+one of the adversaries, and in which consequently
+the fighting seldom reached any high degree of
+severity. We must now consider some others
+in which each of the opponents acts as a
+stimulus to the pugnacious instinct of the other.
+It is here, of course, that we find the most
+violently contested battles, and it is here, too,
+that the purpose of the fighting seems clear.
+The persecution which the Green Woodpecker
+suffers from the Starling is well known. The
+purpose of the Starling's behaviour is clear,
+namely the possession of the hole occupied
+by the Woodpecker. Bird for bird, the Woodpecker
+is more than the equal of the Starling,
+but persistent endeavour ultimately wins the
+day. The Starlings perch close beside the hole,
+and, whenever the Woodpecker shows itself,
+attack with determination; and not only do
+they do so but they are assisted, so there is
+reason to believe, by other individuals or pairs
+in the attainment of their end, so that no matter
+how stoutly the Woodpecker defends itself, in
+time it is almost certain to be deprived of its
+ownership.</p>
+
+<p>In like manner different kinds of Woodpeckers
+contend with one another for the
+possession of a hole, and here the opponents
+are more equally matched. I have seen a pair
+of Lesser Spotted Woodpeckers endeavouring
+to drive away a Great Spotted Woodpecker.
+The excitement of all three birds was exceptional.
+Each of the Lesser Spotted Woodpeckers kept
+swooping in turn at their rival, sometimes in the<span class='pagenum'><a name="Page_238" id="Page_238">238</a></span>
+air and sometimes when it was settled on the
+topmost branches of a dead tree, and the sounds
+produced reminded one of the piping of a flock
+of Oyster-Catchers in flight.</p>
+
+<p>A battle between a pair of Green Woodpeckers
+and a Great Spotted Woodpecker is
+worth mentioning. It occurred on the 24th of
+April. Passing through the middle of a wood,
+I noticed a Great Spotted Woodpecker fly out
+of a hole in an oak-tree. Shortly afterwards,
+a pair of Green Woodpeckers settled near the
+hole and then flew to some oak-trees close at
+hand, where they were joined by their rival and
+signs of hostility were soon apparent. Presently
+the Great Spotted Woodpecker returned to the
+hole and entered. Both of the Green Woodpeckers
+then flew into the tree; and one of
+them, settling upon the trunk, climbed up to
+the level of the hole and, when it became
+aware of the Great Spotted Woodpecker within,
+extended its wings fully and proceeded to peck
+viciously at its opponent. Whereupon there
+was a scuffle at the mouth of the hole and
+the Great Spotted Woodpecker hurriedly left.
+After this, all was quiet and the Green Woodpecker
+eventually descended and entered the
+hole. The Great Spotted Woodpecker, however,
+returned again, but, after fluttering around
+the hole, disappeared, leaving the Green Woodpeckers
+in possession.</p>
+
+<div class="figcenter" style="width: 500px;"><a name="f281" id="f281"></a><img src="images/fig281.jpg" width="500" height="925"
+alt="A battle between a pair of Green Woodpeckers
+and a pair of Pied Woodpeckers for the
+possession of a hole in an oak tree." title="A battle between a pair of Green Woodpeckers
+and a pair of Pied Woodpeckers for the
+possession of a hole in an oak tree." /></div>
+
+
+<p class="underline">ERRATUM</p>
+
+<p class="center"><i>For</i> "pair of Pied Woodpeckers"<br />
+&nbsp;&nbsp;<i>read</i> "Great Spotted Woodpecker"<br />
+</p>
+
+<p>In this varied field of hostile behaviour
+which we have explored, one feature stands
+out prominently, namely, that the interest<span class='pagenum'><a name="Page_239" id="Page_239">239</a></span>
+which a bird displays in other species varies
+not only at different seasons but even from
+hour to hour. I have used the word "nature"
+as equivalent to "interest," and I have spoken
+of the bird's nature changing or altering according
+to the circumstances in which it was placed.
+But its nature is its inborn constitution, and its
+constitution cannot change from day to day,
+still less from hour to hour. So that, in a sense,
+and having regard to strict scientific accuracy,
+it is misleading in this particular connotation to
+say that the bird's nature changes.</p>
+
+<p>What then does happen? The instinct of
+pugnacity must form just as much a part of
+the hereditary make-up of the migrant, when
+on migration, as when finally it reaches its
+destination; still more must it form part of
+the constitution of the Bunting when it leaves
+its headquarters temporarily and joins the flock.
+And, if it is there, the question arises as to
+why it does not respond. Now every instinct
+requires for its response a stimulus of an appropriate
+kind, and, therefore, a reasonable view
+to take would be that the necessary stimulus
+was lacking. But this is a view which we
+cannot uphold, because on all these occasions
+an opposing male was present&mdash;and, so far as it
+is possible to judge by observation, that is the
+stimulus which in the main evokes a hostile
+response. We must therefore look elsewhere
+than in its direction for a reason which will
+adequately explain the behaviour.</p>
+
+<p>Though it be true that every instinct<span class='pagenum'><a name="Page_240" id="Page_240">240</a></span>
+requires for its functioning a stimulus of an
+appropriate kind, yet it is also true that the
+condition which will render it responsive must
+be present. What we have then to consider is
+whether the phenomena which we have explored
+give us any clue as to the particular nature of
+that condition. In the first place, we have the
+general fact that the hostility is not confined to
+a few species belonging to a few families, but
+that it is of wide application&mdash;birds of prey,
+Warblers, Woodpeckers, all supply us with
+evidence which serves to show, in greater or
+less degree, its nature and extent. Next, we
+found that the hostility was peculiar to a
+certain season&mdash;and that one the season of
+reproduction. And if the question were asked:
+What condition would then be most likely to
+render the instinct susceptible, the answer that
+would most certainly be given would be&mdash;the
+presence of a female. And in reply to a
+further question as to the particular nature of
+the stimulus to which the instinct would
+respond, we should be told&mdash;the presence of
+another male of the same species. Now the
+possible influence of the female on the course
+of the male's behaviour was the subject of
+inquiry in the second chapter, wherein we
+endeavoured to explain the hostility between
+males of the same species, and we came to
+the conclusion that it was not alone sufficient
+to account for the facts disclosed. Still
+less likely, therefore, is it that her presence
+can bear any direct relation to the hostility<span class='pagenum'><a name="Page_241" id="Page_241">241</a></span>
+between different species, the more so since
+the biological end of securing a mate is
+definitely excluded. And we have something
+in the nature of proof of the correctness of
+this view in the fact that she accompanies her
+mate when he joins the flock, and that there
+his instinct is not susceptible to stimulation.
+We then proceeded to examine certain cases
+in which all the indications pointed to the fact
+that the "will to fight" was present in only
+one of the opponents; and we attached considerable
+importance to this circumstance, because
+we knew from experience that the same bird
+which seemed to lack courage, could at other
+times and in other situations be most aggressive.
+If then we ask what condition was present on
+the one occasion that was absent on the other,
+we have no difficulty in finding a reply&mdash;on
+every occasion on which the opponents appeared
+to be unevenly matched, one was in occupation
+of a territory and the other was not. And if
+we inquire further as to which of the two was
+the aggressor, the answer is again clear, namely,
+the bird that occupied a territory. Finally we
+considered some particular instances in which
+the "will to fight" was present alike in both
+opponents, and in which the battles were
+protracted and severe.</p>
+
+<p>But the fact that a bird has established a
+territory is not in itself sufficient to render its
+hostile nature susceptible; it must be actually
+in occupation if a response is to be elicited.
+We reach this conclusion step by step: the<span class='pagenum'><a name="Page_242" id="Page_242">242</a></span>
+behaviour of the migrant, that lacks the "will
+to fight" when on migration but is pugnacious
+when it has secured a territory, shows it; the
+behaviour of the resident, which temporarily
+joins the flock and is there sociable, shows it;
+and it is shown also by the determination with
+which both opponents fight when the question
+of ownership of a station is in dispute. And of
+all the facts we have reviewed, this is perhaps
+the most important in relation to our present
+subject, for it demonstrates that the change
+from sociability to hostility is not merely an
+incident of the sexual season, not merely an
+indirect result of the functioning of the general
+disposition which leads to the establishment of a
+territory, but that it is intimately associated
+with the whole process, and that the particular
+part of the bird's nature which is concerned is so
+nicely balanced that it will respond under one
+condition and one only.</p>
+
+<p class="tb">Thus we are led to the only conclusion
+which seems consistent with the facts, namely
+that there is a relationship between the
+"territory" and the hostility.</p>
+
+<p>If we are satisfied that all this warfare is not
+merely an expression of an instinct which is
+serviceable in another direction, what part does
+it play in the whole scheme of reproduction?</p>
+
+<p>The young of many birds are delicate at
+birth and unable to withstand exposure to cold,
+and in the previous chapter we came to the conclusion
+that the territory was serviceable in that<span class='pagenum'><a name="Page_243" id="Page_243">243</a></span>
+it provided an adequate supply of food in the
+vicinity of the nest, and thus obviated the
+necessity of the parents being absent from them
+for long. But manifestly no matter how active
+a male may be in driving away members of
+its own sex and kind, it will neither make
+its position secure, nor insure a supply of food
+for its young, so long as any number of
+individuals of different kinds are allowed to
+establish themselves in the same space of
+ground. On the one hand, then, we have the
+fact that there is constant strife between males
+of close affinity, whilst on the other, we know
+that many species require like conditions of
+existence and are bound to assemble wherever
+these conditions are suitable; and we can infer
+that the territory would fail to serve its purpose
+if no restriction were imposed upon the measure
+of such assemblies.</p>
+
+<p>The question then arises: Does all this
+warfare contribute towards the attainment of
+reproduction? Not far from my house there is
+a small water meadow, three acres in extent,
+which for some years has been derelict and is
+now overgrown with the common rush (<i>Juncus
+communis</i>) and small alder trees. For three
+successive seasons I watched the bird life of this
+meadow, and more especially the Reed-Buntings
+whose behaviour I was studying at the time.
+In every respect the meadow was suitable for
+this bird; there was an abundance of food and
+numberless situations in which nests could be
+placed. Each year all the pairs were successful<span class='pagenum'><a name="Page_244" id="Page_244">244</a></span>
+in rearing one, if not two broods, yet the
+number of pairs never exceeded five&mdash;the first
+year there were three; the second year five;
+and the third year four. In addition to the
+four pairs of Reed-Buntings, there were in the
+spring of 1915, six pairs of Whitethroats, one
+pair of Lesser Whitethroats, four pairs of
+Willow-Warblers, one pair of Sedge-Warblers,
+two pairs of Grasshopper-Warblers, one pair of
+Chiffchaffs, three pairs of Hedge-Sparrows, two
+pairs of Tree-Pipits, one pair of Skylarks, one
+pair of Whinchats, one pair of Flycatchers, two
+pairs of Song-Thrushes, one pair of Blackbirds,
+one pair of Redstarts, three pairs of Chaffinches,
+and one pair of Wrens&mdash;in all, thirty-five pairs,
+whose young were mainly dependent for their
+living upon the insect life of that meadow and
+the ground immediately surrounding it. If we
+allow three young to each pair&mdash;and this would
+take no account of second broods&mdash;we arrive at
+the following result, namely, that one hundred
+and five young and seventy adults had to be
+supplied with food from that locality, which
+would mean, if the search for food were strictly
+limited to that meadow, that 83 square yards
+would be allotted to each individual.</p>
+
+<p>Suppose now that the four male Reed-Buntings
+had each admitted one other male,
+and that they had secured mates, what would
+have been the effect upon the whole community?
+The four additional pairs with their young
+would have represented twenty individuals,
+which would have represented a decrease of<span class='pagenum'><a name="Page_245" id="Page_245">245</a></span>
+8.5 square yards in the space allotted to each
+individual. The pressure of the bird population
+upon the means of support would then have
+been materially increased; and not only the
+Buntings, but the Warblers, Pipits, and all
+the rest would have suffered. But the result
+would have been the same if, instead of
+the four additional male Reed-Buntings, four
+males of other kinds had been allowed to
+enter the marsh, and we can multiply the
+number four until we arrive at a point when
+the means of subsistence would no longer have
+been adequate for the adults, still less for the
+young. If, then, there were nothing to prevent
+this happening, many of the birds in that
+marsh would have no chance of rearing their
+young successfully. Hence, if the territory is
+adequately to serve the purpose for which we
+believe it has been evolved, some provision must
+have been included in the system to meet the
+difficulty.</p>
+
+<p>There are three ways by which this may have
+been accomplished&mdash;indirectly, by increasing the
+size of the area occupied by each individual,
+and thereby reducing the relative number of
+each species; or directly, by rendering the
+fighting instinct of the bird susceptible to
+stimulation by individuals of other species; or,
+possibly, by a combination of the two. There
+were four pairs of Reed-Buntings in the marsh,
+and their territories covered the whole of it.
+But inasmuch as other insectivorous birds were
+established there also, and found sufficient food<span class='pagenum'><a name="Page_246" id="Page_246">246</a></span>
+to maintain both themselves and their families,
+it is clear that the area these Reed-Buntings
+occupied was in excess of that which they
+would have required if they had been the sole
+inhabitants. And such often appears to be
+the case. Many a Warbler allocates to itself
+a space of ground more than sufficient to supply
+it with all that it needs; so, too, does the Finch,
+or the Pipit, or the Falcon&mdash;if we take no
+account of kindred species. Thus there is
+reason to believe that, by limiting the number
+of individuals in a given locality, this apparently
+wasteful expanse of territory is serviceable in
+that it provides against the pressure of the bird
+population upon the available means of support
+becoming too great. But though a reduction
+in the numerical standing of the different species
+would certainly follow from any increase in
+the area occupied by the respective individuals,
+and with even greater certainty would place
+them in a more secure position as regards their
+supply of food, yet, when we remember how
+large a number are dependent upon a supply
+of insect life for their young, we can understand
+that it would not alone be a sufficient safeguard
+against the dangers attendant upon overcrowding.
+It is here, I believe, that we shall
+find the true explanation of the hostility; it
+roughly insures that the number of pairs in
+any given area does not exceed the available
+means of support, and indeed it is difficult to
+imagine how such uniformity of distribution
+as would free the young from the risk of<span class='pagenum'><a name="Page_247" id="Page_247">247</a></span>
+exposure could be obtained without some such
+control.</p>
+
+<p>Some birds, however, have no difficulty in
+finding the necessary food for their young, yet
+have great difficulty in finding a station where
+they can rear their young in safety; and the
+area each one occupies has been reduced
+to the smallest proportions in order that the
+maximum number can be accommodated. Here,
+any increase in the size of the territory would
+inevitably lead to the extinction of the race,
+so that nothing stands between failure and
+success except the ability of the bird to defend
+its territory. If we study the bird population
+at one of the breeding stations on the coast,
+we find, generally speaking, that each kind of
+bird inhabits a particular portion of the cliff; on
+the lower ledges are the Guillemots and Kittiwake
+Gulls; higher up are Razorbills and
+Fulmars, and at the top, where the cliff is
+broken and the face of the rock covered with
+turf and soil, the Puffin finds shelter for its
+egg. At the same time there is much overlapping;
+the kind of ledge that suits a Razorbill
+is equally suitable for a Guillemot or a
+Fulmar, and so, no matter how successful the
+Razorbill may be in establishing a territory
+and preventing intrusion upon it by other
+Razorbills, it will be all to no purpose if it
+allows itself to be jostled out of its position
+by a Fulmar. Hence, inasmuch as breeding
+stations are limited and competition for territory
+so severe, only those forms in which the fighting<span class='pagenum'><a name="Page_248" id="Page_248">248</a></span>
+instinct responds freely to a wide range of stimuli
+will be in a position to maintain a footing upon
+the cliff.</p>
+
+<p>In trying to estimate the importance of the
+hostility in its relation to the territory, we must
+bear in mind that competition varies in different
+seasons and in different localities. The surface
+of the land is constantly undergoing modification,
+partly owing to human and partly to physical
+agency&mdash;forests are cleared; marshes are drained;
+the face of the sea-cliffs is altered by the erosion
+of the waves; here the coast may be locally
+elevated, there locally depressed; and so forth.
+Many of these changes are slow and imperceptible,
+many can be observed in our own
+lifetime. The timber is felled and the undergrowth
+cleared in some wood, and the following
+spring we notice a change in the character of
+the bird population. Migrants which formerly
+found in it no suitable accommodation now
+begin to appear, and as the seasons pass by
+and the undergrowth affords more and more
+shelter for the nests and an increasing supply
+of insect life, so their numbers increase until
+the wood becomes an important breeding station,
+resonant with the song of many individuals.
+But slowly the growth increases; the bushes
+pass into saplings and the saplings into trees,
+and the undergrowth then disappears just
+as surely as do the migrants which can no
+longer find there the conditions which they
+require.</p>
+
+<p>Or, as an illustration of the effect produced<span class='pagenum'><a name="Page_249" id="Page_249">249</a></span>
+by natural agency, let me describe a change
+which has taken place in a corner of Co. Donegal.
+The promontory of Horn Head is bounded on
+the west by extensive sand-hills, 100 ft. or more
+in height. On the southern side it is divided
+from the mainland by a channel, which narrows
+down to 100 yards or so in width where it
+fringes the sand-hills, and then widens out again,
+covering an area of approximately 270 acres.
+As far as is known in the memory of man, this
+area has always been tidal. But in recent years
+a change has taken place, and the blown sand
+has silted up the channel, with the result that
+this tidal area has been transformed into a
+brackish lake. What has brought about the
+change is not easy to determine. There is
+evidence, however, of a slow alteration of the
+level of the shore-line; for in the midst of the
+sand-hills, situated 150 yards or so from the
+present sea-margin, and running parallel with it,
+there is an accumulation of pebbles some 3 feet
+high by 4 feet deep. This raised beach is now
+separated from the Atlantic by sand-drifts of
+considerable height, and consequently there are
+some grounds for believing that secular elevation
+is taking place, which, if it be the case, will
+account for the change in progress. Now the
+effect on the bird population can be seen even
+now, and will doubtless become more apparent
+as the years pass by. Sand-Martins used to find
+plenty of places to breed amongst the sand-drifts,
+and moreover do so still. But their
+nesting sites are constantly changing and dis<span class='pagenum'><a name="Page_250" id="Page_250">250</a></span>appearing,
+and the breeding-place of one colony,
+that was situated in the bank of a stream twelve
+years ago, is now buried 10 feet or more below
+the surface of the sand. The area that was once
+tidal, but is now a brackish lake, is fed by
+mountain streams, and as the fresh water
+predominates, so in course of time will it become
+fringed with vegetation; and instead of the
+flocks of Curlew, Dunlin, and other waders that,
+at low water, resorted there to feed, Coots will
+fight with one another for the possession of
+territories, and the Wild Duck will teach her
+young to seek their food.</p>
+
+<p>In whatever direction we turn, we find
+that many breeding grounds are subject to
+incessant change. Ancient haunts disappear,
+new ones come into being, a change which
+makes life impossible for this bird, as likely
+as not benefits that one, and so on. There
+is no stability. Hence in any given district
+each recurring season there must needs be a
+large number of individuals which are obliged
+to seek new stations, and if there were no
+control over their distribution, if each one
+were free to establish itself wherever it chanced
+to alight, this locality might be overcrowded
+and that one deserted; and, bearing in mind
+how many species there are that require similar
+conditions of existence, we can infer that the
+successful attainment of reproduction would
+become impossible for many of those individuals
+so long as each species was indifferent to the
+presence of the others. On the other hand, if<span class='pagenum'><a name="Page_251" id="Page_251">251</a></span>
+there were no control over the range of the
+intolerance, the smaller bird would have no
+chance in competition with the larger, and it
+is doubtful whether the larger would gain an
+advantage commensurate with the energy it
+would expend in ridding its area of the smaller.
+I have described battles in which the opponents
+were only distantly related; for instance, the
+Moor-Hen will attack almost any bird&mdash;Partridge,
+Lapwing, or Starling&mdash;that approaches its
+territory even temporarily. Nevertheless the
+antagonism between kindred forms is more
+prevalent, and, as a rule, characterised by more
+persistent effort; and thus it seems as if the
+susceptibility of the fighting instinct has its
+limitations, the degree of the responsiveness
+being dependent upon the affinity of the
+opponents.</p>
+
+<p>Suppose now that we take an area inhabited
+by a number of different species requiring like
+conditions of existence, divide it into three
+sections, and imagine that in one they were all
+sociable, that in another they were all hostile,
+and that in a third those which were closely
+related were intolerant of one another. Let us
+suppose further that each one of them was
+represented by the full number of individuals
+that the law of territory would allow. In
+the first section an individual would establish
+itself, and, becoming intolerant of its own
+kind, would exercise dominion over an area
+roughly sufficient, providing conditions were
+normal, to insure an adequate supply of food for<span class='pagenum'><a name="Page_252" id="Page_252">252</a></span>
+its young. But it would take no account of
+other species, and since any number might
+occupy the same ground, the fact of its having
+established a territory would not alone suffice to
+render its supply of food secure. Success in the
+attainment of reproduction would then become
+largely a matter of chance, depending upon the
+number of individuals that happened to settle in
+this place or in that. In the second section
+there would be perpetual warfare; for whereas
+the appropriate organic condition which leads to
+pairing arises in different species at different
+times, fresh claimants to occupied ground would
+constantly be appearing, and the efforts of the
+inhabitants to preserve their boundaries intact
+would have to be maintained throughout the
+whole period of reproduction; and while the
+stronger or more persistent forms would be
+more likely to breed, they would do so at the
+expense of their young, to which they would be
+unable to devote proper attention, and with an
+expenditure of energy that would reflect itself
+upon the future of the race. But the conditions
+of life in the third section would be such as
+would be more likely to yield good results.
+The relations of the different members of the
+community would be more evenly balanced, for
+a male would only be called upon to compete
+with those of its own size and strength. Thus,
+on the one hand, accommodation would be so
+divided as to secure the breeding of the maximum
+number of individuals with the minimum
+of expenditure of energy, whilst on the other,<span class='pagenum'><a name="Page_253" id="Page_253">253</a></span>
+any undue pressure upon the available means of
+subsistence would be prevented.</p>
+
+<p class="tb">There can be no question that in the latter
+section a higher percentage of individuals would
+succeed in rearing offspring. And so, by reason
+of the fighting instinct being more susceptible
+or less susceptible according to the affinity of
+the opponents, a control is established which,
+while preventing unnecessary extension of warfare,
+allows for sufficient extension to render the
+biological end secure.</p>
+
+<p>These, then, are the facts&mdash;this the conclusion
+which can be drawn from them. It may,
+however, be said of these facts, as it has been
+said, with even less justification, of the battles
+between individuals of the same species, that
+they do not afford evidence of genuine hostility.
+No doubt there are many naturalists who could
+supplement these facts with others in which the
+conflicts resulted in bodily injury, or terminated
+fatally, or at least were of a more determined
+kind. But I have already drawn attention to
+the fact that, so long as a definite result is
+attained, the severity of the struggle and the
+amount of injury inflicted are matters of small
+moment. Let us, however, run over the substance
+of the argument, and then briefly refer
+again to this point of view.</p>
+
+<p>After enumerating instances of hostility,
+sufficient in number, so it seemed, to constitute
+reasonable ground for the belief that they had
+a part to play in the life-history of the<span class='pagenum'><a name="Page_254" id="Page_254">254</a></span>
+individual, the two questions we set ourselves
+to examine in this chapter were: Is there any
+circumstance in the life behaviour of the
+individual with which the hostility can be
+definitely related; and, will the hostility lead
+to the securing of a greater measure of success
+in the attainment of reproduction?</p>
+
+<p>Many different species assemble together in
+winter and roam from place to place in search of
+food. But in spring their behaviour undergoes
+a remarkable transformation; they avoid one
+another and become quarrelsome, so much so
+that whereas the outstanding feature of the
+winter is sociability, that of the spring is
+hostility. With this general fact before us,
+we proceeded to investigate this change of
+behaviour still further. First of all we took
+the case of a migrant, and, comparing its
+behaviour, as it journeyed, with that when
+finally it reached its destination, we found
+that the bird which was notoriously pugnacious
+when in occupation of a territory betrayed no
+interest in other species as it travelled to the
+accustomed breeding ground. Not only so, but
+even though it was attacked, we found that
+its pugnacious instinct still failed to respond.
+Here, however, it may be contended, and with
+reasonable justification, that in the interval
+which elapses before the ultimate destination
+is reached, some change in the organic condition
+of the bird may occur which will account
+for its altered behaviour; or, it may be urged,
+with no less justification, that whereas on<span class='pagenum'><a name="Page_255" id="Page_255">255</a></span>
+migration the bird is unpaired, when the
+destination is reached it is probably in possession
+of a mate and is therefore quarrelsome.
+Now, at the most, the interval can only be
+a matter of a few days, and it is unlikely
+that organic changes sufficient to bring about
+so important an alteration of behaviour could
+occur in so short a time, still less likely that
+they could be timed to come into functional
+activity just at the moment when the bird
+reaches its breeding ground. And with regard
+to the suggestion that the change can be
+accounted for by the presence of a mate, we
+shall do well to remember not only that males
+as a rule precede the females by some days, but
+that a male may even remain in its territory,
+mateless, for some weeks, and yet display
+hostility.</p>
+
+<p>Nevertheless the case of the migrant did not,
+by itself, afford sufficient evidence upon which
+to base any conclusion. We therefore inquired
+into the behaviour of some of the residents at a
+corresponding period. The Bunting served as
+an illustration. Early in the season it establishes
+a territory, and because food is then
+scarce it is forced to seek it elsewhere than on
+the small plot of ground which it has acquired;
+and so it makes its way to some spot where
+the supply is abundant, and there, meeting
+with other species bent on a similar errand,
+forms with them a flock. Part of its time is
+then spent in the territory and part on the
+feeding ground, and between these two points a<span class='pagenum'><a name="Page_256" id="Page_256">256</a></span>
+highway is formed by the bird passing constantly
+to and fro. But the attention which it pays to
+other species is very different on these two
+occasions&mdash;when in the territory it is intolerant
+of strangers, but when it accompanies the flock
+it displays no interest in their movements.
+From hour to hour its nature seems to change.
+But, as we saw, the inborn constitution of the
+bird cannot change, and therefore we came to
+the conclusion that an explanation of the altered
+behaviour was to be found in the fact that the
+pugnacious instinct is only rendered susceptible
+under a certain condition. So that all the
+evidence tended to confirm the impression which
+we had gained from the course of events in the
+life of the migrant, namely, that the hostility
+bears a direct relation to the occupation of a
+territory.</p>
+
+<p>Finally we were led to inquire whether the
+hostility was serviceable in promoting the
+welfare of the individuals. We saw that many
+different species require similar conditions of
+existence, that ancient breeding haunts disappear
+and that new ones come into being, and
+that in the ordinary course of events such
+species must often assemble in the same area for
+the purpose of reproduction. So that even
+though a male might be successful in protecting
+its ground from intruders of its own kind, yet it
+might still fail to rear offspring, just because it
+happened to choose a position in which other
+kindred forms had gathered. Hence if the
+territory is adequately to serve its purpose,<span class='pagenum'><a name="Page_257" id="Page_257">257</a></span>
+some control over the local distribution of
+species is of paramount importance. Nevertheless,
+if all the different forms that require similar
+conditions of existence were intolerant of one
+another in a like degree, the smaller bird would
+have no chance in competition with the larger.
+This, however, is not the case. Some, as we
+saw, arouse little or no animosity in others, in
+fact the more closely related the rivals, the more
+responsive their pugnacious nature seems to
+become.</p>
+
+<p>To return now to the view that the fighting
+is not really serious, but, on the contrary, that it
+is either vestigial and has no longer any part to
+play in furthering the life of the individual, or
+that it is a by-product of the seasonal sexual
+condition to which no meaning can be attached.
+First, there is the relationship with the territory,
+and this, it seems to me, is a fact of some
+importance; for if the fighting were merely an
+exuberant manifestation of sexual emotion, one
+would expect to find it occurring under all
+conditions, and not merely under one particular
+condition in the life of the bird. The hostility
+is too widespread, however, and too uniform in
+occurrence for us to suppose that it has no root
+in the inherited constitution of the bird; and if
+it served some useful purpose in the past, the
+instinct might still persist, so long as it were not
+harmful. Thus the view that the behaviour is
+vestigial is not perhaps unreasonable. But
+manifestly it makes no difference whether it be
+vestigial or a by-product of sexual emotion,<span class='pagenum'><a name="Page_258" id="Page_258">258</a></span>
+whether the battle be fierce or so trivial as to
+appear to us to be more in the nature of "play,"
+so long as some change in the relative prospects
+of the opponents is the result.</p>
+
+<p>For us, then, the main consideration lies in
+the question: Is the behaviour serviceable
+now in furthering the life of the individual?
+Whether the evidence which we have examined
+affords sufficient ground for the belief that the
+hostility is genuine and has a part to play in the
+whole scheme of reproduction, each must judge
+for himself.</p>
+<hr />
+<p><span class='pagenum'><a name="Page_259" id="Page_259">259</a></span></p>
+<h3>CHAPTER VII</h3>
+
+<h4>THE RELATION OF THE TERRITORY TO
+MIGRATION</h4>
+
+
+<p>Coincident in time with the growth of
+appropriate conditions in the environment,
+organic changes take place rendering certain
+instincts susceptible to stimulation; and the
+stimulus being applied, the Warbler leaves the
+country wherein it had passed the winter and
+finds its way back, with apparently little
+difficulty, to the district in which it was reared
+or had previously reared offspring. What is
+the nature of these changes and of the impulse
+which is first brought into functional activity;
+whence comes the stimulus; and what directs
+the bird on its journey&mdash;these are all different
+aspects of one great problem, the problem of
+migration. I do not propose to discuss all these
+various aspects, for indeed I have no suggestions
+to offer which are in the least likely to be
+helpful, but I seek rather to ascertain whether
+the phenomena which we have explored bear
+any relation to the problem as a whole;
+whether, that is to say, the competition for
+territory and all that appertains to it can have<span class='pagenum'><a name="Page_260" id="Page_260">260</a></span>
+supplied the conditions under which, in the
+process of time, this complex and definite mode
+of behaviour has evolved.</p>
+
+<p>We are sometimes told that we must seek
+the origin of migration in the physical changes
+that have occurred in the ancient history of the
+earth&mdash;in glacial conditions which gradually
+forced birds to the south, or in the "stability of
+the water and mobility of the land" which
+brought about a gradual separation of the feeding
+area from the breeding area&mdash;and which
+continued for a sufficient length of time to
+lead to the formation of an instinct, and that
+the instinct persists because it is serviceable
+in promoting the welfare of the race. But
+when we consider the lapse of time, and the
+changes that must have occurred in the character
+of the bird population&mdash;the appearance of new
+forms and the disappearance of the old, the ebb
+and flow of a given species in a given area&mdash;and
+bear in mind that, notwithstanding this, the
+migratory instinct, if not stronger, is assuredly
+no less strong, and the volume of migration, if
+not greater, is assuredly no less; in short, that
+the whole phenomenon is progressive rather
+than retrogressive, we shall find the view that
+the instinct owes its origin to conditions which
+no longer exist, receives but little encouragement.</p>
+
+<p>I doubt not that, throughout the ages,
+geological changes have been an important
+factor in directing or limiting the scope of
+migration, and moreover are so still; just as<span class='pagenum'><a name="Page_261" id="Page_261">261</a></span>
+climatic changes and the relative abundance or
+scarcity of enemies have influenced the course
+of its evolution. These are all contributory
+factors operating in the external environment.
+But there are, besides, internal factors which
+form part of the inherited constitution of the
+bird, and, being passed on from generation to
+generation, afford the conditions under which
+migration is constantly being renewed. It is, I
+believe, in this field of organic change and
+relationship that the conditions of origin must
+be sought.</p>
+
+<p>Just as the moth in passing from the rudimentary
+to the perfect condition runs through a
+series of changes, each one of which is marked
+by a typical behaviour response adjusted to
+meet some particular circumstance in the
+external environment, so the annual history of a
+bird displays an ordered routine, each phase of
+which can be observed to correspond with one of
+the successive changes in the environment. In
+almost every direction, we find that this routine
+is characterised, in broad outline, by great
+uniformity; so much so that, providing we
+know the history of one species, we can forecast
+with no small degree of certainty the general
+course of behaviour of other members of the
+family. But only the <i>general</i> course. There is
+endless variation in just the particular way in
+which the behaviour is adapted to meet the
+needs of particular species&mdash;the major details
+may be said to be specific, the minor details
+varietal.</p>
+
+<p><span class='pagenum'><a name="Page_262" id="Page_262">262</a></span>Now it is that part of the behaviour routine
+which has reference to the relationship between
+one bird and another upon which, for the time
+being, I wish to dwell; for the interest that
+A displays in B is by no means always the
+same&mdash;it changes according to the season, and
+this change can be observed to be uniform
+throughout a wide range of species.</p>
+
+<p>In winter, in whatsoever direction we turn,
+we observe not only that different individuals
+but that different species also collect together
+in flocks. And since food at that season is not
+always easy to obtain, and, moreover, is only to
+be found in certain situations, which are limited
+both in number and extent, it would seem that
+such assemblages are in the main determined
+by accident. No doubt the abundance or the
+scarcity of food does determine the movements
+of birds, and hence to that extent may be held
+to account for the flocks. But we shall but
+deceive ourselves if we think that it is the sole
+or even the principal reason, or that the situation
+is in no wise affected by internal factors. The
+behaviour of the individual in relation to the
+flock bears ample testimony to the presence of
+a gregarious impulse which derives satisfaction
+from the fact of close association.</p>
+
+<p>As an illustration, let us take a bird whose
+movements are easily watched, and in whose
+hereditary constitution the impulse to which I
+allude seems to be strongly implanted&mdash;the
+Curlew. When the breeding season is over,
+Curlew leave the mountain and the moor and<span class='pagenum'><a name="Page_263" id="Page_263">263</a></span>
+return to the coast or tidal estuaries for the
+remainder of the year. Here, at low water, they
+find an abundant supply of food&mdash;crustaceans
+amongst the sea-weed upon the rocks, and lobworms
+(<i>Arenicola piscatorum</i>) in the mud as the
+tide advances or recedes. But when the tide is
+full, they retire to those parts of the shore that
+remain uncovered&mdash;to isolated rocks, or to sand-dunes,
+or it may even be to pasture-land in the
+neighbourhood. During this period of repose
+large numbers of individuals gather together on
+a comparatively small space of ground. They
+are not constrained to do so by any shortage of
+accommodation, nor by any question relative to
+food, nor, for the matter of that, by any circumstance
+in the external environment; they are
+brought together solely, this at least is the
+impression that one gains, by some inherited
+impulse working towards that end. And their
+subsequent course of behaviour tends to confirm
+that impression. For if we watch the gathering
+together of the different units of which the flock
+is composed, and study more particularly the
+emotional manifestation which accompanies their
+arrival and departure, we shall find that the
+coming of a companion arouses some emotion
+which is expressed by a vocal outburst that
+sweeps through the flock.</p>
+
+<p>Now each call, and the Curlew has a great
+variety, is not only peculiar, generally speaking,
+to certain occasions, but is accompanied by a
+specific type of behaviour, whence we can infer
+in broad outline the type of emotion which is<span class='pagenum'><a name="Page_264" id="Page_264">264</a></span>
+aroused. Thus we come to recognise fear, anger,
+or sexual emotion, by just the particular sound
+which is emitted. But even if we are going
+too far in referring particular calls to particular
+emotions, we can, without a doubt, divide them
+into two broad categories&mdash;those which are
+pleasurable and those which are the reverse.
+And we need have no hesitation in placing the
+particular call to which I allude in the first of
+these two categories, not only on account of the
+nature of the sound produced, but because the
+activities which are aroused are not such as
+normally accompany irritation. This is well
+seen if the behaviour of different individuals
+be closely observed. After resting on one leg
+for some time, first one and then another is
+seized with cramp, and running a few yards
+in an ungainly way, bumps up against its companions
+as if it had not full control over its
+movements. Its behaviour produces irritation
+which is expressed by a vocal outburst, and
+followed by actions the meaning of which is
+clear. Moreover, the call is taken up by
+other individuals and sweeps over part of the
+flock as does the greeting. But the nature of
+the cry is entirely different from that which
+greets the arrival of a companion&mdash;humanly
+speaking it is a passionate and impatient utterance,
+the height of displeasure. The arrival,
+then, acts as a stimulus to something in the
+inherited constitution which is expressed in, and
+presumably is satisfied by, this vocal outburst;
+and, since the bird that arrives joins also in the<span class='pagenum'><a name="Page_265" id="Page_265">265</a></span>
+chorus, there is reason to think that the impulse
+which determines its movements is similar to
+that which is temporarily aroused in the flock.</p>
+
+<p>Apart, however, from the evidence derived
+from the affective aspect of the operation of the
+instinct, the general course of behaviour lends
+support to the view that the assemblies are
+determined by internal factors, and are not
+merely the outcome of circumstances in the
+external environment. Observe, for example,
+the manner in which the flock is built up.
+Single individuals are content to rest alone so
+long as no assembly is in sight, but they are
+drawn towards their companions directly the
+opportunity arises, just as surely as the smaller
+aggregation is drawn towards the flock; and so,
+as the flock increases, it gradually absorbs all
+the lesser flocks and smaller parties, for the
+greater the flock the greater the attraction
+seems to be; and different individuals appear
+to gain some satisfaction from being in close
+bodily contact with one another.</p>
+
+<p>When the Curlew flies to that part of the
+mud-flat which is first exposed by the receding
+tide, and there associates with others, it does
+not then do so because it has any interest in its
+fellows, nor because they serve as an attraction,
+but because it is constrained by hunger&mdash;in
+other words, the association is determined by
+accident. But when, during periods of repose,
+it sees a flock, flies to it, and takes up a position
+in the midst of it, it does so not because suitable
+accommodation is lacking&mdash;not therefore because<span class='pagenum'><a name="Page_266" id="Page_266">266</a></span>
+of external constraint&mdash;but because it derives
+some pleasure from satisfying something in its
+organic complex. We speak of this behaviour
+and of the emotion which characterises it as the
+<i>gregarious instinct</i>: by which we mean that the
+inherited nature of the Curlew, as a tribe, is so
+constituted that, given the appropriate internal
+conditions and adequate external stimulation,
+every individual will respond in a similar manner&mdash;that
+is, the behaviour is primarily determined
+by racial preparation. This is what we mean
+by the <i>gregarious instinct</i> biologically considered.
+We may resolve our own experience in relation
+to the crowd into its simplest constituents,
+project our own primitive feelings into the
+Curlew, and say that the bird feels uneasiness
+in isolation and satisfaction in being one of the
+flock. But in truth we know nothing, save by
+analogy, of the correlated psychical state. All
+the knowledge we possess is derived from a
+study of the objective aspect of the behaviour,
+which in simple terms may be expressed thus:
+the individual is drawn towards its companions;
+there is a relation between the size of the flock
+and the strength of the attraction; and all
+Curlew behave similarly under similar circumstances.</p>
+
+<p>This instinct controls the movements of
+many birds from early autumn to the commencement
+of the breeding season. And so
+powerful is the control that the individual is
+suppressed and its activities subordinated to the
+welfare of the community as a whole. Flocks<span class='pagenum'><a name="Page_267" id="Page_267">267</a></span>
+of Waders roam about the tidal estuaries in
+search of food, and different kinds of Gulls
+assemble there and preen their feathers or sleep;
+Warblers alter their mode of life, and in the
+osier bed, or amongst the elders, seek their food
+together in peace; Finches, Buntings, Pipits,
+and Wagtails, though food is everywhere
+abundant, gather themselves together respectively
+into bands which, as winter approaches,
+grow into flocks and even into composite flocks;
+and as the Warblers leave for the south, so their
+places are filled by flocks of Thrushes and
+Finches from the north. In whatever direction
+we turn, when the days begin to shorten, it is
+the community, not the individual, that thrusts
+itself upon our attention; and throughout the
+winter continues to be the outstanding feature
+of bird life.</p>
+
+<p>With the approach of the breeding season
+we witness that remarkable change which I have
+endeavoured to make clear in the previous
+chapters&mdash;the disintegration of the flock and
+the reinstatement of the individual. Instead
+of continuing with the flock, the individual now
+goes forth to seek the appropriate breeding
+ground; and having arrived there, is not only
+content to remain in isolation, but so behaves
+that isolation is insured. Intolerant of the
+approach of a stranger, intolerant even of the
+approach of the very members of the community
+whose companionship was previously welcomed,
+it not only fights to maintain the position it has
+selected, but fights indeed for the possession of<span class='pagenum'><a name="Page_268" id="Page_268">268</a></span>
+ground already occupied, and, until reproduction
+is completed, asserts its individuality and exercises
+dominion over its territory. What, then,
+is the prospective value, biologically considered,
+of the changing interest that A displays in B,
+and to what will such changes lead? These are
+the questions to which we will now direct
+inquiry.</p>
+
+<p>The annual life-history of a bird is in broad
+outline conditioned by two powerful and at first
+sight opposing impulses&mdash;the one to live in
+society, the other to live solitary. But, manifestly,
+a bird cannot be governed by opposing
+impulses. It has but one character, within
+which, according to the season and the circumstances,
+different impulses predominate. But
+these impulses, no matter how different they
+may appear to be, have their respective parts to
+play in furthering the life of the individual.
+Hence they cannot oppose, though they may
+conflict, if the resultant behaviour contributes
+towards survival.</p>
+
+<p>The majority of birds live to-day in constant
+danger from predatory species, and that this
+danger was still greater in bygone ages there
+can be but little doubt. A curious mode of
+behaviour of the Curlew, Whimbrel, and Godwit
+demonstrates this, for it must be the outcome
+of the necessity for constant watchfulness.
+Whilst resting with its head turned back and
+its beak buried in the feathers of the mantle,
+the bird constantly moves the axis of its body,
+so that an observer, if placed in a direct line<span class='pagenum'><a name="Page_269" id="Page_269">269</a></span>
+behind it, sees at one moment the right eye
+and at another the left. No movement of the
+feet or of the legs is perceptible, and the shifting
+of the body continues whether the eyes are
+open or closed. This body movement enables
+the bird to survey a much larger area of ground
+than it would otherwise be capable of doing,
+and thus adds to its security. As far as my
+experience goes, the movement is less evident
+amongst the members of a flock than when
+an individual is resting alone, or even with a
+few companions, which may be due to the fact
+that since some members are always awake
+and watchful, a bird of prey would have more
+difficulty in approaching a flock unawares than
+it would have in approaching a single individual.
+With the greatest ease a Sparrow-Hawk can
+pick up a Thrush as it feeds on the meadow
+by itself, but if it attempts to seize one of a
+flock, the chances are that its approach is
+signalled and that its prey escapes. And not
+only do the different members give warning
+one to another of the approach of danger,
+but they also combine to harass or even to
+drive away an enemy. So that there can be
+no doubt that the gregarious instinct is serviceable
+in promoting the welfare of the race, and
+has, as its end, the preservation of the individual
+in order that it may take its share at the
+appropriate time in procreating its kind.</p>
+
+<p>In winter, then, the individual loses its
+individuality and is subordinated to the welfare
+of the community, whilst in spring it regains<span class='pagenum'><a name="Page_270" id="Page_270">270</a></span>
+its individuality, and all its inherited instincts
+which then come into operation lead to its
+isolation from the flock. The impulse to seek
+isolation is dependent upon internal organic
+conditions which are peculiar to a certain
+season; whereas the gregarious impulse depends
+upon internal organic conditions which inhere
+at all times, though its functioning is inhibited
+by the functioning of the former impulse. The
+evidence which leads to this conclusion is to
+be found in the fact that a male often deserts
+its territory temporarily and joins the flock,
+where it remains at peace with its companions&mdash;an
+aspect of behaviour which we have discussed
+on various occasions. The former impulse becomes
+dominant in the spring owing to its
+innately superior strength; the latter becomes
+dominant in the autumn because the organic
+condition which determines the functioning of
+the former then subsides. The impulse to
+seek the appropriate breeding ground and to
+dwell there would seem to be the strongest
+of all the impulses save one&mdash;the sexual.
+When, however, I speak of the sexual, I
+refer to the actual discharge of the sexual
+function, which is the consummation of the
+whole process. But the territory and all that
+appertains to it is part of that process&mdash;the
+search for the breeding ground, the dwelling
+there, and the intolerance of intrusion are but
+different stages, each one of which must
+have an impulse peculiar to it; and since the
+completion of the sexual act can only be<span class='pagenum'><a name="Page_271" id="Page_271">271</a></span>
+successfully accomplished providing that success
+is attained at every stage, the probability is
+that, of the impulses concerned, one is neither
+more powerful nor less powerful than another.</p>
+
+<p>So that we have two impulses operating at
+different seasons and guiding the behaviour
+into widely divergent channels. But though
+the proximate end to which the behaviour is
+directed is apparently different, there are not
+two biological ends in view, but one&mdash;the
+attainment of reproduction; and the changes
+that we witness are not contrary but complementary,
+and their prospective value lies in the
+circumstance that they contribute towards the
+preservation of the race.</p>
+
+<p>If, then, every male is driven by inherited
+impulse to seek the appropriate breeding ground
+each recurring season; if, having arrived there,
+it is driven to seek a position of its own; if,
+in order to secure isolation it is obliged to
+attack other males or to ward off the attacks
+of intruders; if, in short, success can only be
+attained providing that the inherited nature is
+so adjusted that the bird can accomplish all
+that is here demanded&mdash;what will be the general
+result? That the individual will rear its offspring
+in safety and that they will inherit the
+peculiarities of their parents, enabling them,
+in their turn, to procreate their kind; all this
+will certainly follow. We are not concerned,
+however, at the moment, with the direct effect
+upon the individual, but with the consequences
+that will accrue to the species as a whole.</p>
+
+<p><span class='pagenum'><a name="Page_272" id="Page_272">272</a></span>Now certain facts are presented to observation
+which enable us not only to understand the
+nature of the change that is wrought in the
+history of the species, but to foreshadow, with
+no small degree of certainty, the extent of that
+change. I suppose that it has come within the
+experience of most of us to observe, at one time
+or another, the ebb and flow of a given species
+in a given district. Some favourite haunt is
+deserted for a year, or for a term of years, and
+is then revisited; or, if it is always occupied,
+the number of inhabitants fluctuates&mdash;plenty
+of pairs in this season, only a few in that.
+Many intricate relationships, both external and
+internal, contribute towards this state of affairs.
+Fluctuation in a downward direction, or
+temporary extinction, is brought about by
+changes in the physical world, by changes in
+the available supply of food, by the increase
+of enemies, or by adverse climatic conditions;
+whilst fluctuation in an upward direction, though
+due indirectly to a combination of circumstances
+in the external world favourable to the survival
+of large numbers of individuals, is directly
+determined by the impulse to seek isolation.
+As individuals of different species establish
+themselves, and form kingdoms and lesser
+kingdoms, we can watch the gradual quickening
+into life of moorland and forest and we can
+observe the manner in which it all comes to
+pass. Males that for weeks or months have
+lived in society, drifting from locality to locality
+according to the abundance of food or its<span class='pagenum'><a name="Page_273" id="Page_273">273</a></span>
+scarcity, now set forth alone and settle first here
+and then there in search of isolation. Lapwings
+settle in the water meadows, and, finding themselves
+forestalled, pass on in search of other
+ground; Blackbirds arrive in a coppice or in a
+hedgerow and, meeting with opposition, disappear;
+and the Curlew, wandering with no
+fixed abode but apparently with a fixity of
+purpose, searches out the moorland where it can
+find the particular environmental conditions to
+which its inherited nature will respond. In
+fact, wherever we choose to look, we can
+observe in a general way the gradual appropriation
+of breeding ground; and if we fix our
+attention upon particular males, we can watch
+the method by which success or failure is
+achieved.</p>
+
+<p>On more than one occasion I have watched
+the efforts of Reed-Buntings to appropriate
+territories in a marsh that was already inhabited.
+Sometimes their efforts met with success, at
+other times with failure. In the former case,
+the males, whose ground was intruded upon, were
+severally forced to yield part of their holding
+and were thus left in possession of a smaller
+area. The success of the intruder seemed to
+depend upon persistent determination, rather
+than upon superior skill in battle. Recently I
+had an opportunity of observing the intrusion of
+a male Willow-Warbler upon ground already
+occupied. By persistent effort it succeeded in
+appropriating one half of the territory of its
+rival. The intruder occupied some trees on the<span class='pagenum'><a name="Page_274" id="Page_274">274</a></span>
+outskirts of the territory it was invading, and
+used them as a base from which it made
+repeated efforts to enter the ground of its rival.
+These efforts were time after time frustrated.
+No sooner did it leave its base than it was seen
+and intercepted, or else attacked; and no matter
+from which direction it attempted to effect an
+entrance, its efforts, for a time, were all to no
+purpose. The fighting was of a determined
+character, and after each attack the owner of
+the territory showed signs of great excitement,
+and, sitting upright upon a branch, spread and
+waved its wings, which is the specific emotional
+manifestation during the period of sexual
+activity. Eventually the intruding male succeeded
+by persistent effort in appropriating part
+of the occupied ground.</p>
+
+<p>Thus we can actually witness the efforts of
+the individual to isolate itself from members of
+its own kind, and can observe the immediate
+consequences that follow from success or from
+failure. And from these consequences we can
+infer that, within a certain range but in accordance
+with the relative abundance of the species
+that dwell in it, every corner of the available
+breeding ground will be explored and every
+situation that evokes the appropriate response
+will be occupied. Moreover, since the annual
+dispersion is not merely a repetition in this
+season of that which occurred in a previous one,
+a progressive increase in the area occupied will
+follow. Yet, if the majority of species desert
+their breeding ground so soon as reproduction is<span class='pagenum'><a name="Page_275" id="Page_275">275</a></span>
+ended, how can this be? An answer to the
+question will be found in the fact that a bird
+has an innate capacity to return to the neighbourhood
+of its birthplace, or to the place
+wherein it had previously reared offspring&mdash;which
+means that the results of prior process
+persist as the basis and starting-point of
+subsequent process.</p>
+
+<p>Bearing then in mind that the seeming
+peace in bird life around us in the spring is
+but the expression of transitory adjustments in
+the distribution of individuals and of species;
+bearing in mind how widespread is the search for
+isolation each recurring season, how frequently
+the search leads to competition and competition
+to failure, and how failure implies a renewal of
+the search; bearing in mind that situations,
+which appear to be eminently suitable for
+breeding purposes, are passed by year after year
+and remain unoccupied, just because, for reasons
+which have yet to be ascertained, the environment
+fails to supply some condition which is
+essential if the inherited nature of the bird is to
+respond&mdash;can there be any doubt that the
+general result of the functioning of the disposition
+will be expansion; or, since no limit is
+placed upon it from within but only from
+without&mdash;that is, by unfavourable circumstances
+in the external world, that the expansion will
+not merely be in one direction but in every
+direction?</p>
+
+<p>If now, when reproduction is ended, all
+the impulses relating to it die away, and the<span class='pagenum'><a name="Page_276" id="Page_276">276</a></span>
+gregarious instinct again predominates, what are
+the consequences to which this change will
+lead? Just as the consequences which flow
+from the functioning of the former impulse are
+accessible to observation, so likewise can we
+observe the change that is wrought by the latter
+impulse. The process is a gradual one. Less
+and less attention is paid by the individual to
+intruders, more and more is it disposed to pass
+beyond its accustomed limits. Little by little,
+accompanied by its young or without them, as
+the case may be, the bird deserts its territory
+and wanders out into the wilderness. Here it
+associates with others, and finds in them a new
+interest and, I doubt not, a new enjoyment.
+All this we can observe as it takes place. But
+just as there is an innate capacity to seek, in the
+spring, the place where the pleasures of breeding
+had formerly been enjoyed, so we are bound to
+infer the existence in the adult of an innate
+capacity to revisit the former area of association;
+and this capacity will strengthen and confirm the
+gregarious instinct and set the direction of the
+general course of movement.</p>
+
+<p class="tb">We have seen, then, that the interest displayed
+by one bird in another changes with
+the seasons; we have seen that it is so modified
+as to be in useful relation to different environmental
+circumstances; as far as possible we
+have traced out the consequences, and have
+reached the conclusion that the change of
+behaviour must, on the one hand, lead to
+expansion, and on the other, to contraction;<span class='pagenum'><a name="Page_277" id="Page_277">277</a></span>
+and we have seen that this conclusion is in
+accord with the facts of observation&mdash;that is the
+general result of our inquiry into the functioning
+of the two powerful impulses, the impulse
+associated with the disposition to secure a
+territory and the gregarious impulse.</p>
+
+<p>The phenomenon of migration embraces a
+number of separate problems, each one of which
+presents features of great interest and of still
+greater difficulty. On some of these problems
+I do not intend to touch; I seek only to
+ascertain whether the impulses that are concerned
+in the securing of a territory, and in the
+search for society, bear any relation to the
+problem as a whole. I hold that the origin of
+migration is not to be found merely in conditions
+peculiar to a remote past, but that the conditions
+inhere in the organic complex of the bird,
+and are thus handed down from generation to
+generation. Starting with this assumption I
+examined the behaviour which normally accompanies
+the seasonal life-history of the individual,
+and found, in that behaviour, manifestations of
+cyclical change leading to definite biological
+consequences. I now propose to inquire whether
+those consequences are such as might, in the
+course of time, give rise to the seasonal change
+of abode.</p>
+
+<p>We are apt to think of migration in terms of
+the Warbler that enlivens our hedgerows in the
+spring after travelling hundreds of miles from
+the south, or of the Redwing that comes from<span class='pagenum'><a name="Page_278" id="Page_278">278</a></span>
+the far north and seeks its food during the
+winter on the meadows, or perhaps of the
+American Golden Plover that each year covers
+a vast expanse of ocean in its journey from its
+breeding ground. The length of the distance
+strikes the imagination and constrains us to
+focus attention upon the extremes.</p>
+
+<p>But migration is of much wider significance
+than is here represented. I sit beside the River
+Severn in April and watch Swallows, Tree-Pipits,
+and Yellow Wagtails passing in twos
+and threes, in small parties, or it may be in
+small flocks; and I observe that while some
+establish themselves in the neighbourhood,
+others pass on. Or I watch Herring-Gulls
+returning to the breeding station at Bolt Head,
+an endless stream of individuals coming from the
+east as far as eye can reach; following them for
+some miles inland I see them still, first as specks
+upon the horizon, then passing beside me as
+they beat their way slowly against the strong
+south-westerly winds, and finally disappearing
+from view in the direction of the cliffs. Or
+again, I watch Buntings and Finches deserting
+the flock and seeking stations in the marsh, or
+amongst the furze-bushes on the common, or in
+the spinneys. In each case the proximate end
+of the behaviour is alike&mdash;wherein then lies
+the difference? Only in the distance which
+separates the territory from the area in which
+the birds formerly associated. And intermediate
+between the extremes, I doubt not, if we had
+a sufficient body of observations, that we should<span class='pagenum'><a name="Page_279" id="Page_279">279</a></span>
+find numerous gradations, the lesser merging
+step by step into the greater. Is the Swallow
+a migrant and the Herring-Gull not; is the
+Tree-Pipit a migrant and the Bunting not;
+must a bird cross many miles of sea or of
+land before it can be considered a migrant; is
+the length of the distance traversed a criterion of
+migration? Surely not. The distance traversed
+is merely a collateral consequence of the process
+as a whole.</p>
+
+<p>The annual life-history of a bird presents, as
+we have seen, two distinct phases&mdash;the one in
+which the individual dominates the situation,
+the other in which it is subordinated to the
+welfare of the community. Let us take these
+two phases separately and endeavour to see how
+they may have influenced the seasonal movements;
+and first let us take the more important
+of the two, namely that one which is directly
+concerned in the continuance of the race.</p>
+
+<p>In this phase we must consider the three
+factors to which allusion has already been
+made:&mdash;(1) the internal impulse, (2) the innate
+ability to return to the former breeding ground,
+(3) the conditions in the external environment.
+These three work in close relation and, as I shall
+endeavour to show, lead to important results.</p>
+
+<p>(1) If there were nothing in the inherited
+nature beyond an impulse to seek the breeding
+ground, if, that is to say, when the appropriate
+locality were reached, the bird took no further
+interest in the developing situation, the attainment
+of reproduction would become largely a<span class='pagenum'><a name="Page_280" id="Page_280">280</a></span>
+matter of chance. A male in a congested
+district, having no incentive to seek fresh
+ground, would remain inactive until a female
+happened to cross its path and stimulate its
+sexual impulse, when its activity would take
+another form. Hence some districts would be
+over-populated, whilst others would remain
+unexplored. But the system of reproduction
+does not consist merely of a search for the
+breeding ground, and of the discharge of the
+sexual function; it is a much more complex
+business, yet withal more complete. Nothing
+is left to chance; the end is attained step by
+step; and each successive stage marks the
+appearance of some specific factor which contributes
+towards the success of the whole. We
+start with the appropriate organic condition
+under which, when adequate stimulation is
+provided, the disposition to secure a territory
+comes into functional activity. Within the
+field of this disposition we can distinguish
+certain specific impulses. In sequential order
+we have the impulse to seek the breeding
+ground; the appropriate situation which gives
+rise to an impulse to dwell in it; and the act
+of establishment which supplies the condition
+under which the impulse to drive away intruders
+is rendered susceptible to stimulation. Grouping
+these impulses, for the convenience of treatment,
+under one general heading, I speak of
+an impulse to seek isolation. It implies some
+kind of action with some kind of change as
+its correlated effect; and from it there flows<span class='pagenum'><a name="Page_281" id="Page_281">281</a></span>
+a ceaseless energy directed towards a definite
+end which for us, who can perceive its prospective
+value, is isolation in an appropriate environment.
+The emphasis here is on "isolation," for it
+involves competition, and there cannot be competition
+without some change in the relative
+positions occupied by different individuals; so
+that in each recurring season there will be
+not only a re-arrangement of ground formerly
+occupied but an arrangement of ground formerly
+deserted.</p>
+
+<p>(2) That the older birds return to the
+locality wherein they had formerly reared
+offspring, and the younger to the neighbourhood
+of their birthplace, was always deemed
+probable. But in recent years evidence which
+cannot be rebutted has been supplied by the
+marking of birds. This evidence, details of
+which can be found in the summary of results
+published annually by Mr. Witherby in <i>British
+Birds</i>, demonstrates that the adult frequently
+returns not only to the same locality in which
+it formerly bred, but even to the same station;
+that it does so year after year; that this mode
+of behaviour is not peculiar to one sex; and
+that many of the young breed in the locality
+in which they were reared. Such being well-established
+facts, we can infer the existence of
+an innate ability to revisit the place wherein
+the enjoyment of breeding, or of birth, had
+formerly been experienced. Of its nature we
+know little or nothing. It would almost seem
+as if there must be some recollection of past<span class='pagenum'><a name="Page_282" id="Page_282">282</a></span>
+enjoyment, but all that can be definitely asserted
+is&mdash;that past experience somehow becomes
+ingrained in the life of the individual and
+determines present behaviour. What, however,
+is of importance to us at the moment is not the
+<i>ad hoc</i> nature of the bird, but the biological
+consequences to which the behaviour leads.
+For if, on the average, individuals return to
+their former haunts, it follows that the annual
+dispersion will not be merely a repetition in this
+season of that which had occurred in a previous
+one, but that the little added this year will
+become the basis for further additions in the
+next. The innate ability is handed down from
+generation to generation, and, in so far as it
+contributes to success, is fostered and developed
+by selection; and the modifications of behaviour
+to which it leads, since the results of prior
+process in the parent persist as the basis and
+starting-point of subsequent process in the
+offspring may in a sense also be said to be
+handed down.</p>
+
+<p>(3) The conditions in the external world may
+be organic or inorganic. By organic I mean
+the conditions which depend upon the number
+of competitors or enemies by which a bird is
+surrounded. The competitors may include other
+species which require a similar environment; and
+the enemies, species which prey upon it, or
+animals which take its young or its eggs. They
+vary in different seasons, in different districts,
+and in nature and extent&mdash;the success of one
+species leads to the failure of another, and the<span class='pagenum'><a name="Page_283" id="Page_283">283</a></span>
+multiplication of the Jay or of the Magpie
+robs us of many a songster.</p>
+
+<p>By inorganic I refer to the changes in the
+climate and in the surface of the earth. The
+nourishment of the young depends upon a
+regular supply of food, and the supply of food
+depends upon the climate which alters in
+different periods; in one decade the temperature
+falls below, whilst in another it rises above,
+the normal, and, as the insect life fluctuates,
+so there is fluctuation in the bird population.
+The changes in the surface of the earth are
+manifold. Little by little the alder (<i>Alnus
+glutinosa</i>) overspreads the marsh. Young
+shoots spring up here and there, in a few
+years grow into bushes, and in a few more
+years are trees; and the dense masses of rush
+which seemed to choke their growth, yielding
+their position of importance, slowly disappear.
+And where formerly the <i>Orchis latifolia</i>, <i>Orchis
+mascula</i>, and <i>Juncus communis</i> grew in mingled
+confusion, nothing but water, moss, and the
+spreading roots of alder cover the ground.
+As the rush disappears, many birds that for
+generations have inhabited that marsh must
+seek accommodation elsewhere. Ancient breeding
+haunts thus disappear, new ones come into
+being, and even those which appear to be
+permanent are almost imperceptibly changing.</p>
+
+<p>Now the bird inherits a nervous system,
+which works under internal excitation and
+external stimulation. Given the appropriate
+organic condition and adequate stimulation,<span class='pagenum'><a name="Page_284" id="Page_284">284</a></span>
+and the impulse to seek isolation comes into
+functional activity. What the organic condition
+is and how it arises we do not exactly know;
+all we know is that organic changes do take
+place in the breeding season, that these changes
+profoundly modify character, and that they
+correspond with the seasonal growth of the
+sexual organs. And with regard to the question
+of stimulation, we have again to confess to
+much ignorance, although certain facts are presented
+to observation which seem to indicate
+the direction in which the stimulus lies. For
+example, it is well known that abnormal climatic
+conditions influence behaviour; we see migrants
+retracing their flight along the very course they
+travelled a short time previously&mdash;driven headlong
+by the blizzard, that at least is what we
+say. But if the wind, instead of being cold and
+from the north, is warm and from the west, do
+they retrace their flight? I have not found it
+so. And if there be no wind and the temperature
+is low, are they still affected? Again, I
+have not found it so. When, as we commonly
+say, they fly before the storm, some change
+takes place in their organic complex, some new
+impulse receives stimulation or the former one
+lacks it. If, after Lapwings have established
+themselves in their territories, the weather
+becomes exceptionally severe, the birds collect
+together again in flocks and revert to their
+winter routine; and under similar circumstances,
+Buntings fail to sing and temporarily desert
+their territories. In such cases it is clear that<span class='pagenum'><a name="Page_285" id="Page_285">285</a></span>
+the impulse to seek isolation ceases for a time
+to dominate the situation. The inference, therefore,
+is that atmospheric changes bear some
+relation to the functioning of the instinct; but
+whether it be temperature, or humidity, or the
+direction and velocity of the wind, or a combination
+of two or more of these factors that supplies
+the stimulus, we cannot tell.</p>
+
+<p>The appropriate organic condition and the
+stimulus have then still to be determined, and
+we must pursue our inquiry from the point at
+which the impulse comes into functional activity.
+We will take a simple case, and one free from
+complication.</p>
+
+<p>Let us suppose that there is an area bereft
+of bird life, if it can be so imagined, but in
+proximity to other inhabited areas. Into this
+area, whilst in search of isolation, let us imagine
+that a Yellow Bunting finds its way. After the
+manner of its race it establishes a territory and
+occupies, let us say at a low computation, half an
+acre of ground. It then obtains a mate, breeds,
+and rears offspring, two of which we will assume
+are males. Reproduction ended, the birds desert
+the area, and in the following spring, when the
+impulse again asserts itself, parents and offspring
+seek again their former haunts. We now have
+three males, each of which occupies half an acre,
+and each of which rears two offspring&mdash;that is the
+position at the close of the second year. In the
+third year the number will have increased to
+nine and the area occupied to 4&frac12; acres; and so
+on in succeeding years, until by the beginning of<span class='pagenum'><a name="Page_286" id="Page_286">286</a></span>
+the eleventh year, we have 59,048 Yellow
+Buntings occupying 29,524&frac12; acres or 46 square
+miles. This, then, will be the result of the
+operation of the impulse, providing that all the
+individuals survive and that no complications
+supervene.</p>
+
+<p>But of course complications are numerous,
+some of which retard while others accelerate the
+rate of expansion. These complications arise
+from various sources&mdash;in the first place from
+natural enemies which prey upon the birds or
+upon their eggs; in the next place from climate
+which, if it happens to be unfavourable, may
+mean that food is scarce and that only a small
+percentage of the young survive; and lastly
+from rivals&mdash;and by rivals I mean closely related
+forms that require a similar station and similar
+food&mdash;which, by occupying available ground,
+may check expansion, or, by forcing a continuation
+of the search, may widen it.</p>
+
+<p>Now when individuals fail as many do fail
+in their initial attempt to secure territory, the
+activity of the impulse still persists, and there is
+no control over the direction in which the bird
+continues to wander whilst in search of its end.
+Some therefore seek in this direction, others in
+that; some wander inwards into inhabited areas
+and fail to find accommodation, or, according to
+the relative strength of their impulse, perhaps
+succeed and so set free a new competitor,
+others wander outwards into country uninhabited
+by the species. These latter we will
+call "pioneers." They may find accommoda<span class='pagenum'><a name="Page_287" id="Page_287">287</a></span>tion
+within a comparatively short distance of
+their base, or they may come into competition
+with rivals and fail, not necessarily on account
+of any congenital weakness of ability, but
+because being warned by an alien song, they
+may be precluded from coming into contact
+with just the environing conditions which can
+supply the stimulus and allow behaviour to run
+its further course&mdash;and so be obliged to extend
+their search into remoter districts. But it must
+not be overlooked that they will be placed in a
+most advantageous position so far as the attainment
+of reproduction is concerned. In their
+search for territory they will meet with little
+opposition and will be free to select whatsoever
+ground they will; and be free also from
+intrusion by neighbouring males, which is so
+frequent in occurrence and continues for so
+long in congested areas. Moreover, in thinly
+populated districts, the pressure upon the
+available means of support will not be so
+great, neither will natural enemies be so plentiful;
+and since the offspring, guided by prior
+experience, return to the neighbourhood of
+their birthplace, the advantages thus gained
+will be shared by the succeeding generation.
+It follows, then, that the range of a species
+will not always be continuous, will not, that
+is to say, proceed by a series of successive
+steps, but that sometimes in this direction and
+at other times in that, the chain of territories
+will be interrupted and different individuals
+separated by distances of greater or lesser<span class='pagenum'><a name="Page_288" id="Page_288">288</a></span>
+extent. New colonies will thus come into
+being; and as the unlimited increase of the
+population over limited areas gradually reintroduces
+into them the struggle for territory, new
+centres of distribution, where the process will
+repeat itself and from which expansion will
+proceed afresh, will be formed. Hence, though
+it is clearly impossible for the progeny of one
+pair of Yellow Buntings to overspread the whole
+of the 46 square miles, it is by no means impossible
+for the limits of their range to exceed even
+those limits within the eleven years.</p>
+
+<p>To sum up our knowledge regarding this
+phase. Of the organic condition which renders
+the impulse responsive to stimulation we know
+very little; and though certain facts of observation
+seem to indicate the direction in which the
+stimulus is to be found, we must here again
+confess to much ignorance. So far as can be
+seen, however, the impulse to seek isolation
+with its correlative territory, leads to constant
+modification in the breeding range of most
+species. The occupation of the small space of
+ground which each individual requires, the
+extent of which has been gradually adjusted to
+suit the needs of different species, results in
+expansion not only in one direction but in every
+direction, and not only in one season but in every
+season. And if there were no complications in
+the external world this expansion would proceed,
+as we have seen, with astonishing rapidity. But
+complications, some of which are favourable and
+others unfavourable, are numerous, and it is<span class='pagenum'><a name="Page_289" id="Page_289">289</a></span>
+difficult to estimate their importance or to
+indicate their precise effect; the former, however,
+accelerate the rate of expansion, whilst the
+latter retard it. Those individuals that wander
+outwards and seek territory on the outskirts of
+the range we have called "pioneers." They will
+have advantages over others that, wandering
+inwards, seek isolation in congested districts,
+and will succeed where the latter fail; and since
+there is in the young an innate ability to
+return to the district wherein they were reared,
+the advantages so gained may be said to be
+handed on from generation to generation.</p>
+
+<p>Let us now turn to the contra-phase, and
+endeavour to ascertain whether the gregarious
+instinct bears any relation to the seasonal
+desertion of the breeding ground. The conclusion
+at which we have already arrived regarding
+this instinct is that it forms part of the inherited
+nature of most species; that its functioning is
+suppressed when a bird is actually in occupation
+of a territory; and that it is serviceable in promoting
+the welfare of the individual. We
+cannot of course observe the instinct. What
+we observe, when reproduction is ended, is a
+change in the relations of different individuals;
+instead of arousing mutual hostility, they attract
+one another, from which we infer the existence
+of something which determines their conduct,
+and this "something" we speak of as an
+instinct.</p>
+
+<p>To what does this change lead? Let us
+suppose that there is an area inhabited by one<span class='pagenum'><a name="Page_290" id="Page_290">290</a></span>
+species; that the number of inhabitants has
+reached the maximum that the means of
+sustenance will allow; and that the season
+of reproduction is drawing to a close. The
+position will then be as follows. All the
+available breeding ground is divided into territories;
+each territory is occupied by one unit,
+the family, and each individual is able to fend
+for itself; changes both internal and external
+begin to take place, the gregarious instinct
+comes into functional operation, and the supply
+of food diminishes&mdash;that roughly is the position.
+The internal factor operates so that the sight
+of this individual or the call of that, instead of
+evoking hostility as heretofore and keeping
+different units apart, proves now an irresistible
+attraction; so that in place of a number of
+individuals evenly dispersed over the whole of
+this area, a small number of flocks of various
+dimensions are stationed at certain points, which
+points are determined partly by experience,
+partly by the supply of food, and partly by
+accident. This implies for each individual some
+movement in some direction. But since the
+population of this imaginary area has reached
+the maximum, and the supply of food, though
+limited in distribution, is nevertheless plentiful,
+such movements will be irregular and will proceed
+in no definite direction.</p>
+
+<p>Now let us suppose that the breeding range
+extends and that fresh ground is occupied by
+pioneers. When reproduction and the rearing
+of broods are ended and the gregarious instinct<span class='pagenum'><a name="Page_291" id="Page_291">291</a></span>
+becomes dominant, these pioneers, or at least
+some of them, will revisit the area wherein
+formerly they associated with companions.
+Their offspring, however, though they will
+have the inherited impulse and the innate
+tendency, will not have the experience; how
+then will they behave? There can be no doubt
+that some will accompany the older birds, and,
+being led by them, will share the experience of
+a former generation; nor any question that
+others will collect together in the neighbourhood
+of their birthplace and, if their impulse is
+satisfied, will remain there so long as food is to
+be found. Thus the gregarious instinct, working
+in close relation with acquired experience,
+will on the one hand lead to the formation of
+organised movements in certain directions,
+whilst on the other it will lead to the formation
+of new areas of association which will follow in
+the wake of the expansion.</p>
+
+<p>We have assumed, in the imaginary case
+which we have just taken, that the conditions
+in the external world are such as enable the
+birds to endure throughout the year&mdash;in short,
+that there are no complications regarding the
+supply of food. But we must bear in mind
+that so long as conditions are favourable during
+the period of reproduction, which is of short
+duration, the breeding range can continue to
+expand, and that therefore, in the course of
+centuries, regions will come to be occupied
+wherein, owing to alternations of climate or
+physical changes in the surface of the earth,<span class='pagenum'><a name="Page_292" id="Page_292">292</a></span>
+food will be impossible, or at any rate difficult
+to obtain at certain seasons. Hence there will
+come a time when the area of association ceases
+to follow in the wake of the expansion, and
+the breeding area begins to diverge from the
+subsistence area.</p>
+
+<p>How, then, is the gulf between these two
+areas to be bridged? We can of course say
+that those individuals which, in virtue of some
+slight variation of hereditary tendency, return
+to regions where food is plentiful will survive;
+whilst others, less well endowed, will perish.
+We can state the position in some such general
+terms, and doubtless there would be truth in
+the statement, but it does not carry us far;
+we wish to know more of the nature of the
+tendency, and of the manner in which it has
+evolved. Well now, in this new situation
+which arises, two things are apparent&mdash;that
+the struggle for existence becomes a struggle
+for the means of subsistence, and that anything
+in the inherited constitution of the bird which
+can be organised to subserve the biological end
+in view becomes of selection value. So long as
+food can always be procured in the new areas of
+association, the individuals that behave in
+accordance with ancestral routine gain thereby
+no particular advantage; but directly the
+breeding range extends into regions where
+the supply fluctuates, traditional experience
+becomes a factor in survival, and those individuals
+that come under its influence will, on
+the average, be more likely to endure and so<span class='pagenum'><a name="Page_293" id="Page_293">293</a></span>
+to procreate their kind and maintain the
+tradition. Let it once be granted that there
+is an innate capacity to retain in later phases
+of routine the experience gained in earlier
+phases, and it is difficult to see how traditional
+guidance can be refused recognition as a factor
+in the developing situation. But only <i>a</i> factor,
+and by no means the most important one; for
+observation has shown that the young are
+capable of performing the return journey
+without guidance. Something therefore <i>is</i>
+inherited, some impulse which comes into
+functional activity at a specified time, and leads
+the bird to set forth in a given direction.</p>
+
+<p>There are no grounds for supposing that
+the experience of one generation forms any
+part of the hereditary equipment of subsequent
+generations. In what direction then are we to
+look for the congenital factor? What is given
+is an inherited tendency to co-operation and
+mutual help, and an innate capacity to make
+use of the results of experience. The inherited
+tendency, as we have seen, leads on the one
+hand to the formation of new areas of association,
+whilst on the other, since it is the means
+of bringing isolated individuals into contact,
+it leads to experience being handed on from
+generation to generation, which, in its turn,
+results in a certain amount of backward movement
+along the line of expansion. It forms
+part of the hereditary equipment of many
+species, and is serviceable in promoting the
+welfare of the individual. Moreover, there is<span class='pagenum'><a name="Page_294" id="Page_294">294</a></span>
+reason to believe that its origin dates back to
+an early period in the evolution of the higher
+forms of life; and if in the subsequent course
+of evolution it could have been so organised
+as to serve a double purpose, so much the more
+reason would there have been for its survival.
+In what does the instinct consist? Is it merely
+that the sight of this individual or the call of
+that proves at some particular moment an
+irresistible attraction, or does the appropriate
+organic condition give rise, as is generally
+supposed, to some preceding state of uneasiness?
+In the former case, the temporarily isolated
+individual or colony would have but little
+chance of sharing in the benefits which mutual
+association confers upon the associates; in the
+latter, the feeling of discomfort would lead to
+restlessness, and would thus bring the bird into
+touch with the environing circumstances under
+which instinctive behaviour could run its
+further course. So that it is probable that the
+movements of each individual, prior to its
+becoming a unit in the flock, are not accidental
+but are determined in some measure by racial
+preparation.</p>
+
+<p>Now if the fundamental assumption of the
+doctrine of the struggle for existence be true,
+the gregarious instinct will not be quite alike in
+all the members of different broods, nor even in
+each member of the same brood; that is,
+variation will occur in all possible directions.
+And we shall not, I think, exceed the limits of
+probability if we assume that different individuals<span class='pagenum'><a name="Page_295" id="Page_295">295</a></span>
+vary in the persistency with which they strive
+to attain their unknown end, and in the direction
+in which they travel in pursuit of it. So that in
+each generation they will fall into three classes:
+(1) those which are inert, (2) those which
+wander along the line of expansion, (3) those
+which wander in other directions. If then the
+struggle for life at this particular juncture in the
+evolution of the breeding range is a struggle for
+the means of subsistence, the members of these
+three classes will not be in a like satisfactory
+position so far as the competition for food is
+concerned. Those in the first class&mdash;<i>i.e.</i>, those
+in which the activity feelings are weak&mdash;will
+neither gain the benefits which arise from
+mutual help, nor will they have much prospect
+of enduring through the season of scarcity.
+Those in the third class will, it is true, derive
+some assistance one from another, and so be in
+a better position to discover what food may be
+available; but inasmuch as they will remain in
+regions where the climate alternates and the
+supply of food is liable to fall below the
+minimum required, the chances are that a high
+percentage will fail in the struggle for existence.
+We come now to those in the second class, and
+it is upon them that I wish more particularly to
+focus attention. The initial movement in their
+case will be in the direction from which outward
+expansion has all along taken place. Within a
+comparatively short distance they will reach
+districts where the species is plentiful, and here,
+associating with others that have some traditional<span class='pagenum'><a name="Page_296" id="Page_296">296</a></span>
+experience, they will be guided by them and
+will find themselves in regions where food is
+plentiful. Hence in each generation those will
+survive that, owing to some congenital variation
+of their instinct, seek satisfaction for their
+impulse in a direction which brings them under
+the influence of tradition. And though at first
+but slight and not in themselves of survival
+value, such variations, since they coincide with
+modifications of behaviour due to acquired
+experience, will be preserved and in the process
+of time so accumulated as to be capable of
+determining the direction and extent of the
+movement.</p>
+
+<p class="tb">But the young Cuckoo deserts this country
+many weeks after its parents, and there is no
+reason to suppose that it lives in society when
+eventually its destination is reached; and the
+young Falcon passes to the south, and is
+certainly not gregarious&mdash;how then can we
+explain their behaviour in terms of something
+which they show no signs of possessing? I do
+not wish to make light of a difficulty which
+admittedly, at first sight, is a grave objection to
+the view that the gregarious instinct has been
+operative in the manner here claimed for it. It
+must, however, be borne in mind that this
+instinct, though originally developed to serve
+the purpose of mutual protection, supplies the
+material upon which evolution works when the
+extension of the breeding range creates a
+situation requiring readjustment on the part of
+the organism to new conditions of life; and that<span class='pagenum'><a name="Page_297" id="Page_297">297</a></span>
+those variations which can be so modified as to
+be in useful relation to the new environmental
+circumstances are seized upon by natural selection
+and, being transmitted, form the foundation of
+a specific inherited response, no longer dependent
+upon, though operating in close relation with
+the primitive response whence originally it
+sprang. Thus the primordial instinct becomes
+so organised as to serve a secondary purpose,
+that of rendering secure a means of access to
+a certain food supply. In the course of evolution
+species were bound to arise which, owing
+to some peculiar conditions, derived greater
+advantage from living solitary than from living
+in society. Does it then follow, because such
+species manifest no inclination to live in society,
+that the instinct never has played any part in
+their lives? Or because the primary purpose
+has lapsed, does it follow that the secondary
+no longer exists?</p>
+
+<p>Let me recapitulate the principal considerations
+which I have discussed in this chapter.</p>
+
+<p>Though I have been advancing a theory, and
+though I have taken much for granted, yet it
+will, I think, be admitted that both the theory
+and what has been taken for granted rest on
+observational grounds. As our starting-point
+we have a bird whose inherited nature alternates
+according to the season, and in whose nature we
+can distinguish two contra-phases&mdash;the one to
+live in society, the other to live solitary. While
+both have their part to play in furthering the<span class='pagenum'><a name="Page_298" id="Page_298">298</a></span>
+life of the individual, for biological interpretation
+there is only one end, the prospective value of
+which is the continuance of the race. We may
+say that the latter phase is the more important
+of the two because it is directly concerned with
+reproduction. But we shall make a great mistake
+if we attach peculiar importance to one
+phase, or to one mode of behaviour within that
+phase, or to one action within that mode of
+behaviour; for if there is one thing certain it is
+that the whole is an inter-related whole in which
+each part depends for its success upon that
+which precedes it.</p>
+
+<p>In that phase in which the territory is the
+central feature of the situation, the struggle
+for existence is in operation in its acutest form;
+all the congenital and acquired capacities of the
+bird&mdash;pugnacity, song, capacity to utilise in
+later phases the experience gained in prior
+phases, all these are organised to subserve an
+end&mdash;a proximate end&mdash;which in its simplest
+terms may be described as "isolation." Isolation
+is then the first step in the process of reproduction,
+and any individual that fails to make it
+good, fails to procreate its kind. But isolation
+implies separation, and the degree of separation
+varies in different species, from the few square
+feet of cliff required by the Guillemot to the
+few square miles of barren moor over which the
+Peregrine exercises dominion. One species must
+occupy sufficient ground to enable it to secure
+food for its young; another requires sufficient,
+but no more, upon which to deposit its egg; and<span class='pagenum'><a name="Page_299" id="Page_299">299</a></span>
+a third must secure a position for its nest within
+the community. Hence it follows that the
+degree of separation varies with the conditions
+of existence. Since, however, the conditions in
+the external world are constantly changing
+according to the relative abundance or scarcity
+of enemies, the rise or fall of rivals, the physical
+changes in the earth's surface, and the alterations
+of climate, it is clear that isolation can only be
+obtained with difficulty, and that the competition
+for it must be severe. Some individuals
+therefore fail to breed, whilst others, perhaps
+because their impulse is stronger, persevere
+and seek stations elsewhere. What are their
+prospects of finding them? By extending the
+field of their activities, they will wander into
+districts remote from the scene of competition,
+districts where not only food is plentiful but
+where enemies and rivals are scarce; and to
+these pioneers, if to any, success in reproduction
+will most certainly be assured. But not only is
+it they who will benefit; their offspring also,
+when the time comes for them to take their part
+in the maintenance of the race, will share in the
+success of their parents, for even though they
+may not escape competition from individuals of
+closely related forms, they will meet with but
+little from those of their own kind. Now
+species which live throughout the year in the
+vicinity of their territory are comparatively few,
+the majority are obliged to wander in search
+of food so soon as reproduction is ended, and
+their behaviour is determined not only by its<span class='pagenum'><a name="Page_300" id="Page_300">300</a></span>
+abundance or scarcity, but also by the powerful
+gregarious impulse which waxes in proportion
+as the instincts connected with reproduction
+wane. If, then, when the sexual instinct again
+becomes predominant, the experience of the
+former season nowise affects their movements,
+little or no progress will be made in the expansion
+of the range. But just as a certain entrance
+into the bush and pathway through it, when
+once made use of in the process of building,
+becomes so firmly established as to form the
+sole highway to and from the nest, so likewise,
+when the impulse to seek isolation repeats
+itself, the bird is constrained to seek the
+neighbourhood wherein it had experienced the
+enjoyment of breeding or of birth. Thus the
+little that is added one year becomes the basis
+for further additions in the next, and new
+centres of distribution are continually being
+formed from which expansion proceeds anew.</p>
+
+<p>Now as the range gradually extends into
+regions where the climate alternates and food at
+certain seasons is consequently scarce, the
+distance between the customary area of association
+and that of reproduction must perforce
+widen. The question then arises: How will the
+young that have no experience find their way to
+regions wherein they can endure? The forces
+which may have been organised to subserve the
+end in view are three: (1) Acquired experience,
+(2) tradition, (3) the gregarious instinct. The
+pioneer that carries the range a little further
+forward starts from a base where it has associated<span class='pagenum'><a name="Page_301" id="Page_301">301</a></span>
+with companions and found food plentiful; and
+when the impulse to live in society again asserts
+itself, it not only repeats its former experience
+but hands on the habit thus acquired to those of
+the next generation that happen to accompany
+it. Granting, however, that by successive
+increments in the distance traversed, traditional
+guidance may in time accomplish much, it
+cannot account for all the known facts, it
+cannot at any rate explain the fact that in some
+cases the inexperienced offspring finds its way
+to the food area without guidance. Something,
+therefore, <i>is</i> inherited. And my suggestion is
+this: That the gregarious instinct, the ancient
+origin of which we can infer from its manifestation
+in so many and diverse forms of life,
+supplies the material upon which evolution
+works; that variations of the initial impulse, at
+first slight and not in themselves of selection
+value, in so far as they coincide in direction with
+modifications of procedure due to experience or
+tradition, are preserved; and that, in the process
+of time, they are so accumulated as to form
+a specific congenital endowment determining
+a definite mode of behaviour.</p>
+
+<hr />
+
+<h3>FOOTNOTES:</h3>
+
+<div class="footnote"><p><a name="Footnote_1_1" id="Footnote_1_1"></a><a href="#FNanchor_1_1"><span class="label">1</span></a> June 1915, R. M. Barrington.</p></div>
+
+<div class="footnote"><p><a name="Footnote_2_2" id="Footnote_2_2"></a><a href="#FNanchor_2_2"><span class="label">2</span></a> <i>Dictionary of Birds</i>, p. 556.</p></div>
+
+<div class="footnote"><p><a name="Footnote_3_3" id="Footnote_3_3"></a><a href="#FNanchor_3_3"><span class="label">3</span></a> <i>Social Psychology.</i></p></div>
+
+<div class="footnote"><p><a name="Footnote_4_4" id="Footnote_4_4"></a><a href="#FNanchor_4_4"><span class="label">4</span></a> <i>Manual of Psychology.</i></p></div>
+
+<div class="footnote"><p><a name="Footnote_5_5" id="Footnote_5_5"></a><a href="#FNanchor_5_5"><span class="label">5</span></a> <i>Ibis</i>, April 1918.</p></div>
+
+<div class="footnote"><p><a name="Footnote_6_6" id="Footnote_6_6"></a><a href="#FNanchor_6_6"><span class="label">6</span></a> <i>Zoologist</i>, 1912, p. 327.</p></div>
+
+<hr />
+<p><span class='pagenum'><a name="Page_302" id="Page_302">302</a></span></p>
+
+<h3>INDEX<br /><br /></h3>
+<ul class="IX"><li>
+Acquired experience, <a href="#Page_300">300</a>
+</li><li>
+Adjustments, transitory, of distribution, <a href="#Page_275">275</a>
+</li><li>
+Alarm notes, <a href="#Page_119">119</a>
+</li><li>
+Arrival, advantages and disadvantages of late, <a href="#Page_33">33</a>-44
+</li><li>
+Assemblies in winter, <a href="#Page_262">262</a>, <a href="#Page_263">263</a>
+</li><li>
+Assembly grounds, <a href="#Page_173">173</a>
+</li><li>
+Attainment of reproduction, <a href="#Page_171">171</a>
+</li><li>&nbsp;
+</li><li>
+<span class="smcap">Barrington, R. M.</span>, on the sex of migrants, <a href="#Page_25">25</a>
+</li><li>
+Battle between two male Cuckoos, <a href="#Page_82">82</a>
+</li><li>
+&mdash;&mdash; between two Moor-Hens, <a href="#Page_86">86</a>, <a href="#Page_92">92</a>, <a href="#Page_93">93</a>, <a href="#Page_94">94</a>
+</li><li>
+&mdash;&mdash; &mdash;&mdash; Pied Wagtails, <a href="#Page_86">86</a>
+</li><li>
+&mdash;&mdash; &mdash;&mdash; Raven and Buzzard, <a href="#Page_217">217</a>
+</li><li>
+&mdash;&mdash; &mdash;&mdash; Raven and Peregrine, <a href="#Page_216">216</a>
+<span style="margin-left: 1em;">law of, <a href="#Page_13">13</a>,19</span>
+</li><li>
+Behaviour routine, <a href="#Page_262">262</a>
+</li><li>
+&mdash;&mdash; sexual, <a href="#Page_3">3</a>
+</li><li>
+Bickerings, <a href="#Page_96">96</a>
+</li><li>
+Birthplace, return to, <a href="#Page_43">43</a>, <a href="#Page_50">50</a>
+</li><li>
+Blackbird, <a href="#Page_87">87</a>, <a href="#Page_182">182</a>, <a href="#Page_222">222</a>, <a href="#Page_244">244</a>
+</li><li>
+Blackcap, <a href="#Page_81">81</a>, <a href="#Page_156">156</a>, <a href="#Page_224">224</a>, <a href="#Page_230">230</a>
+</li><li>
+Black Grouse, <a href="#Page_63">63</a>
+</li><li>
+Black-tailed Godwit, <a href="#Page_53">53</a>
+</li><li>
+Boundaries, <a href="#Page_1">1</a>, <a href="#Page_5">5</a>
+</li><li>
+&mdash;&mdash; conflicts for retention of, <a href="#Page_7">7</a>, <a href="#Page_62">62</a>
+</li><li>
+&mdash;&mdash; disputes as to, <a href="#Page_1">1</a>
+</li><li>
+Brambling, <a href="#Page_124">124</a>
+</li><li>
+Breeding ground, search for appropriate, <a href="#Page_270">270</a>, <a href="#Page_271">271</a>
+</li><li>
+&mdash;&mdash; range, extension of, <a href="#Page_291">291</a>-92
+</li><li>
+&mdash;&mdash; site, acquirement of, <a href="#Page_3">3</a>
+</li><li>
+&mdash;&mdash; stations, evolution of, <a href="#Page_15">15</a>-19
+</li><li>
+&mdash;&mdash; &mdash;&mdash; repeatedly visited long before nesting-time, <a href="#Page_64">64</a>
+</li><li>
+&mdash;&mdash; territory, <a href="#Page_2">2</a>, <a href="#Page_3">3</a>, <a href="#Page_7">7</a>
+</li><li>
+&mdash;&mdash; &mdash;&mdash; evolution of, <a href="#Page_18">18</a>
+</li><li>
+&mdash;&mdash; &mdash;&mdash; foundation of, <a href="#Page_7">7</a>
+</li><li>
+&mdash;&mdash; &mdash;&mdash; innate capacity to return to former, <a href="#Page_279">279</a>-81
+</li><li>
+Bridled Guillemot, <a href="#Page_64">64</a>
+</li><li>
+Brooding, <a href="#Page_180">180</a>
+</li><li>
+&mdash;&mdash; impulse, <a href="#Page_191">191</a>
+</li><li>
+Bunting, Cirl, <a href="#Page_28">28</a>, <a href="#Page_140">140</a>
+</li><li>
+&mdash;&mdash; Corn, <a href="#Page_28">28</a>
+</li><li>
+&mdash;&mdash; Reed, <a href="#Page_28">28</a>, <a href="#Page_68">68</a>, <a href="#Page_69">69</a>, <a href="#Page_85">85</a>, <a href="#Page_104">104</a>, <a href="#Page_132">132</a>, <a href="#Page_158">158</a>, <a href="#Page_160">160</a>, <a href="#Page_244">244</a>
+</li><li>
+&mdash;&mdash; Yellow, <a href="#Page_28">28</a>, <a href="#Page_30">30</a>, <a href="#Page_47">47</a>, <a href="#Page_64">64</a>, <a href="#Page_140">140</a>, <a href="#Page_159">159</a>, <a href="#Page_162">162</a>, <a href="#Page_183">183</a>, <a href="#Page_187">187</a>, <a href="#Page_188">188</a>, <a href="#Page_189">189</a>, <a href="#Page_235">235</a>, <a href="#Page_236">236</a>,
+<a href="#Page_286">286</a>
+</li><li>
+Buzzard, <a href="#Page_217">217</a>
+</li><li>&nbsp;
+</li><li>
+<span class="smcap">Capacity,</span> innate, to return to former breeding territory, <a href="#Page_279">279</a>-81
+</li><li>
+Carrion Crow, <a href="#Page_226">226</a>
+</li><li>
+Chaffinch, <a href="#Page_28">28</a>, <a href="#Page_31">31</a>, <a href="#Page_32">32</a>, <a href="#Page_33">33</a>, <a href="#Page_45">45</a>, <a href="#Page_87">87</a>, <a href="#Page_103">103</a>, <a href="#Page_156">156</a>, <a href="#Page_159">159</a>, <a href="#Page_235">235</a>, <a href="#Page_236">236</a>, <a href="#Page_244">244</a>
+</li><li>
+&mdash;&mdash; Donegal, <a href="#Page_160">160</a>
+<span class='pagenum'><a name="Page_303" id="Page_303">303</a></span>
+Change of breeding quarters owing to unsuitableness, <a href="#Page_50">50</a>
+</li><li>
+Chiffchaff, <a href="#Page_49">49</a>, <a href="#Page_51">51</a>, <a href="#Page_80">80</a>, <a href="#Page_139">139</a>, <a href="#Page_140">140</a>, <a href="#Page_221">221</a>, <a href="#Page_224">224</a>, <a href="#Page_244">244</a>
+</li><li>
+Cirl Bunting, <a href="#Page_28">28</a>, <a href="#Page_140">140</a>
+</li><li>
+Clarke, W. Eagle, <i>Studies in Bird Migration</i>, <a href="#Page_24">24</a>
+</li><li>
+Cleanliness of nest, <a href="#Page_180">180</a>
+</li><li>
+Cliff-breeding species, <a href="#Page_63">63</a>
+</li><li>
+Climatic changes, alteration of routine, due to, <a href="#Page_284">284</a>
+</li><li>
+&mdash;&mdash; changes, food dependent on, <a href="#Page_283">283</a>
+</li><li>
+&mdash;&mdash; conditions, influence of, <a href="#Page_20">20</a>
+</li><li>
+Communities, <a href="#Page_202">202</a>
+</li><li>
+&mdash;&mdash; birds after breeding-season remain in, <a href="#Page_265">265</a>-67
+</li><li>
+Competition, female, for males, <a href="#Page_13">13</a>
+</li><li>
+Complexity of strife, <a href="#Page_84">84</a>-85
+</li><li>
+Conflicts between males during the mating period, <a href="#Page_74">74</a>, <a href="#Page_86">86</a>
+</li><li>
+&mdash;&mdash; between males during the nesting period, <a href="#Page_87">87</a>
+</li><li>
+&mdash;&mdash; for areas, <a href="#Page_10">10</a>, <a href="#Page_11">11</a>, <a href="#Page_13">13</a>, <a href="#Page_62">62</a>
+</li><li>
+&mdash;&mdash; of Ruff, <a href="#Page_54">54</a>
+</li><li>
+&mdash;&mdash; sexual, <a href="#Page_10">10</a>
+</li><li>
+Congenital disposition, <a href="#Page_135">135</a>
+</li><li>
+Contests between males for possession of females, <a href="#Page_80">80</a>
+</li><li>
+Coot, <a href="#Page_61">61</a>
+</li><li>
+Corn-Bunting, <a href="#Page_28">28</a>
+</li><li>
+Corncrake, <a href="#Page_39">39</a>
+</li><li>
+Crow, Carrion, <a href="#Page_226">226</a>, <a href="#Page_227">227</a>
+</li><li>
+Crow, Hooded, <a href="#Page_202">202</a>
+</li><li>
+Cuckoo, <a href="#Page_52">52</a>, <a href="#Page_82">82</a>, <a href="#Page_144">144</a>, <a href="#Page_296">296</a>
+</li><li>
+&mdash;&mdash; restricted breeding area, <a href="#Page_52">52</a>
+</li><li>
+Curlew, <a href="#Page_119">119</a>, <a href="#Page_138">138</a>, <a href="#Page_140">140</a>, <a href="#Page_250">250</a>, <a href="#Page_262">262</a>, <a href="#Page_263">263</a>, <a href="#Page_265">265</a>, <a href="#Page_273">273</a>
+</li><li>&nbsp;
+</li><li>
+<span class="smcap">Danger</span> warnings, <a href="#Page_269">269</a>
+</li><li>
+Darwin, C., <i>Descent of Man</i>, <a href="#Page_35">35</a>
+</li><li>
+&mdash;&mdash; on the arrival of males before females, <a href="#Page_35">35</a>
+</li><li>
+Defence of territory, <a href="#Page_6">6</a>
+</li><li>
+Development, sexual, <a href="#Page_6">6</a>
+</li><li>
+Disposition, congenital, <a href="#Page_135">135</a>
+</li><li>
+&mdash;&mdash; functioning of, <a href="#Page_74">74</a>
+</li><li>
+&mdash;&mdash; inherited, <a href="#Page_5">5</a>
+</li><li>
+&mdash;&mdash; to defend the territory, <a href="#Page_73">73</a>-118
+</li><li>
+&mdash;&mdash; to mate, <a href="#Page_27">27</a>
+</li><li>
+&mdash;&mdash; to remain in a particular place in a particular environment, <a href="#Page_6">6</a>
+</li><li>
+&mdash;&mdash; to secure a territory, <a href="#Page_6">6</a>, <a href="#Page_20">20</a>-72
+</li><li>
+Distribution, adjustment of, <a href="#Page_275">275</a>
+</li><li>
+Dove, Turtle, <a href="#Page_126">126</a>, <a href="#Page_232">232</a>
+</li><li>
+Dunlin, <a href="#Page_250">250</a>
+</li><li>&nbsp;
+</li><li>
+<span class="smcap">Emotional</span> behaviour, <a href="#Page_53">53</a>, <a href="#Page_82">82</a>, <a href="#Page_114">114</a>
+</li><li>
+&mdash;&mdash; manifestation, <a href="#Page_90">90</a>, <a href="#Page_283">283</a>
+</li><li>
+&mdash;&mdash; response, <a href="#Page_26">26</a>
+</li><li>
+Enemies, <a href="#Page_282">282</a>
+</li><li>
+Energy, waste of, <a href="#Page_219">219</a>
+</li><li>
+Environment, <a href="#Page_6">6</a>
+</li><li>
+&mdash;&mdash; and food, <a href="#Page_56">56</a>
+</li><li>
+&mdash;&mdash; changes of, <a href="#Page_283">283</a>
+</li><li>
+&mdash;&mdash; external, conditions in, <a href="#Page_279">279</a>, <a href="#Page_282">282</a>
+</li><li>
+Equipment, hereditary, <a href="#Page_6">6</a>
+</li><li>
+Evolution of breeding stations or territory, <a href="#Page_15">15</a>, <a href="#Page_19">19</a>
+</li><li>
+&mdash;&mdash; of the territory, <a href="#Page_176">176</a>
+</li><li>
+&mdash;&mdash; of the voice, <a href="#Page_163">163</a>
+</li><li>
+Existence, struggle for, <a href="#Page_294">294</a>
+</li><li>
+Experience, acquired, <a href="#Page_300">300</a>
+</li><li>
+Experiments, removal of nests for, <a href="#Page_181">181</a>, <a href="#Page_185">185</a>, <a href="#Page_190">190</a>, <a href="#Page_213">213</a>, <a href="#Page_214">214</a>
+</li><li>
+Exposure, its effect on nestlings, <a href="#Page_180">180</a>
+</li><li>
+External environment, conditions in, <a href="#Page_279">279</a>, <a href="#Page_282">282</a>
+</li><li>&nbsp;
+</li><li>
+<span class="smcap">Falcon,</span> <a href="#Page_48">48</a>, <a href="#Page_71">71</a>
+</li><li>
+Feeding grounds, neutral, 125 in communities, <a href="#Page_70">70</a>
+<span class='pagenum'><a name="Page_304" id="Page_304">304</a></span>
+Females, fighting amongst, <a href="#Page_109">109</a>-118
+</li><li>
+&mdash;&mdash; sexual impulse of, <a href="#Page_13">13</a>
+</li><li>
+Fieldfare, <a href="#Page_124">124</a>
+</li><li>
+Fighting instinct, <a href="#Page_79">79</a>, <a href="#Page_82">82</a>
+</li><li>
+Flight, emotional behaviour of Godwit during, <a href="#Page_53">53</a>
+</li><li>
+Flocks, in winter, birds collect together in, <a href="#Page_262">262</a>
+</li><li>
+Flycatcher, <a href="#Page_244">244</a>
+</li><li>
+Food, procuring of, <a href="#Page_5">5</a>
+</li><li>
+&mdash;&mdash; abundance, or scarcity of, its relation to prosperity of young, <a href="#Page_15">15</a>, <a href="#Page_16">16</a>
+</li><li>
+&mdash;&mdash; its bearing, on the movement of flocks, <a href="#Page_262">262</a>
+</li><li>
+&mdash;&mdash; rearing of young dependent on rapid and regular, <a href="#Page_179">179</a>, <a href="#Page_195">195</a>
+</li><li>
+&mdash;&mdash; supply, proximity to, necessary for rearing young, <a href="#Page_179">179</a>, <a href="#Page_195">195</a>
+</li><li>
+Fortuitous mating, <a href="#Page_174">174</a>
+</li><li>
+Fowler, Ward, on the value of communities, Rooks, <a href="#Page_202">202</a>
+</li><li>
+Fulmar, <a href="#Page_121">121</a>, <a href="#Page_247">247</a>
+</li><li>
+Functional activity, <a href="#Page_259">259</a>
+</li><li>
+&mdash;&mdash; instinct of Reeve, <a href="#Page_173">173</a>
+</li><li>
+Functioning of the disposition, <a href="#Page_275">275</a>
+</li><li>
+&mdash;&mdash; of the primary dispositions, <a href="#Page_100">100</a>
+</li><li>&nbsp;
+</li><li>
+<span class="smcap">Garden</span> Warbler, <a href="#Page_223">223</a>, <a href="#Page_225">225</a>, <a href="#Page_230">230</a>
+</li><li>
+G&auml;tke, H., <i>Birds of Heligoland</i>, <a href="#Page_24">24</a>
+</li><li>
+&mdash;&mdash; on the absence of song in birds on Heligoland, <a href="#Page_124">124</a>
+</li><li>
+&mdash;&mdash; on the early arrival of Guillemots on Heligoland, <a href="#Page_64">64</a>
+</li><li>
+Godwit, emotional behaviour of, during flight, <a href="#Page_53">53</a>
+</li><li>
+&mdash;&mdash; Black-tailed, <a href="#Page_53">53</a>
+</li><li>
+Grasshopper Warbler, <a href="#Page_39">39</a>, <a href="#Page_131">131</a>, <a href="#Page_139">139</a>, <a href="#Page_153">153</a>, <a href="#Page_155">155</a>, <a href="#Page_187">187</a>, <a href="#Page_244">244</a>
+</li><li>
+Greenfinch, <a href="#Page_28">28</a>, <a href="#Page_33">33</a>, <a href="#Page_140">140</a>, <a href="#Page_235">235</a>, <a href="#Page_236">236</a>
+</li><li>
+Gregarious instinct, <a href="#Page_20">20</a>, <a href="#Page_61">61</a>, <a href="#Page_141">141</a>,
+<a href="#Page_265">265</a>-66, <a href="#Page_269">269</a>, <a href="#Page_276">276</a>, <a href="#Page_289">289</a>, <a href="#Page_290">290</a>, <a href="#Page_291">291</a>, <a href="#Page_296">296</a>, <a href="#Page_300">300</a>
+</li><li>
+Grouse, Black, <a href="#Page_63">63</a>
+</li><li>
+Guillemot, Bridled, <a href="#Page_64">64</a>
+</li><li>
+&mdash;&mdash; Common, <a href="#Page_63">63</a>, <a href="#Page_64">64</a>, <a href="#Page_121">121</a>, <a href="#Page_192">192</a>, <a href="#Page_195">195</a>, <a href="#Page_206">206</a>, <a href="#Page_211">211</a>, <a href="#Page_247">247</a>
+</li><li>
+&mdash;&mdash; Ringed, <a href="#Page_64">64</a>
+</li><li>
+Gull, Common, <a href="#Page_119">119</a>
+</li><li>
+&mdash;&mdash; Herring, <a href="#Page_210">210</a>, <a href="#Page_278">278</a>
+</li><li>&nbsp;
+</li><li>
+<span class="smcap">Habit</span> formation, law of, <a href="#Page_8">8</a>, <a href="#Page_62">62</a>, <a href="#Page_65">65</a>, <a href="#Page_66">66</a>, <a href="#Page_67">67</a>, <a href="#Page_205">205</a>
+</li><li>
+Hawfinch, <a href="#Page_28">28</a>
+</li><li>
+Headquarters, <a href="#Page_176">176</a>, <a href="#Page_206">206</a>, <a href="#Page_207">207</a>, <a href="#Page_274">274</a>
+</li><li>
+&mdash;&mdash; restricted, <a href="#Page_8">8</a>, <a href="#Page_9">9</a>, <a href="#Page_30">30</a>, <a href="#Page_50">50</a>, <a href="#Page_58">58</a>, <a href="#Page_64">64</a>, <a href="#Page_127">127</a>
+</li><li>
+Hedge-Sparrow, <a href="#Page_213">213</a>, <a href="#Page_221">221</a>, <a href="#Page_244">244</a>
+</li><li>
+Hereditary equipment, <a href="#Page_6">6</a>
+</li><li>
+Herring-Gull, <a href="#Page_210">210</a>, <a href="#Page_278">278</a>
+</li><li>
+Hooded-Crow, <a href="#Page_202">202</a>
+</li><li>
+Hostility and territory, relationship between, <a href="#Page_242">242</a>
+</li><li>
+House-Sparrow, <a href="#Page_218">218</a>
+</li><li>&nbsp;
+</li><li>
+<span class="smcap">Imitation,</span> vocal, powers of, <a href="#Page_156">156</a>, <a href="#Page_157">157</a>, <a href="#Page_161">161</a>
+</li><li>
+Impulse, internal, <a href="#Page_279">279</a>
+</li><li>
+&mdash;&mdash; to brood, <a href="#Page_191">191</a>
+</li><li>
+Inherited disposition, <a href="#Page_5">5</a>
+</li><li>
+Instinct, fighting, <a href="#Page_79">79</a>-82
+</li><li>
+&mdash;&mdash; gregarious, <a href="#Page_20">20</a>, <a href="#Page_61">61</a>, <a href="#Page_141">141</a>, <a href="#Page_265">265</a>, <a href="#Page_266">266</a>, <a href="#Page_269">269</a>, <a href="#Page_276">276</a>, <a href="#Page_289">289</a>, <a href="#Page_290">290</a>, <a href="#Page_291">291</a>, <a href="#Page_296">296</a>, <a href="#Page_300">300</a>
+</li><li>
+&mdash;&mdash; migratory, <a href="#Page_37">37</a>
+</li><li>
+&mdash;&mdash; of song related to establishment of territory, <a href="#Page_125">125</a>
+</li><li>
+&mdash;&mdash; sexual, reawakening of, <a href="#Page_4">4</a>, <a href="#Page_18">18</a>
+</li><li>
+Instinctive response, <a href="#Page_180">180</a>
+</li><li>
+Instincts susceptible to stimulation, <a href="#Page_259">259</a>
+</li><li>
+Internal impulse, <a href="#Page_279">279</a>
+<span class='pagenum'><a name="Page_305" id="Page_305">305</a></span>
+Internal stimulation, <a href="#Page_62">62</a>, <a href="#Page_123">123</a>
+</li><li>
+Interpretation of battles, <a href="#Page_75">75</a>
+</li><li>
+Intolerance of other birds, <a href="#Page_218">218</a>, <a href="#Page_219">219</a>
+</li><li>
+Intrusion resented, <a href="#Page_274">274</a>
+</li><li>
+Isolation, impulse to seek, <a href="#Page_288">288</a>
+</li><li>
+&mdash;&mdash; of male, <a href="#Page_12">12</a>, <a href="#Page_62">62</a>, <a href="#Page_65">65</a>, <a href="#Page_73">73</a>, <a href="#Page_81">81</a>
+</li><li>
+&mdash;&mdash; of male during breeding season, <a href="#Page_267">267</a>, <a href="#Page_272">272</a>, <a href="#Page_273">273</a>, <a href="#Page_275">275</a>, <a href="#Page_281">281</a>
+</li><li>&nbsp;
+</li><li>
+<span class="smcap">Jay,</span> <a href="#Page_87">87</a>, <a href="#Page_156">156</a>, <a href="#Page_283">283</a>
+</li><li>&nbsp;
+</li><li>
+<span class="smcap">Kestrel,</span> <a href="#Page_228">228</a>
+</li><li>
+Kittiwake, <a href="#Page_116">116</a>, <a href="#Page_200">200</a>, <a href="#Page_247">247</a>
+</li><li>&nbsp;
+</li><li>
+<span class="smcap">Lapwing,</span> <a href="#Page_58">58</a>, <a href="#Page_59">59</a>, <a href="#Page_61">61</a>, <a href="#Page_62">62</a>, <a href="#Page_64">64</a>, <a href="#Page_84">84</a>, <a href="#Page_103">103</a>, <a href="#Page_104">104</a>, <a href="#Page_126">126</a>, <a href="#Page_189">189</a>, <a href="#Page_190">190</a>, <a href="#Page_220">220</a>, <a href="#Page_251">251</a>, <a href="#Page_284">284</a>
+</li><li>
+Lapwing, life-history of, <a href="#Page_58">58</a>-61
+</li><li>
+Late arrival, advantages and disadvantages of, <a href="#Page_33">33</a>-44
+</li><li>
+Law of battle, <a href="#Page_74">74</a>, <a href="#Page_75">75</a>, <a href="#Page_86">86</a>
+</li><li>
+Lesser Whitethroat, <a href="#Page_230">230</a>, <a href="#Page_244">244</a>
+</li><li>
+Linnet, <a href="#Page_156">156</a>
+</li><li>&nbsp;
+</li><li>
+<span class="smcap">M'Dougall,</span> Dr, <i>Social Psychology</i>, <a href="#Page_77">77</a>
+</li><li>
+Magpie, <a href="#Page_219">219</a>, <a href="#Page_283">283</a>
+</li><li>
+Males arrive before advent of females, <a href="#Page_24">24</a>
+</li><li>
+Marsh-Warbler, <a href="#Page_39">39</a>, <a href="#Page_40">40</a>, <a href="#Page_52">52</a>, <a href="#Page_81">81</a>, <a href="#Page_132">132</a>, <a href="#Page_140">140</a>, <a href="#Page_153">153</a>, <a href="#Page_155">155</a>, <a href="#Page_156">156</a>, <a href="#Page_165">165</a>, <a href="#Page_225">225</a>
+</li><li>
+Martin, <a href="#Page_201">201</a>, <a href="#Page_218">218</a>
+</li><li>
+Mating, difficulties of, <a href="#Page_172">172</a>
+</li><li>
+&mdash;&mdash; fortuitous, <a href="#Page_174">174</a>
+</li><li>
+Maximum number supportable in a given locality, <a href="#Page_49">49</a>
+</li><li>
+Meadow-Pipit, <a href="#Page_188">188</a>
+</li><li>
+Meeting places for antics, <a href="#Page_54">54</a>, <a href="#Page_63">63</a>
+</li><li>
+Mental Image, <a href="#Page_77">77</a>
+</li><li>
+Merlin, <a href="#Page_227">227</a>
+</li><li>
+Migration, <a href="#Page_3">3</a>-4
+</li><li>
+&mdash;&mdash; distance no criterion, <a href="#Page_279">279</a>
+</li><li>
+&mdash;&mdash; its relation to territory, <a href="#Page_259">259</a>
+</li><li>
+Migration, origin of, <a href="#Page_260">260</a>, <a href="#Page_277">277</a>
+</li><li>
+&mdash;&mdash; phenomenon of, <a href="#Page_277">277</a>
+</li><li>
+Migratory instinct, <a href="#Page_37">37</a>
+</li><li>
+&mdash;&mdash; species more highly specialised than resident species, <a href="#Page_56">56</a>
+</li><li>
+Missel-Thrush, <a href="#Page_21">21</a>
+</li><li>
+Mobility of the land and stability of the water, <a href="#Page_260">260</a>
+</li><li>
+Moor-hen, <a href="#Page_61">61</a>, <a href="#Page_85">85</a>, <a href="#Page_103">103</a>, <a href="#Page_218">218</a>, <a href="#Page_250">250</a>, <a href="#Page_251">251</a>
+</li><li>
+Morgan, Professor Lloyd, on instinctive behaviour, <a href="#Page_74">74</a>
+</li><li>
+&mdash;&mdash; on emotional behaviour, <a href="#Page_114">114</a>
+</li><li>&nbsp;
+</li><li>
+<span class="smcap">Nest,</span> cleaning of, <a href="#Page_180">180</a>
+</li><li>
+&mdash;&mdash; construction of, <a href="#Page_3">3</a>
+</li><li>
+Nests, removal of, for experiments, <a href="#Page_181">181</a>, <a href="#Page_185">185</a>, <a href="#Page_190">190</a>, <a href="#Page_213">213</a>, <a href="#Page_214">214</a>
+</li><li>
+Neutral feeding grounds, <a href="#Page_62">62</a>, <a href="#Page_125">125</a>
+</li><li>
+&mdash;&mdash; ground, <a href="#Page_98">98</a>
+</li><li>
+Newton, E., on the arrival at breeding stations of males before female, <a href="#Page_24">24</a>, <a href="#Page_35">35</a>
+</li><li>
+Nightingale, <a href="#Page_39">39</a>, <a href="#Page_156">156</a>
+</li><li>
+Notes of alarm, <a href="#Page_119">119</a>
+</li><li>
+&mdash;&mdash; of anger, <a href="#Page_119">119</a>
+</li><li>
+&mdash;&mdash; of recognition, <a href="#Page_139">139</a>
+</li><li>
+&mdash;&mdash; of warning, <a href="#Page_119">119</a>, <a href="#Page_139">139</a>, <a href="#Page_141">141</a>, <a href="#Page_145">145</a>, <a href="#Page_151">151</a>, <a href="#Page_153">153</a>
+</li><li>&nbsp;
+</li><li>
+<span class="smcap">Offspring,</span> rearing of, <a href="#Page_3">3</a>, <a href="#Page_4">4</a>
+</li><li>
+Organic change, sexual, <a href="#Page_92">92</a>, <a href="#Page_123">123</a>
+</li><li>
+&mdash;&mdash; changes, <a href="#Page_65">65</a>
+</li><li>
+&mdash;&mdash; condition of Reeve, <a href="#Page_173">173</a>
+</li><li>
+Owl, Wood, <a href="#Page_156">156</a>
+</li><li>&nbsp;
+</li><li>
+<span class="smcap">Paired</span> for life, <a href="#Page_55">55</a>-56
+</li><li>
+Parental instinctive response, failure of, <a href="#Page_185">185</a>
+</li><li>
+Partridge, <a href="#Page_87">87</a>, <a href="#Page_218">218</a>
+</li><li>
+Persecution, Carrion Crow and Magpie, <a href="#Page_226">226</a>
+<span class='pagenum'><a name="Page_306" id="Page_306">306</a></span>
+Persecution, Carrion Crow and Rook, <a href="#Page_227">227</a>
+</li><li>
+&mdash;&mdash; House Sparrow and Martin, <a href="#Page_218">218</a>
+</li><li>
+&mdash;&mdash; Lapwing and Snipe, <a href="#Page_220">220</a>
+</li><li>
+&mdash;&mdash; Raven and Buzzard, <a href="#Page_217">217</a>
+</li><li>
+&mdash;&mdash; &mdash;&mdash; and Peregrine, <a href="#Page_216">216</a>
+</li><li>
+&mdash;&mdash; Starling and Woodpecker, <a href="#Page_218">218</a>, <a href="#Page_237">237</a>
+</li><li>
+Persistency to remain in territory, <a href="#Page_68">68</a>
+</li><li>
+Pied-Wagtail, <a href="#Page_86">86</a>, <a href="#Page_155">155</a>
+</li><li>
+Pigeon, Wood, <a href="#Page_219">219</a>
+</li><li>
+Pipit, Meadow, <a href="#Page_188">188</a>
+</li><li>
+&mdash;&mdash; Tree, <a href="#Page_51">51</a>, <a href="#Page_188">188</a>, <a href="#Page_189">189</a>, <a href="#Page_222">222</a>, <a href="#Page_244">244</a>, <a href="#Page_278">278</a>
+</li><li>
+Polyandrous females, <a href="#Page_144">144</a>
+</li><li>
+Predatory species, <a href="#Page_268">268</a>
+</li><li>
+Promiscuous pairing of Ruffs, <a href="#Page_172">172</a>
+</li><li>
+Proximity to food-supply necessary for rearing young, <a href="#Page_179">179</a>, <a href="#Page_195">195</a>
+</li><li>
+<i>Psychology, Manual of</i>, <a href="#Page_1">1</a>
+</li><li>
+Puffin, <a href="#Page_63">63</a>, <a href="#Page_116">116</a>, <a href="#Page_200">200</a>
+</li><li>
+Pugnacious instinct, <a href="#Page_87">87</a>-109
+</li><li>
+Pugnacity, <a href="#Page_11">11</a>, <a href="#Page_62">62</a>
+</li><li>
+&mdash;&mdash; of females to obtain mates, <a href="#Page_109">109</a>-118
+</li><li>
+&mdash;&mdash; of males, prior to mating-season, <a href="#Page_77">77</a>-81
+</li><li>
+&mdash;&mdash; of Moor-Hen, <a href="#Page_218">218</a>
+</li><li>&nbsp;
+</li><li>
+<span class="smcap">Racial</span> preparation, <a href="#Page_41">41</a>, <a href="#Page_43">43</a>, <a href="#Page_46">46</a>, <a href="#Page_67">67</a>, <a href="#Page_205">205</a>, <a href="#Page_206">206</a>, <a href="#Page_266">266</a>
+</li><li>
+Rail, Water, <a href="#Page_218">218</a>
+</li><li>
+Raven, <a href="#Page_48">48</a>, <a href="#Page_202">202</a>, <a href="#Page_216">216</a>
+</li><li>
+Razor-bill, <a href="#Page_63">63</a>, <a href="#Page_64">64</a>, <a href="#Page_200">200</a>, <a href="#Page_247">247</a>
+</li><li>
+Readjustment of territory, <a href="#Page_146">146</a>
+</li><li>
+Rearing of offspring, <a href="#Page_3">3</a>, <a href="#Page_4">4</a>
+</li><li>
+Red-backed Shrike, <a href="#Page_39">39</a>, <a href="#Page_50">50</a>, <a href="#Page_51">51</a>, <a href="#Page_156">156</a>
+</li><li>
+Redbreast, <a href="#Page_47">47</a>
+</li><li>
+Redshank, <a href="#Page_139">139</a>
+</li><li>
+Redwing, <a href="#Page_124">124</a>
+</li><li>
+Redstart, <a href="#Page_230">230</a>, <a href="#Page_244">244</a>
+</li><li>
+Reed-Bunting, <a href="#Page_28">28</a>, <a href="#Page_68">68</a>, <a href="#Page_69">69</a>, <a href="#Page_85">85</a>, <a href="#Page_104">104</a>, <a href="#Page_132">132</a>, <a href="#Page_156">156</a>, <a href="#Page_158">158</a>, <a href="#Page_160">160</a>, <a href="#Page_244">244</a>, <a href="#Page_246">246</a>, <a href="#Page_273">273</a>
+</li><li>
+Reed-Warbler, <a href="#Page_49">49</a>, <a href="#Page_51">51</a>, <a href="#Page_68">68</a>, <a href="#Page_81">81</a>, <a href="#Page_132">132</a>, <a href="#Page_140">140</a>, <a href="#Page_152">152</a>, <a href="#Page_153">153</a>, <a href="#Page_211">211</a>, <a href="#Page_225">225</a>
+</li><li>
+Reeve, <a href="#Page_171">171</a>
+</li><li>
+Relation of song to the territory, <a href="#Page_119">119</a>-68
+</li><li>
+&mdash;&mdash; of territory to migration, <a href="#Page_259">259</a>
+</li><li>
+&mdash;&mdash; of territory to the system of reproduction, <a href="#Page_169">169</a>-214
+</li><li>
+Relationship to a territory, <a href="#Page_169">169</a>
+</li><li>
+Reproduction, <a href="#Page_14">14</a>, <a href="#Page_15">15</a>
+</li><li>
+&mdash;&mdash; and territory, <a href="#Page_169">169</a>-214
+</li><li>
+&mdash;&mdash; attainment of, <a href="#Page_2">2</a>, <a href="#Page_6">6</a>, <a href="#Page_37">37</a>
+</li><li>
+&mdash;&mdash; goal of, <a href="#Page_6">6</a>
+</li><li>
+Ringed Guillemot, <a href="#Page_64">64</a>
+</li><li>
+Robbery of territory, <a href="#Page_104">104</a>-107
+</li><li>
+Rock-formation, suitability for Guillemots nesting on, <a href="#Page_196">196</a>
+</li><li>
+Rook, <a href="#Page_202">202</a>, <a href="#Page_227">227</a>
+</li><li>
+Routine behaviour, <a href="#Page_262">262</a>
+</li><li>
+Ruff, <a href="#Page_54">54</a>, <a href="#Page_63">63</a>, <a href="#Page_172">172</a>
+</li><li>
+&mdash;&mdash; meeting places for conflicts, <a href="#Page_54">54</a>
+</li><li>
+Ruffs, promiscuous pairing of, <a href="#Page_172">172</a>
+</li><li>&nbsp;
+</li><li>
+<span class="smcap">Savi's</span> Warbler, <a href="#Page_139">139</a>
+</li><li>
+Sedge-Warbler, <a href="#Page_25">25</a>, <a href="#Page_44">44</a>, <a href="#Page_152">152</a>, <a href="#Page_226">226</a>, <a href="#Page_244">244</a>
+</li><li>
+Selous, E., on the life-history of Ruffs and Reeves, <a href="#Page_172">172</a>
+</li><li>
+&mdash;&mdash; on meeting places for conflicts and antics, <a href="#Page_54">54</a>
+</li><li>
+&mdash;&mdash; on the meeting places of Black Grouse, <a href="#Page_63">63</a>
+</li><li>
+Service, Robert, on flocks of unmated Sedge-Warblers, <a href="#Page_44">44</a>, <a href="#Page_45">45</a>
+</li><li>
+Sexual behaviour, <a href="#Page_3">3</a>
+</li><li>
+&mdash;&mdash; conflicts, <a href="#Page_10">10</a>
+</li><li>
+&mdash;&mdash; development, <a href="#Page_6">6</a>
+</li><li>
+&mdash;&mdash; function, discharge of, <a href="#Page_2">2</a>, <a href="#Page_3">3</a>, <a href="#Page_26">26</a>
+</li><li>
+&mdash;&mdash; impulse of females, <a href="#Page_13">13</a>
+<span class='pagenum'><a name="Page_307" id="Page_307">307</a></span>
+Sexual instinct in the migratory male, <a href="#Page_26">26</a>
+</li><li>
+&mdash;&mdash; of Reeve, <a href="#Page_173">173</a>
+</li><li>
+&mdash;&mdash; &mdash;&mdash; reawakening of, <a href="#Page_4">4</a>, <a href="#Page_18">18</a>
+</li><li>
+&mdash;&mdash; life of birds, <a href="#Page_1">1</a>
+</li><li>
+&mdash;&mdash; maturity, males arrive at, before females, <a href="#Page_36">36</a>
+</li><li>
+&mdash;&mdash; organic change, <a href="#Page_92">92</a>, <a href="#Page_123">123</a>
+</li><li>
+&mdash;&mdash; selection, <a href="#Page_166">166</a>
+</li><li>
+Shag, <a href="#Page_121">121</a>
+</li><li>
+Shrike, Red-backed, <a href="#Page_39">39</a>, <a href="#Page_50">50</a>, <a href="#Page_51">51</a>, <a href="#Page_156">156</a>
+</li><li>
+Skylark, <a href="#Page_188">188</a>, <a href="#Page_236">236</a>, <a href="#Page_244">244</a>
+</li><li>
+Snipe, <a href="#Page_153">153</a>, <a href="#Page_156">156</a>, <a href="#Page_219">219</a>, <a href="#Page_220">220</a>
+</li><li>
+Sociability when not paired, <a href="#Page_125">125</a>, <a href="#Page_126">126</a>
+</li><li>
+Song, as an aid in searching for a mate, <a href="#Page_12">12</a>
+</li><li>
+&mdash;&mdash; its influence on mating, <a href="#Page_167">167</a>
+</li><li>
+&mdash;&mdash; origin of, <a href="#Page_138">138</a>
+</li><li>
+&mdash;&mdash; relation to reproduction, <a href="#Page_123">123</a>
+</li><li>
+&mdash;&mdash; relation to territory, <a href="#Page_119">119</a>-168
+</li><li>
+&mdash;&mdash; volume of, influenced by age, seasonal sexual development, or isolation, <a href="#Page_166">166</a>
+</li><li>
+Song-Thrush, <a href="#Page_222">222</a>, <a href="#Page_244">244</a>
+</li><li>
+Sparrow, House, <a href="#Page_218">218</a>
+</li><li>
+Sparrow-Hawk, <a href="#Page_269">269</a>
+</li><li>
+Spring, at approach of, birds lose their shyness, <a href="#Page_138">138</a>
+</li><li>
+Stability of the water and mobility of the land, <a href="#Page_260">260</a>
+</li><li>
+Starling, <a href="#Page_217">217</a>, <a href="#Page_218">218</a>, <a href="#Page_237">237</a>, <a href="#Page_251">251</a>
+</li><li>
+Stimulation, internal, <a href="#Page_62">62</a>, <a href="#Page_123">123</a>
+</li><li>
+&mdash;&mdash; question of, <a href="#Page_284">284</a>
+</li><li>
+Stonechat, 87 <a href="#Page_187">187</a>, <a href="#Page_188">188</a>, <a href="#Page_189">189</a>, <a href="#Page_222">222</a>, <a href="#Page_233">233</a>, <a href="#Page_234">234</a>
+</li><li>
+Stout, Dr, <i>Manual of Psychology</i>, <a href="#Page_1">1</a>, <a href="#Page_77">77</a>
+</li><li>
+Struggle for existence, <a href="#Page_294">294</a>
+</li><li>
+Susceptibility to position, <a href="#Page_96">96</a>
+</li><li>
+Swallow, <a href="#Page_21">21</a>, <a href="#Page_156">156</a>, <a href="#Page_278">278</a>
+</li><li>&nbsp;
+</li><li>
+<span class="smcap">Territory,</span> <a href="#Page_1">1</a>, <a href="#Page_5">5</a>
+</li><li>
+&mdash;&mdash; adjustment of, <a href="#Page_10">10</a>
+</li><li>
+Territory and reproduction, <a href="#Page_169">169</a>-214
+</li><li>
+&mdash;&mdash; breeding, <a href="#Page_2">2</a>, <a href="#Page_3">3</a>, <a href="#Page_7">7</a>
+</li><li>
+&mdash;&mdash; dates of acquisition of, <a href="#Page_33">33</a>
+</li><li>
+&mdash;&mdash; defence of, <a href="#Page_6">6</a>
+</li><li>
+&mdash;&mdash; desertion of, after rearing young, <a href="#Page_276">276</a>
+</li><li>
+&mdash;&mdash; disposition to defend, <a href="#Page_73">73</a>-118
+</li><li>
+&mdash;&mdash; disposition to secure, <a href="#Page_6">6</a>, <a href="#Page_20">20</a>-72
+</li><li>
+&mdash;&mdash; establishment of, <a href="#Page_74">74</a>, <a href="#Page_285">285</a>
+</li><li>
+&mdash;&mdash; evolution of, <a href="#Page_176">176</a>
+</li><li>
+&mdash;&mdash; failure to secure, <a href="#Page_286">286</a>
+</li><li>
+&mdash;&mdash; fights for, <a href="#Page_10">10</a>, <a href="#Page_11">11</a>, <a href="#Page_13">13</a>, <a href="#Page_62">62</a>
+</li><li>
+&mdash;&mdash; ownership of, <a href="#Page_189">189</a>
+</li><li>
+&mdash;&mdash; possession of, a stimulus to song, <a href="#Page_136">136</a>
+</li><li>
+&mdash;&mdash; its relation to migration, <a href="#Page_259">259</a>
+</li><li>
+&mdash;&mdash; its relation to reproduction, <a href="#Page_169">169</a>-214
+</li><li>
+&mdash;&mdash; readjustment of, <a href="#Page_147">147</a>
+</li><li>
+&mdash;&mdash; restriction of, advantageous for mating, <a href="#Page_172">172</a>
+</li><li>
+&mdash;&mdash; restricted, <a href="#Page_8">8</a>, <a href="#Page_9">9</a>, <a href="#Page_30">30</a>, <a href="#Page_50">50</a>, <a href="#Page_58">58</a>, <a href="#Page_64">64</a>
+</li><li>
+&mdash;&mdash; separate for male and female Cuckoo, <a href="#Page_144">144</a>
+</li><li>
+&mdash;&mdash; song, its relation to the, <a href="#Page_119">119</a>-68
+</li><li>
+&mdash;&mdash; temporary desertion of, <a href="#Page_28">28</a>, <a href="#Page_35">35</a>, <a href="#Page_58">58</a>, <a href="#Page_59">59</a>
+</li><li>
+&mdash;&mdash; and hostility, relationship between, <a href="#Page_242">242</a>
+</li><li>
+Thrush, Song, <a href="#Page_222">222</a>, <a href="#Page_244">244</a>
+</li><li>
+Tit, Blue, <a href="#Page_221">221</a>, <a href="#Page_226">226</a>
+</li><li>
+&mdash;&mdash; Great, <a href="#Page_221">221</a>
+</li><li>
+&mdash;&mdash; Long-tailed, <a href="#Page_226">226</a>
+</li><li>
+Tradition, <a href="#Page_300">300</a>
+</li><li>
+Tree-Pipit, <a href="#Page_51">51</a>, <a href="#Page_188">188</a>, <a href="#Page_189">189</a>, <a href="#Page_222">222</a>, <a href="#Page_232">232</a>, <a href="#Page_244">244</a>, <a href="#Page_278">278</a>
+</li><li>
+Turtle-Dove, <a href="#Page_126">126</a>, <a href="#Page_232">232</a>
+</li><li>&nbsp;
+</li><li>
+<span class="smcap">Union</span> of sexes, <a href="#Page_12">12</a>
+</li><li>
+Ussher, H. B., on the hostility between Choughs and Hooded Crows and Choughs and Ravens, <a href="#Page_227">227</a>
+</li><li>&nbsp;
+<span class='pagenum'><a name="Page_308" id="Page_308">308</a></span>
+</li><li>
+<span class="smcap">Vocal</span> Imitation, <a href="#Page_156">156</a>, <a href="#Page_157">157</a>, <a href="#Page_161">161</a>
+</li><li>
+Voice calls of Curlew, <a href="#Page_263">263</a>
+</li><li>&nbsp;
+</li><li>
+<span class="smcap">Wagtail,</span> Pied, <a href="#Page_86">86</a>, <a href="#Page_155">155</a>
+</li><li>
+&mdash;&mdash; Yellow, <a href="#Page_278">278</a>
+</li><li>
+Wanderings from land, Guillemots, <a href="#Page_193">193</a>
+</li><li>
+Warbler, Garden, <a href="#Page_223">223</a>, <a href="#Page_225">225</a>, <a href="#Page_230">230</a>
+</li><li>
+&mdash;&mdash; Grasshopper, <a href="#Page_39">39</a>, <a href="#Page_131">131</a>, <a href="#Page_139">139</a>, <a href="#Page_155">155</a>, <a href="#Page_187">187</a>, <a href="#Page_244">244</a>
+</li><li>
+&mdash;&mdash; Marsh, <a href="#Page_39">39</a>, <a href="#Page_40">40</a>, <a href="#Page_52">52</a>, <a href="#Page_81">81</a>, <a href="#Page_132">132</a>, <a href="#Page_140">140</a>, <a href="#Page_155">155</a>, <a href="#Page_156">156</a>, <a href="#Page_225">225</a>
+</li><li>
+&mdash;&mdash; Reed, <a href="#Page_49">49</a>, <a href="#Page_51">51</a>, <a href="#Page_68">68</a>, <a href="#Page_81">81</a>, <a href="#Page_132">132</a>, <a href="#Page_140">140</a>, <a href="#Page_152">152</a>, <a href="#Page_153">153</a>, <a href="#Page_211">211</a>, <a href="#Page_225">225</a>
+</li><li>
+&mdash;&mdash; Savi's, <a href="#Page_139">139</a>
+</li><li>
+&mdash;&mdash; Sedge, <a href="#Page_25">25</a>, <a href="#Page_44">44</a>, <a href="#Page_152">152</a>, <a href="#Page_226">226</a>, <a href="#Page_244">244</a>
+</li><li>
+&mdash;&mdash; Willow, <a href="#Page_25">25</a>, <a href="#Page_47">47</a>, <a href="#Page_50">50</a>, <a href="#Page_51">51</a>, <a href="#Page_80">80</a>, <a href="#Page_91">91</a>, <a href="#Page_140">140</a>, <a href="#Page_187">187</a>, <a href="#Page_211">211</a>, <a href="#Page_232">232</a>, <a href="#Page_244">244</a>, <a href="#Page_273">273</a>
+</li><li>
+&mdash;&mdash; Wood, <a href="#Page_50">50</a>, <a href="#Page_51">51</a>, <a href="#Page_132">132</a>, <a href="#Page_221">221</a>
+</li><li>
+Warfare between different species and its relation to the territory, <a href="#Page_215">215</a>-58
+</li><li>
+Warning notes, <a href="#Page_119">119</a>
+</li><li>
+&mdash;&mdash; of danger, <a href="#Page_269">269</a>
+</li><li>
+Water Rail, <a href="#Page_218">218</a>
+</li><li>
+Wheatear, <a href="#Page_25">25</a>, <a href="#Page_51">51</a>
+</li><li>
+Whimbrel, <a href="#Page_140">140</a>
+</li><li>
+Whinchat, <a href="#Page_39">39</a>, <a href="#Page_50">50</a>, <a href="#Page_51">51</a>, <a href="#Page_81">81</a>, <a href="#Page_222">222</a>, <a href="#Page_232">232</a>, <a href="#Page_233">233</a>, <a href="#Page_234">234</a>, <a href="#Page_244">244</a>
+</li><li>
+Whitethroat, <a href="#Page_25">25</a>, <a href="#Page_50">50</a>, <a href="#Page_68">68</a>, <a href="#Page_69">69</a>, <a href="#Page_124">124</a>, <a href="#Page_140">140</a>, <a href="#Page_182">182</a>, <a href="#Page_187">187</a>, <a href="#Page_189">189</a>, <a href="#Page_190">190</a>, <a href="#Page_213">213</a>, <a href="#Page_230">230</a>, <a href="#Page_244">244</a>
+</li><li>
+&mdash;&mdash; Lesser, <a href="#Page_230">230</a>, <a href="#Page_244">244</a>
+</li><li>
+Wild Duck, <a href="#Page_250">250</a>
+</li><li>
+Will, the, to fight, <a href="#Page_102">102</a>
+</li><li>
+Willow-Warbler, <a href="#Page_25">25</a>, <a href="#Page_47">47</a>, <a href="#Page_50">50</a>, <a href="#Page_51">51</a>, <a href="#Page_80">80</a>, <a href="#Page_91">91</a>, <a href="#Page_140">140</a>, <a href="#Page_187">187</a>, <a href="#Page_211">211</a>, <a href="#Page_232">232</a>, <a href="#Page_244">244</a>, <a href="#Page_273">273</a>
+</li><li>
+Winter assemblies, <a href="#Page_262">262</a>-63
+</li><li>
+Witherby, H. F., in <i>British Birds</i>, on the return to former breeding-ground, <a href="#Page_281">281</a>
+</li><li>
+Wood-Owl, <a href="#Page_156">156</a>
+</li><li>
+Wood-Pigeon, <a href="#Page_219">219</a>
+</li><li>
+Wood-Warbler, <a href="#Page_50">50</a>, <a href="#Page_51">51</a>, <a href="#Page_132">132</a>, <a href="#Page_221">221</a>
+</li><li>
+Woodpecker, Lesser Spotted, <a href="#Page_237">237</a>
+</li><li>
+&mdash;&mdash; Great Spotted, <a href="#Page_237">237</a>, <a href="#Page_238">238</a>
+</li><li>
+&mdash;&mdash; Green, <a href="#Page_20">20</a>, <a href="#Page_71">71</a>, <a href="#Page_156">156</a>, <a href="#Page_208">208</a>, <a href="#Page_218">218</a>, <a href="#Page_237">237</a>
+</li><li>
+Wren, <a href="#Page_244">244</a>
+</li><li>&nbsp;
+</li><li>
+<span class="smcap">Yellow</span> Bunting, <a href="#Page_28">28</a>, <a href="#Page_30">30</a>, <a href="#Page_47">47</a>, <a href="#Page_64">64</a>, <a href="#Page_140">140</a>, <a href="#Page_159">159</a>, <a href="#Page_162">162</a>, <a href="#Page_183">183</a>, <a href="#Page_187">187</a>, <a href="#Page_188">188</a>, <a href="#Page_189">189</a>, <a href="#Page_235">235</a>, <a href="#Page_236">236</a>, <a href="#Page_286">286</a>
+</li><li>
+Young die in nest from exposure, <a href="#Page_184">184</a>, <a href="#Page_185">185</a>
+</li></ul>
+
+
+<hr />
+<h3>PRINTED BY OLIVER AND BOYD, EDINBURGH, SCOTLAND</h3>
+
+
+
+
+
+
+
+<pre>
+
+
+
+
+
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+The Project Gutenberg EBook of Territory in Bird Life, by H. Eliot Howard
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: Territory in Bird Life
+
+Author: H. Eliot Howard
+
+Illustrator: G. E. Lodge
+             H. Groenvold
+
+Release Date: April 14, 2010 [EBook #31987]
+
+Language: English
+
+Character set encoding: ASCII
+
+*** START OF THIS PROJECT GUTENBERG EBOOK TERRITORY IN BIRD LIFE ***
+
+
+
+
+Produced by Chris Curnow, Turgut Dincer, Joseph Cooper and
+the Online Distributed Proofreading Team at
+https://www.pgdp.net
+
+
+
+
+
+
+
+  +-------------------------------------------------------+
+  |  TRANSCRIBER'S NOTE:                                  |
+  |                                                       |
+  |  There are a large number of compound words in        |
+  |  this book including bird names which occur joined,   |
+  |  spaced and hyphenated. No attempt has been made to   |
+  |  correct these discrepancies as these are mostly      |
+  |  alternative spellings of the same word. In the case  |
+  |  of bird names it is difficult to decide as           |
+  |  ornithologists are still debating on this subject.   |
+  +-------------------------------------------------------+
+
+
+  TERRITORY IN BIRD LIFE
+
+
+  [Illustration: A pair of Lesser Spotted Woodpeckers attacking a Great
+     Spotted Woodpecker
+
+  Emery Walker ph.sc.]
+
+
+  TERRITORY IN
+  BIRD LIFE
+
+  BY H. ELIOT HOWARD
+
+
+  WITH ILLUSTRATIONS BY
+  G. E. LODGE AND H. GROeNVOLD
+
+
+  NEW YORK
+  E. P. DUTTON AND COMPANY
+  1920
+
+
+
+
+PREFACE
+
+
+When studying the Warblers some twenty years ago, I became aware of the
+fact that each male isolates itself at the commencement of the breeding
+season and exercises dominion over a restricted area of ground. Further
+investigation, pursued with a view to ascertaining the relation of this
+particular mode of behaviour to the system of reproduction, led to my
+studying various species, not only those of close affinity, but those
+widely remote in the tree of avian life. The present work is the outcome
+of those investigations. In it I have endeavoured to interpret the
+prospective value of the behaviour, and to trace out the relationships
+in the organic and inorganic world which have determined its survival.
+Much is mere speculation; much with fuller knowledge may be found to be
+wrong. But I venture to hope that a nucleus will remain upon which a
+more complete territorial system may one day be established.
+
+I have to thank Mr. G. E. Lodge and Mr. H. Groenvold for the trouble they
+have taken in executing my wishes; I also want to record my indebtedness
+to the late E. W. Hopewell; and to Professor Lloyd Morgan, F.R.S., I am
+beholden more than I can tell.
+
+
+
+
+  CONTENTS
+
+                                                        PAGE
+  CHAPTER I
+
+  INTRODUCTION                                             1
+
+
+  CHAPTER II
+
+  THE DISPOSITION TO SECURE A TERRITORY                   20
+
+
+  CHAPTER III
+
+  THE DISPOSITION TO DEFEND THE TERRITORY                 73
+
+
+  CHAPTER IV
+
+  THE RELATION OF SONG TO THE TERRITORY                  119
+
+
+  CHAPTER V
+
+  THE RELATION OF THE TERRITORY TO THE SYSTEM
+    OF REPRODUCTION                                      169
+
+
+  CHAPTER VI
+
+  THE WARFARE BETWEEN DIFFERENT SPECIES AND ITS
+    RELATION TO THE TERRITORY                            216
+
+
+  CHAPTER VII
+
+  THE RELATION OF THE TERRITORY TO MIGRATION             259
+
+
+  INDEX                                                  302
+
+
+
+  LIST OF ILLUSTRATIONS
+
+
+                                                             _Face page_
+
+  A pair of Lesser Spotted Woodpeckers attacking a Great
+      Spotted Woodpecker                                  _Frontispiece_
+
+  Territorial flight of the Black-tailed Godwit                       54
+
+  Competition for territory is seldom more severe than
+      among cliff-breeding seabirds, and the efforts of
+      individual Razorbills to secure positions on the
+      crowded ledges lead to desperate struggles                      64
+
+  Male Blackbirds fighting for the possession of territory.
+      The bare skin on the crown of the defeated bird shows
+      the nature of the injuries from which it succumbed              74
+
+  Male Cuckoos fighting before the arrival of a female                82
+
+  Two pairs of Pied Wagtails fighting in defence of their
+      territories                                                     86
+
+  Long-tailed Tit: males fighting for the possession of
+      territory. The feathers have been torn from the crown
+      of the defeated and dying rival                                 96
+
+  A battle between two pairs of Jays                                 106
+
+  The Female Chaffinch shares in the defence of the territory
+      and attacks other females                                      110
+
+  Peregrine Falcon attacking a Raven                                 216
+
+  A battle between a pair of Green Woodpeckers and a
+      Great Spotted Woodpecker for the possession of a hole
+      in an oak-tree                                                 238
+
+  Plans of the Water-meadow showing the Territories
+      occupied by Lapwings in 1915 and 1916          _Between_ 58 and 59
+
+
+SCIENTIFIC NAMES OF BIRDS MENTIONED IN THE TEXT
+
+  Raven                       _Corvus corax._
+
+  Carrion-Crow                _Corvus corone._
+
+  Hooded Crow                 _Corvus cornix._
+
+  Rook                        _Corvus frugilegus._
+
+  Magpie                      _Pica pica._
+
+  Jay                         _Garrulus glandarius rufitergum._
+
+  Chough                      _Pyrrhocorax pyrrhocorax._
+
+  Starling                    _Sturnus vulgaris._
+
+  Greenfinch                  _Chloris chloris._
+
+  Hawfinch                    _Coccothraustes coccothraustes._
+
+  House-Sparrow               _Passer domesticus._
+
+  Chaffinch                   _Fringilla coelebs._
+
+  Brambling                   _Fringilla montifringilla._
+
+  Linnet                      _Acanthis cannabina._
+
+  Corn-Bunting                _Emberiza calandra._
+
+  Yellow Bunting              _Emberiza citrinella._
+
+  Cirl Bunting                _Emberiza cirlus._
+
+  Reed-Bunting                _Emberiza schoeniclus._
+
+  Sky-Lark                    _Alauda arvensis._
+
+  Pied Wagtail                _Motacilla lugubris._
+
+  Tree-Pipit                  _Anthus trivialis._
+
+  Meadow-Pipit                _Anthus pratensis._
+
+  Great Titmouse              _Parus major newtoni._
+
+  Blue Titmouse               _Parus coeruleus obscurus._
+
+  Long-tailed Titmouse        _AEgithalus caudatus roseus._
+
+  Red-backed Shrike           _Lanius collurio._
+
+  Whitethroat                 _Sylvia communis._
+
+  Lesser Whitethroat          _Sylvia curruca._
+
+  Blackcap                    _Sylvia atricapilla._
+
+  Grasshopper-Warbler         _Locustella noevia._
+
+  Savi's Warbler              _Locustella luscinioides._
+
+  Reed-Warbler                _Acrocephalus scirpaceus._
+
+  Marsh-Warbler               _Acrocephalus palustris._
+
+  Sedge-Warbler               _Acrocephalus schoenobaenus._
+
+  Willow-Warbler              _Phylloscopus trochilus._
+
+  Wood-Warbler                _Phylloscopus sibilatrix._
+
+  Chiffchaff                  _Phylloscopus collybita._
+
+  Song-Thrush                 _Turdus musicus clarkii._
+
+  Redwing                     _Turdus iliacus._
+
+  Blackbird                   _Turdus merula._
+
+  Redstart                    _Phoenicurus phoenicurus._
+
+  Redbreast                   _Erithacus rubecula melophilus._
+
+  Nightingale                 _Luscinia megarhyncha._
+
+  Stonechat                   _Saxicola rubicola._
+
+  Whinchat                    _Saxicola rubetra._
+
+  Wheatear                    _OEnanthe oenanthe._
+
+  Hedge-Sparrow               _Accentor modularis._
+
+  Wren                        _Troglodytes troglodytes._
+
+  Spotted Flycatcher          _Muscicapa striata._
+
+  Swallow                     _Hirundo rustica._
+
+  Martin                      _Delichon urbica._
+
+  Sand-Martin                 _Riparia riparia._
+
+  Great Spotted Woodpecker    _Dryobates major anglicus._
+
+  Lesser Spotted Woodpecker   _Dryobates minor._
+
+  Green Woodpecker            _Picus viridis._
+
+  Cuckoo                      _Cuculus canorus._
+
+  Tawny Owl                   _Strix aluco._
+
+  Buzzard                     _Buteo buteo._
+
+  Sparrow-Hawk                _Accipiter nisus._
+
+  Peregrine Falcon            _Falco peregrinus._
+
+  Merlin                      _Falco aesalon._
+
+  Kestrel                     _Falco tinnunculus._
+
+  Shag                        _Phalacrocorax graculus._
+
+  Wild Duck                   _Anas boschas._
+
+  Snipe                       _Gallinago gallinago._
+
+  Dunlin                      _Tringa alpina._
+
+  Ruff                        _Machetes pugnax._
+
+  Redshank                    _Totanus totanus._
+
+  Black-tailed Godwit         _Limosa limosa._
+
+  Curlew                      _Numenius arquata._
+
+  Whimbrel                    _Numenius phaeopus._
+
+  American Golden Plover      _Charadrius dominicus._
+
+  Lapwing                     _Vanellus vanellus._
+
+  Oyster-Catcher              _Haematopus ostralegus._
+
+  Herring-Gull                _Larus argentatus._
+
+  Kittiwake                   _Rissa tridactyla._
+
+  Razorbill                   _Alca torda._
+
+  Guillemot                   _Uria troille._
+
+  Puffin                      _Fratercula arctica._
+
+  Fulmar                      _Fulmarus glacialis._
+
+  Water-Rail                  _Rallus aquaticus._
+
+  Corn-Crake                  _Crex crex._
+
+  Moor-Hen                    _Gallinula chloropus._
+
+  Coot                        _Fulica atra._
+
+  Wood-Pigeon                 _Columba palumbus._
+
+  Turtle-Dove                 _Streptopelia turtur._
+
+  Partridge                   _Perdix perdix._
+
+  Black Grouse                _Lyrurus tetrix britannicus._
+
+  Red Grouse                  _Lagopus scoticus._
+
+
+
+
+TERRITORY IN BIRD LIFE
+
+
+
+
+CHAPTER I
+
+INTRODUCTION
+
+
+In his _Manual of Psychology_ Dr Stout reminds us that "Human language
+is especially constructed to describe the mental states of human beings,
+and this means that it is especially constructed so as to mislead us
+when we attempt to describe the working of minds that differ in a great
+degree from the human."
+
+The use of the word "territory" in connection with the sexual life of
+birds is open to the danger which we are here asked to guard against,
+and I propose, therefore, before attempting to establish the theory on
+general grounds, to give some explanation of what the word is intended
+to represent and some account of the exact position that representation
+is supposed to occupy in the drama of bird life.
+
+The word is capable of much expansion. There cannot be territories
+without boundaries of some description; there cannot well be boundaries
+without disputes arising as to those boundaries; nor, one would
+imagine, can there be disputes without consciousness as a factor
+entering into the situation; and so on, until by a simple mental
+process we conceive of a state in bird life analogous to that which we
+know to be customary amongst ourselves. Now, although the term "breeding
+territory," when applied to the sexual life of birds, is not altogether
+a happy one, it is difficult to know how otherwise to give expression to
+the facts observed. Let it then be clearly understood that the
+expression "securing a territory" is used to denote a process, or rather
+part of a process, which, in order to insure success to the individual
+in the attainment of reproduction, has been gradually evolved to meet
+the exigencies of diverse circumstances. Regarded thus, we avoid the
+risk of conceiving of the act of securing a territory as a detached
+event in the life of a bird, and avoid, I hope, the risk of a conception
+based upon the meaning of the word when used to describe human as
+opposed to animal procedure.
+
+Success in the attainment of reproduction is rightly considered to be
+the goal towards which many processes in nature are tending. But what is
+meant by success? Is it determined by the actual discharge of the sexual
+function? So many and so wonderful are the contrivances which have
+slowly been evolved to insure this discharge, that it is scarcely
+surprising to find attention focused upon this one aspect of the
+problem. Yet a moment's reflection will show that so limited a
+definition of the term "success" can only be held to apply to certain
+forms of life; for where the young have to be cared for, fostered, and
+protected from molestation for periods of varying lengths, the actual
+discharge of the sexual function marks but one stage in a process which
+can only succeed if all the contributory factors adequately meet the
+essential conditions of the continuance of the species.
+
+Securing a territory is then part of a process which has for its goal
+the successful rearing of offspring. In this process the functioning of
+the primary impulse, the acquirement of a place suitable for breeding
+purposes, the advent of a female, the discharge of the sexual function,
+the construction of the nest, and the rearing of offspring follow one
+another in orderly sequence. But since we know so little of the organic
+changes which determine sexual behaviour, and have no means of
+ascertaining the nature of the impulse which is first aroused, we can
+only deal with the situation from the point at which the internal
+organic changes reflect themselves in the behaviour to a degree which is
+visible to an external observer. That point is reached when large
+numbers of species, forsaking the normal routine of existence to which
+they have been accustomed for some months, suddenly adopt a radical
+change in their mode of behaviour. How is this change made known to us?
+By vast numbers of individuals hurrying from one part of the globe to
+another, from one country to another, and even from mid-ocean to the
+coasts; by detachments travelling from one district to another; by
+isolated individuals deserting this place for that; by all those
+movements, in fact, which the term migration, widely applied, is held to
+denote. Now the impulse which prompts these travelling hosts must be
+similar in kind whether the journey be long or short; and it were
+better, one would think, to regard such movements as a whole than to
+fix the attention on some one particular journey which fills us with
+amazement on account of the magnitude of the distance traversed or the
+nature of the difficulties overcome. For, after all, what does each
+individual seek? There may be some immature birds which, though they
+have not reached the necessary stage of development, happen to fall in
+with others in whom the impulse is strong and are led by them--they know
+not where. But the majority seek neither continent nor country, neither
+district nor locality is their aim, but a place wherein the rearing of
+offspring can be safely accomplished; and the search for this place is
+the earliest visible manifestation in many species of the reawakening of
+the sexual instinct.
+
+The movements of each individual are then directed towards a similar
+goal, namely, the occupation of a definite station; and this involves
+for many species a distinct change in the routine of behaviour to which
+previously they had been accustomed. Observe, for example, one of the
+numerous flocks of Finches that roam about the fields throughout the
+winter. Though it may be composed of large numbers of individuals of
+different kinds, yet the various units form an amicable society actuated
+by one motive--the procuring of food. And since it is to the advantage
+of all that the individual should be subordinated to the welfare of the
+community as a whole there is no dissension, apart from an occasional
+quarrel here and there.
+
+In response, however, to some internal organic change, which occurs
+early in the season, individuality emerges as a factor in the developing
+situation, and one by one the males betake themselves to secluded
+positions, where each one, occupying a limited area, isolates itself
+from companions. Thereafter we no longer find that certain fields are
+tenanted by flocks of greater or less dimensions, while acres of land
+are uninhabited, but we observe that the hedgerows and thickets are
+divided up into so many territories, each one of which contains its
+owner. This procedure, with of course varying detail, is typical of that
+of many species that breed in Western Europe. And since such a radical
+departure from the normal routine of behaviour could scarcely appear
+generation after generation in so many widely divergent forms, and still
+be so uniform in occurrence each returning season, if it were not
+founded upon some congenital basis, it is probable that the journey,
+whether it be the extensive one of the Warbler or the short one of the
+Reed-Bunting, is undertaken in response to some inherited disposition,
+and probable also that the disposition bears some relation to the few
+acres in which the bird ultimately finds a resting place. Whilst for the
+purpose of the theory I shall give expression to this behaviour in terms
+of that theory, and speak of it as a disposition to secure a territory,
+using the word disposition, which has been rendered current in recent
+discussion, for that part of the inherited nature which has been
+organised to subserve a specific biological purpose--strict compliance
+with the rules of psychological analysis requires a simpler definition;
+let us therefore say "disposition to remain in a particular place in a
+particular environment."
+
+But even granting that this disposition forms part of the hereditary
+equipment of the bird, how is the process of reproduction furthered? The
+mere fact of remaining in or about a particular spot cannot render the
+attainment of reproduction any less arduous, and may indeed add to the
+difficulties, for any number of individuals might congregate together
+and mutually affect one another's interests. A second disposition comes,
+however, into functional activity at much the same stage of sexual
+development, and manifests itself in the male's intolerance of other
+individuals. And the two combined open up an avenue through which the
+individual can approach the goal of reproduction. In terms of the theory
+I shall refer to this second disposition as the one which is concerned
+with the defence of the territory.
+
+Broadly speaking, these two dispositions may be regarded as the basis
+upon which the breeding territory is founded. Yet inasmuch as the
+survival value of the dispositions themselves must have depended upon
+the success of the process as a whole, it is manifest that peculiar
+significance must not be attached to just the area occupied, which
+happens to be so susceptible of observation; other contributory factors
+must also receive attention, for the process is but an order of
+relationships in which the various units have each had their share in
+determining the nature and course of subsequent process, so that, as Dr
+Stout says, when they were modified, it was modified.
+
+Now the male inherits a disposition which leads it to remain in a
+restricted area, but the disposition cannot determine the extent of that
+area. How then are the boundaries fixed? That they are sometimes adhered
+to with remarkable precision, that they can only be encroached upon at
+the risk of a conflict--all of this can be observed with little
+difficulty. But if we regard them as so many lines definitely delimiting
+an area of which the bird is cognisant, we place the whole behaviour on
+a different level of mental development, and incidentally alter the
+complexion of the whole process. It would be a mistake, I think, to do
+this. Though conscious intention as a factor may enter the situation,
+there is no necessity for it to do so; there is no necessity, that is to
+say, for the bird to form a mental image of the area to be occupied and
+shape its course accordingly. The same result can be obtained without
+our having recourse to so complex a principle of explanation, and that
+by the law of habit formation. In common with other animals, birds are
+subject to this law in a marked degree. An acquired mode of activity
+becomes by repetition ingrained in the life of the individual, so that
+an action performed to-day is liable to be repeated to-morrow so long as
+it does not prejudice the existence or annul the fertility of the
+individual.
+
+Let us see how this may have operated in determining the limits of the
+area acquired, and for this purpose let us suppose that we are observing
+a male Reed-Bunting recently established in some secluded piece of marsh
+land. Scattered about this particular marsh are a number of small
+willows and young alder trees, each one of which is capable of providing
+plenty of branches suitable for the bird to perch upon, and all are in a
+like favourable position so far as the outlook therefrom is concerned.
+Well, we should expect to find that each respective tree would be made
+use of according to the position in which the bird happened to find
+itself. But what actually do we find--one tree singled out and resorted
+to with ever-increasing certainty until it becomes an important point in
+relation to the occupied area, a headquarters from which the bird
+advertises its presence by song, keeps watch upon the movements of its
+neighbours, and sets out for the purpose of securing food. We then take
+note of its wanderings in the immediate vicinity of the headquarters,
+especially as regards the direction, frequency, and extent of the
+journeys; and we discover not only that these journeys proceed from and
+terminate in the special tree, but that there is a sameness about the
+actual path that is followed. The bird takes a short flight, searches a
+bush here and some rushes there, returns, and after a while repeats the
+performance; we on our part mark the extreme limits reached in each
+direction, and by continued observation discover that these limits are
+seldom exceeded, that definition grows more and more pronounced, and
+that by degrees the movements of the bird are confined within a
+restricted area. In outline, this is what happens in a host of cases. By
+repetition certain performances become stereotyped, certain paths fixed,
+and a routine is thus established which becomes increasingly definite as
+the season advances.
+
+But while it would be quite untrue to say that this routine is never
+departed from, and equally profitless to attempt to find a point beyond
+which the bird will under no circumstances wander, yet there is enough
+definition and more than enough to answer the purpose for which the
+territory has, I believe, been evolved, that is to say the biological
+end of reproduction. Again, however, the process of adjustment is a
+complex one. Habit plays its part in determining the boundaries in a
+rough and ready manner, but the congenital basis, which is to be found
+in the behaviour adapted to a particular environment, is an important
+factor in the situation. For example, if instead of resting content with
+just a bare position sufficient for the purpose of reproduction, the
+Guillemot were to hustle its neighbours from adjoining ledges, the
+Guillemot as a species would probably disappear; or if instead of
+securing an area capable of supplying sufficient food both for itself
+and its young, the Chiffchaff were to confine itself to a single tree,
+and, after the manner of the Guillemot, trust to spasmodic excursions
+into neutral ground for the purpose of obtaining food, the Chiffchaff
+as a species would probably not endure. All such adjustments have,
+however, been brought about by relationships which have gradually become
+interwoven in the tissue of the race.
+
+The intolerance that the male displays towards other individuals,
+usually of the same sex, leads to a vast amount of strife. Nowhere in
+the animal world are conflicts more frequent, more prolonged, and more
+determined than in the sexual life of birds; and though they are
+acknowledged to be an important factor in the life of the individual,
+yet there is much difference of opinion as to the exact position they
+occupy in the drama of bird life. Partly because they frequently happen
+to be in evidence, partly because they are numerically inferior, and
+partly, I suppose, because the competition thus created would be a means
+of maintaining efficiency, the females, by common consent, are supposed
+to supply the condition under which the pugnacious nature of the male is
+rendered susceptible to appropriate stimulation. And so long as the
+evidence seemed to show that battles were confined to the male sex, so
+long were there grounds for hoping that their origin might be traced to
+such competition. But female fights with female, pair with pair, and,
+which is still more remarkable, a pair will attack a single male or a
+single female; moreover, males that reach their destination in advance
+of their prospective mates engage in serious warfare. How then is it
+possible to look upon the individuals of one sex as directly
+responsible for the strife amongst those of the other, or how can the
+female supply the necessary condition? As long as an attempt is made to
+explain it in terms of the female, the fighting will appear to be of a
+confused order; regard it, however, as part of a larger process which
+demands, amongst other essential conditions of the breeding situation,
+the occupation of a definite territory, and order will reign in place of
+confusion.
+
+But even supposing that the male inherits a disposition to acquire a
+suitable area, even supposing that it inherits a disposition which
+results indirectly in the defence of that area, how does it obtain a
+mate? If the female behaved in a like manner, if she, too, were to
+isolate herself and remain in one place definitely, that would only add
+to the difficulties of mutual discovery. We find, however, in the
+migrants, that the males are earlier than the females in reaching the
+breeding grounds, and, in resident species, that they desert the females
+and retire alone to their prospective territories, so that there is a
+difference in the behaviour of the sexes at the very commencement of the
+sexual process. What is the immediate consequence? Since the male
+isolates itself, it follows, if the union of the sexes is to be
+effected, that the discovery of a mate must rest largely with the
+female. This of course reverses the accepted course of procedure. But
+after all, what reason is there to suppose that, the male seeks the
+female, or that a mutual search takes place; what reason to think that
+this part of the process is subject to no control except such as may be
+supplied by the laws of chance?
+
+Now, clearly, much will depend upon the rapidity with which the female
+can discover a male fit to breed; for if the course of reproduction is
+to flow smoothly, there must be neither undue delay nor waste of energy
+incurred in the search--some guidance is therefore necessary, some
+control in her external environment. Here the song, or the mechanically
+produced sound, comes into play, and assists in the attainment of this
+end. Nevertheless if every male were to make use of its powers whether
+it were in occupation of a territory or not, if the wandering individual
+had an equal chance of attracting a mate, then it would be idle to
+attempt to establish any relation between "song" on the one hand, and
+"territory" on the other, and impossible to regard the voice as the
+medium through which an effectual union of the sexes is procured. But
+there is reason to believe that the males utilise their powers of
+producing sound only under certain well-defined conditions. For
+instance, when they are on their way to the breeding grounds, or moving
+from locality to locality in search of isolation, or when they desert
+their territories temporarily, as certain of the residents often do,
+they are generally silent; but when they are in occupation of their
+territories they become vociferous--and this is notoriously the case
+during the early hours of the day, which is the period of maximum
+activity so far as sexual behaviour is concerned. So that just at the
+moment when the sexual impulse of the female is most susceptible to
+stimulation, the males are betraying their positions and are thus a
+guide to her movements. Nevertheless, even though she may have
+discovered a male ready to breed, success is not necessarily assured to
+her; for with multitudes of individuals striving to procreate their
+kind, it would be surprising if there were no clashing of interests, if
+no two females were ever to meet in the same occupied territory.
+Competition of this kind is not uncommon, and the final appeal is to the
+law of battle, just as an appeal to physical strength sometimes decides
+the question of the initial ownership of a territory.
+
+I shall try to make clear the relations of the various parts to the
+whole with the assistance of whatever facts I can command. I shall do so
+not only for the purposes of the theory, but because one so often finds
+the more important features of sexual behaviour regarded as so many
+distinct phenomena requiring separate treatment, whereas they are
+mutually dependent, and follow one another in ordered sequence. I spoke
+of the process as a series of relationships. Some of these relationships
+have already been touched upon; others will become apparent if we
+consider for a moment the purposes for which the territory has been
+evolved. Indirectly its purpose is that of the whole process, the
+rearing of offspring. But inasmuch as a certain measure of success could
+be attained, and that perhaps often, without all the complications
+introduced by the territory, there are manifestly advantages to be
+gained by its inclusion in the scheme. The difficulties which beset the
+path of reproduction are by no means always the same--all manner of
+adjustments have to be made to suit the needs of different species.
+There are direct relationships, such as we have been speaking of, which
+are essential to the every-day working of the process, and others which
+are indirect, though none the less important for they must have
+exercised an influence throughout the ages. These latter are furnished
+by the physical--the inorganic world, by climate, by the supply of the
+particular kind of breeding stations, by the scarcity or abundance of
+the necessary food and by the relative position of the food supply to
+the places suitable for breeding. Why does the Reed-Bunting cling so
+tenaciously to an acre or more of marshy ground, while the Guillemot
+rests content with a few square feet on a particular ledge of rock? The
+answer is the same in both cases--to facilitate reproduction. But why
+should a small bird require so many square yards, whilst a very much
+larger one is satisfied with so small an area? The explanation must be
+sought in the conditions of existence. The Reed-Bunting has no
+difficulty in finding a position suitable for the construction of its
+nest; there are acres of waste land and reedy swamps capable of
+supplying food for large numbers of individuals, and the necessary
+situations for countless nests. But its young, like those of many
+another species, are born in a very helpless state. For all practical
+purposes they are without covering of any description and consequently
+require protection from the elements, warmth from the body of the
+brooding bird, and repeated supplies of nourishment. A threefold burden
+is thus imposed upon the parents: they must find food for themselves,
+they must afford protection to the young by brooding, and they must
+supply them with the necessary food at regular intervals. And their
+ability to do all this that is demanded of them will be severely taxed
+by the brooding which must perforce curtail the time available for the
+collection of food.
+
+Let us then suppose that the Reed-Buntings inhabiting a certain piece of
+marsh are divided into two classes, those which are pugnacious and
+intolerant of the approach of strangers, and those which welcome their
+presence. The nests of the former will be built in isolation, those of
+the latter in close proximity. In due course eggs will be laid and
+incubation performed, and thus far all alike will probably be
+successful. Here, however, a critical point is reached. If the young are
+to be freed from the risk of exposure, the parents must find the
+necessary supply of food rapidly. But manifestly all will not be in a
+like satisfactory position to accomplish this, for whereas the isolated
+pairs will have free access to all the food in the immediate vicinity of
+the nest, those which have built in proximity to one another, meeting
+competition in every direction, will be compelled to roam farther
+afield and waste much valuable time by doing so; and under conditions
+which can well be imagined, even this slight loss of time will be
+sufficient to impede the growth of the delicate offspring, or to lead
+perhaps to still greater disaster. If any one doubts this, let him first
+examine one of the fragile offspring; let him then study the conditions
+under which it is reared, observing the proportion of time it passes in
+sleep and the anxiety of the parent bird to brood; and finally let him
+picture to himself its plight in a wet season if, in order to collect
+the necessary food, the parents were obliged to absent themselves for
+periods of long duration.
+
+Now take the case of the Guillemot. Its young at birth are by no means
+helpless in the sense that the young Reed-Bunting is, and food is
+readily procured. But breeding stations are scarce, for although there
+are many miles of cliff-bound coast, yet not every type of rock
+formation produces the fissures and ledges upon which the bird rests.
+Hence vast stretches of coast-line remain uninhabited, and the birds are
+forced to concentrate at certain points, where year after year they
+assemble in countless numbers from distant parts of the ocean. If, then,
+different individuals were to jostle one another from adjoining
+positions, and each one were to attempt to occupy a ledge in solitary
+State, not only would the successful ones gain no advantage from the
+additional space over which they exercised dominion, but inasmuch as
+many members that were fitted to breed would be precluded from doing
+so, the status of the species as a whole would be seriously affected.
+The amount of space occupied by each individual is therefore a matter of
+urgent importance. A few square feet of rock sufficient for the
+immediate purpose of incubation is all that can be allowed if the
+species is to maintain its position in the struggle for existence.
+
+Our difficulty in estimating the importance of the various factors that
+make for success or failure arises from our inability to see more than a
+small part of the scene as it slowly unfolds itself. The peculiar
+circumstances under which these cliff-breeding forms dwell does,
+however, enable us to picture, on the one hand, the precarious situation
+of an individual that was incapable of winning or holding a position at
+the accustomed breeding station, and, on the other, the plight of the
+species as a whole if each one exercised authority over too large an
+area. With the majority of species it is difficult to do this. So many
+square miles of suitable breeding ground are inhabited by so few
+Reed-Buntings that, even supposing certain members were to establish an
+ascendency over too wide an area, it would be impossible to discover by
+actual observation whether the race as a whole were being adversely
+affected. Competition doubtless varies at different periods and in
+different districts according to the numerical standing of the species
+in a given locality and according to the numerical standing of others
+that require similar conditions of existence; at times it may even be
+absent, just as at any moment it may become acute. These examples show
+how profoundly the evolution of the breeding territory may have been
+influenced by relationships in the inorganic world, and they give some
+idea of the intricate nature of the problem with which we have to deal.
+
+I mentioned that the first visible manifestation of the revival of the
+sexual instinct was to be found in the movements undertaken by the males
+at the commencement of the breeding season. Such movements are
+characterised by a definiteness of purpose, whether they involve a
+protracted journey of some hundreds of miles or merely embrace a parish
+or so in extent, and that purpose is the acquirement of a territory
+suitable for rearing offspring. They are thus directly related to the
+territory, and the question arises as to whether their origin may not be
+traced to such relatedness. So long as we fix our attention solely upon
+the magnitude of the distance traversed the suggestion may seem a
+fanciful one. Nevertheless, if the battles between males of the same
+species _are_ directly related to the occupation of a position suitable
+for breeding purposes, if those which occur between males of closely
+related forms _can_ be traced to a similar source, if the females take
+their share in the defence of the ground that is occupied, if, in short,
+the competition is as severe as I believe it to be, and is wholly
+responsible for the strife which is prevalent at the commencement of the
+breeding season--then such competition must have introduced profound
+modifications in the distribution of species; it must have even
+influenced the question of the survival of certain forms and the
+elimination of others; and since the powers of locomotion of a bird are
+so highly developed it must have led to an extension of breeding range,
+limited only by unfavourable conditions of existence.
+
+
+
+
+CHAPTER II
+
+THE DISPOSITION TO SECURE A TERRITORY
+
+
+Those who have studied bird life throughout the year are aware that the
+distribution of individuals changes with the changing seasons. During
+autumn and winter, food is not so plentiful and can only be found in
+certain places, and so, partly by force of circumstances and partly on
+account of the gregarious instinct which then comes into functional
+activity, different individuals are drawn together and form flocks of
+greater or less dimensions, which come and go according to the
+prevailing climatic conditions. But with the advent of spring a change
+comes over the scene: flocks disperse, family parties break up, summer
+migrants begin to arrive, and the hedgerows and plantations are suddenly
+quickened into life. The silence of the winter is broken by an outburst
+of song from the throats of many different species, and individuals
+appear in their old haunts and vie with one another in advertising their
+presence by the aid of whatever vocal powers they happen to possess--the
+Woodpecker utters its monotonous call from the accustomed oak; the
+Missel-Thrush, perched upon the topmost branches of the elm,
+persistently repeats its few wild notes; and the Swallow returns to the
+barn.
+
+All of this we observe each season, and our thoughts probably travel to
+the delicate piece of architecture in the undergrowth, or to the hole
+excavated with such skill in the tree trunk; to the beautifully shaped
+eggs; to the parent birds carrying out their work with devoted zeal--in
+fact, to the whole series of events which complete the sexual life of
+the individual; and the attachment of a particular bird to a particular
+spot is readily accounted for in terms of one or other of the emotions
+which centre round the human home.
+
+But if this behaviour is to be understood aright; if, that is to say,
+the exact position it occupies in the drama of bird life is to be
+properly determined, and its biological significance estimated at its
+true value, it is above all things necessary to refrain from appealing
+to any one of the emotions which we are accustomed to associate with
+ourselves, unless our ground for doing so is more than ordinarily
+secure. I shall try to show that, in the case of many species, the male
+inherits a disposition to secure a territory; or, inasmuch as the word
+"secure" carries with it too much prospective meaning, a disposition to
+remain in a particular place when the appropriate time arrives.
+
+If the part which the breeding territory plays in the sexual life of
+birds is the important one I believe it to be, it follows that the
+necessary physiological condition must arise at an early stage in the
+cycle of events which follow one another in ordered sequence and make
+towards the goal of reproduction, and that the behaviour to which it
+leads must be one of the earliest visible manifestations of the seasonal
+development of the sexual instinct. When does this seasonal development
+occur? For how long does the instinct lie dormant? In some species there
+is evidence of this first step in the process of reproduction early in
+February; there is reason to believe that in others the latter part of
+January is the period of revival; and the possibility must not be
+overlooked of still earlier awakenings, marked with little definiteness,
+though nevertheless of sufficient strength to call into functional
+activity the primary impulse in the sexual cycle. Here, then, we meet
+with a difficulty so far as direct observation is concerned, for the
+duration of the period of dormancy and the precise date of revival vary
+in different species; and, if accurate information is to be obtained,
+the study of the series of events which culminate in the attainment of
+reproduction ought certainly to begin the moment behaviour is
+influenced by the internal changes, whatever they may be, which are
+responsible for the awakening of the sexual instinct.
+
+In considering how this difficulty might be met, the importance of
+migratory species as a channel of information was gradually borne in
+upon me; for it seemed that the definiteness with which the initial
+stage in the sexual process was marked off, as a result of the incidence
+of migration, would go far towards removing much of the obscurity which
+appeared to surround the earlier stages of the breeding problem in the
+case of resident species. Recent observation has shown that I
+exaggerated this difficulty, and that it is generally possible to
+determine with reasonable accuracy the approximate date at which the
+internal changes begin to exert an influence on the behaviour of
+resident species also. Nevertheless, the specialised behaviour of the
+migrants furnished a clue, and pointed out the direction which further
+inquiry ought to take.
+
+Those who are accustomed to notice the arrival of the migrants are aware
+that the woods, thickets, and marshes do not suddenly become occupied by
+large numbers of individuals, but that the process of "filling up" is a
+gradual one. An individual appears here, another there; then after a
+pause there is a further addition, and so on with increasing volume
+until the tide reaches its maximum, then activity wanes, and the slowly
+decreasing number of fresh arrivals passes unnoticed in the wealth of
+new life that everywhere forces itself upon our attention. If now,
+instead of surveying the migrants as a whole, our attention be directed
+to one species only, this gradual arrival of single individuals in their
+accustomed haunts will become even more apparent; and if the
+investigation be pursued still further and these single individuals
+observed more closely, it will be found that in nearly every case they
+belong to the male sex. Males therefore arrive before females. This does
+not mean, however, that the respective times of arrival of the males and
+females belonging to any one species are definitely divided, for males
+continue to arrive even after some of the females have reached their
+destination; and thus a certain amount of overlapping occurs. A truer
+definition of the order of migration would be as follows:--Some males
+arrive before others, and some females arrive before others, but on the
+average males arrive before females. This fact has long been known.
+Gaetke refers to it in his _Birds of Heligoland_. "Here in Heligoland,"
+he says, "the forerunners of the spring migration are invariably old
+males; a week or two later, solitary old females make their appearance;
+and after several weeks, both sexes occur mixed, _i.e._, females and
+younger males; while finally only young birds of the previous year are
+met with." Newton alludes to it as follows:--"It has been ascertained by
+repeated observation that in the spring movement of most species of the
+northern hemisphere, the cock birds are always in the van of the
+advancing army, and that they appear some days, or perhaps weeks, before
+the hens"; and Dr Eagle Clarke, in his _Studies in Bird Migration_,
+makes the following statement:--"Another characteristic of the spring
+is that the males, the more ardent suitors, of most species, travel in
+advance of the females, and arrive at their meeting quarters some days,
+it is said in some cases even weeks, before their consorts." Some
+interesting details were given in _British Birds_[1] in regard to the
+sex of the migrants that were killed by striking the lantern at the
+Tuskar Rock, Co. Wexford, on the 30th April 1914. In all, there were
+twenty-four Whitethroats, nine Willow-Warblers, eight Sedge-Warblers,
+and six Wheatears; and on dissection it was found that twenty
+Whitethroats, seven Willow-Warblers, eight Sedge-Warblers, and one
+Wheatear were males.
+
+What a curious departure this seems from the usual custom in the animal
+world! Here we have the spectacle afforded us of the males, in whom
+presumably the sexual instinct has awakened, deserting the females just
+at the moment when we might reasonably expect their impulse to accompany
+them would be strongest; and this because of their inherited disposition
+to reach the breeding grounds. If, in order to attain to reproduction,
+the male depended primarily upon securing a female--whether by winning
+or fighting matters not at the moment--if her possession constituted the
+sole difference in his external environment between success and failure,
+then surely one would suppose that an advantage must rest with those
+individuals which, instead of rushing forward and inflicting upon
+themselves a life of temporary isolation, remained with the females and
+increased their opportunities for developing that mutual appreciation
+which, by some, is held to be a necessary prelude to the completion of
+the sexual act, and to which close companionship would tend to impart a
+stimulus.
+
+In thus speaking, however, we assume that the revival of the sexual
+instinct in the migratory male is coincident in time with its return to
+the breeding quarters; and we do so because the act of migrating is
+believed to be the first step in the breeding process. But it is well to
+bear in mind just how much of this assumption is based upon fact, and
+how much is due to questionable inference. All that can be definitely
+asserted is this, that appropriate dissection reveals in most of the
+migrants, upon arrival at their destination, unquestionable evidence of
+seasonal increase in the size of the sexual organs. Beyond this there is
+nothing to go upon. Yet if the term "sexual instinct" is held to
+comprise the whole series of complex relationships which are manifest to
+us in numerous and specialised modes of behaviour, which ultimately lead
+to reproduction, and which have gradually become interwoven in the
+tissue of the race, there can be little doubt that the assumption is a
+reasonable one. To some, the term may recall the fierce conflicts which
+are characteristic of the season; to others, emotional response; to not
+a few, perhaps, the actual discharge of the sexual function--all of
+these, it is true, are different aspects of the one instinct; but at the
+same time each one marks a stage in the process, and the different
+stages follow one another in ordered sequence. However, we are not
+concerned at the moment with the term in its wider application; we wish
+to know the precise stage at which the disposition to mate influences
+the behaviour of the male. Is the female to him, from the moment the
+seasonal change in his sexual organs takes place, a goal that at all
+costs must be attained? Or is it only when the cycle of events which
+leads up to reproduction is nearing completion that she looms upon his
+horizon? One would like to be in a position to answer these questions,
+but there is nothing in the way of experimental evidence to go upon; and
+if I say that there is reason to believe that, in the earlier stages,
+the female is but a shadow in the external environment of the male, it
+must be taken merely as an expression of opinion, though based in some
+measure upon a general observation of the behaviour of various species.
+
+Before attempting to explain the difference in the times of arrival of
+the male and female migrant, let us examine the behaviour of some
+resident species at a corresponding period. My investigations have been
+made principally amongst the smaller species--the Finches and the
+Buntings--which often pass the winter in or near the localities wherein
+they brought up offspring or were reared. It is true that they wander
+from one field to another according to the abundance or scarcity of
+food; it is also true that, if the weather is of a type which precludes
+the possibility of finding the necessary food, these wanderings may
+become extensive or even develop into partial migrations. But under the
+normal climatic conditions which prevail in many parts of Britain, these
+smaller resident species seem to find all that they require without
+travelling any great distance from their breeding haunts. Flocks
+composed of Yellow Buntings, Cirl Buntings, Corn-Buntings, Chaffinches,
+Greenfinches, etc., can be observed round the farmsteads or upon arable
+land; small flocks of Reed-Buntings take up their abode on pieces of
+waste land and remain there until the supply of food is exhausted,
+deserting their feeding ground only towards evening when they retire to
+the nearest reed-bed to pass the night; flocks of Hawfinches visit the
+same holly-trees day after day so long as there is an abundance of
+berries on the ground beneath; and so on.
+
+I have mentioned the Reed-Bunting; let us take it as our first example
+and try to follow its movements when the influence exerted by the
+internal secretions begins to be reflected on the course of its
+behaviour. First, it will be necessary to discover the exact localities
+in any given district to which the species habitually returns for the
+purpose of procreation; otherwise the earlier symptoms of any
+disposition to secure a territory may quite possibly be overlooked in
+the search for its breeding haunts.
+
+In open weather Reed-Buntings pass the winter either singly, in twos or
+threes, or in small flocks, on bare arable ground, upon seed fields, or
+in the vicinity of water-courses; but in the breeding season they
+resort to marshy ground where the _Juncus communis_ grows in abundance,
+to the dense masses of the common reed (_Arundo phragmites_), and such
+like places. During the winter, the male's routine of existence is of a
+somewhat monotonous order, limited to the necessary search for food
+during the few short hours of daylight and enforced inactivity during
+the longer hours of darkness. But towards the middle of February a
+distinct change manifests itself in the bird's behaviour. Observe what
+then happens. When they leave the reed-bed in the morning, instead of
+flying with their companions to the accustomed feeding grounds, the
+males isolate themselves and scatter in different directions. The
+purpose of their behaviour is not, however, to find fresh feeding
+grounds, nor even to search for food as they have been wont to do, but
+rather to discover stations suitable for the purpose of breeding; and,
+having done so, each male behaves in a like manner--it selects some
+willow, alder, or prominent reed, and, perching thereon, leads a quiet
+life, singing or preening its feathers. Now if the movements of one
+particular male are kept in view, it will be noticed that only part of
+its time is spent in its territory. At intervals it disappears. I do not
+mean that one merely loses sight of it, but that it actually deserts its
+territory. As if seized with a sudden impulse it rises into the air and
+flies away, often for a considerable distance and often in the same
+direction, and is absent for a period which may vary in length from a
+few minutes to an hour or even more. But these periodical desertions
+become progressively less and less frequent in occurrence until the
+whole of its life is spent in the few acres in which it has established
+itself.
+
+The behaviour of the Yellow Bunting is similar. In any roadside hedge
+two or more males can generally be found within a short distance of one
+another, and in such a place their movements can be closely and
+conveniently followed. Under normal conditions the ordinary winter
+routine continues until early in February; but the male then deserts the
+flock, seeks a position of its own, and becomes isolated from its
+companions. Now the position which it selects does not, as a rule,
+embrace a very large area--a few acres perhaps at the most. But there is
+always some one point which is singled out and resorted to with marked
+frequency--a tree, a bush, a gate-post, a railing, anything in fact
+which can form a convenient perch, and eventually it becomes a central
+part of the bird's environment. Here it spends the greater part of its
+time, here it utters its song persistently, and here it keeps watch upon
+intruders. The process of establishment is nevertheless a gradual one.
+The male does not appear in its few acres suddenly and remain there
+permanently as does the migrant; at first it may not even roost in the
+prospective territory. The course of procedure is somewhat as
+follows:--At dawn it arrives and for a while utters its song, preens its
+feathers, or searches for food; then it vanishes, rising into the air
+and flying in one fixed direction as far as the eye can follow, until it
+becomes a speck upon the horizon and is ultimately lost to view. During
+these excursions it rejoins the small composite flocks which still
+frequent the fields and farm buildings. For a time the hedgerow is
+deserted and the bird remains with its companions. But one does not have
+to wait long for the return; it reappears as suddenly as it vanished,
+flying straight back to the few acres which constitute its territory,
+back even to the same gate-post or railing, where it again sings. This
+simple routine may be repeated quite a number of times during the first
+two hours or so of daylight, with, of course, a certain amount of
+variation; on one occasion the bird may be away for a few minutes only,
+on another for perhaps half an hour, whilst sometimes it will fly for a
+few hundred yards, hesitate, and then return--all of which shows clearly
+enough that these few acres possess some peculiar significance and are
+capable of exercising a powerful influence upon the course of its
+behaviour. And so the disposition in relation to the territory becomes
+dominant in the life of the bird.
+
+Or take the case of the Chaffinch. In winter large or small flocks can
+be found in many varied situations. But in the latter part of February,
+or the early days of March, these flocks begin to disperse. At daylight
+males can then be observed in all kinds of situations, either calling
+loudly, uttering their spring note, or exercising their vocal powers to
+the full; and it will be found that, in the majority of instances, these
+males are solitary individuals, that they pass the early hours of the
+morning alone, and that their normal routine of calling, singing, or
+searching for food, is only interrupted by quarrels with their
+neighbours. The same locality is visited regularly--not only the same
+acre or so of ground, but even the same elm or oak, has, as its daily
+occupant, the same cock Chaffinch. And temporary desertions from the
+territory occur also, much like those referred to in the life of the
+Bunting, but perhaps not so frequently. One has grown so accustomed
+during the dark days of winter to the sociable side of Chaffinch
+behaviour--to the large flocks searching for food, to the endless stream
+of individuals returning in the evening to roost in the holly-trees, to
+the absence of song--that this radical departure from the normal routine
+comes as something of a surprise; for the days are still short, the
+temperature is still low, the nesting season is still many weeks ahead,
+and yet for part of the day, and for just that part when the promptings
+of hunger must be strongest, the male, instead of joining the flock,
+isolates itself and expends a good deal of energy in insuring that its
+isolation shall be complete. And in place of the silence we hear from
+all directions the cheerful song uttered with such marked persistency
+that it almost seems as if the bird itself must be aware that by doing
+so it was advertising the fact of its occupation of a territory. This is
+surely a remarkable change, and the females in the meantime continue
+their winter routine.
+
+One other example. The monotonous call of the Greenfinch is probably
+familiar to all. In winter these birds accompany other Finches and form
+with them flocks of varying sizes, but in the spring the flocks
+disperse, and the Greenfinch, in common with other units of the flock,
+alters its mode of life. But whereas the Chaffinch or the Bunting begins
+to acquire its territory in February, the Greenfinch only does so in
+April. When the organic changes do at length begin to make themselves
+felt, the male seeks a position of its own, and having found one remains
+there, uttering its characteristic call. But owing probably to the fact
+that it is much later than the aforementioned species in acquiring a
+territory, temporary desertions are not so much in evidence. The species
+is so very plentiful, and the bird is so prone to nest in gardens and
+shrubberies surrounding human habitations, that this seasonal change in
+its routine of existence cannot fail to be noticed. One can hear its
+call in every direction, one can watch the same individual in the same
+tree; and it is the male that is thus seen and heard, the female appears
+later. Thus the behaviour falls into line with that of the Bunting or
+the Chaffinch.
+
+The behaviour of these resident species throws some light upon the early
+arrival of the males which we are endeavouring to explain in the case of
+the migrants. Let us see how their actions compare. The male resident
+deserts the female early in the year and establishes itself in a
+definite position, where it advertises its presence by song; the male
+migrant travels from a great distance, arrives later, and also
+establishes itself in a definite position, where it, too, advertises its
+presence by song. The male resident passes only the earlier part of the
+day in its territory at the commencement of the period of occupation;
+the male migrant remains there continuously from the moment it arrives.
+The male resident deserts its territory at intervals, even in the
+morning; the male migrant betrays no inclination to do so. Thus there is
+a very close correspondence between the behaviour of the two, and what
+difference there is--slight after all--cannot be said to affect the main
+biological end of securing territory. One is apt to think of the problem
+of migration in terms of the species instead of in terms of the
+individual. One pictures a vast army of birds travelling each spring
+over many miles of sea and land, and finally establishing themselves in
+different quarters of the globe; and so it comes about, I suppose, that
+a country or some well-defined but extensive area is regarded as the
+destination, the ultimate goal, of the wanderers. But the resident male
+has a journey to perform, short though it may be; it, too, has a
+destination to reach, neither a country nor a locality, but a place
+wherein the rearing of offspring can be safely accomplished, and it,
+too, arrives in that place in advance of the female.
+
+With these facts at our disposal, we will endeavour to find an
+explanation. It is unlikely that specialised behaviour would occur in
+generation after generation under such widely divergent conditions,
+and, moreover, expose the birds to risk of special dangers, if it were
+but an hereditary peculiarity to which no meaning could be attached.
+Hence the appearance of the males in their breeding haunts ahead of the
+females becomes a fact of some importance, and suggests that the
+extensive journey in the one case, and the short journey in the other,
+may both have a similar biological end to serve.
+
+Darwin evidently attached importance to this difference between the
+males and the females in their times of arrival. In the _Descent of Man_
+he referred to it as follows: "Those males which annually first migrated
+in any country, or which in spring were first ready to breed, or were
+the most eager, would leave the largest number of offspring; and these
+would tend to inherit similar instincts and constitutions. It must be
+borne in mind that it would have been impossible to change very
+materially the time of sexual maturity in the females without at the
+same time interfering with the period of the production of the young--a
+period which must be determined by the season of the year." Newton
+suggested the following explanation[2]: "It is not difficult to
+imagine that, in the course of a journey prolonged through some 50 deg.
+or 60 deg. of latitude, the stronger individuals should outstrip the
+weaker by a very perceptible distance, and it can hardly be doubted that
+in most species the males are stouter, as they are bigger than the
+females." Granting that the males are the stronger, how can this account
+for their outstripping the females by a week, ten days, or even a
+fortnight, in a journey of perhaps 1500 miles? To expect the birds to
+accomplish such a distance in seven days is surely not estimating their
+capabilities too highly, and any slight inequality in the power of
+flight or endurance could give the males an advantage of a few hours
+only. But this explanation, based upon inequalities in the power of
+flight and endurance on the one hand, and the magnitude of the distance
+traversed on the other, cannot afford a solution of the behaviour of the
+resident males, and is less likely, therefore, to be a true solution of
+that of the migrants.
+
+There is another theory, simple enough in its way, which will probably
+occur to many. It is based on the assumption that the males reach sexual
+maturity before the females; and it is contended that the functioning of
+the instincts which contribute towards the biological end of
+reproduction depend upon the organic changes which the term "sexual
+maturity" is held to embrace, and that, inasmuch as the migratory
+instinct belongs to the group of such instincts, the males must be the
+first to leave their winter quarters.
+
+What is meant by the "migratory instinct"? To speak of it as one of the
+instincts concerned in reproduction is not enough. Reproduction involves
+the actual discharge of the sexual function, which involves the
+females; but the first visible manifestation of organic change in the
+male is its desertion of the females. Yet this is the behaviour which is
+referred to as the "migratory instinct," and which comes into play,
+according to this theory, because the bird has reached sexual maturity.
+Manifestly we must have some clear understanding as to what these terms
+represent. That organic changes determine the functioning of certain
+definite instincts at certain specified times there can be no doubt;
+that these changes may occur at a somewhat earlier date in the male than
+in the female is more than probable, but that this explains the
+behaviour in question I do not believe. One wants to know why the
+changes should occur earlier in the male, what disposition it is which
+first comes into functional activity, and to what such disposition is
+related.
+
+It may, however, be urged that, after all, this apparent eagerness to
+reach the breeding grounds is but a modification of hereditary procedure
+under the guiding hand of experience. What more likely result would
+follow from the enjoyment associated with previous success in the
+attainment of reproduction than a craving to repeat the experience? What
+stronger incentive to a hurried return could be imagined? It must be
+admitted that there are certain facts which might be used in support of
+an appeal to experience as a reasonable explanation. For example, the
+first males to arrive often display that richness of colouring which is
+generally supposed to indicate a fuller maturity. Gaetke even speaks of
+the "most handsome old birds being invariably the first to hasten back
+to their old homes." But if experience is a factor, if some dim
+recollection of the past is held to explain the hurried departure of the
+male migrant, one wants to know with what such recollection is
+associated. Is it associated with the former female, or with the former
+breeding place, or with both? I take it that any recollection, no matter
+how vague, must be primarily associated with the particular place
+wherein reproduction had previously been accomplished; and I grant that
+if the first individuals to appear were invariably the older and
+experienced birds, their early return might be explained on the basis of
+such an association. But if there is reason to believe that a proportion
+are young birds on the verge of carrying out their instinctive routine
+for the first time, then we cannot appeal to past experience in
+explanation of their behaviour.
+
+The age of a bird is difficult to determine. Experience leads me to
+believe that some of the males that arrive before the females are birds
+born the previous season; one finds, for instance, individuals with
+plumage of a duller hue, which denotes immaturity, amongst the first
+batch of arrivals. But though plumage may sometimes be a satisfactory
+guide, yet to rely upon it alone, or upon a more perfect development of
+feather, is to exceed the limits of safety. How, then, can we ascertain
+whether all the males that arrive before the females have had some
+previous experience of reproduction? Well, we take a particular locality
+and note the migrants that visit it year after year, and we find that
+the respective numbers of the different species are subject to wide
+annual fluctuations. Not every species lends itself to an inquiry of
+this kind: some are always plentiful and fluctuation is consequently
+difficult to discern; others are scarce and variation is easily
+determined. Those which are of local distribution but conspicuous by
+their plumage, or easily traced by the beauty or the peculiarity of
+their song, afford the more suitable subjects for investigation. For
+example, the Grasshopper-Warbler, Marsh-Warbler, Nightingale, Corncrake,
+Red-backed Shrike, or Whinchat have each some distinctive peculiarity
+which makes them conspicuous, and each one is subject to marked
+fluctuation in numbers. The small plantation or wooded bank may hold a
+Nightingale one year, but we miss its song there the next; the osier bed
+or gorse-covered common which vibrates with the trill of the
+Grasshopper-Warbler one April is deserted the following season; the
+plantation which is occupied by a host of common migrants this summer
+may be enlivened next year by the song of the rarer Marsh-Warbler also;
+and so on. The fluctuation is considerable: we observe desertion on the
+one hand, appropriation on the other, and yet males appear before
+females whether the particular plantation, osier bed, or swamp had been
+inhabited or not the previous season. This fact is not without
+significance. It shows that similar conditions prevail both amongst the
+males that appropriate breeding grounds new to them, and amongst those
+that return to some well-established haunt; and on the assumption that
+the earlier arrivals are experienced males, the same birds evidently do
+not return to the same place year after year. Granting, then, that the
+males which appropriate new breeding-grounds are young birds, how can
+their earlier arrival be explained in terms of past experience; and
+granting that they are old, and therefore experienced, how can it be
+explained in terms of association?
+
+Again, it may be urged that if there is some biological end to be
+furthered by this hurried return, and if recollection of past experience
+is a means towards that end, such recollection need not necessarily be
+associated with a definite place, but only in a vague way with the whole
+series of events leading up to reproduction--in which series the
+migratory journey may even have acquired meaning. Whether there be any
+recollection of a previous journey or of a nest with young, I do not
+know. But the young bird is capable of performing its journey, of
+building its nest, and of rearing its young antecedent to
+experience--racial preparation has fitted it thus far; why then exclude
+the other event in the series, the earlier departure of the male, from
+hereditary equipment? If the journey were a casual affair without any
+goal attaching to it, if the males upon arrival wandered about in search
+of a mate, there would be some ground for thinking that a vague
+recollection of the whole former experience was sufficient to explain
+the hurried return; but since the pleasurable effect of association,
+founded upon previous experience of a definite place, cannot well be
+established, and since it is so difficult to study the objective aspect
+of the behaviour in question without coming to the conclusion that the
+journey is related to the appropriation of a place suitable for the
+rearing of offspring, one is tempted to ask whether the hurried return
+may not also be so related.
+
+Now the males of some of the migratory species, especially of those
+which are accustomed to return to their breeding haunts early in the
+season, are called upon to face greater dangers and have a greater
+strain imposed upon their strength by starting forth upon their journey
+ten days or a fortnight before their prospective mates. The blizzards
+which so often sweep across the northern parts of Europe in the latter
+half of March, destroying in their course the all too scanty supply of
+insect life, may take toll of their numbers; or the westerly gales,
+which are not infrequent at that period, may meet them in mid-ocean and
+add to the perils of their journey; or the temperature of the previous
+weeks may have been sufficiently low to arrest the development of insect
+life--and yet males are annually exposed to these risks in hurrying to
+their breeding grounds. For what purpose? The answer will largely depend
+upon the way in which we regard those few acres wherein a resting place
+is ultimately found. For myself, I believe that they are of importance,
+inasmuch as the securing of a place suitable for the rearing of
+offspring is a primary condition of success in the attainment of
+reproduction; and if this be so, it is evident that the interests of
+the race will be better served by the males making good this first step
+before the females are ready to pair, otherwise they might oscillate
+between two modes of behaviour, created by the premature functioning of
+conflicting impulses.
+
+The different steps in the process seem to follow one another in ordered
+sequence. The male inherits a disposition--which for us, of course, has
+prospective meaning--to seek the appropriate breeding ground and there
+to establish itself; and as early a functioning of this disposition as
+possible, consonant with the conditions of existence in the external
+environment, may have been evolved for the following reasons--firstly,
+the earlier individuals will meet with less interference wherever they
+may settle, every locality will be open to them, every acre free, their
+only need being that particular environment for which racial preparation
+has fitted them. In the second place, being already established when
+other males appear upon the scene, and advertising their presence by
+song, they will be less liable to molestation; thirdly, in those cases
+in which a long journey is undertaken, they will have ample time to
+recover from the fatigue, and, if attacked by later arrivals, will thus
+be in a better position to defend their territories; and lastly, a
+greater uniformity in their distribution will be insured before the
+females begin their search.
+
+There is, besides, another good reason for thinking that the earlier
+males will have an advantage. We will assume--and from the abundant
+evidence supplied by the marking of birds, it is quite a reasonable
+assumption--that there is a tendency, generally speaking, for
+individuals to return to the neighbourhood of their birthplace, or to
+the place in which they had previously reared their offspring. Now the
+earlier arrivals will have no difficulty in securing territories; those
+that come later may have to search more diligently, still they will gain
+all that they require so long as any available space remains. Then comes
+the point when all suitable ground is occupied, and yet there are males
+to be provided for. What will be the position of these males? Urged by
+their inherited nature, they will leave the district and possibly
+continue their search into those adjoining, only, however, to add to the
+difficulties of the males there similarly situated; and even allowing
+that they are at length successful in establishing themselves, what are
+their prospects of securing mates? Since the earlier females will not
+extend their wanderings farther than is absolutely necessary, but will
+pair whenever the opportunity for doing so arises, it is to the later
+females, forced onwards by competition, that the late males must look
+for mates; so that when at length pairing does take place, much valuable
+time will have been lost.
+
+The disadvantages which the late arrivals have to face are therefore
+great, and it is probable that the percentage which attain to
+reproduction will on the average be somewhat lower than the percentage
+in the case of the earlier arrivals. The district in which my
+observations have been made lies well within the limits of the breeding
+range of most of our common species, and it is not surprising that I
+should have met with little evidence of failure to breed as a result of
+failure to secure territory. Some interesting information was supplied
+to me, however, by the late Robert Service. He found, in certain seasons
+in Dumfriesshire, flocks of from ten to fifty unmated Sedge-Warblers,
+which, from the time of their arrival in May until the middle of July,
+haunted reed-filled spaces along stagnant streams. These flocks appeared
+to him to be composed of loosely-attached individuals of a migrant flock
+that had failed to find things congenial enough to entice them to
+disperse. But may they not have been composed of males that had failed
+to secure territories, or of females that had failed to discover males
+in possession of territories, or of both?
+
+
+We have seen that, in the case of many species, each male establishes
+itself in a particular place at the commencement of the breeding season,
+even though this may mean a partial or perhaps a complete severance from
+former companions. We must now discuss this fact in greater detail
+because it is opposed to the views often held regarding the sexual
+behaviour of birds, and is manifestly of importance when considering
+the theory of breeding territory.
+
+First, however, there is a point which requires some explanation. I
+speak of the _same_ male being in the _same_ place. How can I prove its
+identity? In the first place it is highly improbable that a bird which
+roams about within the same small area of ground, makes regular use of a
+certain tree and a certain branch of that tree, and observes a similar
+routine day after day, can be other than the same individual. But, apart
+from this general consideration, are there any means by which
+individuals of the same species can be identified? Well, there is
+variation in the plumage. Supposing we take a dozen cock Chaffinches and
+examine them carefully, we shall find slight differences in pattern and
+in colour--more grey here or a duller red there, as the case may be--and
+though these differences may not be sufficient to enable us to pick out
+a bird at a distance, they are nevertheless conspicuous when it is close
+at hand. Then again there is variation in the song; and the more highly
+developed the vocal powers the greater scope there is for variation. But
+even the phrases of a simple song can be split up and recombined in
+different ways. If one were asked casually whether the different phrases
+of the Reed-Bunting's song always followed one another in the same
+sequence, the answer would probably be that they certainly did so,
+whereas the bird is capable of combining the few notes it possesses in a
+surprising number of different ways. And lastly, there are differences
+in just the particular way in which specific behaviour, founded upon a
+congenital basis, is adapted by each individual to its own special
+environment. Racial preparation determines behaviour as a whole, but the
+individual is allowed some latitude in the execution of details which
+are in themselves of small moment--the selection of a particular tree as
+a headquarters and a particular branch upon that tree, the direction of
+the distant excursion, and the direction of the limited wanderings
+within the small area surrounding the headquarters which in the course
+of time determine the extent of the territory, are matters for each
+individual to decide when the occasion for doing so arises. Moreover
+instances of abnormal coloration or abnormal song are not rare, and they
+are valuable since they place the identity of the individual beyond
+dispute. I can recall the case of a Willow-Warbler whose song was unlike
+that of its own or any other species, and of a Redbreast whose voice
+puzzled me not a little. I can recollect also a male Yellow Bunting
+whose foot was injured or deformed. Of this bird's behaviour I kept a
+record for two months or so; and inasmuch as it inhabited a roadside
+hedge, and was of fearless disposition, the deformed foot could plainly
+be seen whenever it settled upon the road to search for food.
+Identification is not, therefore, a difficulty. There is always some
+small difference in colour or in song, or some well-defined routine
+which makes recognition possible.
+
+Owing to their great powers of locomotion, birds have generally been
+regarded as wanderers more or less; anything in the nature of a fixed
+abode, apart from the actual nest, having been accounted foreign to
+their mode of life; and even the locality immediately surrounding the
+nest has not been apprehended as possessing any meaning for the owner of
+that nest. No doubt the supply of food determines their movements for a
+considerable part of the year; they seek it where they can find it, here
+to-day, there to-morrow--in fact few species fail to move their quarters
+at one season or another, so that there is much truth in the notion that
+birds are wanderers. Yet to suppose that every individual one sees or
+hears--every Lapwing on the meadow, or Nightingale in the withy bed--is
+in that particular spot just because it happens to alight there as it
+roams from place to place, is to take a view which the observed facts do
+not support. For as soon as the question of reproduction dominates the
+situation, a new condition arises, and the habits formed during the
+previous months are reversed, and the males, avoiding one another, or
+even becoming actively hostile, prefer a life of seclusion to their
+former gregariousness--all of which occurs just at the moment when we
+might reasonably expect them to exhibit an increased liveliness and
+restlessness as a result of their endeavour to secure mates; and so
+universal is the change that it might almost be described as an
+accompaniment of the sexual life of birds generally.
+
+That the Raven and certain birds of prey exert an influence over the
+particular area which they inhabit has long been known, and it has been
+recognised more especially in the case of the Peregrine Falcon,
+possibly because the bird lives in a wild and attractive country, and,
+forcing itself under the notice of naturalists, has thus had a larger
+share of attention devoted to its habits. Moreover, when a species is
+represented by comparatively few individuals, and each pair occupies a
+comparatively large tract of country, it is a simple matter to trace the
+movements and analyse the behaviour of the birds. There is a rocky
+headland in the north-west of Co. Donegal comprising some seven miles or
+so of cliffs, where three pairs of Falcons and two pairs of Ravens have
+nested for many years. Each year the different pairs have been more or
+less successful in rearing their young; each year the young can be seen
+accompanying their parents up to the time when the sexual instinct
+arises; and yet the actual number of pairs is on the whole remarkably
+constant, and there is no perceptible increase. It seems as if the
+numbers of three and two respectively were the maximum the headland
+could maintain. But this is no exceptional case; it represents fairly
+the conditions which obtain as a rule amongst those species, granting,
+of course, a certain amount of variation in the size of each territory
+determined by the exigencies of diverse circumstances.
+
+If we take a given district, and devote our attention to the smaller
+migrants that visit Western Europe each returning spring for the purpose
+of procreation, we shall find that the movements of the males are
+subject to a very definite routine. This, however, is not true of every
+male; some may be wending their way to breeding grounds at a distance;
+others may be seeking the particular environment to which they may be
+adapted; others again, having found their old haunts destroyed, may
+consequently be seeking new.
+
+Of all this there is evidence. Small parties of Chiffchaffs pass through
+a district on their way to other breeding grounds, flitting from hedge
+to hedge as they move in a definite direction with apparently a definite
+purpose; Reed-Warblers settle in a garden or plantation, eminently
+unsuited to their requirements, and disappear; Wood-Warblers arrive in
+some old haunt, and finding it no longer suitable for their purpose,
+seek new ground. So that plenty of individuals are always to be found,
+which, for the time being at least, are wanderers.
+
+In the district which I have in mind, the wandering males form only a
+small part of the incoming bird population. The majority of individuals
+that fall under observation are those that have made this particular
+district their destination; and in doing so, they may possibly have been
+guided by their experience as owners or inmates of former nests, for it
+cannot be doubted that a return to the neighbourhood of the birthplace
+would lead to a more uniform distribution and therefore be advantageous,
+and the tendency to do so might consequently have become interwoven in
+the tissue of the race. How, then, do they behave? A certain amount of
+movement, an interchanging of positions, even though restricted to an
+area defined, let us say, by experience, might be expected under the
+circumstances--that, however, is not what we find; we observe the
+available situations plotted out into so many territories, each one of
+which is occupied by a male who passes the whole of his time therein.
+Take whatever species we will--Whitethroat, Whinchat, Willow-Warbler,
+Red-backed Shrike, it matters not which, for there is no essential
+difference in the general course of procedure--this condition will be
+found to prevail. Generally speaking, the behaviour in relation to the
+territory can be studied more conveniently where a number of individuals
+of the same species have established themselves in proximity to one
+another. Such species as the Chiffchaff, Willow-Warbler, or Wood-Warbler
+are often sufficiently common to allow of three or more of their
+respective males being kept in view at the same time; and the
+disposition to occupy a definite position can be readily observed. The
+Reed-Warbler is a suitable subject for an investigation of this kind;
+for since it is restricted by its habits to localities wherein the
+common reed (_Arundo phragmites_) grows in abundance, and since such
+localities are none too plentiful and often limited in extent, the area
+occupied by each individual is necessarily small--if it were not so the
+species would become extinct. Hence it is a simple matter to study the
+routine of the different individuals and to mark the extent of their
+wanderings.
+
+In this way the males of all the Warblers that breed commonly in Great
+Britain establish themselves, each one in its respective station at the
+respective breeding ground; so, too, do those of many other
+migrants--for example, the Whinchat, Wheatear, Tree-Pipit, and Red-backed
+Shrike. All of these, it is true, are common species--numbers of
+individuals can often be found in close proximity--and therefore it may
+be argued that they keep to one position more from pressure of
+population than from any inherited disposition working towards that end.
+But the rarer species behave similarly. Districts frequented by the
+Marsh-Warbler and offering plenty of situations of the type required by
+the bird are often inhabited by a few members only, and yet the
+disposition to remain in a definite position is just as marked.
+
+You will say, however, that these smaller migrants have no exceptional
+powers of flight; that they have besides just completed a long and
+arduous journey; and you will ask why they should be expected to wander,
+whether it is not more reasonable to expect that, in order to overcome
+their fatigue, they should remain where they settle. The Cuckoo is a
+wanderer in the wider sense of the term, and is gifted with considerable
+powers of flight. Upon arrival the male flies briskly from field to
+field, showing but little signs of weariness; yet we have only to follow
+its movements for a few days in succession to assure ourselves that the
+bird is no longer a wanderer; for just as the Warbler or the Chat moves
+only within a definitely delimited area, so the male Cuckoo, strange as
+it may seem, restricts itself to a particular tract of land. The area
+over which it wanders is often considerable and consequently it is not
+possible to keep the bird always in view, but inasmuch as the variation
+in the voices of different individuals is quite appreciable,
+identification is really a simple matter. If we cannot keep the bird in
+sight, we can trace its movements by sound and mark the extent of its
+wanderings, which by repetition become more and more defined, until a
+belt of trees here, or an orchard there, mark a rough and rarely passed
+boundary line.
+
+Let us take another example from the larger migrants--the Black-tailed
+Godwit, a bird common enough in the Dutch marshes but no longer breeding
+in this country. On suitable stretches of marsh land, numbers will be
+found in proximity one to another after the manner of the Lapwing, each
+male occupying a definite space of ground wherein it passes the time
+preening, searching for food, or in sleep--though at the same time
+keeping a strict watch over its territory. Now the preference shown for
+a particular piece of ground, and the determination with which it is
+resorted to, is the more remarkable when we take into consideration the
+specific emotional behaviour arising from the seasonal sexual condition.
+This behaviour is expressed in a peculiar flight. The bird rises high in
+the air, circles round with slowly beating wings above the marsh, and
+utters a call which, as far as my experience goes, is characteristic of
+the performance. The air is often full of individuals circling thus
+even beyond the confines of the marsh, for a male does not limit its
+flight to a space immediately above its territory; but nevertheless
+careful observation will show how unerringly each one returns to its own
+position on the breeding ground, no matter how extensive the aerial
+excursion may have been. And so, when the males of the smaller migrants
+confine their movements to an acre of ground at the completion of their
+long journey, they are acting no more under the influence of fatigue
+than the Cuckoo, which keeps within certain bounds yet flies about
+briskly, or the Godwit which, though holding to its few square yards on
+the ground, executes most tiring and extensive flights above the marsh.
+
+Of all the migrants, however, the behaviour of the Ruff is perhaps the
+most strange, and though it has long been known that these birds have
+their special meeting places where they perform antics and engage in
+serious strife, yet it is only within recent years that the primary
+purpose of these gatherings has been ascertained--that purpose being the
+actual discharge of the sexual function. Mr. Edmund Selous has carried
+out some exhaustive investigations into their activities at the meeting
+places, and he makes it clear that each bird has its allotted position.
+He says, for example, that "It begins to look as though different birds
+had little seraglios of their own in different parts of the ground,"
+that "each Ruff has certainly a place of its own," or again that "this
+Ruff indeed, which I think must be a tender-foot, does not seem to have
+a place of its own like the others." Nevertheless it is only at the
+meeting places that they have their special positions; there is no
+evidence to show that each one has a special territory, wherein it seeks
+its food, as the Warbler has, and therefore some may think that we are
+here confronted with behaviour of a different order. But we must bear in
+mind that the process has been adjusted to meet the requirements of
+different species: the size of the territory, the period of its daily
+occupation, the purpose which it serves--these all depend upon manifold
+relationships and do not affect the principle. Why it has been
+differentiated in different circumstances we shall have occasion to
+discuss later; for the moment it is enough that at the end of its
+migratory journey each Ruff occupies one position on the meeting ground.
+
+[Illustration: Territorial flight of the Black-tailed Godwit
+
+Emery Walker ph.sc.]
+
+Now birds that are paired for life, whose food-supply is not affected by
+alternations of climate, have no occasion to desert the locality wherein
+they have reared their offspring, and so their movements, being subject
+to a routine which would tend to become increasingly definite, must in
+the course of time and according to the law of habit formation become
+organised into the behaviour we observe. Is it necessary, therefore, to
+seek an explanation of their tendency to remain in one place in anything
+so complex as an inherited disposition? Again, since we have to confess
+to so very much ignorance on so many points connected with the whole
+phenomenon of migration, may there not be some condition, hitherto
+shrouded in mystery, which might place so different a complexion on the
+corresponding aspect of migrant behaviour as to rid us, in their case
+also, of the necessity of appealing to an inherited disposition? Such
+questions are justifiable. And if the life-histories of other species
+gave no further support to our interpretation, if, in short, the
+evidence were to break down at this point, then we should be forced to
+seek some other explanation more in keeping with the general body of
+facts.
+
+But far from placing any obstacle in the way of an interpretation in
+terms of inherited disposition, the behaviour of many of those residents
+which are not paired for life gives us even surer ground for that
+belief. Moreover in their case the initial stages in the process are
+more accessible to observation. I will endeavour to explain why. In the
+process of reproduction the environment has its part to play--whether in
+the manner here suggested, or indirectly through the question of
+food-supply, matters not at the moment. Now, migratory species are more
+highly specialised than resident species as regards food, and are
+affected more by variations of temperature, so that they can live for
+only a part of the year in the countries which they visit for the
+purpose of procreation. Hence the organic changes, which set the whole
+process in motion, must be coincident in time with the growth of
+appropriate conditions in the environment; for if it were not so, if the
+internal organic changes were to develop prematurely, the bird would
+undertake its journey only to find an insufficiency of food upon its
+arrival, and this would scarcely contribute towards survival. Definite
+limitations have therefore been imposed upon the period of organic
+change. But in the case of many resident species the conditions are
+somewhat different, for they remain in the same locality throughout the
+year, and a gradual unfolding of the reproductive process cannot
+therefore have a similarly harmful effect. Thus it comes about that the
+behaviour of the migrant, when it arrives at the breeding ground and
+first falls under observation, represents a stage in the process which,
+in the case of the resident, is only reached by slow degrees; and by
+closely observing the behaviour as it is presented to us in the life of
+the resident male, we not only gain a better insight into the changes in
+operation, but can actually witness the breaking down of the winter
+routine, stereotyped through repetition, by the new disposition as it
+arises.
+
+The first visible manifestations, even though they may be characterised
+by a certain amount of vagueness, are therefore of great importance if
+the behaviour is to be interpreted aright; and in order to insure that
+none of these earlier symptoms shall be missed, it is necessary to begin
+the daily record of the bird's movements at an early date in the season.
+As a rule the second week in February is sufficiently early for the
+purpose, but the date varies according to the prevailing climatic
+conditions. Even in species widely remote there is great similarity of
+procedure, and the behaviour of the Buntings is typical of that of many.
+With the rise of the appropriate organic state the male resorts at
+daybreak to a suitable environment, occupies a definite position, and
+singling out some tree or prominent bush, which will serve as a
+headquarters, advertises its presence there by song. At first the bird
+restricts its visits, which though frequent in occurrence are of short
+duration, for the most part to the early hours of the morning; it
+disappears as suddenly as it appeared, and one can trace its flight to
+the feeding grounds--a homestead or perhaps some newly sown field. But
+by degrees the impulse to seek the society of the flock grows less and
+less pronounced, the visits to the territory are more and more
+prolonged, and the occupation of it then becomes the outstanding feature
+of the bird's existence. This in outline is the course of procedure as
+it appears to an external observer.
+
+But although much can be learnt from the lives of these smaller species,
+there is no gain-saying the fact that a great deal of patient
+observation is required, and the process is apt to become tedious. There
+are others, however, which are more readily observed, whilst their
+life-histories afford just as clear an insight into the effect produced
+by the new disposition upon the developing situation; and among these
+the Lapwing takes a prominent position, because it is plentiful and
+inhabits open ground where it is easily kept in view.
+
+There is a water meadow with which I am familiar, where large numbers
+resort annually for the purpose of procreation. Here they begin to
+arrive towards the end of February, and at first collect in a small
+flock at one end of the meadow. A male, here and there, can then be seen
+to break away from the flock, and to establish itself in a definite
+position upon the unoccupied portion of the ground, where it remains
+isolated from its companions. Others do likewise until the greater part
+of the meadow is divided into territories. Six of these territories I
+kept under observation for approximately two months in the year 1915.
+The occupant of the one marked No. 6 upon the 1915 plan was a lame bird,
+a fortunate occurrence as it enabled me to follow its movements with
+some accuracy; and though it maintained its position for some weeks, it
+ultimately disappeared, as a result, I believe, of the persistent
+attacks of neighbouring males. The behaviour of the males during the
+first fortnight or so after they broke away from the flock was
+interesting. Though they retired to their territories and remained in
+them for the greater part of their time, yet it was only by degrees that
+they finally severed their connection with the flock, for so long as a
+nucleus of a flock remained, so long were they liable to desert their
+territories temporarily and to rejoin their companions.
+
+[Illustration: Emery Walker Ltd. sc.
+
+Plan of the water meadow showing the territories occupied by Lapwings in
+the year 1915.]
+
+[Illustration: Emery Walker Ltd. sc.
+
+Plan of the water meadow showing the territories occupied by Lapwings in
+the year 1916.
+
+_Between pages 58 and 59._]
+
+Lapwings, as is well known, collect in flocks during the winter months,
+and these flocks, which sometimes reach vast proportions, are to be
+found on tidal estuaries, water meadows, arable land, and such like
+places, according to the prevailing climatic conditions. This flocking
+may contribute towards survival, and may therefore be the result of
+congenital dispositions which have been determined on biological
+grounds. On the other hand, since food at that season is only to be
+obtained in a limited number of situations, the birds may be simply
+drawn together by accident. In the former case the behaviour would be
+instinctive, in the latter, though accidental at first, recurrent
+repetition would tend to make it habitual; but in either case the
+impulse to accompany the flock must be a powerful one, for on the one
+hand it would depend upon inherited, and on the other hand upon
+acquired, connections in the nervous system. Now observe that soon
+after the flock arrived in the meadow, single males detached themselves;
+there was no hesitation, they just retired from their companions and
+settled in their respective territories. They were not expelled, for if
+their leaving had been compulsory much commotion would have preceded
+their departure, and their return would certainly not have been
+welcomed. A reference to the plan will make the position clearer; the
+neutral zone inhabited by the flock is there shown as situated in one
+corner of the meadow, the territories that fell under observation are
+plotted out as far as possible to scale, and the more important zones of
+conflict are also marked.
+
+The males spent part of their time in their respective territories and
+part with the flock, so long as it remained in existence. When a male
+was in its territory it avoided companions and was openly hostile to
+intruders; when it was with the flock it wandered about with companions
+in search of food. The contrast between the two modes of behaviour was
+very marked, and it was evident that the gregarious instinct was
+gradually yielding its position of importance to the new factor--the
+territory. If there had been no flock, if a few solitary individuals had
+appeared here and there and had established themselves in different
+parts of the meadow, one would have had no definite evidence of the
+strength of the impulse in the male to seek a position of its own, one
+could only have argued from the general fact of males flocking in the
+winter and isolating themselves in spring that something more than
+accident was required to explain so radical a change. But since the
+birds returned in a flock to the ground upon which they intended to
+breed, and since the flock occupied temporarily part of the ground
+whilst the partitioning of the remainder was still proceeding, it was
+possible to gauge the strength of the impulse, which was forcing the
+males to isolate themselves in particular areas of ground, by comparing
+it with the impulse to accompany the flock--and the measure of its
+intensity was the rapidity with which the latter impulse yielded its
+position of importance.
+
+Like the Lapwing, the Coot and Moor-Hen are easily kept under
+observation, and since many individuals often breed in proximity, more
+than one can be watched at the same moment; moreover the area occupied
+by each male generally embraces an open piece of water as well as part
+of the fringe of reeds, so that the movements of the bird can be
+followed without much difficulty. Under favourable conditions
+manifestations of the developing situation become visible at a
+comparatively early date in the season--the middle or the latter part of
+February--and these manifestations resemble those of other species. But
+the Moor-Hen passes summer and winter alike in the same situation, and
+being therefore in a position to respond at once to internal
+stimulation, however vague, the change from the one state to the other
+is gradual. This, however, is a matter of detail; the main consideration
+lies in the fact that the impulse to retire to a definite position, to
+avoid companions, and to live in seclusion, is strongly marked, and
+produces a type of behaviour similar on the whole to that of the
+Lapwing. First of all there is the appropriation of a certain position,
+the limits of which are fixed according to the law of habit formation,
+and according to the pressure exerted by neighbouring individuals; then
+there is the neutral ground over which the birds wander amicably in
+search of food; and finally there is the contrast between the pugnacity
+of the male whilst in its territory, and its comparative friendliness
+when upon neutral ground.
+
+Evidence of similar behaviour is to be found in the life of the Black
+Grouse, a bird which has always excited the curiosity of naturalists on
+account of the special meeting places to which both sexes resort in the
+spring. Mr. Edmund Selous watched these birds in Scandinavia, where he
+kept a daily record at one of the meeting places. In various passages he
+refers to the appropriation of particular positions by particular males,
+and concludes thus: "It would seem from this that, like the Ruffs, each
+male Blackcock has its particular domain on the assembly ground, though
+the size of this is in proportion to the much greater space of the
+whole. On the other mornings, too, the same birds, as I now make no
+doubt they are, have flown down into approximately the same areas."
+
+The cliff-breeding species--Guillemots, Razorbills, and Puffins--are
+difficult to investigate because individuals vary so little, and the
+sexes resemble one another so closely; yet, despite these difficulties,
+we can gain some idea of the general purport of their activities. But
+when the ledges are crowded and the air is filled with countless
+multitudes, how is it possible to keep a single bird in view for a
+sufficient length of time to understand its routine? The difficulty is
+not an insuperable one. The flights, undertaken seemingly for no
+particular purpose, are often of short duration and are completed before
+the strain of observation becomes too great; moreover an individual
+sometimes possesses a special mark or characteristic which serves to
+make it conspicuous. For example, there is a well-marked variety of the
+Common Guillemot, the Ringed or Bridled Guillemot of science,
+distinguished by an unusual development of white round the eye and along
+the furrow behind it. One such individual I was fortunate in discovering
+upon a crowded cliff, and, as in the case of the Lapwing with the broken
+leg or the Yellow Bunting with the injured foot, the identity of the
+bird was beyond dispute, and one could observe that it appropriated to
+itself a particular position upon a particular ledge.
+
+Guillemots and Razorbills return at intervals to the breeding stations
+early in the season, and these visits are repeated with growing
+frequency until the birds are finally established. I have witnessed
+these periodic returns during March in the south of England, and during
+April in the north-west of Ireland, and I am informed that in the latter
+district such visits may occur as early as February. Gaetke, who had
+ample opportunity of observing the birds in Heligoland, puts their
+return at an even earlier date. "They visit their breeding places," he
+says, "in flocks of thousands at the New Year, often even as early as
+December, as though they wanted to make sure of their former haunts
+being well preserved and ready for their reception." Such visits,
+however, are irregular in occurrence; the birds arrive, and, after
+spending a short time upon the ledges, disappear. And since there is not
+the same evidence in their coming and going of that method which we
+observe in the periodical returns of the Bunting or the Finch, it may be
+thought that needless importance is being attached to an episode in
+their lives which is quite intelligible in terms of a feeble response
+determined by a dawning organic change. While it may be quite
+intelligible in such terms it is not thereby explained; for every
+response must have as its antecedent an inherited connection in the
+nervous system determined on biological grounds. Besides, these early
+periodic returns conform in general to the type of behaviour displayed
+by other species, the males of which return to their breeding grounds
+many weeks before the real business of reproduction begins. Are we then
+justified in regarding them as accidents of the developing situation?
+Are we not rather bound to admit that they have some definite biological
+end to serve?
+
+[Illustration: Competition for territory is seldom more severe than
+amongst cliff-breeding sea birds, and the efforts of individual
+Razorbills to secure positions on the crowded ledges lead to desperate
+struggles.
+
+Emery Walker ph.sc.]
+
+These examples show that the males of many species reverse their mode of
+life at the commencement of the breeding season and proceed to isolate
+themselves, each one in a definitely delimited area.
+
+
+There are three ways in which we may attempt to interpret this
+particular mode of male behaviour. We may regard it as an accidental
+circumstance, nowise influencing the course of subsequent procedure; or,
+appealing to the law of habit formation, we may regard it as an
+individual acquirement; or again, we may invest it with a deeper
+significance and seek its origin in some specific congenital disposition
+determined on purely biological grounds.
+
+Which of these three shall we choose? The first by itself requires but
+little consideration; for though it might explain the initial visit, it
+cannot account for the persistency with which the plot of ground is
+afterwards resorted to. Supposing, however, that we combine the first
+and the second; supposing, that is to say, we assume, for the purpose of
+argument, that the initial visit is fortuitous, and that constancy is
+supplied by habit formation--would that be a satisfactory
+interpretation? It is a simple one, inasmuch as it only requires that a
+male shall alight by chance in a particular place for a few mornings in
+succession in order that the process may be set in motion. Now an
+essential condition of habit formation is recurrent repetition; given
+this repetition and, it is true, any mode of activity is liable to
+become firmly established. But how can we explain the repetition? Even
+if we are justified in assuming that the initial visit is purely an
+accidental occurrence, we cannot presume too far upon the laws of chance
+and assume that the repetition, at first, is also fortuitous.
+
+So that we come back to the congenital basis, the last of our three
+propositions. And it will, I think, be admitted that the facts give us
+some grounds for believing that the securing of the territory has its
+root in the inherited constitution of the bird. In comparing the
+behaviour of the migratory male with that of the resident, attention was
+drawn to the manner in which the occupation of a territory was effected:
+the former bird, it may be remembered, established itself without delay,
+whereas the latter did so only by degrees, and the difference was
+attributed to the incidence of migration which required a closer
+correspondence between organic process and external environment. But the
+significance for us just now lies in the fact that the definiteness,
+which accompanies the initial behaviour of the migratory male in
+relation to the territory, cannot have been acquired by repetition; for
+this reason, that when the male occupies its space of ground at the end
+of its long and arduous journey, it does so without preparation or
+experiment, even without hesitation, as if aware that it was making good
+the first step in the process of reproduction. No doubt, if it happened
+to be an individual that had already experienced the enjoyment of
+reproduction, it might be aware of the immediate results to be achieved
+and act accordingly. But among the hosts of migrants that one observes,
+there must be many males which have not previously mated; and yet, upon
+arrival, they all behave in a similarly definite manner--so that
+experience cannot well be the primary factor in the situation. If, then,
+the essential condition of habit formation is absent and experience is
+eliminated, there is nothing left but racial preparation to fall back
+upon.
+
+Nevertheless, it is true that many resident males seem to pass through
+a period of indecision before they establish themselves permanently in
+their respective territories; they come and go, their visits grow more
+and more prolonged, and only after the lapse of some considerable time
+does the process of establishment attain that degree of completeness
+which is represented in the initial behaviour of the migratory male.
+Their whole procedure seems therefore to bear the stamp of individual
+acquirement; and, if it stood alone, we might be content to construe it
+thus, but the example of the migratory male necessitates our looking
+elsewhere for the real meaning of the indecision.
+
+Let me first of all give some instances of the persistence with which a
+male remains in one spot, and this despite the fact that it has no mate.
+
+A Reed-Bunting occupied a central territory in a strip of marshy ground
+inhabited annually by four or five males of this species. Throughout
+April, May, and until the 19th June, it clung to its small plot of
+ground, tolerated no intrusion, and sang incessantly.
+
+Two Whitethroats arrived at much the same time--the 30th April
+approximately--and occupied the corner of a small plantation; the one
+obtained a mate the day following its arrival, the other remained
+unpaired for a fortnight.
+
+A Reed-Warbler established itself amongst some willows and alders
+adjoining a reed-bed and made its headquarters in a small willow bush.
+Not more than fifteen yards away, on the edge of the main portion of the
+reeds, another male was established and was paired on the 22nd May. Each
+morning the single male behaved in much the same way, singing
+continuously whilst perched upon the bush. And so the days passed by
+until it seemed improbable that it would ever secure a mate, but one
+appeared on the 20th June, and a nest was built forthwith.
+
+Now it is difficult to believe that a chance visit, even though repeated
+for a few mornings in succession, could have accounted for the
+Reed-Bunting remaining so persistently in the marsh, or the Whitethroat
+in one corner of the osier bed, or the Reed-Warbler in that one
+particular willow. Not only so, but if a habit of such evident strength
+can be acquired so readily, we have a right to ask why it should only be
+acquired in the spring--why not at every season? Considerations such as
+these lead to the belief that there must be some congenital basis to
+account for such persistent endeavour; the more so since it is difficult
+not to be impressed with the conative aspect of the male's behaviour. To
+a stranger, unacquainted with its previous history, the bird might
+appear to be leading a life of hesitation, whereas, if carefully
+watched, its whole attitude will be found to betray symptoms of a
+striving towards some end; and the frequent departure and return, which
+might be pointed to as the material from which a definite mode of
+procedure would be likely to emerge, is in reality behaviour of a
+determinate sort.
+
+My interpretation, then, of the apparent indecision in the behaviour of
+the resident male is this. During the winter most species live in
+societies, together they seek their food and together they retire in the
+evening to the accustomed roosting places; and the association of
+different individuals confers mutual benefits upon the associates. The
+movements of these societies are dominated by the question of food; all
+else is subservient, and the supply of the necessary sustenance may,
+under certain conditions, become a difficulty which can only be met by
+energy and resource. After the long night the sensation of hunger is
+strong, and the birds, on awakening, fly to the accustomed feeding
+grounds, returning again in the evening to the selected spot, and by
+frequent repetition a routine becomes established. Thus the behaviour of
+each individual is determined not only by the powerful gregarious
+impulse but also by the habits formed in connection therewith during
+many weeks in succession. Now with the rise of the appropriate organic
+state, the disposition to seek the breeding ground and there to
+establish itself becomes dominant in the male. But the process is a
+gradual one. There is no need, as happens amongst the migrants, for the
+period of organic change to conform rigidly to the growth of any
+particular condition in the environment, and hence for a time the bird
+oscillates between two modes of behaviour--between that one organised by
+frequent repetition and that one determined by the functioning of this
+new disposition.
+
+To look at the matter broadly, it is scarcely likely that so definite a
+mode of behaviour would recur with such regularity, generation after
+generation, in the individuals belonging to so many widely divergent
+forms, if it had no root in the inborn constitution of the bird. But the
+law of habit formation has its part to play also. By itself it is
+inadequate; yet it probably does assist very materially in adding still
+greater definition, and it probably is responsible in a large measure
+for determining the limits of the territory according to the conditions
+of existence of the species--thus the Falcon seeks its prey over wide
+tracts of land, and, by hunting over certain ground repeatedly,
+establishes a routine, which broadly fixes the area occupied; the
+Woodpecker cannot find food upon every tree, and every forest does not
+contain the necessary trees, and therefore the bird regulates its flight
+according to the position of the trees; and the Warbler, finding food
+close at hand, does not need to travel far, and the area it occupies is
+consequently small.
+
+So that the most likely solution of the problem will be found in a
+combination of our second and third propositions; that is to say, in an
+initial responsive behaviour provided for in the inherited constitution
+of the nervous system, and in a definiteness acquired by repetition and
+determined by relationships in the external environment.
+
+
+
+
+CHAPTER III
+
+THE DISPOSITION TO DEFEND THE TERRITORY
+
+
+In the previous chapter I endeavoured to show that each male establishes
+a territory at the commencement of the breeding season, and there
+isolates itself from members of its own sex. And further I gave my
+reasons for believing that this particular mode of behaviour is
+determined by the inherited nature of the bird, and that we are
+justified in speaking of it as "a disposition to secure a territory"
+because we can perceive its prospective value. But the act of
+establishment is only one step towards "securing." By itself it can
+achieve nothing; for any number of different individuals might fix upon
+the same situation, and if there were nothing in the inherited
+constitution of the bird to prevent this happening, where would be the
+security, or how could any benefit accrue to the species?
+
+In withdrawing from its companions in the spring, the male is breaking
+with the past, and this action marks a definite change in its routine of
+existence. But the change does not end in attempted isolation; it is
+carried farther and extends to the innermost life and affects what,
+humanly speaking, we should term its emotional nature, so that the bird
+becomes openly hostile towards other males with whom previously it had
+lived on amicable terms.
+
+The seasonal organic condition is responsible for the functioning of the
+disposition which results in this intolerance, just as it is for the
+functioning of the disposition which leads to the establishment of the
+territory; and the effect of these two dispositions is that a space of
+ground is not only occupied but made secure from intrusion. The process
+is a simple one. There is no reason to believe, there is no necessity to
+believe, that any part of the procedure is conditioned by anticipatory
+meaning; the behaviour is "instinctive" in Professor Lloyd Morgan's
+definition of the word, since it is of a "specific congenital type,
+dependent upon purely biological conditions, nowise guided by conscious
+experience though affording data for the life of consciousness."
+
+That the males of many animals are apt to become quarrelsome during the
+mating period is notorious. Darwin collected a number of facts, many of
+which related to birds, showing the nature and extent of the strife when
+the sexual instinct dominated the situation. And pondering over these
+facts, he deduced therefrom a "law of battle," which, he believed, bore
+a direct relation to the possession of a female. And it must be admitted
+that he had excellent ground for his conclusion in the fact not only
+that the conflicts occur mainly during the pairing season, but that
+the female is often a spectator and seems even to pair with the victor.
+I accepted it, therefore, as the most reasonable interpretation of the
+facts. But, as time passed by, incidents of a conflicting character led
+me to think that after all there might be another solution of the
+problem. And when it was no longer possible to doubt that there was a
+widespread tendency to establish territories, it at once became manifest
+that the battles might have an important part to play in the whole
+scheme. But how was this to be proved? What sort of evidence could show
+whether the proximate end for which the males were fighting had
+reference to the female or to the territory? Clearly nothing but a
+complete record of the whole series of events leading up to reproduction
+could supply the necessary data upon which a decision might rest. In the
+present chapter I shall give, in the first place, the reasons which lead
+me to think that the origin of the fighting cannot be traced to the
+female; afterwards, the evidence which seems to show that it must be
+sought in the territory; and finally, I shall make a suggestion as to
+the part the female may play in the whole scheme.
+
+[Illustration: Male Blackbirds fighting for the possession of territory.
+The bare skin on the crown of the defeated bird shows the nature of the
+injuries from which it succumbed.
+
+Emery Walker ph.sc.]
+
+The facts upon which the "law of battle" was founded were ample to
+establish the truth of its main doctrine. But the evidence upon which
+the interpretation of the battles was based was somewhat superficial. It
+was based mainly upon the general observation that one or more females
+could frequently be observed to accompany the combatants; and if this
+were the sole condition under which the fighting occurred, one must
+admit that this view would have much to recommend it. But it is not
+merely a question of males disputing in the presence of a female; for
+males fight when no female is present, pair attacks pair, or a male may
+even attack a female--in fact there is a complexity of strife which is
+bewildering.
+
+In attributing the rivalry to the presence of the female, it is assumed
+that males are in a preponderance, and that consequently two or more are
+always ready to compete for a mate. Her presence is presumably the
+condition under which his pugnacious nature is rendered susceptible to
+its appropriate stimulus, the stimulus being, of course, supplied by the
+opponent. There would be nothing against this interpretation if it were
+in accord with the facts; but it can, I think, be shown that the males
+are just as pugnacious and the conflicts just as severe even when the
+question of securing a mate is definitely excluded; and I shall now give
+the evidence which has led me to this conclusion.
+
+In the previous chapter we had occasion to refer to the difference in
+the times of arrival of the male and female migrants, and we came to the
+conclusion, it may be remembered, that this was a fact of some
+importance, because it gave us a clue to the meaning of much that was
+otherwise obscure in their behaviour. But it is also of importance in
+connection with the particular aspect of the problem which we now have
+in view, for if it can be shown that males, when they first reach their
+breeding grounds, are even then intolerant of one another's presence, if
+their actions and attitudes betray similar symptoms of quasi-conation,
+if disputes are rife and the struggles of a kind to preclude all doubt
+as to their reality, then it is manifest that in such cases their
+intolerance cannot be due to the presence of the female.
+
+Here, however, I must refer to a view which is held by some
+psychologists, namely, that amongst the higher animals, even on the
+occasion of the first performance of an instinctive act, there is some
+vague awareness of the proximate end to be attained. Discussing the
+nature of instincts, Dr M'Dougall[3] says, "Nor does our definition
+insist, as some do, that the instinctive action is performed without
+awareness of the end towards which it tends, for this, too, is not
+essential; it may be, and in the case of the lower animals no doubt
+often is, so performed, as also by the very young child, but in the case
+of the higher animals some prevision of the immediate end, however
+vague, probably accompanies an instinctive action that has often been
+repeated." A similar view seems to be held by Dr Stout.[4] "As I have
+already shown," he says, "animals in their instinctive actions do
+actually behave from the outset as if they were continuously interested
+in the development of what is for them one and the same situation or
+course of events; they actually behave as if they were continuously
+attentive, looking forward beyond the immediately present experience in
+preparation for what is to come. They apparently watch, wait, search,
+are on the alert. They also behave exactly as if they appreciated a
+difference between relative success and failure, trying again when a
+certain perceptible result is not attained and varying their procedure
+in so far as it has been unsuccessful. All these characters are found in
+the first nest-building of birds as well as in the second; they are
+found also in courses of conduct which occur only once in the lifetime
+of the animal." Both these writers would, I imagine, contend that, even
+when a female is absent, the idea of the female, as the end in view
+throughout, is present; and they would argue that the fact of her
+absence during the fighting in no way disposes of the belief that she is
+the condition under which the pugnacious instinct of the male is
+rendered susceptible to stimulation. What reason is there to think that
+this interpretation is applicable to the case under consideration? When
+a female is present, we observe that the males are pugnacious, and, when
+she is absent, that they still continue to be hostile--that is to say,
+they behave _as if_ she were present. Now, as far as I can ascertain,
+the "_as if_" is the only ground there is for supposing that the female
+is represented in imaginal form--there is no evidence of the fact, if
+fact it be. On the contrary, the behaviour of the male affords some
+fairly conclusive evidence that no such image is the primary factor in
+exciting the instinctive reaction. For if it be the actual presence of
+the female, or, in the absence of such, a mental image, that renders the
+pugnacious nature of the male responsive; provided the usual stimulus
+were present, the instinct ought surely to respond, not only under one
+particular circumstance, but under all circumstances. Yet, as we shall
+presently see, a male is by no means consistently intolerant of other
+males. It may be sociable at one moment or pugnacious at another, but
+the pugnacity is always peculiar to a certain occasion--the occupation
+of a territory. What shall we say then--that a mental image is a
+situational item only when the territory is occupied? It may be so; it
+may be that the fact of occupation gives rise to the mental image which,
+in its turn, renders the fighting instinct explosive, which again
+renders the possession of the territory secure. That such an
+interpretation is possible we must all admit. But if it were true,
+though it would not affect the main consideration, namely, whether the
+fighting has reference to the possession of a particular female, or to
+the protection of the territory, it would make further discussion as to
+which of these is the condition of the fighting unprofitable, for each
+would have its part to play in the process, the territory remaining,
+however, the principal factor in the situation.
+
+Now the difference in the times of arrival of the male and female
+migrant varies in different species from a few days to a fortnight or
+even more. It is most marked in those that return to their breeding
+grounds early in the season, and the greater the margin of difference
+the greater scope is there for observation. In my records for the past
+twelve years, there are frequent references to these initial male
+contests in the life of the Willow-Warbler and of the Chiffchaff; and in
+the district which I have in mind, these two species arrive early in the
+season, the males preceding the females by a week or even as much as a
+fortnight. Suppose, then, that two Chiffchaffs establish themselves in
+adjoining territories; or suppose that a male settles in a territory
+already occupied; what is the result? Well, scenes of hostility soon
+become apparent; as the birds approach one another they become more and
+more restive, their song ceases, they no longer search for food in the
+usual methodical manner, but instead their movements are hurried and
+their call-notes are uttered rapidly--all of which betrays a heightened
+emotional tone. Then the climax is reached, there is a momentary
+fluttering of tiny wings, a clicking of bills, and for the time being
+that may be all. But unless one or other of the combatants retires, this
+scene may be repeated many times in the course of a few hours, and
+repeated with varying degrees of severity. Yet the fighting, even in the
+most extreme form, when the birds locked together fall slowly to the
+ground, is seldom of an impressive kind, and one has to bear in mind the
+capabilities of the actors, remembering that the most severe struggle
+might readily be interpreted as a game if it were not for certain
+symptoms which reveal its inner nature.
+
+The males of many other migrants can frequently be observed to fight
+when there was every reason to believe that females had still to arrive.
+The Blackcap is notoriously pugnacious, but not more so than the
+Marsh-Warbler or the Whinchat. Here in Worcestershire, the _Arundo
+phragmites_ grows mainly on certain sheets of water which are
+comparatively few and far between, and the Reed-Warbler is consequently
+restricted to isolated and more or less confined areas. The males arrive
+early in May before the new growth of reeds has attained any
+considerable height, and each one has its own position in the reed-bed,
+sings there, and throughout the whole period of reproduction actively
+resists intrusion on the part of other males. I have kept watch upon a
+small area of reeds daily from the date of the first arrival; each
+individual was known to me, and as the growing reeds were only a few
+inches in height, a female could scarcely have escaped detection. Yet
+time and again disputes arose, and males pursued and pecked one
+another, striving to attain that isolation for which racial preparation
+had fitted them.
+
+But on account of their violence, or their novelty, or because the
+absence of a female was beyond question, some battles stand out in one's
+memory more prominently than others. An instance of this was a struggle
+between two Whitethroats which happened in the latter part of April and
+lasted for three successive days. The scene of its occurrence was more
+or less the same on each occasion, and the area over which the birds
+wandered was comparatively small. The fighting was characterised by
+persistent effort and was of a most determined kind, and so engrossed
+did the assailants become that they even fluttered to the ground at my
+feet. No trace of a female was to be seen at any time during these three
+days, nor, during the pauses in the conflict, was the emotional
+behaviour of a kind which led me to suppose that a female was anywhere
+in the vicinity. And, if she had been near, she must have made her
+presence known, for the belief that she is a timid creature, skulking on
+such occasions in the undergrowth, is by no means borne out by
+experience.
+
+Even more impressive was a battle between two male Cuckoos. It occurred
+high up in the air above the tops of some tall elm-trees which roughly
+marked the boundary line between their respective areas, and the actions
+of the birds were plainly visible. At the moment of actual collision
+the opponents were generally in a vertical position, and wings, feet,
+and beaks were made use of in turn; one could plainly see them strike at
+one another with their feet, and one could observe the open bill which
+generally denotes exhaustion, but may of course have been due to anger,
+or used as a means of producing terror. Yet no female appeared in the
+locality until six days after the occurrence of this struggle--and
+she certainly is not easily overlooked, for her note is unmistakable
+even when the behaviour of the male does not betray her arrival.
+
+[Illustration: Male Cuckoos fighting before the arrival of a female
+
+Emery Walker ph.sc.]
+
+That the actual presence of the respective females exercised any
+influence on the course of these struggles is more than doubtful. Not
+only did one fail to detect them, but one's failure to do so was
+confirmed by the knowledge that they had not yet arrived in those
+particular localities. Hence the fact of the male preceding the female
+is a valuable aid to the interpretation of subsequent behaviour; and one
+appreciates it the more after having experienced the difficulty of
+deciding whether she is present during the conflicts between resident
+males, for no matter how carefully we may observe the conditions which
+lead up to, and which accompany, such conflicts, or how closely we may
+scrutinise the surrounding trees, undergrowth, or ground, there always
+remains the possibility that she may, after all, have been overlooked.
+But this must not be taken to imply that in such cases direct
+observation alone can lead to no serviceable result, or that the
+evidence gained therefrom is worthless. Far from it. Failure to detect a
+female is so very common an occurrence that, even if we lacked the
+corroborative evidence supplied in the life of the migratory male, it
+would still be unreasonable to suppose that it were solely due to
+mistaken observation. We mark her absence during the conflicts between
+the respective males of many common species--the Finches, Buntings, and
+Thrushes that occupy their territories early in the season when the
+hedgerows and trees are still bare; but more frequently amongst those
+that inhabit open ground, because the movements of the birds are there
+more accessible to observation. For instance, half a dozen or more
+Lapwings can be kept in view at the same time, and as they stand at dawn
+in solitary state, keeping watch upon their respective territories, they
+are conspicuous objects on the short, frosted grass; no stranger can
+enter the arena without the observer being aware of it, no commotion can
+occur but one detects it, no movement however small need be missed. And
+so they fight, in a manner which leaves no doubt as to the reality of
+the struggle, when their prospective mates are absent not only from the
+particular territories in which the conflicts take place, but absent too
+from those adjoining.
+
+If the fact that males fight before they are paired and in the absence
+of a female could be placed beyond all question, it would no longer be
+possible to regard her possession as the end for which they are
+contending, and consequently there would be no need to produce further
+evidence. But the examples which I have given refer, of course, to only
+a few migrants and a few residents--and moreover it must be admitted
+that a female _is_ often conspicuous during the battles--so that by
+themselves they must be regarded, and rightly so, as inconclusive. We
+must therefore pass on to consider evidence of a somewhat different
+character.
+
+I spoke of the complexity of the strife. By this I mean that it is not
+merely a matter of disputes between adjoining males, but that it is a
+far more comprehensive business involving both sexes. Thus female fights
+with female and pair with pair, or a male will attack a female, or,
+again, a pair will combine against a single male or a single female. And
+from all this complexity of strife we gain much valuable evidence in
+regard to the question immediately before us. For when one pair attacks
+another, or males that are definitely paired fight with one another, or
+an unpaired male attacks either sex of a neighbouring pair
+indiscriminately, there is surely little ground for supposing that the
+possession of a mate is the reason of it all.
+
+The battles between pairs of the same species are by no means uncommon.
+Observe, for example, the central pair of three pairs of Reed-Buntings
+occupying adjoining territories, and keep a daily record of the routine
+of activity practised by both sexes during the early hours of the
+morning; then, at the close of the season, summarise all the fighting
+under different headings, and it will be found that the number of
+occasions upon which the central pair attacked, or was attacked by,
+neighbouring pairs will form a considerable portion of the whole.
+
+Or watch the Moor-Hen, and for the purpose choose some sheet of water
+large enough to accommodate three or more pairs, and so situated that
+the birds can always be kept in view. Early in February the pool will be
+haunted by numbers of individuals of both sexes, all swimming about
+together, and, if the pool is surrounded by arable land, wandering over
+that land subject to no territorial restrictions, apparently free to
+seek food where they will. But as time goes by, their number gradually
+decreases until a few pairs only remain, and these will occupy definite
+areas. If careful watch is then kept and the relations of the pairs
+closely studied, there will be no difficulty in observing the particular
+kind of warfare to which I am alluding, and it will be noticed that the
+encounters are of a particularly violent description. Thus two pairs
+approach one another, and, when they meet, throw themselves upon their
+backs, each bird striking at its adversary with its feet or seizing hold
+of it with its beak; and though, in the commotion that ensues, it is
+almost impossible to determine what exactly is happening, there is
+reason to believe that the sexes attack one another indiscriminately.
+
+A struggle between two pairs of Pied Wagtails is worth mentioning. It
+impressed itself upon my memory because of the unusual vigour with which
+it was conducted. The battle lasted for fifteen minutes or more, and
+the four birds, collecting together, pursued and attacked one
+another--at one moment in the air, at another upon the roof of a house
+where they would alight and flutter about on the slates, uttering their
+call-note without ceasing--until finally they disappeared from view,
+still, however, continuing the struggle.
+
+[Illustration: Two pairs of Pied Wagtails fighting in defence of their
+territories.
+
+Emery Walker ph.sc.]
+
+Such is the nature of the warfare which prevails between neighbouring
+pairs, and which can be observed in the life of many other species--the
+Chaffinch, Stonechat, Blackbird, Partridge, Jay, to mention but a few.
+
+The conflicts between males that are definitely paired are of such
+common occurrence that it is scarcely necessary to mention specific
+instances. But the occasions on which a male attacks either sex of a
+neighbouring pair indiscriminately, or on which a pair combine to attack
+a female, are less frequent.
+
+Now if it be true that males fight for no other purpose than to gain
+possession of a mate, what meaning are we to attach to the battles
+between the pairs, or what explanation are we to give of the fact that
+paired males are so frequently hostile? Those who hold this view will
+probably argue thus: "The presence of the female is the condition under
+which the pugnacious instinct of the male is rendered susceptible to
+appropriate stimulation, and the stimulus is supplied by a rival male;
+we admit that all the fighting which occurs after pairing has taken
+place has nothing to do strictly speaking with gaining a mate, but,
+inasmuch as the fact of possession is always liable to be
+challenged--and no male can differentiate between a paired and an
+unpaired intruder--we contend that it would add to the security of
+possession if the pugnacious instinct remained susceptible to
+stimulation so long as there were any possibility of challenge from an
+unpaired male; and we think that the waste of energy involved in the
+struggles between paired birds, and which we grant is purposeless, would
+be more than balanced by the added security." This is a possible
+explanation and requires consideration. It cannot account for all the
+diverse ways in which the sexes are mixed up in the fighting--it cannot,
+for instance, explain the fact that an unpaired male will attack either
+sex of an adjoining pair indiscriminately--but nevertheless it appears
+at first sight to be a reasonable explanation of some of them. We must
+remember, however, that fighting continues throughout the whole period
+of reproduction. Even after the discharge of the sexual function has
+ceased, and the female is engaged in incubation or in tending her young,
+the male is still intolerant of intruders; and it is difficult to
+believe that, at so late a stage in the process, a female could be any
+attraction sexually to an unpaired male. But apart from any theoretical
+objection, there remains the fact--namely that there is no evidence
+that a male, after having once paired, is liable to be robbed of its
+mate. And in support of this fact I have only to state that I have met
+with no single instance of failure to obtain and hold a mate when once a
+territory had been secured. Bearing in mind then that both sexes
+participate in the fighting, and that individuals of the opposite sex
+frequently attack one another; that all such conflicts are characterised
+by persistent effort, and that they are not limited to just the
+particular period when the sexual instinct is dominant but continue
+throughout the breeding season; bearing in mind that in at least one
+form of this promiscuous warfare the influence of the female can be
+definitely excluded, and that, in the remaining forms, the evidence
+which is required to link them up with the biological end of securing
+mates is lacking--can it be denied that the complexity of the strife
+makes against the view that the possession of a female is the proximate
+end for which the males are fighting?
+
+We started with the most simple aspect of the whole problem, the
+fighting of two males in the presence of one female--the aspect upon
+which attention has usually been fixed. And if it remained at that, if
+observation failed to disclose any further development in the situation,
+then there would be no need to probe the matter deeper, there would be
+no reason to doubt the assertion that the quarrel had direct reference
+to the female. But assuredly no one can ponder over the diversity of
+battle and still believe that the possession of a mate furnishes an
+adequate solution of the mystery. Clearly such an hypothesis cannot
+cover all the known facts; there are conflicts between separate pairs,
+and there are conflicts between males when females are known to be
+absent and when their mates are even engaged in the work of
+incubation--these cannot be due to an impulse in a member of one sex to
+gain or keep possession of one of the other sex. So that taking all
+these facts into consideration, we are justified, I think, in hesitating
+to accept this view, and must look elsewhere for the real condition
+under which the pugnacious nature of the male is rendered susceptible to
+appropriate stimulation.
+
+
+What then is the meaning of all this warfare? The process of
+reproduction is a complex one, built up of a number of different parts
+forming one inter-related whole; it is not merely a question of
+"battle," or of "territory," or of "song," or of "emotional
+manifestation," but of all these together. The fighting is thus one link
+in a chain of events whose end is the attainment of reproduction; it is
+a relationship in an inter-related process, and to speak of it as being
+even directly related to the territory is scarcely sufficient, for it is
+intimately associated with the disposition which is manifested in the
+isolation of the male from its companions, and forms therewith an
+_imperium in imperio_ from which our concept of breeding territory is
+taken. But let me say at once that it is no easy matter to prove this,
+for since so many modes of behaviour, which can be interpreted as
+lending support to this view, are likewise interpretable on the view
+that the presence of a female is a necessary condition of the fighting,
+it is difficult to find just the sort of evidence that is required.
+Nevertheless, after hearing the whole of the evidence and at the same
+time keeping in mind the conclusion which we have already reached, I
+venture to think that the close relationship between the warfare on the
+one hand and the territory on the other will be fully admitted.
+
+Formerly I deemed the spring rivalry to be the result of accidental
+encounters, and I believed that an issue to a struggle was only reached
+when one of the combatants succumbed or disappeared from the locality, a
+view which neither recognised method nor admitted control. Recent
+experience has shown, however, that I was wrong, and that there is a
+very definite control over and above that which is supplied by the
+physical capabilities of the birds.
+
+Let us take some common species, the Willow-Warbler being our first
+example; and, having found three adjoining territories occupied by
+unpaired males, let us study the conflicts at each stage in the sexual
+life of the three individuals, observing them before females have
+arrived upon the scene, again when one or two of the three males have
+secured mates, and yet again when all three have paired. Now we shall
+find that the conditions which lead up to and which terminate the
+conflicts are remarkably alike at each of these periods. A male
+intrudes, and the intrusion evokes an immediate display of irritation on
+the part of the owner of the territory, who, rapidly uttering its song
+and jerking its wings, begins hostilities. Flying towards the intruder,
+it attacks viciously, and there follows much fluttering of wings and
+snapping or clicking of bills. At one moment the birds are in the
+tree-tops, at another in the air, and sometimes even on the ground, and
+fighting thus they gradually approach and pass beyond the limits of the
+territory. Whereupon a change comes over the scene; the male whose
+territory was intruded upon and who all along had displayed such
+animosity, betrays no further interest in the conflict--it ceases to
+attack, searches around for food, or sings, and slowly makes its way
+back towards the centre of the territory.
+
+Scenes of this kind are of almost daily occurrence wherever a species is
+so common, or the environment to which it is adapted so limited in
+extent, that males are obliged to occupy adjacent ground. The Moor-Hen
+abounds on all suitable sheets of water, and it is a bird that can be
+conveniently studied because, as a rule, there is nothing, except the
+rushes that fringe the pool, to hinder us from obtaining a panoramic
+view of the whole proceedings, and moreover the area occupied by each
+individual is comparatively small. Towards the middle of February,
+symptoms of sexual organic change make themselves apparent, and the pool
+is then no longer the resort of a peaceable community; quarrels become
+frequent, and as different portions of the surface of the water are
+gradually appropriated, so the fighting becomes more incessant and more
+severe. Each individual has its own particular territory, embracing a
+piece of open water as well as a part of the rush-covered fringe, within
+which it moves and lives. But in the early part of the season, when the
+territories are still in process of being established, and definiteness
+has still to be acquired, trespassing is of frequent occurrence, and the
+conflicts are often conspicuous for their severity.
+
+Now these conflicts are not confined to unpaired individuals, nor to one
+sex, nor to one member of a pair--every individual that has settled upon
+the pool for the purpose of breeding will at one time or another be
+involved in a struggle with its neighbour. If then we single out certain
+pairs and day by day observe their actions and their attitude towards
+intruders, we shall notice that, instead of their routine of existence
+consisting, as a casual acquaintance with the pool and its inmates might
+lead us to believe, of an endless series of meaningless disputes, the
+behaviour of each individual is directed towards a similar goal--the
+increasing of the security of its possession; and further, if we pay
+particular attention to the circumstances which lead up to the quarrels
+and the circumstances under which such quarrels come to an end, we shall
+find, when we have accumulated a sufficient body of observations, that
+the disputes always originate in trespass, and that hostilities always
+cease when the trespasser returns again to its own territory. By careful
+observation it is possible to make oneself acquainted with the
+boundaries--I know not what other term to use--which separate this
+territory from that; and it is the conduct of the birds on or near these
+boundaries to which attention must be drawn. A bird may be feeding
+quietly in one corner of its territory when an intruder enters. Becoming
+aware of what is happening it ceases to search for food, and approaching
+the intruder, at first swimming slowly but gradually increasing its
+pace, it finally rises and attacks with wings and beak, and drives its
+rival back again beyond the boundary. Thereupon its attitude undergoes a
+remarkable change; ceasing to attack, but remaining standing for a few
+moments as if still keeping guard, it betrays no further interest in the
+bird with which a few seconds previously it was fighting furiously. On
+one occasion I watched a trespasser settle upon a conspicuous clump of
+rushes situated near the boundary. The owner, who was at the moment some
+distance away, approached in the usual manner, and, having driven off
+the trespasser, returned immediately to the clump, where it remained
+erect and motionless.
+
+A feature which marks all the fighting, and which we cannot afford to
+disregard, is the conative aspect of the behaviour of the owner of the
+territory. The bird attacks with apparent deliberation _as if_ it were
+striving to attain some definite end. I recollect an incident which was
+interesting from this point of view. A pair of Reed-Buntings were
+disturbed by a Weasel which had approached their nest containing young.
+Both birds betrayed symptoms of excitement; as the Weasel threaded its
+way amongst the rushes, so they fluttered from clump to clump or clung
+to the stems, uttering a note which is peculiar to times of distress,
+and followed it thus until finally it disappeared in a hedge. The
+rapidly uttered note and the excitement of the birds caused some
+commotion, and the male from an adjoining territory approached the
+scene. Now one would have expected that the presence of this bird, and
+possibly its aid in driving away a common enemy, would have been
+welcomed; one would have thought that all else would have been
+subservient to the common danger, and that so real a menace to the
+offspring would have evoked an impulse in the parent powerful enough to
+dominate the situation and subordinate all the activities of the bird to
+the attainment of its end. But what happened? Three times during this
+incident, the male, whose young were in danger, abandoned the pursuit of
+the Weasel and pursued the intruder. It was not merely that he objected
+to the presence of this neighbouring male in a passive way, nor even
+that he had a momentary skirmish with it, but that he determinedly drove
+the intruder beyond the boundary and only then returned to harass the
+Weasel.
+
+Thus it seems clear that the proximate end to which the fighting is
+directed is not necessarily the defeat of the intruder, but its removal
+from a certain position. And inasmuch as this result will be obtained
+whether the retreat is brought about by fear of an opponent or by
+physical exhaustion, it is manifest that too much significance need not
+be attached to the amount of injury inflicted. It is necessary to bear
+this in mind, because it is held by some, who have carefully observed
+the actions of various species, that overmuch importance is attached to
+the conflicts, that in a large number of instances they are mere
+"bickerings" and lead to nothing, and that they are now only "formal,"
+which means, I suppose, that they are vestigial--fragments of warfare
+that determined the survival of the species in bygone ages. But if the
+conclusion at which we have just arrived be correct, if we can recognise
+a single aim passing through the whole of the warfare--and that one the
+removal of an intruder from a certain position, then we need no longer
+concern ourselves as to the degree of severity of the battles--we see it
+all in true perspective. Neither exhaustion nor physical inability are
+the sole factors which determine the nature and extent of the fighting;
+there is a more important factor still--position. According, that is to
+say, to the position which a bird occupies whilst fighting is in
+progress, so its pugnacious nature gains or loses susceptibility, and it
+is this gain or loss of susceptibility which I refer to when I speak of
+the fighting as being controlled.
+
+What we have then to consider is the relation of "susceptibility" to
+"position." We can explain the relationship in two ways. We can say that
+the part of the nature of the male which leads to the occupation of a
+territory, and is partly hereditary and partly acquired, is stronger
+than the part which leads the bird to fight, and which is conditioned by
+the presence of a female, and that consequently when the male passes the
+boundary, the impulse to return asserts itself and the conflict ceases;
+or we can say that the occupation of a territory is the condition under
+which the pugnacious instinct is rendered susceptible to stimulation,
+that the stimulus is supplied by the intruder, and that when the male
+passes outside the accustomed area its instinct is no longer so
+susceptible and it therefore retires from the conflict.
+
+[Illustration: Long-tailed Tit Males fighting for possession of
+territory. The feathers have been torn from the crown of the defeated
+and dying rival.
+
+Emery Walker ph.sc.]
+
+Of these explanations, the first is not altogether satisfactory. It
+requires the presence of a female and, as we have seen, a female is by
+no means always present. Then it attributes to the one side of the
+inherited nature an influence which is not borne out by the facts, for
+in the ordinary routine of existence, without the incentive of battle,
+every individual is liable to wander occasionally beyond its boundary
+and to intrude temporarily upon its neighbours; and this it could
+scarcely do, providing its nature to remain within the territory were
+powerful enough to dominate its movements and curtail its activities
+even during the excitement of an encounter. But there is nothing
+inherently improbable in the alternative hypothesis, nor anything that
+is at all inconsistent with the behaviour as observed; on the contrary,
+if it is admitted, the facts become connected together and exhibit a
+meaning which they otherwise would not have possessed.
+
+So much for the controlling influence of "position," which alone seems
+to me sufficient ground for believing that the fighting has reference to
+the territory. But it is not the whole of the evidence.
+
+Now if it were possible to demonstrate by actual observation that those
+males which had not established territories were not pugnacious, we
+should have something in the nature of proof of the correctness of this
+view. Demonstrative evidence of this kind is, however, unattainable. Yet
+we can come very near to obtaining it by reason of a peculiar feature
+which marks the process of acquiring territory--the neutral ground. The
+Lapwing will serve as an illustration. In the previous chapter I
+referred to the small flocks that appeared in the accustomed water
+meadow early in February, and I described how they settled day after day
+in that meadow, but only in a limited part of it, where they passed
+their time in rest, in preening their feathers, or in running this way
+and that lazily searching for food; and how, at length, the flock
+dwindled by reason of individuals breaking away in order to secure
+positions on the remaining part of the meadow. Here the neutral ground
+is adjacent to the territories, and, while still occupied by the flock,
+is resorted to by the males that had deserted that flock in order to
+establish those territories.
+
+Suppose now that we have the whole meadow in view from some point of
+vantage. In front of us are the territories, in the distance the neutral
+ground; and in each territory there is a solitary male, while on the
+neutral ground a number of individuals of both sexes are assembled, and
+move about freely one amongst another. So that the scene presented to
+view is somewhat as follows: a flat meadow, at one end of which, and at
+fairly regular intervals, a few solitary individuals are dotted about,
+each one keeping at a distance from its neighbours; while at the other
+end a number of individuals are collected together in a comparatively
+small space, apparently deriving some satisfaction from their close
+association. That surely is a very remarkable contrast. But let us
+continue our investigation, first fixing our attention upon the solitary
+individuals; one is standing preening its feathers, another is squatting
+upon the ground, a third runs a few yards in this direction then a few
+yards in that, stimulated apparently by the sight of food, and so on.
+Moreover, each one keeps strictly to a well-defined area and makes no
+attempt to associate with its fellows. One of the males, however, whilst
+roaming backwards and forwards approaches the limit of its territory,
+and this brings the neighbouring bird, whose boundary is threatened,
+rapidly to the spot. In an upright position both stand face to face, and
+the battle then begins; with their wings they attempt to beat one
+another about the body, with their beaks they aim blows at the head, and
+in the melee wings and legs seem to be inextricably mixed; whilst at
+intervals, driven backwards by the force of the collision, they are
+compelled to separate, only, however, to return to the charge--and the
+sound of beating wings and the feathers that float in the air are tokens
+of earnestness. Such scenes are of frequent occurrence; but the
+conflicts vary in intensity, and the circumstances under which they
+occur vary too, and females come and go without leaving any clue as to
+their ultimate intentions.
+
+Turning now to the flock one is impressed with the friendship that seems
+to exist between the various members. There are, it is true, occasional
+displays of pugnacity which never seem to develop into anything very
+serious; for instance, one bird will fly at another, and a momentary
+scuffle is followed by a short pursuit but nothing more--nothing, that
+is to say, in the least comparable with the battle previously described.
+Of what is the flock composed? Of members of both sexes. There is no
+difficulty in assuring oneself that this is so. But is it entirely
+composed of individuals in whom development has not reached a stage
+adequate for the functioning of the primary dispositions? No, not
+entirely; for it will be observed that its number is a fluctuating one,
+that birds come and go, and, if a close watch is kept upon the different
+individuals as they leave, it will be noticed that some at least are
+inmates of the territories at the opposite end of the meadow--the
+solitary members whose behaviour we were recently watching. This fact is
+an important one. We were impressed, it may be remembered, with the
+contrast between the general behaviour of the birds at the opposite
+ends of the meadow. But now it appears as if the contrast were not
+between this individual and that, but between the behaviour of the same
+one under different circumstances. The male, that is to say, which,
+while in its territory, tolerates the approach of no other male, flies
+to the flock and is there welcomed by the very individuals with whom a
+short time previously it had been engaged in serious conflict.
+
+But if the conditions are reversed and the flock happens to settle in an
+occupied territory, the attitude of the owner towards the flock is very
+different. In the year 1916 an incident of this kind occurred in the
+meadow to which reference has already been made. The weather had been
+exceptionally severe--very cold easterly and north-easterly winds,
+frost, and frequent falls of snow had affected the behaviour of the
+Lapwings, and seemed to have checked the normal development of their
+sexual routine. The males would attempt to establish themselves, and
+then, when the temperature fell and the ground was covered with snow,
+would collect again in flocks and follow their winter routine. It was on
+the 9th March, during one of the spells of milder weather, that the
+flock on the neutral ground was disturbed and settled mainly in the
+territory marked No. 3 on the 1916 plan, but partly on that marked No.
+2. The owners thereupon began to attack the different members of the
+invading flock. Fixing attention upon a particular bird whilst ignoring
+the remainder, the No. 3 male drove it away, and then after a pause
+drove another away, and so on until by degrees all the invaders were
+banished, and the No. 2 male did likewise. The interest of this incident
+lies, however, in the behaviour of the different individuals of which
+the flock was composed; when attacked they made no real show of
+resistance, but accepted the situation and left. The will to fight was
+clearly lacking, yet their presence was a source of annoyance to the
+owners of the territories. A short time previously a female had
+accompanied one of the males and was at that time somewhere in the
+vicinity, but beyond this there was no evidence to show that either of
+them were paired, and even if the presence of the female were the reason
+of the pugnacity of the one, it could not well account for that of the
+other.
+
+The neutral ground does not always happen to be so close at hand as in
+the case of the meadow referred to. Sometimes the birds will resort to a
+particular field, attracted probably by a plentiful supply of food, and
+here they collect and behave as they do during the winter, running this
+way and that as the fancy takes them, meeting together by accident at
+one moment, parting at another, according to the direction in which they
+happen to wander. Of animosity there is little sign; the season might be
+the middle of winter instead of the middle of March for all the
+indication there is of sexual development, and yet one knows that they
+will behave differently when they leave this ground, as presently they
+will, and return to their territories in the surrounding neighbourhood,
+and that there each one will fight if necessary to preserve its acre
+from intrusion.
+
+It would seem, then, from this that the fighting must bear some relation
+to the particular area of ground in which it occurs; and unless it can
+be shown that there is some other factor in the external environment of
+the male, that is the direction in which we must look for the condition
+under which the instinct is rendered susceptible. One's thoughts turn,
+of course, to the female, but she too passes backwards and forwards
+between the territories and the neutral ground, and if her presence were
+really a _conditio sine qua non_ of the strife, one would like to know
+why, when she leaves those territories and joins the flock and the males
+do likewise, similar conflicts should not prevail there also.
+
+Other species have their neutral ground, but the environment seldom
+affords such facilities for observation as does that of the Lapwing.
+Even though the Moor-Hens, who are so conspicuously intolerant upon the
+pool, _do_ feed together amicably upon the meadows adjoining; and the
+Chaffinch that is so pugnacious in the morning, _does_ seek out the
+flock later in the day; yet their conditions of existence prevent our
+obtaining a panoramic view of the whole proceeding, and we have to study
+each scene separately before discovering that the relationship between
+intolerance and the territory on the one hand, and friendship and the
+neutral ground on the other, is just as strong a feature as it is in the
+behaviour of the Lapwing.
+
+I shall now give a brief account of the conduct of a male Reed-Bunting
+which by persistent effort established itself late in the season, and I
+shall do so because its behaviour tends to confirm much that has been
+said in the preceding pages.
+
+Early in March three male Reed-Buntings occupied a small water meadow
+overgrown with the common rush, and by the third week all of them were
+paired. On the 30th March two of the males were unusually pugnacious,
+and on the following day fighting continued and at times was very
+severe. Now I knew that the occupants of the ground in which the
+fighting was taking place were paired, and not doubting that the
+combatants were the owners of two territories marked for convenience
+sake Nos. 1 and 2, I was at a loss to understand the meaning of so
+determined and persistent a struggle. My attention, however, was
+presently drawn to a third bird, which also joined in the conflict and
+made the whole situation still more perplexing. This bird, as it soon
+became clear, was none other than the owner of No. 2 territory, and the
+one that I had previously regarded as such was a new arrival. On the
+following day, the 1st April, fighting continued, and in my record for
+that day there is a note to the effect that "No. 2 female seems to be of
+no interest to No. 5 male (the new arrival); its purpose seems to be to
+drive away intruders." On the 2nd April and subsequent days, this bird
+attacked every other male that approached, and not only maintained its
+position but ultimately succeeded in securing a mate. Here then we have
+two territories occupied by two males, both of which had obtained a
+mate. The relation of these two birds was normal, a month's routine had
+defined their boundaries, and conflicts were less frequent than
+formerly. But upon this comparatively peaceful scene a strange male
+intrudes. Observe the manner of the intrusion. The stranger does not
+wander about first in this direction and then in that, but acts _as if_
+it had some definite end in view, and establishing itself in a small
+alder bush which it uses as a base or headquarters, it gradually extends
+its dominion, gains the mastery over the surrounding ground, part of
+which belonged to No. 1 male and part to No. 2, and finally drives a
+wedge, so to speak, between the two territories.
+
+How is its behaviour to be explained, and why did its presence cause
+such commotion? No one could have watched the gradual unfolding of this
+incident day by day and not have been impressed by the persistent
+endeavour with which this male maintained its position in one small part
+of the meadow. This is the first and most important consideration. Then
+there is the attitude, also significant, which it adopted towards the
+females; for I take it that, apart from the question of territory, the
+explanation of its intrusion must be sought in the necessity for
+securing a mate--that it was attracted by the presence of the females,
+and that the proximate end of its behaviour was the possession of one of
+them. But if there is one thing that emerges from the facts more clearly
+than another it is that the course of its behaviour was in no way
+influenced by the presence or absence of either of the females. My
+reasons for saying so are the following: in the first place, it made no
+attempt to pursue or to thrust its attention upon either one or the
+other of them; secondly, it even went so far as to attack and drive them
+away when they approached too closely; and in the third place, when an
+unpaired female did at length appear, it adopted a different attitude
+and forthwith paired. And bearing in mind that these two females had
+already been with their respective mates for some considerable time, and
+that there was reason to believe that coition had actually taken place,
+is it likely that any counter-attraction would have proved successful in
+tempting either of them away from its mate, or probable, if they were
+the sole attraction, that the intruding male would have been so
+persistent in remaining? How very much simpler it is to fit the pieces
+together, if for the time being we ignore the female and fix our
+attention upon the territory. Each item of behaviour then falls into its
+proper place, and the fighting which seemed so perplexing and
+meaningless becomes a factor of prime importance. First of all the male
+arrives; then it establishes itself in a small alder bush and advertises
+its presence by song; next, by persistent effort in attacking the
+neighbouring males, it frees a piece of ground from their dominion; and
+finally, in proper sequence, a female arrives, pairing takes place, and
+reproduction is secured.
+
+[Illustration: A battle between two pairs of Jays
+
+Emery Walker ph.sc.]
+
+How then does the whole matter stand? If it were males only that engaged
+in serious conflict, and if they fought only in the presence of a
+female, the problem would resolve itself into one simply of obtaining
+mates. But the warfare extends in a variety of directions, it is not
+confined to one sex, nor to unpaired individuals, nor need the opponents
+necessarily be of the same sex; it involves both sexes alike singly or
+combined. Now the view that the biological end of battle is, in its
+primary aspect, related to the female, cannot, as we have seen, apply to
+the conflicts between different pairs, and only by much stretching of
+the imagination can it be held responsible for the hostility that males
+frequently display towards females or _vice versa_. It is valid only for
+a certain form of warfare. But that form represents, you will say, a
+large proportion of the whole, which is true; and so long as we ignore
+the remainder, we might rest content in the belief that we had solved
+the major part of the problem. But can we ignore the remainder? Can we
+say that the conflicts between paired males, for example, are simply
+offshoots of the pugnacious disposition, and have no part to play in the
+process of reproduction? They recur with marked persistency season after
+season and generation after generation; they are to be found in species
+widely remote; they are frequent in occurrence; and no one who had
+observed them and noted the vigour with which they are conducted, could,
+I think, conclude that they were meaningless--and be satisfied. They
+must somehow be explained. So that if anyone thinks fit to maintain that
+possession of a mate is an adequate explanation of part of the
+hostilities, it is clearly impossible to regard all the fighting as a
+manifestation of one principle directed towards a common biological end.
+
+But wherever we extend our researches, we find that the facts give
+precision to the view that the occupation of a territory is the
+condition under which the pugnacious instinct is rendered susceptible to
+stimulation. The Lapwing, when in its territory, displays hostility
+towards other males of its own species, but when upon neutral ground,
+treats them with indifference; the Chiffchaff pursues its rival up to
+the boundary and is then apparently satisfied that its object has been
+achieved; the cock Chaffinch in March permits no other male to intrude
+upon its acre or so of ground during the early hours of the morning, but
+for the rest of the day it joins the flock and is sociable; the
+Herring-Gull resents the approach of strangers so long as it occupies
+its few square feet of cliff, but welcomes companions whilst it is
+following the plough--all of which points to a relation between the
+territory and the fighting. And this view has at least one merit--it
+accounts for all the fighting no matter what degree of severity may be
+reached or in what way the sexes may be involved. The complexity of the
+strife presents no obstacle; for if the biological end of the fighting
+is to render the territory, which has already been established, secure
+from intrusion, each sex will have its allotted part to play at the
+allotted time: thus the battles between the males before females appear
+on the scene will decide the initial question of ownership; those
+between the females will give an advantage to the more virile members
+and insure an even distribution of mates for the successful males; the
+constant struggles between paired males will roughly maintain the
+boundaries and prevent such encroachment as might hamper the supply of
+food for the young; and the co-operation of male and female in defence
+of the territory will be an additional safeguard. Each form of battle
+will contribute some share towards the main biological function of
+reproduction.
+
+
+Hitherto we have dealt principally with the male. We have referred, it
+is true, to the fact that the female co-operates with her mate in order
+to drive away intruders, but beyond this, we have made no attempt to
+trace what part, if any, she plays in the whole scheme. We must do so
+now.
+
+The various steps by which the territory is not only established but
+made secure from invasion, imply an inherited nature nicely balanced in
+many directions--first of all the male must be so attuned as to be ready
+to search for a territory at the right moment; then it must be capable
+of selecting a suitable environment; and, having established itself, it
+must be prepared to defend its area from a rival, and to resist
+encroachment by its neighbours--and if it failed in any one of these
+respects, it would run the risk of failure in the attainment of
+reproduction. Each individual has therefore to pass, so to speak,
+through a number of sieves--the meshes of which are none too
+wide--before it can have a reasonable prospect of success. This being
+so, we ask, in the first place, whether the female, too, may not have an
+eliminating test to pass; and in the second place, whether she may not
+also assist in furthering the biological end of securing the territory.
+
+Now the answer to the first of these questions will be found to be in
+the affirmative. Just as, in the securing of a territory, the ultimate
+appeal is to the physical strength of the male, so, in the course of her
+search for a mate, the female may be called upon to challenge, or may be
+challenged by a rival, and the issue is decided by force. My attention
+was first drawn to this fact by a struggle between two female
+Whitethroats, which I have described elsewhere. The scene of its
+occurrence was the corner of a small osier bed occupied by one male, and
+the females that took part in it had only recently arrived, but the
+male, an unpaired bird, had been in possession of its territory for some
+days. The sequel to this struggle, which was protracted and severe, was
+the disappearance of both females, the male being left without a mate
+for a further ten days.
+
+[Illustration: Emery Walker ph.sc.
+
+The female Chaffinch shares in the defence of the territory and attacks
+other females.]
+
+Numerous instances have since come under my notice. Hen Chaffinches
+become so absorbed that they fall to the ground and there continue the
+struggle. Seizing hold of one another by the feathers of the head, they
+roll from side to side, and then, without relaxing their grip, lie
+exhausted--the quickened heart-beat, altered respiration, tightly
+compressed feathers and partially expanded wings betraying the intensity
+of the conflict.
+
+As the breeding season approaches, hen Blackbirds grow more pugnacious.
+Individuals that early in the year have frequented the same spot daily
+and have even shown every sign of friendship, become openly hostile. For
+two years in succession I had an opportunity of observing females under
+such conditions, and of studying the gradual change in their
+relationship. Each morning at break of day and for some hours afterwards
+they could be seen in the same place, one following the other as they
+searched for food first in this direction and then in that, as if they
+derived some special pleasure from the fact of their companionship. Then
+a change began to manifest itself. Indications of animosity became
+apparent; one would run towards the other in a threatening attitude and,
+in a half-hearted manner, peck at it; and gradually the hostility grew,
+until the tentative pecking developed into a scuffle and the scuffle
+into a conflict.
+
+Much fighting also occurs between the females of the Reed-Bunting, and
+likewise between those of the Moor-Hen, and because these two species
+are not only common but inhabit respectively open stretches of marshy
+ground or large sheets of water, the fighting can be readily observed.
+
+Why do the females fight before they are definitely paired? To obtain
+mates? This certainly seems to be the obvious explanation because any
+question of securing territory can be excluded; yet if it be true that
+their sex is numerically inferior, it is difficult to understand the
+necessity for such strenuous competition. But what is the condition
+under which the pugnacious instinct of the female is rendered
+susceptible to stimulation? It cannot be merely the presence of a male
+ready to breed, for then there would be endless commotion amongst the
+flocks of Chaffinches or of Lapwings which in March are composed of both
+sexes, including even males that have secured territories. There must be
+some other circumstance; and, judging by experience, it is to be found
+in the territory--a male, that is to say, in occupation of one, is the
+condition under which the inherited nature of the female is allowed free
+play. We must bear in mind, however, that the competition between the
+males is very severe, that large numbers probably fail to pass even this
+preliminary test, and that only a proportion are in a position to offer
+to the female the condition under which her process can successfully run
+its course; so that the presumption is--though it is incapable of
+demonstration--that there is a competition for such males each recurring
+season, and that, on the average, the weaker females fail to procreate
+their kind.
+
+But apart from any direct assistance she may give in driving away
+intruders, does she in any way help to further the biological end of
+reproduction? This is a difficult question to answer, and the suggestion
+I have to make can only apply in those cases in which the territory is
+occupied throughout the breeding season. Much of the fighting between
+the males occurs in her presence, and it must be admitted--though it is
+difficult to speak with any degree of certainty--that such fighting,
+taken as a whole, bears the stamp of exceptional determination. Let us
+then grant that the excitement of a male does, under these
+circumstances, reach a higher level of intensity, and let us see how
+this will add to the security of the territory. The fact that the male
+has established itself and obtained a mate is not alone sufficient to
+accomplish the end for which the territory has been evolved. During the
+period between the initial discharge of the sexual function and the time
+when incubation draws to a close, much may happen to prejudice the
+future of the offspring; there is always the possibility of invasion by
+an individual whose development is backward or which has been
+unsuccessful in making good the first step, and, as we saw in the case
+of the Reed-Bunting, a portion of the ground won may be lost; there is
+always the danger of gradual encroachment by neighbouring owners; and
+there is even a possibility that a pair may be so persistently harassed
+by more virile neighbours as to forsake the locality permanently. If
+then a male is to attain a full measure of success it must be capable
+of keeping its boundaries intact up to the time when the young are able
+to fend for themselves, and consequently it is important that its
+intolerant nature should remain susceptible to stimulation throughout
+the greater part of the season.
+
+Does the presence of a female serve to promote this end? Now we know
+very little of the influence exerted by one sex upon the other.
+Professor Lloyd Morgan has suggested that the male raises the emotional
+tone of the female, a suggestion which seems to me in accordance with
+the facts. There is reason to believe, however, that the converse is
+also true--namely that the excitement of the male reaches a higher level
+of intensity when a female is present. Granting then that his emotional
+tone is raised, how will this affect the question? So great is the
+difference of opinion as to the part that the emotions play in
+furthering the life of the individual that one hesitates to accept any
+particular one. But it seems to be generally admitted that emotion adds
+to the efficacy of behaviour, and this is the view of Professor Lloyd
+Morgan. "Whatever may be the exact psychological nature of the emotions,
+it may be regarded," he says, "as certain that they introduce into the
+conscious situation elements which contribute not a little to the energy
+of behaviour. They are important conditions to vigorous and sustained
+conation." Therefore, if it be true that the female raises the emotional
+tone of the male, the result will be an increased flow of energy into
+all the specific modes of behaviour connected with reproduction, amongst
+which those directly concerned in the securing and defence of the
+territory will receive their share; so that instead of a progressive
+weakening of just those elements in the situation which make for
+success, the level of their efficiency will be maintained as a result of
+such reinforcement. But the female becomes intolerant of her own sex
+when she has discovered a male ready to breed, and, later, assists her
+mate in resisting intrusion; and by raising her emotional tone, he may
+be the means of furthering more strenuous behaviour on her part. Each
+member of the pair would in this way contribute towards the energy of
+behaviour of its mate, and hence add indirectly to the security of the
+territory.
+
+It may be well to illustrate the foregoing remarks. Suppose that there
+is a small piece of woodland barely sufficient to hold three pairs of
+Willow-Warblers, and suppose that the male and female in the middle
+territory did not respond to one another's influence quite as readily as
+the adjoining males and females, what would be the result? The emotional
+tone of the central pair would stand at a lower level of intensity; and,
+since their congenital dispositions would lack the necessary
+reinforcement, the birds would tend to become less and less punctilious
+in keeping their boundaries intact, whereas the adjoining pairs, always
+on the alert and meeting with little opposition, would encroach more and
+more and gradually extend their dominion. And so, by the time the young
+were hatched, the parents would be in occupation of an area too limited
+in extent to insure the necessarily rapid supply of food, and would be
+compelled to intrude upon the adjoining ground. But knowing how routine
+becomes ingrained in the life of the individual, knowing that for weeks
+this pair had submitted to their neighbours, can we believe that they
+would be capable of asserting their authority and that the young would
+be properly cared for? Or suppose that different pairs of Kittiwake
+Gulls on the crowded ledges, or different pairs of Puffins in the
+crowded burrows, varied in like manner, would they all have equal
+chances of rearing their offspring? The struggle for reproduction is
+nowhere more severe than amongst the cliff-breeding sea birds; it is not
+for nothing that one sees Kittiwake Gulls, locked together, fall into
+the water hundreds of feet below and struggle to the point of
+exhaustion, or, as has been reported, to the point of death; it is not
+for nothing that Puffins fight with such desperation. And surely success
+will be attained by that pair whose emotional tone stands high and whose
+impulse to fight is therefore strong, rather than to the ill-assorted
+couple.
+
+
+The argument, then, is briefly this. In the spring, a marked change
+takes place in the character of the males of very many species; instead
+of being gregarious they either avoid one another and become hostile,
+or, if their conditions of existence require that they shall still live
+together, they become irritable and pugnacious. This change is made
+known to us by the battles of varying degrees of severity which are such
+a feature of bird life in the spring; and since a female can commonly be
+observed to accompany the combatants, the possession of a mate appears
+at first sight to be the proximate end for which the males are
+contending. But when the circumstances which lead up to the quarrels are
+investigated closely, the problem becomes more difficult; for it is not
+merely a question of males fighting in the presence of a female, as is
+generally supposed to be the case, but on the contrary there is a
+complexity of strife which is bewildering--males attack females or _vice
+versa_; female fights with female; or a pair combine to drive away
+another pair, or even a solitary individual no matter of which sex. This
+complexity of strife makes against the view that the possession of a
+mate is the reason of the fighting. But an even stronger objection is to
+be found in the fact that males are hostile when no female is
+present--and hence we must seek elsewhere for the true explanation.
+
+Now if the behaviour of a male be closely observed, it will be found
+that its pugnacious instinct gains or loses susceptibility according to
+the position which it happens to occupy--when its ground is trespassed
+upon, the impulse to fight is strong; but when it crosses the boundary
+it seems to lose all interest in the intruder. Moreover, in some
+species, the male rejoins the flock at intervals during the early part
+of the season and for a time leads a double existence, passing backwards
+and forwards between its territory and the neutral ground. Its behaviour
+under these circumstances affords some valuable evidence, for the bird
+displays little if any hostility when accompanying the flock, yet when
+it returns to the ground over which it exercises dominion, no male can
+approach without being attacked. The conclusion, therefore, seems to be
+inevitable, namely that the actual occupation of a territory is the
+condition under which the pugnacious nature of the male is rendered
+susceptible to appropriate stimulation.
+
+
+
+
+CHAPTER IV
+
+THE RELATION OF SONG TO THE TERRITORY
+
+
+If we listen to the voices of the Waders as, in search of food, they
+follow the slowly ebbing tide, we shall notice that each species has a
+number of different cries, some of which are uttered frequently and
+others only occasionally. Not only so, but if we study the circumstances
+under which they are uttered, we shall in time learn to associate
+certain specific notes with certain definite situations.
+
+The Curlew, when surprised, utters a cry with which most of us, I
+suppose, are familiar; but when with lowered head it drives away another
+individual from the feeding ground, it gives expression to its feelings
+by a low, raucous sound, which again is different from its cry when a
+Common Gull steals the _arenicola_ that has been drawn out of the mud
+with such labour.
+
+Thus we come to speak of "alarm notes," "notes of anger," "warning
+notes"--naming each according to the situations which normally accompany
+their utterance. And so, all species, or at least a large majority of
+them, have, in greater or lesser variety, cries and calls which are
+peculiar to certain seasons and certain situations; and since on many
+occasions we have indisputable evidence of the utility of the sound
+produced--as when, upon the alarm being given by one individual, the
+flock of Lapwing rises, or when, in response to a particular note of the
+parent, the nestling Blackcap ceases to call--so are we bound to infer
+that all the cries are, in one way or another, serviceable in furthering
+the life of the individual.
+
+But besides these call-notes, birds produce special sounds during the
+season of reproduction--some by instrument, others by voice, others
+again by the aid of mechanical device. And not only is this the case,
+but many accompany their songs with peculiar flights, such as soaring to
+a great height, or circling, or floating in the air upon outstretched
+wings. These special sounds and special flights are those with which I
+now propose to deal, including under the heading "song" all sounds
+whether harsh or monotonous or beautiful, and whether vocally or
+otherwise produced; and I shall endeavour to show not only that they are
+related to the "territory," but that they contribute not a little to the
+successful attainment of reproduction.
+
+The vocal productions are infinite in variety and combination. At the
+one extreme we have songs composed of a single note repeated slowly or
+rapidly as the case may be, whilst at the other we have the complex
+productions of the Warblers; and between these two extremes, notes and
+phrases are combined and recombined in ways innumerable. And just as
+there is a rich variety of combination, so there is a very wide
+variation in the purity and character of the notes--some are harsh,
+others melodious, some flute-like, others more of a whistle, and others
+again such as can only be likened to the notes of a stringed instrument.
+Hence in variety of phrase combination added to variety in the character
+of the note, there is a possibility of infinite modes of expression.
+
+If, in the latter part of May, we take up a position at dawn in some
+osier bed, we listen to songs which have reached a high degree of
+specialisation, songs, moreover, which appeal to us on account of their
+beauty; if, on the other hand, we climb down the face of the sea cliff,
+we hear an entirely different class of songs--harsh, guttural, weird,
+monotonous sounds, which, appeal to us though they may, lack the music
+of the voices in the osier bed. And just as, in the osier bed, we can
+recognise each species by its voice, so we can distinguish the "cackle"
+of the Fulmar, the "croak" of the Guillemot, or the "grunt" of the Shag.
+In the osier bed, however, there is considerable variation in the song
+of different individuals of the same species, so much so that we can
+recognise this one from that; whereas on the cliff we cannot distinguish
+between the voices of different individuals. And the more highly
+developed the song, the greater the range of variation appears to be;
+but notwithstanding this--notwithstanding the fact that the pitch may
+differ, the phrase combination may differ, and the timbre may
+differ--the song remains nevertheless specific. So that the two
+principal features of "song," broadly speaking, are "diversity" and
+"specific character."
+
+In contrast with the call-notes, the majority of which can be heard at
+all times of the year, the song is restricted as a rule to one season,
+and that one the season of reproduction. It is true, of course, that
+some birds sing during the autumn, and, if the climatic conditions are
+favourable, in the winter also, just as others betray, in the autumn,
+symptoms of emotional manifestation peculiar to the spring; but just as
+the manifestation of the latter is feeble and vestigial, so, too, does
+the song of the former lack the vigour and persistency which is
+characteristic of the spring. Again, in contrast with the call-notes,
+which are common alike to both sexes, song is confined to one sex--a
+peculiar property of the males.
+
+Now all, I think, will agree that it must serve some biological
+purpose--this at least seems to be the conclusion to be drawn from the
+two outstanding features of "diversity" and "specific character"; and
+since the voices of different individuals of the same species vary, it
+has been suggested that, by creating a more effective pairing situation,
+it is serviceable in furthering the life of the individual. I do not
+propose at the moment to enquire whether this doctrine be true, but
+rather to direct attention to other ways in which the song may be
+useful.
+
+Is the instinct susceptible to stimulation under all conditions during
+the season of reproduction, or only under some well-defined condition?
+This is the question to which we will first direct inquiry.
+
+Song in its full development belongs, as we have seen, to the season of
+reproduction; it is heard at the dawn of the seasonal sexual process,
+and is the most conspicuous outward manifestation of the internal
+organic changes which ultimately lead to reproduction. These changes
+would appear, at first sight, to be the primary condition which renders
+the instinct susceptible to appropriate stimulation. But while this is
+true up to a point, in so far, that is to say, as organic changes are a
+necessary antecedent of all behaviour connected with the attainment of
+reproduction, closer acquaintance with the circumstances under which the
+instinct is allowed full play leads to the belief that they are not
+alone sufficient to account for the facts as observed. In order to
+arrive at a decision we must seek out the specific factors in the
+external environment with which "song" is definitely related.
+
+Some birds cross whole continents on their way to the breeding grounds,
+others travel many miles, others again find suitable accommodation in a
+neighbouring parish--nearly all have a journey to perform, it may be
+short or it may be long. The flocks of Finches gradually decrease and we
+observe the males scattering in different directions in search of
+territories; we watch the summer migrants on their way--small parties
+halting for a few hours in the hedgerows and then continuing their
+journey, single individuals alighting on trees and bushes and resting
+there for a few minutes, and the constant passage of flocks of various
+dimensions at various altitudes; and we see Fieldfares, Redwings, and
+Bramblings slowly making their way from the south and the west to their
+homes in the far north. Occasionally we hear their song, not the
+emotional outburst customary at this season, but, except in isolated
+cases, a weak and tentative performance. Gaetke speaks of the absence of
+song on the Island of Heligoland, and refers to the Whitethroat as one
+of the few migrants that enliven that desolate rock with their melody.
+On the other hand, many migrants that rest temporarily on the Isle of
+May sing vigorously.[5] But on the whole there is, I think, no question
+that the male whilst travelling to its breeding grounds, and, even after
+its arrival, whilst in search of a territory, sings but little--and that
+little lacks the persistency characteristic of the period of sexual
+activity. Yet, when a suitable territory is eventually secured, the
+nature of the bird seems to change; for, instead of being silent and
+retiring, as if aware of some end not fully attained, it not only makes
+itself conspicuous but advertises its presence by a song uttered with
+such perseverance as to suggest that that end is at length attained.
+Hence, in a general way, the instinct of song seems to be related to the
+establishment of a territory.
+
+Now the subsequent course of behaviour tends to confirm this view. We
+have already had occasion to refer to the fact that the males of some
+species desert their territories temporarily and join together on ground
+which is regarded by the birds that associate there as neutral, and that
+they do so not merely for the purpose of securing food but because they
+derive some special pleasure from the act of association, and we shall
+find that the altered behaviour of the male when it leaves its territory
+to seek food or to join the flock is an important point for us just now.
+
+Buntings desert their territories temporarily and collect in flocks on
+the newly sown fields of grain. Some of the males are single, others are
+paired, and accompanied, it may be, by their mates; they wander over the
+ground in search of food, uttering their call-notes from time to time,
+or, settling upon the hedges and trees surrounding the field, rest there
+and preen their feathers. But even though a male may be surrounded by
+other males, even though it may occupy a position where it is
+conspicuous to all around, even though, that is to say, it is
+apparently in contact with just those stimulating circumstances which
+will evoke a response when it returns to its territory, yet it makes no
+attempt to sing.
+
+Lapwings, when they resort to the neutral ground, run this way and that
+in full enjoyment of one another's companionship, behaving as they do
+when they flock in autumn and winter. Specific emotional manifestation
+is, however, absent, and their actions seem to be in nowise affected by
+the powerful impulse which only a few minutes previously determined
+their conduct, for of the characteristic flight with its accompanying
+cry there is no sign.
+
+Early in the season Turtle Doves often collect from the surrounding
+country at certain spots where their favourite food is abundant. The
+croak of this Dove--its true song--is a familiar sound during the
+summer, but in addition the bird has a sexual note characteristic of the
+race. I watched a flock of upwards of one hundred on some derelict
+ground approximately eight acres in extent. Here, in May, the birds were
+attracted by the seeds of _Stellaria media_ which was growing in
+profusion. After 5 A.M. there was continuous traffic between this piece
+of ground and the surrounding neighbourhood, a constant arrival and
+departure of single individuals or pairs; and, as they fed, the sexual
+note could be heard in all directions. Now some of the males occupied
+territories close at hand, and one could watch their passage to and
+fro; yet in no single instance did I hear the true song uttered on the
+feeding ground, although the moment a male returned to its territory its
+monotonous croak could be heard, uttered moreover with that persistence
+which is so marked a feature of all song or of the sounds that
+correspond to it.
+
+Thus it will be seen that, even after the internal organic changes have
+taken place, the instinct of song is not susceptible to stimulation at
+all times and under all circumstances, but only at certain specified
+times and under special circumstances which can be observed to
+correspond with the occupation of the territory.
+
+In many species each male singles out within its territory some
+prominent position to which it resorts with growing frequency. This
+position is an important feature of the territory, and exercises a
+dominating influence on the life of the bird. I have referred to it as
+the "headquarters," and it may be a solitary tree or bush, an
+outstanding mound or mole hillock, a gatepost or a railing--anything in
+fact that supplies a convenient resting place so long as it fulfils one
+condition, namely that the bird when it is there is conspicuous. It need
+not, however, be a tree or a mound or indeed anything upon which the
+bird can perch, for there is reason to think that the soaring flight
+undertaken at this season by so many males, since it is generally
+accompanied by the specific sexual sound, answers the same purpose as
+the topmost branch of a tree.
+
+Now there is nothing in the external environment to which the song is
+more definitely related than to the "headquarters"--this at least is the
+conclusion to be drawn from the behaviour, and I will indicate the sort
+of evidence upon which such conclusion is based. There is, first of all,
+the persistency with which the male resorts to the same tree, even to
+the same branch, and, as it seems, solely for the purpose of
+advertisement. We know by experience the approximate routine of the
+male's behaviour; we know where to seek it, where to hear it, and when
+once we have discovered its headquarters, we know that there it will
+sing day after day for weeks or it may be for months together--perhaps
+the most striking feature of its behaviour at this season. Next, we find
+that other trees, though made use of, are not made use of to a similar
+extent for the purpose of song. The area occupied varies much according
+to the nature of the environment; it is sometimes extensive, and seldom
+less than half an acre or so in extent; but in most instances it
+contains plenty of trees and bushes which could, one would imagine,
+serve the purpose of a "headquarters" just as well as the particular one
+selected, and yet the bird, when there, betrays no inclination to sing
+at all comparable with that which can be observed when it occupies its
+accustomed perch. Further evidence is afforded in the behaviour of those
+species that make temporary excursions from their territories. The male,
+on its return, flies as a rule direct to its special tree and sings.
+Sometimes, however, it settles upon the ground, not unfrequently
+accompanied by the female, and while there remains silent; but presently
+rising from the ground and deserting its mate, it flies to the
+headquarters and sings. Again, nearly every male at one time or another
+in the course of the season is aroused to action by the intrusion of a
+rival. The emotional tone of the owner of the territory is then raised,
+and the intruder is pursued and attacked; but this alone is not
+sufficient, it seems as if the chain of instinctive activities, when
+once aroused by appropriate stimulation, must pursue its course to the
+end--and the end in such a case is only reached and complete
+satisfaction only gained when the bird has not merely returned to his
+"headquarters" but has given vocal expression to his emotion. Finally,
+we must bear in mind these two facts, that the "headquarters" is
+occupied solely by the male--it forms no part of the life of the
+female--and that it is the male only that sings.
+
+Many such subtle incidents of behaviour as the foregoing can be
+perceived but not readily described, and trifling though they may seem
+to be in themselves, yet in the aggregate they yield full assurance of a
+close relationship.
+
+The distant song of a male, or the presence of an intruding male, have
+also stimulating effects, though in somewhat different ways. The former
+evokes the normal reply, that is to say the bird, if silent, is liable
+to utter a corresponding reply; the latter arouses hostility into which
+is infused much feeling tone, the bird sings hurriedly while in pursuit
+of its rival, and, which is more remarkable still, even in the midst of
+an encounter. Both the normal reply and the emotional song must be
+similar in origin--different aspects of the same situation--and both are
+clearly related to the other male.
+
+The arrival of a female may also be followed by an emotional outburst
+which can be heard at intervals for some days; on the other hand, the
+song may continue as before or, for a time, entirely cease.
+
+To take the emotional outburst first. This would appear to be
+susceptible of explanation on the hypothesis that the voice contributes
+to a more effective pairing situation; an hypothesis which admittedly,
+at first sight, gains some support from the fact that a second or a
+third male is frequently present. But, in truth, the presence of a
+second male makes the situation, so far as the relationship between the
+song and the female is concerned, all the more perplexing; for, as we
+have already seen, the instinct of pugnacity, when aroused by the
+appearance of an intruder, is also liable to be accompanied by a
+similarly extravagant song. On each occasion the vocal effort is infused
+with much feeling tone, and it would be impossible to point to any one
+feature which is peculiar to only one occasion. The question therefore
+arises as to whether the emotional outburst which we are attributing to
+the arrival of a female may not after all be due to the presence of an
+intruding male. It may be so. But although I can recall no single
+instance in which the presence of an intruder could be definitely
+excluded, yet I should hesitate to base upon this any broad
+generalisation.
+
+When the normal course of the song is not interrupted by the arrival of
+a female, when, that is to say, the male still pursues the routine to
+which he has all along been accustomed, and still sings at stated
+intervals in stated places with a voice that betrays no heightened
+emotional tone, even though the song may convey some meaning to the
+delicate perceptual powers of the female, we have nothing to lay hold
+upon which can be construed as an indication of direct relationship
+between the song and the presence of the female.
+
+The partial or complete suspension of the song after pairing has taken
+place is the most interesting, as it is the most noticeable, feature.
+Not that it is by any means universal--if it were so, some of the
+difficulties that beset the path of interpretation would be removed, but
+it is sufficiently widespread to demand explanation. In nearly every
+case it is, however, only temporary, the period during which the male is
+silent varying from a few days to a few weeks. The male
+Grasshopper-Warbler, when it first reaches us, sings persistently, but
+when it is joined by a female a change becomes apparent; instead of the
+incessant trill, there are spasmodic outbursts of short duration, and in
+the course of a few days the bird lapses into a silence which may be
+broken for a short while at dawn, or late in the evening, but is often
+complete. More striking still is the change in the case of the
+Marsh-Warbler, and the sudden deterioration, or even suspension, of
+strains so beautiful and so varied, at a moment, too, when it might
+least be expected, at once arrests the attention. The Reed-Warbler that
+had its headquarters in a willow sang vigorously from the middle of May
+until a female arrived on the 20th June, when its voice was hushed,
+except for occasional outbursts which lacked force and were of short
+duration. When the Wood-Warbler secures a territory it repeats its
+sibilant trill with unwearying zeal, yet no sooner does a mate appear
+than its emotion is manifested in other directions. The Reed-Bunting is
+vociferous during February and March; but when a female arrives, periods
+of silence are frequent and the instinct of the bird becomes
+progressively less susceptible to stimulation. After the manner of the
+race the male makes temporary excursions from its territory accompanied
+by his mate, and it is noteworthy that when he returns and she is absent
+he sings, but that the moment she joins him, or even comes into sight,
+he is silent. In fact, in greater or less degree, a change is noticeable
+in the song of many resident and migratory species under similar
+circumstances, a deterioration so marked that we learn by experience to
+regard it as a certain indication of the arrival of a mate.
+
+Thus it becomes clear that there are certain specific factors in the
+external environment with which the instinct can be definitely related,
+and in the order of their importance they are (1) the territory as a
+whole; (2) the headquarters; (3) an intruding male; (4) the female.
+
+To what extent are these relationships interrelated? Are they all
+mutually dependent upon one another, or is there one which conditions
+the remainder?
+
+In the first place it is evident that if a male were not to establish a
+territory, no opportunity would be afforded for making use of any
+special post or for acquiring a habit in relation to it, and so without
+further consideration we may say that the connection between the song
+and the headquarters, whatever it may be, is primarily dependent upon
+the establishment of a territory.
+
+Next, we have the fact that the distant voice, or still more so the
+presence, of another male has an exciting influence and evokes a
+corresponding reply. Here we have a direct relationship, and one which
+at first sight appears to be exclusive of cross-correlation. But is it
+really so; does no circumstance arise under which even the proximity of
+a rival fails to evoke response? The reply is not doubtful. Such a
+circumstance _does_ arise--when a male for one reason or another passes
+outside the limits of its accustomed area. This aspect of behaviour has
+already been fully discussed in connection with the question of
+hostility, and everyone, I imagine, must by now be pretty well familiar
+with the facts. However, it does not often happen that we are given
+such an aid to interpretation as is vouchsafed to us in the altered
+behaviour of the male when it joins the flock, and if, as I believe,
+song and hostility are intimately associated, forming part of an
+inter-related whole which, for biological interpretation, has, as its
+end, the attainment of reproduction, it is not surprising that
+circumstances which lead to the modification of the one should likewise
+affect the other; I offer no apology, therefore, for adverting to this
+aspect of behaviour once again.
+
+Now a male may leave its territory for three reasons--to pursue an
+intruder, to join the flock on neutral ground, or to find the necessary
+means of subsistence on other feeding grounds. On each of these
+occasions it hears the song of, and is in close contact with, other
+males; and if the relationship of which we are speaking be really
+exclusive of cross-correlation, its instinct ought to respond with the
+customary freedom. But what happens? A male pursues its rival, betraying
+much emotion and singing extravagantly, until the boundary is passed,
+when emotion subsides and it is silent; or, it flies to the flock on
+neutral ground, and, although surrounded by the very males that a short
+time previously evoked response, is there unresponsive; or again, it
+goes in search of food and collects with other males bent on a similar
+errand, and in presence of what we know would be an exciting influence
+under other circumstances, it nevertheless remains silent. Hence the
+relationship between the song and a male rival seems, as in the case of
+the headquarters, to depend in the first instance upon the occupation
+of a territory.
+
+So that the relationship between the song and the territory as a whole
+is clearly of a different order from that which obtains between the song
+and the headquarters, or the song and a male rival; for the first, as
+far as can be judged by observation, is exclusive of, whilst the second
+and the third involve, cross-correlation. How are these facts to be
+explained? We have already seen that it belongs to the nature of the
+male during the season of reproduction to establish itself in a definite
+place, and this action is just as much a part of its hereditary nature
+as the building of the nest is of that of the female, and it is just as
+necessary for the successful attainment of reproduction. What exactly
+the stimulus is to this mode of behaviour we do not know; we can go no
+further back than the internal organic changes which are known to occur
+and which we assume, not without some reason, are responsible for its
+initiation. Granting, then, that there is this congenital disposition,
+what relation does it bear to the song? Without a doubt the song is
+likewise founded upon a congenital basis; it is truly instinctive, and
+as such requires appropriate stimulation; furthermore the male sings
+only when in occupation of its territory. Having regard to these two
+facts we might say that the territory is the stimulus to the song. But
+this can scarcely be a true interpretation, for inasmuch as the stimulus
+would be relatively constant, a relatively constant response ought to
+follow, and even a slight acquaintance with the daily round of
+behaviour will furnish plenty of evidence to the contrary, seeing that
+the song, though persistent, is never continuous--in fact there are long
+periods of silence during the daytime, and only in the morning and the
+evening does the male become really vociferous. What then is the
+stimulus? Through awareness of something in the environment the male
+responds to stimulation, and the only reply we can give is that the
+headquarters, or a distant song, or the proximity of another male--with
+all of which, as we have seen, the instinct is definitely related--are
+the specific factors which normally evoke response--and experience
+teaches us that the periods of quiescence are just those when life is at
+its lowest ebb and these stimulating factors less in evidence. Bearing
+this in mind, bearing in mind the fact that when a male joins the flock
+or crosses the boundary its instinct ceases to respond, bearing in mind,
+that is to say, that there is evidence of relationship between these
+specific factors and the song only when the territory is actually
+occupied, the conclusion seems inevitable that we have here the
+determining condition which renders the instinct susceptible to
+appropriate stimulation.
+
+There remains the female. I place her last in order of importance, not
+because I regard her influence as of small consequence, but because the
+evidence is of a varied and complex kind, so much so that it is
+difficult to ascertain by observation just how far she is a situational
+item. It will be remembered that the only direct evidence we had of such
+influence was a deterioration or, in some instances, a complete
+cessation of vocal manifestation. Clearly then we are confronted with a
+relationship of a different kind from that which we have been
+discussing; for not only is anything in the nature of stimulation
+absent, but, and this is a remarkable fact, the other items in the
+environment which formerly evoked response no longer do so in quite the
+same way. Is there any awareness on the part of the male of the relation
+between his voice and the mate that is to be, or is it merely that as
+the sexual situation increases in complexity some inhibiting influence
+comes into play? These are questions which lead up to difficult
+problems. But it is no part of my task to discuss the psychological
+aspect of the behaviour; my purpose is merely to show that the situation
+on the arrival of a female undergoes marked modification, that the
+instinct of the male is then less susceptible to stimulation, and that
+the factors in the external environment which formerly elicited response
+become relatively neutral.
+
+Hence the appearance of the female on the scene marks the opening of a
+new stage in the life-history of the male, and, to judge by the course
+of events, it would seem as if the song with its network of
+relationships had now served its main biological purpose.
+
+And now, what is the purpose, and what the origin, of song? Is it, as
+some naturalists have conceived, a means of raising the emotional tone
+of the female, of creating a more effective pairing situation, and so
+of removing a barrier to the successful discharge of the sexual
+function; or, is the emphasis here too much upon the emotional, too
+little upon the strictly utilitarian, aspect? All, I think, will agree
+that it must serve some biological purpose, and the position we have so
+far reached is that the determining condition of its manifestation is
+not merely the establishment, but the actual occupation of a territory,
+and that there are no factors in the external environment which can
+evoke response in the absence of such condition. This being so, the
+further questions arise as to whether it contributes towards the
+attainment of the end for which the whole territorial system has been
+built up, and what precisely is the way in which it does so.
+
+Everyone knows that in the spring the shyest of birds no longer practise
+the art of concealment. The Curlew soars to a great height, and upon
+outstretched wings hovers in the air whilst uttering its plaintive wail;
+the cock Grouse, as if dissatisfied with its "crowing," springs into the
+air and becomes a conspicuous object of the moor; the wary Redshank,
+poised on flickering wings, forgets its mournful alarm cry, and finds
+again its melodious song; and even the secretive Grasshopper-Warbler
+crawls out of the midst of the thicket in order to "reel," just as, for
+a similar reason, Savi's Warbler climbs to the top of a tall reed. In
+fact the males of most species, when they are finally established on the
+breeding grounds, make themselves as conspicuous as possible by sight
+and by sound. And since the sounds produced by no two species are
+exactly alike, the females are able to recognise their prospective
+mates, and the males that are still in search of ground have ample
+warning if that upon which they are treading is already occupied. So
+that you see, from the remarkable development of the vocal powers in the
+male, there follow two important results--"recognition" and "warning."
+
+We here turn from song as the expression of an instinctive disposition,
+and the question of what calls forth this expression, to the impression
+produced by the song on the hearer.
+
+Most birds have a call-note or a number of call-notes, which, generally
+speaking, are specifically distinct. But to the human ear they are not
+always so, perhaps because our power of hearing is less sensitive than
+that of a bird, and unable to appreciate delicate differences of tone.
+Be this as it may, however, the fact remains that we often find it
+difficult, and in not a few cases impossible, to recognise a bird merely
+by its call. The plaintive notes of the Willow-Warbler and of the
+Chiffchaff are to our ears very closely akin, so, too, are those of the
+Marsh-Warbler and of the Reed-Warbler, and there is a great resemblance
+between the hissing sound produced by the two Whitethroats. In Co.
+Donegal I have been deceived by the spring-call of the Chaffinch which,
+owing possibly to the humidity of the atmosphere, is, there, almost
+indistinguishable from the corresponding note of the Greenfinch. The
+Yellow Bunting and the Cirl Bunting frequently make use of a similar
+note, so do the Curlew and the Whimbrel. In fact, numberless instances
+could be quoted in which notes appear to us identical, and, as a rule,
+the more closely related the species, the more difficult it becomes to
+distinguish the sounds--alike in plumage, alike in behaviour, alike in
+emotional manifestation, it would be surprising if they were not alike
+in voice. But the moment we pass from the call-notes to a consideration
+of the songs we are faced with a very remarkable fact, for not only are
+these readily distinguished, but in many cases they bear no resemblance
+in any single characteristic. What could be more unlike than the songs
+of the Willow-Warbler and of the Chiffchaff, of the Marsh-Warbler and
+the Reed-Warbler, or of the Yellow Bunting and the Cirl Bunting?
+
+Now when different individuals collect in flocks at certain seasons,
+they assist one another in finding food, and afford mutual protection by
+giving timely warning of the approach of a common enemy, and the
+gregarious instinct is thus of great advantage to the species; but no
+matter how powerful the impulse to flock might be, if there were no
+adequate means of communication, the different units would frequently
+fail to discover their neighbours. Here the specific cries and calls
+come into play, enabling them as they move about in search of food, or
+change their feeding grounds, or whilst they are on migration, to keep
+constantly in touch with one another; and hence one purpose that these
+call-notes serve is that of recognition. Moreover, they convey their
+meaning to individuals of other species and are acted upon, and are thus
+in every sense socially serviceable; but on the other hand, whilst
+there is much evidence to show that the song is of great individual
+value, there is none to show that it is in any like manner of direct
+advantage to the community.
+
+If, then, there is in the call-notes an adequate means of communication
+and of recognition, why do I suggest that the song has also been evolved
+primarily for the purpose of recognition?
+
+What, first of all, are the conditions in the life behaviour during the
+season of reproduction that make the intervention of the voice a
+consideration of such importance? The general result of our
+investigation might be summed up thus: we found that the male inherits a
+disposition to secure a territory, that at the proper season this
+disposition comes into functional activity and leads to its
+establishment in a definite place, and that it cannot search for a mate
+because its freedom of action in this respect is forbidden by law; that
+the female inherits no such disposition, that she is free to move from
+place to place, free to satisfy her predominant inclination, and to seek
+a mate where she wills; and, since the appropriate organic condition
+which leads to pairing must coincide with appropriate conditions in the
+environment, that the union of the sexes must be accomplished without
+undue delay. Furthermore we found that a territory is essential if the
+offspring are to be successfully reared; that, since the available
+breeding ground is limited, competition for it is severe, and that the
+male is precluded from leaving the ground which he has selected, and is
+obliged, in order to secure a mate, to make himself conspicuous. That
+was our general result. Now there are two ways by which the male can
+make himself conspicuous--by occupying such a position that he can be
+readily seen, or by producing some special sound which will be audible
+to the female and direct her to the spot. The former, by itself, is
+insufficient; in the dim light of the early dawn, when life is at its
+highest, and mating proceeds apace, what aid would it be for a male to
+perch on the topmost branch of a tree, how slender a guide in the depth
+of the forest? But whether in the twilight or in the dark, in the
+thicket or the jungle, on the mountain or on the moor, the voice can
+always be heard--and the voice is the principal medium through which the
+sexes are brought into contact.
+
+Well now, we come back to the question, why, if all species have a
+serviceable recognition call, that call should not be sufficient for the
+purpose, just as, without a doubt, it is adequate for all purposes at
+other seasons? The answer is, I think, clear. The recognition call is
+not confined to one sex, nor only to breeding birds; it is the common
+property of all the individuals of the species, and if the female were
+to rely upon it as a guide she might at one moment pursue another
+female, at another a non-breeding male; she might even be guided to a
+paired female or to a paired male, and time would be wasted and much
+confusion arise. So that no matter how much a male might advertise
+himself by cries and calls which were common alike to all the
+individuals of the species, it would not assist the biological end which
+we have in view. Something else is therefore required to meet the
+peculiar circumstances, some special sound bearing a definite meaning by
+which the female can recognise, amongst the host of individuals of no
+consequence to her, just those particular males in a position to breed
+and ready to receive mates. Hence the vocal powers, the power of
+producing sounds instrumentally, and the power of flight, have been
+organised to subserve the biological end of "recognition."
+
+And this view is strengthened, it seems to me, by the erratic behaviour
+of certain species, more particularly by one remarkable case, the case
+of the Cuckoo. The male, after having established himself, utters his
+call persistently from the day of arrival until approximately the middle
+of June; but, in contrast with the large majority of species, the female
+has a characteristic call which she, too, utters at frequent intervals.
+The female is polyandrous and has a sphere of influence embracing the
+territories of a number of males; she wanders from place to place, is
+often silent, and not unfrequently is engaged in dealing with her egg or
+in searching for a nest in which to deposit it, and therefore she is not
+always in touch with a male, still less with any particular one. Now
+there is much evidence to show that the discharge of the sexual function
+amongst birds is subject to control, and that this control operates
+through the female--through her physiological state becoming
+susceptible to stimulation only at certain periods. So that we have
+these considerations, that the female is polyandrous, that she has a
+territory distinct from that of the male, and that her sexual impulse is
+periodical; and the further consideration that the impulse, since it is
+periodical, is of limited duration and must receive immediate
+satisfaction. Such being the circumstances of the case, would the voice
+of the male serve to insure the union of the sexes at the appropriate
+moment? Well, the fact that she is polyandrous implies that every male
+in her sphere of influence is not always capable of satisfying her
+sexual instinct. Is, then, the male's call an indication of his
+readiness to yield to stimulation? Without a doubt it is an index of the
+general physiological state which generates the sexual impulse, without
+a doubt it denotes a general preparedness to breed, but there is no
+evidence to show that it denotes the degree of ardour of the male at any
+particular moment, and much that proves the contrary. So that only by
+the female producing some special sound which will attract the males
+that are eager and bring them rapidly to the spot where she happens to
+be, only thus is it possible to insure the consummation of the sexual
+act. This, it seems to me, is the purpose of the peculiar call of the
+female--a call which, so far as biological interpretation is concerned,
+is just as much a song as the melody of the Marsh-Warbler--and its
+interest for us just now lies in this, that here we have a special case
+in which the sexes have separate territories, the female is polyandrous,
+and the voice of the male is not sufficient by itself to bring to pass
+the union of the sexes; and in which, consequently, if the purpose of
+song be that of recognition, we should expect to find, as we do find,
+that the female had a distinct and penetrating call.
+
+We now come to the question of "warning," by no means the least
+important purpose of song. I pointed out that one of the chief
+differences between the call-notes and the song was that the former were
+socially serviceable, whereas the latter was only serviceable to certain
+individuals; and in making this statement, I had in mind the direct
+benefits to the community which proceeded from an appreciation of sounds
+having a mutually beneficial meaning, not the indirect, though none the
+less beneficial, consequences to the species as a whole. Biologically
+considered, song, if it acts as a warning and thereby leads in one way
+or another to more complete success in the rearing of offspring, may be
+spoken of as socially serviceable; but it is legitimate to draw a
+distinction between the prospective value of remote relationships which
+we can foresee, and the mutual assistance which the individuals of a
+community derive from their close association.
+
+If there were always sufficient breeding ground to support the offspring
+of all the individuals of each species, if the individuals were always
+so distributed that there was no possibility of overcrowding in any
+particular area, and if the conditions of existence of different
+species were so widely divergent that the presence of this one in no way
+affected the interests of that, no opportunity would be afforded for the
+development of so complex a system as is involved in the "territory" and
+all that appertains to it. But the available breeding ground is by no
+means unlimited. The supply of food, which is a determining factor in
+the environment, is always fluctuating according to the climate and
+according to the changes in the earth's surface; and so the distribution
+of the bird population in any given area, though it may be suitably
+adjusted for one year or even for a period of years, is bound in the
+course of time to require readjustment. Now there cannot be readjustment
+without competition, nor competition without combat. But the appeal to
+physical force is only a means to an end, and, since no male can endure
+incessant warfare and the perpetual strain of always being on the alert,
+without experiencing such physical exhaustion as might affect his power
+of reproduction, its direct effect upon the combatants cannot be
+otherwise than harmful--in fact it is a necessary evil which for the
+good of the species must be kept strictly within bounds. Bearing in
+mind, then, these two facts, namely that the distribution of the males
+is never stable and that overmuch fighting may defeat the end in view,
+we can appreciate the importance of any factor which will lead to a more
+uniform distribution and at the same time insure security by peaceable
+means.
+
+The proximate end of the male's behaviour is isolation--how is it to be
+obtained? If, after having occupied a territory, the bird were to remain
+silent, it would run the risk of being approached by rivals; if, on the
+other hand, it were merely to utter the recognition call of the species,
+it would but attract them. In neither case would the end in view be
+furthered, and isolation would solely depend upon alertness and the
+capacity to eject intruders. Supposing, however, that the song, just as
+it serves to attract the females, serves to repel other males, a new
+element is introduced deserving of recognition; for those males that had
+established themselves would not only be spared the necessity of many a
+conflict, but they would be spared also the necessity of constant
+watchfulness, and so, being free to pursue their normal routine--to seek
+food, to rest, and, if migrants, to recover from the fatigue of the
+journey, they would be better fitted to withstand the strain of
+reproduction; and those that were still seeking isolation in an
+appropriate environment, instead of settling first here and then there
+only to find themselves forestalled, would avoid and pass by positions
+that were occupied, establishing themselves without loss of time in
+those that were vacant. Without the aid of something beyond mere
+physical encounter to regulate dispersal, it is difficult to imagine how
+in the short time at disposal anything approaching uniformity of
+distribution could be obtained. Hence, both in the direction of limiting
+combat, of insuring accommodation for the maximum number of pairs in the
+minimum area, and of conserving energy, the song, by conveying a
+warning, plays an important part in the whole scheme.
+
+And if this be so, if the song repels instead of attracting, it follows
+that the more distinct the sounds, the less likelihood will there be of
+confusion; for supposing that different species were to develop similar
+songs, whole areas might be left without their complement of pairs just
+because this male mistook the voice of that, and avoided it when there
+was no necessity for doing so. So that just as from the point of view of
+"recognition" each female must be able to distinguish the voice of its
+own kind, so likewise the warning can only be adequate providing that
+the sounds are specifically distinct. A point, however, arises here in
+regard to closely related forms. Some species require similar food and
+live under similar conditions of existence; they meet in competition and
+fight with one another; and, if they did not do so, the food-supply of a
+given area would be inadequate to support the offspring of all the pairs
+inhabiting that area. Generally speaking, the more closely related the
+forms happen to be, the more severe the competition tends to become; and
+it may be argued that in such cases a similar song would contribute to
+more effective distribution and in some measure provide against the
+necessity of physical encounter; that, in fact, it would stand in like
+relation to the success of all the individuals concerned, as does the
+song to the individuals of the same species. But we must bear in mind
+that the primary purpose of song is to direct the females to those males
+that are in a position to breed; and to risk the possibility of prompt
+recognition in order that the males of closely related species should
+fight the less, would be to sacrifice that which is indispensable for a
+more remote and less important advantage.
+
+What meaning does the song convey to a male that is unestablished? Does
+the bird recognise that it is forestalled; does it foresee and fear the
+possibility of a conflict, and conclude that the attempt to settle is
+not worth while? I do not imagine that it thinks about it at all. How
+then does the warning warn? We will endeavour to answer this question,
+but, in order to do so, we must review the stages by which a territory
+is secured.
+
+We take as our starting point the internal organic changes which are
+known to occur. These changes are correlated with other changes,
+manifested by a conspicuous alteration in behaviour--to wit, the
+disappearance of sociability and its replacement by isolation. Having
+found a station which meets the requirements of its racial
+characteristics, the male establishes itself for a season, becomes
+vociferous, displays hostility towards others of its kind, and in due
+course is discovered by a female. The whole is thus an inter-related
+whole, a chain of activities which follow one another in ordered
+sequence. Now we have seen that it is neither pugnacious nor vociferous
+until the territory is actually occupied; we have seen that the fact of
+occupation is the condition under which the instincts of pugnacity and
+of song are rendered susceptible to appropriate stimulation; we have
+discussed the nature of the stimulus in each case, and we wish to know
+the sort of meaning that the song conveys to an individual which is
+still in the preliminary stage of seeking a station. In sequential order
+we have the following: (1) internal organic changes which lead to
+isolation, (2) the appropriate environment which gives rise to an
+impulse to remain in it, (3) the occupation of a territory which is the
+condition under which the instincts are rendered susceptible to
+stimulation, (4) the various stimuli. Each is dependent upon that which
+precedes it, and no part can be subtracted without failure of the
+biological end in view, neither can the different stages be combined in
+different order. So that, in considering the significance of song to an
+unestablished male, we are dealing with the situation at a point at
+which all the latent activities have not been fully felt, for all that
+so far has occurred is the change from sociability to isolation
+determined by internal organic changes. The bird has not established a
+territory because it has not come into contact with the appropriate
+environment, and it is not pugnacious because the condition which
+renders its instinct susceptible is absent; and so, as it wanders from
+place to place and hears the voices of males here or males there, it
+merely behaves in accordance with that part of its nature which
+predominates just at that particular moment--the impulse to avoid them.
+
+But given the appropriate environment, given, that is to say, just that
+combination of circumstances which might bring into functional activity
+all the latent instincts of the intruder, and no matter how vociferous
+the occupant of a territory might be, it would not be preserved from
+molestation. The advantage of the song, biologically considered, is then
+this, that it will often prove just sufficient to preclude males in
+search of isolation from coming into contact with the environmental
+conditions adequate to supply the stimulus to their latent activities
+and to convert them into rivals.
+
+If this interpretation be correct, if we are right in attributing the
+withdrawal solely to the fact that the first stage only in the
+relational series has been reached, it follows that the effect of song
+upon males that have reached subsequent stages in that series must be of
+a very different kind. We have dealt with the male when in the
+preliminary stage of seeking isolation, we must deal with it now when
+eventually it occupies a territory. How does it behave when it hears, as
+it is bound to do, the voices of rivals in its neighbourhood? You may
+remember that some allusion was made to the fact that an outburst of
+song from one individual was followed, not unfrequently, by a similar
+outburst on the part of other individuals in the immediate locality. For
+example, silence may reign in the reed-bed except for an occasional note
+of the Reed-Warbler or Sedge-Warbler. Suddenly, however, a dispute
+arises between two individuals, accompanied by a violent outburst of
+song, and forthwith other males in the vicinity begin to sing excitedly
+and continue doing so for some minutes in a strangely vigorous manner,
+the tumult of voices affording a striking contrast to the previous
+silence. Spasmodic outbursts of this kind, stimulated by an isolated
+utterance, are by no means uncommon. But not only does song stimulate
+song; under certain conditions it has the still more remarkable effect
+of arousing hostility. The boundary that separates two adjoining
+territories is by no means a definite line, but rather a fluid area
+wandered over by this owner at one moment, by that at another. Now so
+long as the bird is silent while in this area, the probability is that
+it will escape detection and remain unmolested; let it however sing--it
+often does so--and it will not merely be approached but attacked, and
+consequently this area is the scene of much strife. The point to be
+noticed here is that the song brings about no withdrawal; it elicits a
+response, attracts instead of repelling, and, in short, arouses the
+impulse that is always predominant in the nature of the male when
+eventually it occupies a territory--the impulse of self-assertiveness.
+Therefore it seems clear that the different stages in the process of
+reproduction mark the appearance of different conditions, each of which
+renders some new impulse susceptible to stimulation, and that the
+significance of song depends upon the stage which happens to have been
+reached. Hence when we speak of song acting as a "warning," we do not
+mean that it arouses any sensation of fear; it is but a stimulus to
+that part of the inherited nature of the hearer which predominates at
+the moment.
+
+Are we then justified in the use of such terms as "warning,"
+"significance," or even "meaning," when it is but a matter of stimulus
+and response? In what does the impulse to avoid other males consist?
+There is no reason to suppose that there is any sensation of fear in the
+first stage, and the course of behaviour demonstrates that there is none
+in the later stages. But it is difficult to conceive of an impulse which
+has, as its end, the isolation of the individual from members of its own
+sex and kind, without some feeling-tone, the reverse of pleasurable,
+entering into the situation; just as it is difficult to believe that the
+female experiences no pleasurable sensation when she hears the voice of
+the male that directs her search. So that the song may be actually
+repellent in the one case and attractive in the other; and it is none
+the less repellent when, as in the later stages, it attracts a
+neighbouring male, for the attraction is then of a different order,
+determined by the presence of the condition which renders the pugnacious
+nature susceptible and leads to attack. In a sense, therefore, we can
+speak of "meaning"--though not perhaps of "significance"--and of
+"warning," when we refer to the prospective value of the behaviour.
+
+So much for the purpose of "song"; there still remains the more
+difficult question--the question of origin. Let me make clear what I
+mean by origin. As we have already seen, there is infinite diversity in
+the sexual voice of different species; some are harsh and others
+monotonous, and some strike the imagination by their novelty whilst
+others are melodious; and to the naturalist each, in its particular way
+and in a particular degree, probably makes some appeal according to the
+associations that it arouses. But just why a Marsh-Warbler is gifted
+with a voice that is so beautiful and varied, whilst the
+Grasshopper-Warbler must perforce remain content with a monotonous
+trill; just why the tail feathers of the Snipe have developed into an
+instrument, whilst the Pied Woodpecker has developed muscles which
+enable it to make use of a decayed branch as an instrument--we know no
+more than we do of the nature of the forces which lead the Reed-Warbler
+to weave its nest to reeds, or the caterpillar of the Elephant Hawk Moth
+to assume so peculiar an attitude when disturbed. When therefore I speak
+of the origin, I do not refer to the mode of origin of variation; I take
+for granted that variations somehow arise, and I seek to ascertain
+whether there is anything in the phenomena which we have explored which
+might reasonably be held to determine the survival of this one in
+preference to that.
+
+When we reflect upon the problem of song and consider the numerous and
+diverse forms in which it is manifested, we are apt to draw a
+comparison between the sounds we hear and those produced by musical
+instruments, and hence to conclude that each bird is gifted with a
+special instrument in virtue of which it produces its characteristic
+melody. But there is a very remarkable phenomenon connected with the
+singing of birds which shows that this is really not the case--I mean
+the phenomenon of imitation. There are plenty of good imitators amongst
+our native species, and the power of imitation is not the exclusive
+property of those which have reached a high degree of vocal development,
+nor, for the matter of that, of song-birds at all. Even the Jay, than
+which few birds have a more raucous voice, that "hoots" like the
+Wood-Owl, or copies the sounds produced by the tail feathers of the
+Snipe, will occasionally imitate the most melodious strains of some
+other species; and the Red-backed Shrike, whose sexual call is
+principally a few harsh notes rapidly repeated, bursts at times into
+perfect imitations of the song of the Swallow, Linnet, or Chaffinch.
+Nevertheless it is amongst such typical songsters as the Warblers that
+we find the greatest volume of imitation, and no limit seems to be
+placed upon their capacity. The Marsh-Warbler can utter the call of the
+Green Woodpecker, or sing as the Nightingale does, with as much facility
+as it sings its own song; and the Blackcap is well-nigh as proficient in
+copying the cries and melodies of surrounding species--and so, if it
+were necessary, we might proceed to add to the list.
+
+These examples demonstrate that different songs are not represented by
+a corresponding number of different physiological contrivances; for if
+the difference were really attributable to some structural peculiarity,
+then the range of sounds embraced in the call-notes and the sexual call
+of any given species, must be the measure of the capacity of its
+instrument; and no matter how great its power of imitation may be, it
+follows that it will only be capable of copying those sounds which fall
+within that range. There is plenty of evidence to show that the power of
+imitation is almost unlimited, at all events that it is not confined
+within such narrow limits as are here demanded. Hence it seems clear
+that the diversity of song is not to be sought in structure, but in some
+innate capacity to play one tune in preference to another; and if this
+be so, and if out of the same instrument, which has been primarily
+evolved to further the biological end of intercommunication, all manner
+of diverse sounds can be made to proceed, the problem of the origin of
+song is to that extent simplified.
+
+We must next inquire into the nature of song, and endeavour to ascertain
+whether all the individuals of a species are alike proficient, or,
+failing this, whether there is any quality which can be observed to be
+constant under all conditions. I watch the Reed-Buntings in a marsh and
+find that there are three males occupying adjoining territories. Two of
+them are fully mature and their plumage is bright: that is to say the
+crown is black, the collar and breast are white, the flanks are dull
+white spotted with black, and the mantle is reddish-brown. The third is
+immature: the crown, instead of being black, is suffused with brown; the
+collar, instead of being white, is mottled with brown; and the flanks
+are more heavily streaked with brown. These three birds take up their
+positions in February, and, as is their wont, sing incessantly each day
+at daybreak. The song of the first two is normal, including the usual
+number of phrases which flow in no definite sequence, but are combined
+and recombined in different order, and the tone is pure; that of the
+third, the immature bird, is, however, very different; for just as in
+comparison its plumage is dull, so the phrases of its song are limited
+and reiterated with great monotony, the tone is impure, and the whole
+performance is dull and to our ears unmusical. I watch them from
+February to June, and observe the order in which they are mated--first a
+mature male; next, after a short interval, the immature male; and
+finally, after a still longer interval, the remaining bird gets a mate.
+As the season advances, still keeping watch on the development of the
+plumage and of the voice of the immature male, I observe that no very
+definite change takes place--that the colours remain dull, that there is
+a conspicuous absence in the song of certain phrases, and that the notes
+lack purity of tone.
+
+If now, instead of Reed-Buntings in a marsh, I watch Yellow Buntings on
+a furze-covered common, I find that, establishing themselves early in
+February, they sing persistently, and in a few weeks are paired. But
+what arrests my attention more particularly is the quality of the song;
+for although the voice is unmistakably the voice of the Yellow Bunting,
+yet it is incomplete and lacks the variety of phrases and musical
+notation which we customarily associate with the bird. Nevertheless, as
+the season advances, there is a progressive development in both these
+directions, and by the end of March or the beginning of April the song
+possesses all those qualities which appeal to us so forcibly.
+
+There is one other fact to which attention must be drawn--the variation
+in the song of the same species in different districts. As an
+illustration let us take the case of the Chaffinch. In Worcestershire
+the bird sings what I imagine to be a normal song--the notes are clear
+and the phrases are distinct and combined in numerous ways. With the
+notes fresh in mind I leave them and go to the west of Donegal, where I
+am at once conscious of a difference; not a subtle difference that
+perplexes the mind and is difficult to trace, but a change so remarkable
+that one is conscious of a passing doubt as to whether after all the
+voice is the voice of the Chaffinch; the song is pitched in a lower key,
+certain phrases are absent, the notes lack tone and are sometimes even
+harsh, and the bird seems wholly incapable of reaching the higher notes
+to which I am accustomed.
+
+Now the immature Reed-Bunting, though to our ears its song is but a poor
+representation of that of the adult, gains a mate; the Yellow Bunting
+pairs, and the discharge of the sexual function may even have taken
+place before its voice attains what we judge to be its full development;
+and there are no grounds for supposing that the Donegal Chaffinch, with
+its less musical notes, has on that account any the less chance of
+procreating its kind--facts which demonstrate that the biological value
+of song is neither to be sought in the purity of tone, nor in the
+variety and combination of phrases, nor, indeed, in any of those
+qualities by which the human voice gains or loses merit, and which leave
+us with no alternative but to dismiss from our minds all aesthetic
+considerations in the attempt to estimate its true significance.
+
+What, then, determines its value? Are there any qualities which, whether
+the bird is mature or immature, whether it is untrained or has acquired
+fuller expression by practice, whether it inhabits this district or
+that, are alike constant? Well, no matter how great the variation, no
+matter how much this voice falls below or exceeds the standard, judged
+from the human standpoint, attained by that, even we, with our duller
+perception, have no difficulty in recognising the species to which the
+owner of the voice belongs; in other words, the song is always specific,
+and this is the most noticeable, as it is the most remarkable,
+characteristic.
+
+There is still, however, another quality to which I would draw
+attention--that of loudness. The sounds produced are on the whole alike
+penetrative, and the individuals of any given district, even though the
+climate by affecting their vocal muscles may have modified the character
+of the song, are at no disadvantage in this respect; neither are the
+females on the same account the less likely to hear the undeveloped
+voice of the immature male.
+
+We have then the following considerations: firstly, there is the
+widespread and remarkable phenomenon of imitation, from which we can
+infer that the diversity of song is not due to structural differences
+but must be sought in some innate capacity to play one tune in
+preference to another; secondly, not all the individuals of the same
+species play a similar tune--we find that there is in certain directions
+a noticeable variation which nevertheless does not seem to affect the
+question of success or failure in the attainment of reproduction; in the
+third place, in contrast with this variation, we can observe a striking
+uniformity in two important particulars, namely in the specific
+character and penetrative power of the song--qualities which we know are
+essential for the purposes of "recognition" and "warning"; and finally,
+from the general course of our investigation, we can infer that if a
+male had no certain means of advertising its position, the territory
+would not be brought into useful relation in its life. Have we here
+sufficient ground on which to construct a theory of origin; in other
+words, has the evolution of song been incidental to, and contributory
+to, the evolution of the territory?
+
+We have all along spoken of the song and of the call-notes as if they
+were manifestations of separate emotional states having their respective
+and well-defined spheres of usefulness; and while, speaking generally,
+this is a true statement of the case, there is much evidence to show
+that the relationship between them is nevertheless very close. There
+are, for example, quite a number of cases in which a particular
+call-note is uttered with unusual energy during sexual emotion, and is
+attached to the song, of which it may be said to form a part; but a
+still closer connection can be traced in many simple melodies which are
+merely compositions of social and family calls repeated many times in
+succession, and even in some of the more complex productions there will
+be found indications of a similar construction. And since this is so,
+since moreover, in the seasonal vocal development of such a bird as the
+Yellow Bunting, we can observe the gradual elaboration from simple to
+complex--from the repetition of single notes to phrases and from phrases
+to the complete melody--we have every reason to suppose that it is along
+these lines that the evolution of the voice has proceeded.
+
+In all probability there was a time when vocal expression was limited
+to primitive social and family cries which would be called into play
+with special force during times of excitement, more particularly during
+the sexual season which is the period of maximum emotional excitement.
+But the excitement would express itself in all the congenital modes of
+behaviour peculiar to the season, and thus the repetition of these cries
+would become associated with combat, with extravagant feats of flight,
+and with other forms of motor response. Now the more emotional
+individuals would be the more pugnacious, and all the more likely
+therefore to secure territory and so to procreate their kind; and, being
+of an excitable disposition, they would at the same time be the more
+vociferous. Hence variations of the hereditary tendency to vocal
+expression, even though in themselves they were not of survival value,
+would be fostered and preserved, so long as they were not harmful, in
+virtue of their association with pugnacity. But if, instead of being
+neutral, they helped to further the biological end of combat, the
+relationship between the voice and pugnacity would be of a mutually
+beneficial kind; and those individuals in which variation in both
+directions happened to coincide, would have a better chance of success
+in the attainment of reproduction.
+
+A territorial system, closely corresponding to that which we have
+discussed, forms part of the life behaviour of certain mammals, and of
+its existence much lower in the scale of life evidence is not wanting;
+from which we can infer that it is not of recent origin, but that the
+conditions in the external environment demanded such a system at a
+remote period of avian development. Now even in its incipient stages the
+system must have involved a separation of the sexes, and howsoever
+slight the degree of separation may have been in comparison with that
+which can be observed to-day, inasmuch as the power of locomotion was
+then less highly developed, mating could only have proceeded
+satisfactorily providing that males fit to breed had some adequate means
+of disclosing their positions. Thus there is reason to think that from
+the very commencement of the process variations of emotional disposition
+expressed through the voice would have been of survival value.
+
+But expressed in what direction, in loudness and persistency of
+utterance, these are the qualities which, I imagine, would have been
+more likely to have facilitated the search of the female? Yet if she
+were uncertain as to the owner of the voice, neither loudness nor
+persistent repetition would avail much; and as species multiplied and
+the competition for the means of living became increasingly severe, so
+the necessity of a territory would have become intensified, and so, too,
+with the extension of range, would the separation of the sexes have been
+an ever-widening one; and as with their multiplication, irregularities
+and delays in mating, arising from the similarity of the calls, would
+have increased in frequency, so a distinctive call, which would have
+tended to minimise these risks, would have come to possess biological
+value.
+
+Here we have a theory of origin, but origin of what? Of certain
+characteristics of song--nothing more; and therefore to suppose that it
+furnishes a complete explanation, which satisfies all the requirements
+of scientific logic, of so wonderful an intonation as that, for example,
+of the Marsh-Warbler, or that no other relationships, except that of the
+territory, enter into the total emotional complex, simplifying here or
+elaborating there to meet the exigencies of diverse circumstances--to
+suppose this would be foolish. That there are many relationships which
+even to-day are leading to modifications in important particulars, but
+which at the present time are beyond our cognisance, of this there can
+be no doubt.
+
+There is one process by which song may have attained a fuller
+development, and which would account in some measure for the
+elaboration, inexplicable merely in terms of "recognition." It is this:
+the effect of the sexual call upon the female cannot well be neutral, it
+must be either pleasurable or the reverse--it must, that is to say, be
+accompanied by some suggestiveness, and by suggestion I mean the
+arousing of some emotion akin to that of the male; and if there are
+degrees of suggestiveness, which well there may be, some males will mate
+sooner than others and some will remain mateless--this is the theory of
+sexual selection. The question to be decided here is whether the
+biological emphasis is on loudness, or specific distinctness, or pitch,
+or modulation, or the manner in which the phrases are combined--that is,
+on some qualities in preference to others--or whether the emphasis is on
+the whole. We have already seen, and it is well known, that there is
+much variation in the voices of different individuals of the same
+species, and thus the first condition of the theory is fulfilled. Now
+the conditions which lead to variation are threefold--immaturity,
+seasonal sexual development, and isolation. Of the three, the variation
+in the case of the immature bird is the most instructive; the tone is
+not so pure, the combination of phrases is incomplete, and elaboration
+is imperfect, and yet, notwithstanding all these imperfections, we can
+observe that the bird pairs as readily as does the adult. But even if we
+lacked this demonstrative evidence, we should still be justified in
+assuming that such must be the case, for we know from experience in the
+preservation of game, where there is no surer way of reducing the stock
+than by leaving too high a percentage of old cocks, that for the young
+bird to be at any disadvantage in competition with the adult is
+detrimental, if not disastrous, to the species. So that while there is
+plenty of evidence of variation in those particular qualities which
+appeal to our aesthetic faculties, there is at the same time evidence
+which demonstrates that such variations exercise no influence on the
+course of mating; and inasmuch as it is difficult to conceive of any
+voice departing more from the normal type in these particular qualities
+than the immature does from the adult, if there be degrees of
+suggestive influence, we must seek it in some other direction. There
+remain the two other characteristics which we found to be constant under
+all circumstances, namely, loudness and specific distinctness; and if,
+in addition to serving the purpose of disclosing the positions of the
+males, they serve to evoke some emotion in the female, which helps to
+further the biological end of mating, so much the more reason is there
+for their survival.
+
+There can be no question that this ingenious and attractive theory, if
+it were true in its special application to song, would immensely
+simplify interpretation, and moreover that preferential mating would
+contribute not a little to the success of the whole territorial system.
+No one can deny the strength of the argument: that the sexual instinct,
+like all other instincts, must require a stimulus of an appropriate
+kind; that the effect of the sexual call upon the female cannot be
+neutral; and hence the probability that stimulation varies too; no one,
+I say, can question the strength of this evidence, and, one might add,
+of the evidence derived from the analogy of the human voice. But when we
+have said this, we have said all; and our acceptance of the hypothesis,
+so far as song is concerned, must remain provisional so long as the
+evidence remains but secondary evidence.
+
+
+
+
+CHAPTER V
+
+THE RELATION OF THE TERRITORY TO THE SYSTEM OF REPRODUCTION
+
+
+In the first two chapters I tried to show that the inherited nature of
+the male leads it to remain in a definite place at a definite season and
+to become intolerant of the approach of members of its own sex, and that
+a result is thus attained which the word "territory" in some measure
+describes. But the use of this word is nevertheless open to criticism,
+for it denotes a human end upon which the highest faculties have been
+brought to bear, and consequently we have to be on our guard lest our
+conception of the "territory" should tend to soar upwards into regions
+which require a level of mental development not attained by the bird. It
+is necessary to bear this in mind now we have come to consider the
+meaning of the territory, or rather the position that it occupies in the
+whole scheme of reproduction.
+
+Relationship to a territory within the interrelated whole of a bird's
+life serves more than one purpose, and not always the same purpose in
+the case of every species. We have only to glance at the life-histories
+of divergent forms to see that the territory has been gradually adjusted
+to suit their respective needs--limited in size here, expanded there, to
+meet new conditions as they arose. Now some may think that the theory
+would be more likely to be true if the territory had but one purpose to
+fulfil, and that one the same for every species; and they may see
+nothing but weakness in the multiplication of ways in which I shall
+suggest it may be serviceable. But such an objection, if it were raised,
+would arise from a mistaken conception, a conception which, instead of
+starting with a relationship and working up to the "territory," sees in
+the "territory" something of the bird's own selection and thence works
+back to its origin. Holding the view that it is nothing but a term in a
+complex relationship which has gradually become interwoven in the
+history of the individual, I see no reason why the fact of its serving a
+double or a treble purpose should not be a stronger argument for its
+survival. I now propose to examine the various ways in which the
+territory may have been of use in furthering the life of the individual,
+and the circumstances in the inorganic world which have helped to
+determine its survival.
+
+The purpose that it serves depends largely upon the conditions in the
+external environment--the climate, the supply of food, the supply of
+breeding-stations, and the presence of enemies. Hence its purpose varies
+with varying conditions of existence. But before we proceed to examine
+the particular ways in which it has been modified to suit the needs of
+particular classes of species, and the reason for such modifications, we
+must inquire whether there is not some way in which it has been
+serviceable alike to every species, or at least to a large majority of
+them.
+
+Success in the attainment of reproduction depends upon the successful
+discharge of the sexual function; and the discharge of the sexual
+function depends primarily upon an individual of one sex coming into
+contact with one of the opposite sex at the appropriate season and when
+its appropriate organic condition arises. Now the power of locomotion is
+so highly developed in birds that it may seem unreasonable to suppose
+that males and females would have any difficulty in meeting when their
+inherited nature required that they should do so, still less reasonable
+to suggest that this power might even act as a hindrance to successful
+mating. Nevertheless, if we try to picture to ourselves the conditions
+which would obtain if the movements of both sexes were in no wise
+controlled, and mating were solely dependent upon fortuitous gatherings,
+we shall come, I fancy, to no other conclusion than that much loss of
+valuable time and needless waste of energy would often be incurred in
+the search, and that many an individual would fail to breed just because
+its wanderings took it into districts in which, at the time, there
+happened to be too many of this sex or too few of that. And as the power
+of locomotion increased and the distribution of the sexes became more
+and more irregular, so the opportunity would be afforded for the
+development of any variation which would have tended to facilitate the
+process of pairing, and by so doing have conferred upon the individuals
+possessing it, some slight advantage over their fellows.
+
+What would have been the most likely direction for variation to have
+taken? Any restriction upon the freedom of movement of both sexes would
+only have added to the difficulties of mating; but if restriction had
+been imposed upon one sex, whilst the other had been left free to
+wander, some order would have been introduced into the process. That the
+territory serves to restrict the movements of the males and to
+distribute them uniformly throughout all suitable localities, there can
+be no question; and since the instinctive behaviour in relation to it is
+timed to appear at a very early stage in the seasonal sexual process,
+the males are in a position to receive mates before the impulse to mate
+begins to assert itself in the female.
+
+We will take the Ruff as an example. According to Mr. Edmund Selous,
+pairing, in this species, is promiscuous--the Ruffs are polygamous, the
+Reeves polyandrous. Suppose, then, that upon this island of some few
+miles in circumference, whereon his investigations were made, the
+movements of neither Ruff nor Reeve were subject to control, that the
+birds wandered in all directions, and that the union of the sexes were
+fortuitous, would the result have been satisfactory? We must remember
+that the Reeve requires more than one Ruff to satisfy her sexual
+instinct; we must also bear in mind the possibility that the functioning
+of her instinct may be subject to some periodicity, and we ask whether,
+under these circumstances, accidental gatherings would meet all the
+requirements of the situation. Now, manifestly, she must be in a
+position to find males when her appropriate organic condition arises.
+But in the absence of any system in the distribution of the sexes, how
+could delay be avoided, or how could a uniform discharge of the sexual
+function be assured? There is, however, a system. In the first place,
+there are the assembly grounds to which the birds repair season after
+season; and then, on the assembly grounds, there are the territories,
+represented, as Mr. Selous tells us, by depressions where the grass by
+long use has been worn away, and each depression is owned by one
+particular Ruff. The assembly grounds have the effect of splitting up
+and scattering the birds, and the number of Ruffs at any one particular
+meeting place is limited by the territories; with the result that Ruffs
+fit to breed are evenly distributed and always to be found in certain
+definite places, and the Reeves know by experience where to find them.
+
+The advantage of this territorial system is therefore apparent. Instead
+of this district being overcrowded and that one deserted; instead of
+there being too many of one sex here and too few of the other sex there;
+instead of a high percentage of individuals failing to procreate their
+kind, just because circumstances over which they have no control prevent
+their discovering one another at the appropriate time--each sex has its
+allotted part to play, each district has its allotted number of
+inhabitants, and the waste of energy and the loss of time incurred in
+the process of mating is reduced to a minimum.
+
+Let us return again to the question of fortuitous mating, and consider
+the position of a male and female that have discovered one another by
+accident and have paired; what will be the subsequent course of their
+behaviour? We are assuming, of course, that a territory forms no part of
+their life-history. If the discharge of the sexual function takes place
+immediately and the ovaries of the female are in an advanced state of
+seasonal development, the construction of the nest will proceed without
+delay--and the nest will answer the same purpose as the territory in so
+far as it serves to restrict the movements of the birds and tends to
+make them remain in, or return to, its vicinity; but if not, there will
+be an interval during which both sexes will continue to wander as
+before, guided only by the scarcity or abundance of food. In the first
+case, there will be the attraction of the nest to prevent any untimely
+separation; in the second, there will be nothing in the external
+environment to induce them to remain in any particular spot. Now if we
+turn to any common species and observe the sequence of events in the
+life of different pairs, we shall find that pairing is seldom followed
+by an immediate attempt to build; that an interval of inactivity is the
+rule rather than the exception, and that this interval varies in
+different species, in different individuals, and in different seasons.
+Our imaginary male and female will therefore be faced with considerable
+difficulty; for with nothing in the external environment to attract them
+and with no restriction imposed upon the direction or extent of their
+flight, their union will continue to be, as it began by being,
+fortuitous. Next, let us consider their position were a disposition to
+establish a territory to form part of the inherited nature of the male.
+Each one will then be free to seek food when and where it wills and to
+associate with other individuals without the risk of permanent
+separation from its mate; and, no matter how long an interval may elapse
+between mating and nest-building, each one will be in a position to find
+the other when the appropriate moment for doing so arrives. Hence, while
+preserving freedom of movement for each individual, the territory will
+render their future, as a pair, secure.
+
+No doubt the course of behaviour, as we observe it to-day in the lives
+of many species, is the outcome of, rather than the condition which has
+led to, the evolution of the territory. Thus, in many cases, we find
+that early mating is the rule rather than the exception; we find that
+the sexes frequently separate to seek their food, and fly away
+temporarily in different directions; and, under exceptional climatic
+conditions, we find that they even revert to their winter routine and
+form flocks; only, however, to return to their territories, as pairs,
+under more congenial conditions. Yellow Buntings, for example, pair
+comparatively early in the season--some in the latter part of February,
+others in March, and others again in April; and some build their nests
+in April, others in May. There is a gorse-covered common which I have in
+mind, a favourite breeding resort of this species. Between this common
+and the surrounding country, the birds constantly pass to and fro. If
+you watch a particular male you will observe that it sings for a while
+in its territory, that it then rises in the air and disappears from
+view, and finally that it returns to the tree, bush, or mound which
+constitutes its headquarters, where it again sings. Meanwhile the
+female, with which there is every reason to believe that this male has
+paired, behaves similarly; she, too, flies to the surrounding country
+and in time returns with equal certainty. Sometimes male and female
+accompany one another--that is, they leave simultaneously and likewise
+return; at other times, though they depart together, the male returns
+alone; or the male may disappear in one direction whilst the female does
+so in another--and, on the whole, there is a sameness in the direction
+of flight taken by the same pairs on different occasions. An interval of
+nearly two months may thus elapse between mating and nest-building,
+during which the sexes are not only often apart but often separated by a
+considerable distance.
+
+What does this species gain by the individuals belonging to it mating so
+early in the season? If the appropriate condition which leads the
+females to seek males were to arise in each individual at a late date,
+the first stage in the process--mating--would not be completed before
+the second--the discharge of the sexual function--were due to begin.
+Thus, instead of having ample time, the females would have but a short
+period in which to discover males; and this in some cases might lead to
+delay, in others to failure, and in others again to needlessly severe
+competition, entailing physical exhaustion at a critical moment in
+their lives. Hence those females in which the appropriate organic
+condition developed early in the season would not only be more likely to
+find males, but would be in a position to rear more broods than those in
+which it developed late; and they would have a better chance of leaving
+offspring, which, in their turn, would reproduce the peculiarities of
+their parents. Moreover, within certain limitations, the more these
+successful females varied in the date of their development, the less
+severe would be the competition, and the more uniformly successful would
+the mating of all the individuals in a given district tend to become.
+But all of this renders an interval of sexual inactivity unavoidable; an
+interval which must constitute a danger unless there were something in
+the external environment to prevent the male and female from drifting
+apart. Inasmuch, then, as the occupation of a territory serves to remove
+all possibility of permanent separation, I suggest that its evolution
+has afforded the condition under which this beneficial procedure has
+developed--free to mate when they will, free to seek food where they
+will, free to pursue their normal routine of existence, and to meet all
+exigencies as they arise in their ordinary daily life--whilst free to do
+this, their future, as a pair, is nevertheless secure.
+
+Thus far we have considered the territory in its relation to the
+discharge of the sexual function. In many of the lower forms of life,
+the success or the failure of reproduction, so far as the individual is
+concerned, may be said to end with the completion of the sexual act--the
+female has but to deposit her eggs in a suitable environment and then
+her work is done, because in due course and under normal conditions of
+temperature the young hatch out, and from the first are able to fend for
+themselves. And so, when we come to consider the question of
+reproduction in the higher forms of life, we are apt to focus attention
+too much upon the sexual function and too little upon the contributory
+factors, the failure of any one of which would mean failure of the
+whole. For a bird, success in the attainment of reproduction does not
+merely imply the successful discharge of the sexual function; much more
+is demanded; it must find somewhere to build its nest and to lay its
+eggs, it must shield its young from extremes of temperature and protect
+them from enemies, and it must be in a position to supply them with food
+at regular intervals. And, consequently, every situation is not equally
+favourable for rearing young; there must be a plentiful supply of food
+of the right kind in the immediate vicinity of the nest, and it must be
+in greatest abundance just at the moment when it is most urgently
+needed--that is to say, during the first few weeks after the birth of
+the young. Success, therefore, depends upon manifold relationships which
+centre in the station, and these relationships vary in intensity with
+the conditions of existence.
+
+First, then, let us examine the problem from the point of view of the
+food-supply. There are many species whose success in rearing offspring
+is largely dependent upon the rapidity with which they can obtain food;
+and it makes but little difference which species we choose out of
+many--Finch, Bunting, Warbler, or Chat. I shall choose the Buntings, as
+their life-history in broad outline conforms to the general type, and,
+moreover, their behaviour is fresh in my mind. The young are born in a
+very helpless state; they are without covering--fragile organisms,
+ill-fitted, one would think, to withstand extremes of temperature, and
+wholly incapable of protecting themselves from enemies of any
+description. For the first three days after they are hatched the female
+spends much of her time in brooding them, and, when she is thus
+occupied, the male sometimes brings food to her, which she proceeds to
+distribute or swallows. But all the young cannot be fed, neither are
+they ready to be fed, at the same moment; and the parents have besides
+to find food for themselves, and the nest has to be cleaned--all of
+which necessitates the young being exposed to the elements at frequent
+intervals. Now it is impossible to observe the instinctive routine of
+the parents, when the young need attention, without being impressed with
+the conative aspect of their behaviour. Why, we ask, are the movements
+of the female so brisk; why does she seek food and clean the nest so
+hurriedly; why, if her instinctive routine is interrupted, do her
+actions and her attitude betray such bewilderment? I take it that the
+only answer we can give to these questions is that the part of her
+inherited nature which predominates just at this particular time is to
+brood. But why is brooding of such importance? Partly to maintain the
+young at the proper temperature, and thereby to induce sleep--and sleep
+for offspring newly hatched is as important as food--and partly to
+protect them from the risk of exposure to extremes of temperature. This
+latter danger is no imaginary one. Examine a young bird that has
+recently left the egg; observe its nakedness; and consider what it has
+to withstand--a temperature that may rise to 70 deg. F. or may fall to 40
+deg. F., the tropical rain of a thunderstorm or the persistent drizzle of
+many hours' duration, the scorching effect of a summer sun or the
+chilling effect of a cold north-easterly wind, and, constantly, the
+sudden change of temperature each time that the parent leaves the nest.
+One marvels that it ever does survive; one marvels at the evolution of a
+constitution sufficiently elastic to withstand such changes. But,
+however much the constitution may give us cause to wonder, it is clear
+that much depends upon the parents. A slight inefficiency of the
+instinctive response which the presence of the young evokes, a little
+slowness in searching for food or sluggishness in returning to the nest,
+might lead to exposure and prove fatal. And, however much is demanded of
+the parents, it is clear that much also depends upon the relationships
+in the external environment; for no matter how sensitive or how well
+attuned the instinctive response of the parent may be, it will avail but
+little in the presence of unfavourable conditions in the environment.
+
+Everything turns upon the question of the effect of exposure. And in
+order to ascertain how far extremes of temperature are injurious, I
+removed the nests of various species containing newly hatched young,
+and, placing them in surroundings that afforded the customary amount of
+protection from the elements, I made a note of the temperature and the
+atmospheric conditions and then observed the condition of the young at
+frequent intervals. Details of these experiments will be found at the
+end of the chapter.
+
+The experiments with the Blackbirds and the Whitethroats gave the most
+interesting results. Both broods of each species were respectively of
+much the same age, yet one brood of Blackbirds survived for five, and
+the other only for two and a half hours, and one brood of Whitethroats
+lived for twelve hours whilst the other succumbed in a little over an
+hour. This difference is rather remarkable; and it seems clear that the
+power of resistance of the young diminishes rapidly when the temperature
+falls below 52 deg. F. It must be borne in mind, however, that the
+conditions under which the experiments were made were, on the whole,
+favourable--the weather was dry, the temperature was not unusually low,
+nor was the wind exceptionally strong or cold; and even in those cases
+in which the young succumbed so rapidly, the atmospheric conditions
+could by no means be regarded as abnormal.
+
+What, then, would happen in an unusually wet or cold breeding season?
+For how long would the young then survive? In the spring and early
+summer of the year 1916, I was fortunate in observing the effect of
+exposure under natural but inclement conditions. I happened to be
+watching the Yellow Buntings on Hartlebury Common--200 acres of Upper
+Soft Red Sandstone, profusely overgrown with cross-leaved heath (_Erica
+tetralix_), ling (_Calluna vulgaris_), and furze (_Ulex_)--in one corner
+of which eight males had established adjoining territories covering some
+fifteen acres of ground. The males obtained mates towards the end of
+March or at the beginning of April; nests were built in the middle of
+May, and the successful pairs hatched out their young in June. On the
+10th June the weather became exceptionally cold, and during the next ten
+days the temperature fell at times to 40 deg. F. during the daytime. Slight
+frosts were registered at night in the district, and the young bracken,
+which covered the Common in places, had the appearance of having been
+scorched and eventually withered away. At the coldest period of this
+cold spell the young were hatched in two of the nests--in the first one
+on the 10th June, and in the second a day or so later; and on the
+morning of the 10th June, having found a suitable position near the
+first nest, I began to watch the movements of the parents, with the
+intention of keeping some record of their behaviour each day so long as
+the young needed attention. An hour passed without their appearing, and
+on examining the young I found that they were cold, feeble, and
+unresponsive, but the female presently arrived and went to the nest.
+Later in the day the young were lively and responded freely when the
+nest was approached, but nevertheless I was impressed with the length of
+time during which the parents were absent; for, judging by the
+experience of previous experiment, there seemed to be every likelihood
+of their losing their offspring in such abnormally cold weather, unless
+they brooded them more persistently. On the 11th June at 5.50 A.M.
+neither parent was to be seen and the young could scarcely be made to
+respond; but shortly afterwards both male and female appeared, and,
+after remaining a few minutes, again disappeared without even
+approaching the nest. At 6.45 A.M. no attempt had been made to brood and
+the young were then so feeble that they were scarcely able to open their
+mouths, and at 6 P.M. one was still alive but the remaining three were
+dead. Yet the parents returned and the female went to the nest; and,
+from a distance of a few feet, I watched her brooding the living and the
+dead. At 5.45 A.M. the following day the remaining young bird had
+succumbed, the temperature then being 49 deg. F.
+
+At the second nest, I was unable to watch the behaviour of the parents
+so closely. On the 15th June the nest contained three young from three
+to four days old, and during the morning of that and the succeeding day
+nothing unusual occurred, with the exception that the period of exposure
+seemed, as in the former case, to be too long. On the 17th June at 3.10
+A.M. the young had collapsed and were stiff, but the parents were in
+their territory and anxious apparently to attend to their brood. At 9.15
+A.M. only two of the young were left in the nest, and though I searched
+amongst the undergrowth and in the gorse bush in which the nest was
+placed, no trace of the third bird was to be found. Of the two remaining
+young, one was alive and responsive but the other was dead, and though
+the female attended assiduously to the sole surviving offspring, yet it
+too had succumbed by the following morning.
+
+In a third territory, there was a nest containing four eggs. These eggs
+were due to hatch at much the same time as those in the two nests just
+referred to, but they failed to do so, and an examination showed that
+they contained well developed but dead chicks.
+
+To what can the death of the young and of the chicks in the eggs be
+attributed? Not to any failure in the instinctive response of the
+females, for they fed their young, they brooded them, they even brooded
+the dead as well as the living, and probably did all that racial
+preparation had fitted them to do. Yet the fact that the young in the
+second nest were lifeless and exposed at 3 A.M. seems to betoken absence
+on the part of the parents during the night, and may be interpreted as a
+failure of the parental instinctive response. Let us return for a moment
+to the experiments. These showed, it will be remembered, that a rise or
+fall in the temperature of but a few degrees was sufficient to make an
+astonishing difference in the length of time that the young were able to
+survive without their parents; that when the temperature reached 58 deg. 
+F. the bodies of the young retained their warmth, and that under such
+conditions even a night's exposure had little, if any, effect; so that
+even supposing that the parents were absent during the night, the death
+of the young cannot be said to have been due to a failure of the
+parental instinct, because under normal conditions--and under such has
+their instinctive routine been evolved--their absence would not have
+prejudiced the existence of the offspring. I attribute the collapse of
+the young solely to the exceptional cold that prevailed at just the most
+critical time, and I base this conclusion partly on the experience
+gained from experiment, but mainly on their condition observed at
+different intervals; for during exposure they collapsed rapidly, their
+flesh became cold and their movements sluggish, their response grew
+weak, and gradually they became more and more feeble until they could
+scarcely close their bills after the mandibles had been forced asunder.
+Yet, even after having reached so acute a stage of collapse, the warmth
+from the body of the brooding bird was sufficient to restore them
+temporarily; once more they would become lively and responsive, only,
+however, to revert to the previous condition soon after the parent had
+again abandoned them. Doubtless their power of resistance grew less and
+less during each successive period of exposure.
+
+If the nestling Bunting is to be freed from the risk of exposure, it is
+evident that there must be, in the vicinity of the nest, an adequate
+supply of food upon which the parents can draw liberally. Hence those
+pairs that exercise dominion over the few acres surrounding the nest,
+and are thus able to obtain food rapidly, will stand a better chance of
+rearing their offspring than others which have no certain supply to draw
+upon--and this, I believe, is one of the biological ends for which the
+territory has been evolved. But it must not be supposed that each pair
+finds, or even attempts to find, the whole of the food within its
+territory, or that it is necessary for the theory that it should do so;
+all that is required is that such overcrowding as might lead to
+prolonged absence on the part of the parents and inordinate exposure of
+the young shall be avoided. So that the problem has to be considered not
+merely from the point of view of the individual, but from the larger
+point of view of all the pairs inhabiting a given area.
+
+Now there were eight pairs of Yellow Buntings occupying the one corner
+of Hartlebury Common, and their territories in the aggregate covered
+some fifteen acres. The birds obtained part of their food-supply amongst
+the gorse and in some young scattered oak-trees, and part in an
+adjoining coppice and on the surrounding arable land. But they were not
+the sole occupants of this corner of the Common; other insectivorous
+species had territories there also--amongst which were Whitethroats,
+Grasshopper-Warblers, Willow-Warblers, Whinchats, Stonechats,
+Meadow-Pipits, Tree-Pipits, and Skylarks. Suppose then that there had
+been sixteen pairs of Yellow Buntings instead of eight; that there had
+been other pairs, which assuredly there were, inhabiting the locality;
+that they had also resorted, which assuredly they did, to the coppice
+and arable ground for the purpose of securing food; and that their
+numbers had also been increased in a similar ratio--would a supply of
+food for all have been forthcoming with the necessary regularity and
+promptitude? Well, the parents might have had to travel a little
+farther; but even if they had been compelled to do so, their absence
+would only have been prolonged by so many minutes the more, and under
+normal conditions what harmful result to the offspring could possibly
+have followed? The question for us, however, is not what might have
+occurred under normal conditions, but whether the life behaviour is so
+adjusted as to meet the exigencies of diverse, and in this case of
+abnormal, circumstances. Now the capacity of the young to resist
+exposure diminishes very rapidly when the temperature falls below the
+normal--the danger zone seems to be reached at approximately 52 deg. F.,
+and the length of time during which they survive then becomes
+astonishingly short--and moreover the fall in the temperature would tend
+to decrease the supply of insect life upon which they depend, so that if
+the size of the territories had been reduced by one half, and the parents
+in consequence had been compelled to seek their food at a greater
+distance, can it be doubted that the cumulative effect of even a few
+minutes of additional exposure would have been detrimental, if not
+disastrous, to the offspring?
+
+We speak, however, of the parents extending their journeys a little
+farther in this direction or a little farther in that, as though they
+could do so with impunity except in so far as it affected themselves, or
+their offspring, or the other Yellow Buntings inhabiting that particular
+area. But, most certainly, any extension would have meant so much
+encroachment upon the available means of support of other members of the
+species inhabiting adjoining areas, whose young in turn would have been
+liable to have been affected; and, with even greater certainty, the
+Whitethroats, the Stonechats, the Tree-Pipits, and the Willow-Warblers
+that had also established themselves in that one corner of the Common
+would have been hard pressed to find sufficient food with sufficient
+rapidity.
+
+Let me give another illustration of a somewhat different kind. Lapwings,
+as we saw in the previous chapters, establish territories and guard them
+from intrusion with scrupulous care. The young are able to leave the
+nest soon after they are hatched, and consequently the parents are not
+necessarily obliged to bring food _to_ them--they can, if they so
+choose, lead them _to_ the food. Whether each pair limits its search for
+food to its territory, I do not know. But even supposing that all
+ownership of territory were to lapse directly the young were hatched,
+that the boundaries were to cease to exist, and that the birds were free
+to wander at will without fear of molestation, the end for which the
+territory had been evolved would none the less have been obtained; for
+inasmuch as the parents are accompanied by their young, it matters not
+in what part of the meadow they seek their food; all that matters is
+that the number of families shall not exceed the available supply of
+food. So far, then, as the Lapwing is concerned, the territory fulfils
+its purpose when once it limits the number of males, since, by doing so,
+it limits the number of families and prevents undue pressure upon the
+means of support.
+
+Nevertheless, there are many birds that seem to rely entirely upon the
+territory to supply them with all that is necessary. Each Warbler seeks
+its food within the precincts of its own particular domain, and, except
+in occasional instances, neither resorts to neutral ground nor makes
+excursions into the locality immediately surrounding the territory, as
+does the Bunting. Probably it would be disastrous if it attempted to do
+so, for since its young at birth are so delicate and so susceptible to
+changes of temperature, it cannot afford to be absent from them for
+long. Of the two experiments made with young Whitethroats, one was made
+under favourable and the other under unfavourable conditions. In this
+latter case the temperature was 50 deg. F., and the young, it may be
+remembered, only survived for a little over one hour. Now exposure at
+that temperature is evidently dangerous, but it would be still more
+dangerous if the weather were wet instead of dry, and the temperature
+46 deg. F. instead of 50 deg. F.; and it is, I imagine, on this account
+that the impulse to brood is so strongly implanted in the female. No
+sooner, it seems, does she depart than she returns with a small quantity
+of food which she hurriedly distributes and immediately settles down to
+brood; and if forcibly prevented from returning, her attitude betrays
+symptoms of what, humanly speaking, we should term great distress. If,
+then, the conditions in the external environment were such as would make
+it difficult for the female to obtain food rapidly, what advantage would
+she derive from so strongly developed an impulse? Might it not be a
+disadvantage? Might it not mean that she would abandon the search too
+readily and be content to return with an insufficient supply, and might
+not that be as injurious to the young as prolonged exposure? Manifestly
+the impulse to brood could only have developed strength in so far as it
+fitted in with all the other factors that make for survival; and the
+principal factor in the external environment seems to be the territory.
+How could the young have been freed from the risk of exposure if the
+impulse to brood had not been so strongly implanted in the parent? How
+could the impulse to brood have been free to develop if a supply of food
+had not been first insured? How could the supply of food have been
+insured if numbers of the same species had been allowed to breed in
+close proximity?
+
+From the foregoing facts it is clear that the young of many species are
+at birth susceptible to cold and unable to withstand prolonged exposure.
+The parents must therefore be in a position to obtain food rapidly, and
+consequently it is important that there should be an ample supply in the
+vicinity of the nest. This end the territory certainly serves to
+promote; it roughly insures that the bird population of a given area is
+in proportion to the available means of subsistence, and it thus reduces
+the risk of prolonged exposure to which the young are always liable.
+
+
+This leads on to a consideration of those cases in which the question of
+securing food is subordinate to the question of securing a station
+suitable for reproduction.
+
+I take the Guillemot as an example. In principle its behaviour is
+similar to that of the Bunting; the male repairs to a definite place,
+isolates itself, and becomes pugnacious. But the Guillemot is generally
+surrounded by other Guillemots, and the birds are often so densely
+packed along the ledges that there is scarcely standing room, so it
+seems, for all of them. Nevertheless the isolation of the individual is,
+in a sense, just as complete as that of the individual Bunting, for each
+one is just as vigilant in resisting intrusion upon its few square feet
+as the Bunting is in guarding its many square yards, so that the
+evidence seems to show that that part of the inherited nature which is
+the basis of the territory is much the same in both species. What we
+have then to consider is, What is the biological value to the Guillemot
+of an inherited nature which, for the Bunting, has utility in relation
+to the supply of food for the young? Up to a point, the act of securing
+a territory has like value for each respective species, whether the area
+occupied be large or small--that is to say, it enables the one sex to
+discover the other with reasonable promptitude.
+
+For the greater part of the year, Guillemots live at sea; singly, in
+twos or threes, or in small parties, they move upon the face of the
+waters, extending their wanderings far away from land, out into the
+broad ocean, where for weeks together they face the gales and heavy seas
+of the Atlantic. But in due course and in response to internal organic
+changes, they return, like the Warbler, to their breeding grounds--rocky
+headlands or islands appropriately situated and affording the
+appropriate rock formation. During all these months of wandering, the
+majority seem to ignore the land, to pass away from it altogether, and
+to spread themselves over the surface of the ocean regardless of
+mainland or island. Some useful observations, which throw some light on
+the distance that Guillemots are accustomed to wander from land, were
+made by Lieut. B. R. Stewart during a number of voyages between various
+ports in Great Britain and Ireland and ports in North America,
+principally New York and Quebec. Thus, on the 24th March, large numbers
+were seen in lat. 55 deg. N., long. 24 deg. W., five hundred miles
+approximately from land, though on the following day--four hundred miles
+off Tory Island--they were not so plentiful. Again, on the 1st October, in
+lat. 53 deg. N., long. 27 deg. W., seven hundred miles or so from land, one
+bird was seen, whilst on the following day, in lat. 52 deg. N., long. 21
+deg. W., a single individual was washed on board by the heavy seas and
+seemed little the worse for the adventure. Within two hundred miles of the
+west coast of Ireland, he found them plentiful on various occasions. From
+this it is clear that the circumstances under which the bird lives for
+many months in succession must impose a considerable strain upon its
+constitution; and how it is able to withstand the buffeting of wind and
+water, to secure its food, and to endure, is a mystery. It is important,
+therefore, that the young bird should be properly nourished and
+protected from anything that might harm its constitution, and important,
+too, that the parents should be freed from any undue strain during the
+course of reproduction.
+
+The conditions which the breeding station has to fulfil are threefold:
+in the first place, it must be in proximity to the food-supply;
+secondly, it must provide the necessary shelter for the egg and for the
+helpless offspring; and, in the third place, it must be so situated that
+the young can reach the water in safety. We will examine these
+conditions one by one.
+
+The proximity to the food-supply is a consideration of some importance.
+The life of the Guillemot during the winter is a strenuous one; we know
+that large numbers succumb in stormy weather, and we can infer that
+slight constitutional defects might make all the difference between
+failure and success; and, therefore, the less severely the constitution
+of the parent is taxed during reproduction, and the more securely the
+constitution of the offspring is built up, the greater prospect will
+both have of resisting the hardships of the winter successfully. Much,
+then, will depend upon the distance the parents have to travel in order
+to obtain food. The farther the breeding station is removed from the
+feeding ground the greater the physical strain which will be imposed
+upon the birds, and the greater the chance will there be of the
+offspring being improperly nourished. Now the food consists of small
+fish, largely of sand-eels, which are secured in deep water, and the
+abundance of which varies, possibly according to the nature of the
+currents. Hence cliffs which are situated away from the water, or from
+which the water recedes at low tide, or which are surrounded by an area
+of shallow water, and are thus not in proximity to the feeding ground,
+even though they may fulfil the second and third condition, will not
+answer the requirements of a breeding station.
+
+Of no less importance is the type of rock-formation. Not every formation
+affords the necessary ledges upon which the egg can be deposited with
+safety--the face of the cliff may be too smooth, or too jagged, or the
+shelves may run at too acute an angle. Many of the large assemblages of
+Guillemots in the British Islands are found where the rock is quartzite,
+mica-schist, limestone, or chalk. The reason of this is that such rocks
+are weathered along the planes of stratification, of jointing, of
+cleavage, or of foliation--the strata being probably of unequal
+durability--with the result that innumerable shelves, ledges, and
+caverns, which are taken advantage of by the birds, form a network over
+the face of the cliff. But only those ledges can be made use of which
+are placed at a considerable height above the water, because, when the
+cliff faces the open sea, the lower ones are liable to be washed in
+stormy weather by the incoming swell and thus become untenable. There is
+a small cove in the midst of the most precipitous part of the breeding
+station at Horn Head, wherein the shingly shore shelves rapidly to the
+Atlantic and faces to the west. Here, towards the end of July, young
+Kittiwake Gulls can sometimes be found washed up on the beach--some
+living, but in every stage of exhaustion, others dead, and in every
+stage of decomposition; here is the young bird, recently caught by the
+swell and thrown upon the shore, lying side by side with the remains of
+others that had previously succumbed to starvation--on every side
+evidence of the devastation wrought by the Atlantic. May not some of
+this destruction have been brought about by the nests having been placed
+upon the lower ledges within reach of an exceptionally heavy sea? Hence
+much depends upon the nature of the rock-formation, and many a mighty
+precipice, even though it may fulfil the first and third condition, is
+nevertheless valueless as a breeding station.
+
+Finally, the young bird must occupy a ledge from which it can reach the
+water in safety. There is much difference of opinion as to the manner in
+which it leaves the ledge, but all agree that it does so before it is
+capable of sustained flight. If, then, the face of the cliffs were made
+up of a series of broken precipices, or if the rocks at the base
+projected out into the water, or if detached rocks abounded in the
+waters beneath, the mortality amongst the chicks would no doubt be
+considerable.
+
+The coast-line of Co. Donegal will illustrate the foregoing remarks. On
+the southern and western side of the Slieve League promontory there is
+no real Guillemot station; only on the northern side--the quartzite in
+the vicinity of Tormore--are the birds to be found in large numbers.
+Northwards from here, a wild and rugged coast is passed over before
+other stations are reached--at the eastern end of Tory Island and on
+Horn Head; and beyond this, to the east, there are none, not even on the
+old rocks that form the promontory of Inishowen. Why, we ask, do
+countless numbers crowd the ledges of Horn Head, whilst they are absent
+from the precipices of Slieve League; why, too, are they absent from
+the granite cliffs of Owey? The reason is not far to seek. Either the
+face of the cliff is made up of a series of broken precipices, or the
+face of the precipices is too smooth, or the otherwise suitable ledges
+are situated too near the water, or the water recedes from the base of
+the cliff at low tide. Many miles of rock-bound coast are thus useless
+for the purpose of reproduction.
+
+Now when we bear in mind how large an expanse of coast is formed of
+blown sand or of rocks of low altitude, and how many miles of cliff fail
+to supply the three essential conditions that we have been considering,
+we can see that suitable breeding stations must be limited both in
+number and extent. From a wide expanse of ocean hosts of individuals are
+therefore obliged to converge at certain definite points; and hence,
+each recurring season, there must arise a competition for positions at
+the station, just as there is competition between individual Buntings
+for positions in the marsh. And the ability to obtain a position upon a
+suitable ledge involves, in the first place, an impulse to search for
+it; in the second place, an impulse to dwell in it; and in the third
+place, an impulse to resist intrusion upon it. It would be useless for
+an individual to be pugnacious if it had no fixed abode; equally useless
+for it to establish itself on a particular ledge if it had no power to
+defend it--all of which implies an inherited nature similar to that of
+the Bunting. But the proximate end to which the competition is directed
+is not alike in the case of both species. In the case of the Guillemot
+it has reference solely to the piece of rock whereon the egg is laid; in
+the case of the Bunting to a piece of ground capable of furnishing an
+adequate supply of food for the young; and the reason for the difference
+is this, that there is always an abundance of food in the water beneath
+the cliff, but breeding stations are scarce, whereas there is always an
+abundance of situations in the marsh in which the Bunting can place its
+nest, but the supply of food varies and at times can only be obtained
+with difficulty.
+
+If then the Guillemot were to behave after the manner of the Bunting and
+assign to itself a portion of the face of the cliff, or if it were only
+to occupy a few ledges, or an even lesser area--a single ledge--what
+would be the result? That it would attain to reproduction is beyond
+question; that the egg would be safely deposited there can be no manner
+of doubt; neither is there any reason to suppose that the offspring
+would not be successfully reared. But, indirectly, its behaviour would
+affect the Guillemot race. For if it be true, as the crowded ledges
+certainly seem to show, that there is a dearth of suitable breeding
+ground, no greater calamity could befall the species than that some
+members should exercise dominion over too large an area of the habitable
+part of the cliff and thus prevent others from breeding. Under such
+conditions the race could not endure, since in this, as in every case,
+its survival must depend upon a close correspondence between the
+behaviour of the individual and the circumstances in the external
+environment.
+
+Scarcity of suitable cliffs is the principal reason of the ledges being
+so closely packed with Guillemots, just as it accounts for this part of
+the precipice being crowded with Kittiwake Gulls, that part with
+Herring-Gulls, and that part again with Razorbills and Puffins. Yet each
+individual preserves its few square feet of rock or soil from
+molestation, and the area each one occupies varies according to the
+conditions of existence of the species. Thus the Herring-Gull occupies a
+comparatively small area, although one many times larger than that of
+the Guillemot. It requires more space than the latter, owing to the fact
+that it not only builds a nest but rears four instead of a single
+offspring, and it can be allowed this, because, since its young remain
+in the nest until they are capable of sustained flight, it can make use
+of many miles of cliff from which the tide recedes at the base, or which
+have, at their base, rocks jutting out into the sea; but manifestly it
+cannot be allowed so much space as the Bunting.
+
+Martins build in close proximity to one another, owing probably to
+shortage of accommodation, and, in their case, the nests have to be so
+situated as to be sheltered from the wet. If water drips upon them for
+any length of time, the mud, of which they are composed, crumbles and
+large pieces fall away, with the result that the eggs or the young are
+precipitated to the ground. Consequently, not every house or
+perpendicular cliff will answer the purpose of a breeding station. A few
+pairs build their nests beneath the eaves close against the walls of my
+house, and year after year the result is much the same; after every
+downfall of rain, the water collects into rivulets, trickles down over
+the eaves, is absorbed by the mud and destroys the nests. Thereupon, the
+birds set to work and rebuild; but again the nest is destroyed, and
+again they rebuild, and so on throughout the summer, and only on rare
+occasions do they succeed in rearing offspring at the proper season.
+Similar conditions must prevail in many situations; but, clearly, the
+more binding and plastic the building material, the longer the nest will
+withstand the action of the dripping water and the greater chance will
+there be of the young being reared in safety. Observe, therefore, how
+far-reaching an effect so small a detail as the nature of the mud can
+have upon the status of the species in any given locality. Where the
+conditions are favourable, there the birds must congregate to breed,
+and, like the Guillemot, if each individual exercised dominion over too
+large an area, the species as a whole would suffer.
+
+In all these examples, the fact of different individuals being in such
+close proximity may afford some protection from enemies both as regards
+the egg and the offspring, and in so far as there is a mutual advantage
+such assemblages may be spoken of as communities. A community, however,
+in the true sense of the word, is a collection of individuals brought
+together, not primarily as a result of shortage of breeding ground, but
+in consequence of advantages of communal ownership over individual
+ownership. A rookery is an example of a true community. Neither shortage
+of nesting accommodation nor scarcity of food can account for Rooks
+assembling together to breed; for if the different pairs which go to
+make up the rookery were to scatter throughout the surrounding
+neighbourhood, they would, as a rule, find plenty of trees in which to
+build their nests, and plenty of food.
+
+How, then, can the theory apply to a species that breeds under such
+conditions? What part can the territory play in furthering the life of
+the individual when large numbers of nests are built closely together in
+the same tree? There is much evidence to show that mutual protection is
+a necessary condition of the Rook's existence; many cases are on record
+of rookeries being destroyed by Carrion-Crows, Hooded Crows, and Ravens.
+For instance, Mr. Ward Fowler records a case in which a pair of Crows
+attacked a small rookery, ransacked the nests, and destroyed the eggs,
+with the result that not a single pair of Rooks was left in the
+settlement. Each Rook must therefore secure a position within the
+precincts of the community if it is to have a chance of success in the
+attainment of reproduction. But every locality cannot supply sufficient
+trees of the right kind, appropriately situated and in suitable relation
+to the food supply, in which numbers of nests can be built in close
+proximity; so that if more than one community were to attempt to
+establish itself in a limited area, the supply of food or the supply of
+trees might become a pressing problem. Each community must therefore be
+prepared to defend its own interests, and each must be regarded as one
+unit and the area occupied as one territory within which are included a
+number of lesser territories. The individual may fail to establish
+itself within a community, but, even if it succeeds, the community may
+fail to establish the rights of communal ownership; hence it has to face
+a twofold possibility of failure, and if it lacked the inherited nature
+which leads the Guillemot to secure a position upon the ledge, or the
+Bunting to obtain a position in the marsh, the chances are that it would
+fail in the attainment of reproduction.
+
+The question now arises as to how it comes about that the area occupied
+by each individual conforms in broad outline to that which has proved
+beneficial for the welfare of the species as a whole. We shall find that
+up to a point the answer is a simple one. No one could study the
+behaviour of animals without observing the important part that habit
+plays in the life of the individual; an action performed to-day is
+liable to be repeated to-morrow and the following day until it becomes
+ingrained in the life of the individual. This must not be taken to mean,
+however, that a particular action has to be performed for many days in
+succession before it becomes definitely fixed; if only it is repeated a
+number of times, even within the space of a few hours, it will acquire
+sufficient strength for its continuance; but continued repetition gives
+increased fixity, and, as time goes by, it becomes increasingly
+difficult for the creature to make a change unless the character of the
+situation necessitates readjustment.
+
+For example, when the organic condition which leads to nest-building
+becomes active, the bird tentatively collects some of the necessary
+material in its bill, flies round with it, and then drops it. After a
+while it collects some more, and this time leaves it perhaps in a bush.
+Later on it makes another attempt, and, meeting with a situation which
+calls forth the appropriate response, it thereupon lays the foundation
+of the structure. We will assume that the nest is placed in the midst of
+a tangled bush. Well, the bird lays the first strands of the foundation
+and then goes in search of more material. The next time it approaches
+the nest from the opposite side of the bush, and presently it finds yet
+a third entrance. But each entrance is not made use of in turn: one is
+employed more frequently than the other two, and in the course of time
+becomes the sole highway to and from the nest. Suppose now that, when
+the young are hatched, I cut away the foliage from the bush on the
+opposite side from that on which the bird customarily enters, and by so
+doing leave the nest exposed, what is the result? The female arrives
+with food, threads her way through the bush, and, when beside the nest,
+pauses as if aware that some change had taken place, and then flies away
+through the new opening. In a short time she returns, flits from twig to
+twig on the outskirts of the bush, and comes upon the new opening--there
+she hesitates. But though the nest is in full view and within a few
+inches of her perch, and though the young stretch out their necks, yet
+so strong is the former habit that she is compelled to return to the
+opposite side and approach the nest by the usual circuitous route before
+she distributes the food amongst her offspring.
+
+Let us see how far this law of habit formation may have been effective
+in defining the extent of the area occupied. When a male Warbler arrives
+at its destination in the spring it seeks out a suitable environment,
+and, having found a place unoccupied by any other male, settles in it
+and remains there--its behaviour up to this point being determined by
+racial preparation. After the fatigue of the journey its movements are
+at first sluggish; hunger, however, asserts itself and a search is made
+for food; wandering away from the position in which it first settled and
+which acts as a headquarters, it hunts through certain trees here or
+certain bushes there and returns, and presently it wanders away again,
+perhaps in another direction, but, as before, works its way back again
+to the headquarters. The journeys thus radiate outwards from the
+headquarters, and according to the success with which the bird meets,
+so, probably, it happens that some trees are searched more often than
+others and certain directions are taken more frequently than others, and
+by constant repetition a routine is established which limits the
+direction and scope of its wanderings.
+
+But in the case of the Guillemot the conditions of existence are
+reversed: food can be had in abundance but suitable breeding stations
+are scarce. The few square feet of ledge correspond to the tree or clump
+of bushes which acts as a headquarters for the Warbler, and the
+occupation of them is determined, as it is in the case of the Warbler,
+by racial preparation. Since, however, the ledge is only made use of for
+the immediate purpose of incubation and is in no way affected by
+questions relating to food, there is no occasion for the bird to wander
+along the ledge nor to encroach upon those adjoining. Hunger stimulates
+the Warbler to search the surrounding trees, and so to extend its area;
+but hunger takes the Guillemot down to the water, and hence the area
+which it primarily occupied remains unmodified.
+
+To sum up: the territory is useful in various ways, but not necessarily
+in the same way for every species. Reproduction would always have
+remained fortuitous, and the number of individuals that attained to it
+would seldom have reached the possible maximum unless some provision had
+been included in its system for insuring that the males and females
+could meet at the proper moment and afterwards remain in touch with one
+another, and that the number of pairs inhabiting a given area did not
+exceed the available means of support. I have tried to show that the
+inclusion of a disposition to secure a territory tends to remove these
+difficulties. In the first place, the disposition which leads to its
+occupation comes into functional activity (in the male) early in the
+season; and so, by the time that the appropriate pairing condition
+arises in the females, the process of acquiring territories is well
+advanced, and the males being regularly distributed, each in its
+respective position, are readily found by their prospective mates. The
+behaviour of each sex is thus adjusted to further the end of mutual
+discovery. Next, after mating has taken place, the position occupied by
+the male acts as a headquarters to which the birds can always repair,
+and becomes a bond of union which is serviceable in that it prevents any
+possibility of their drifting apart. And in the third place, the males
+become pugnacious and in this way secure for themselves areas which vary
+in size according to the conditions of existence of the species, so that
+there is no possibility of too many congregating in this locality, and
+all the less likelihood of too few finding their way to that; and hence,
+on the average, different pairs are distributed throughout all suitable
+localities. Furthermore, owing to the fact of their having a
+headquarters, the male and female are allowed a freedom of movement
+which otherwise they would only possess when the construction of the
+nest had actually begun; they can seek their food independently, and,
+even though paired, they can if necessary continue their winter routine
+without risk of separation. This means that the organic condition which
+leads to pairing, is free to develop in the female earlier than would be
+the case if there were nothing in the external environment to attract
+the pair to a particular spot; and the longer the period over which the
+process of pairing can be spread, the greater chance will females have
+of discovering mates, the less severe will the competition tend to
+become, and, consequently, the smaller the percentage of individuals
+that fail to obtain suitable partners.
+
+In these ways the territory has been serviceable alike to a number of
+species. But much as the questions of mutual discovery and regular
+distribution may have influenced the course of its development, there
+can, I think, be little doubt that, on the one hand, the supply of the
+necessary accommodation for rearing offspring, and on the other, the
+necessity for an adequate supply of food in close proximity to the nest,
+have been the main determining factors, and have led to a wide
+divergence in its function. At the one extreme the function is to insure
+a plentiful supply of food for the young; at the other, to insure a
+station suitable for rearing offspring. I took the Bunting and the
+Guillemot as types of the two extremes. The young of the former species
+are born in a very helpless state. They are susceptible to cold and
+unable to withstand prolonged exposure, and therefore it is essential
+that there should be an ample supply of food, upon which the parents can
+draw liberally, in the vicinity of the nest. But the nest is placed in a
+variety of situations, and accommodation in this respect may be said to
+be unlimited. The young of the latter species are not so susceptible to
+exposure, and moreover there is always an abundance of food in the
+waters beneath the cliff; but ledges of rock, upon which the egg can be
+securely deposited and the young successfully reared, are limited both
+in number and extent. The position then is as follows: there are
+situations in plenty in which hosts of Buntings can build their nests
+but the supply of food is a difficulty, and if the respective areas of
+different individuals were insufficient to supply them with the
+necessary food with the necessary rapidity, they would run the risk of
+losing their offspring and the species would not endure; on the other
+hand, cliffs upon which the Guillemot can rear its young are limited,
+but the supply of food presents no difficulty, and consequently the
+smaller the area over which each individual exercises dominion, the
+greater the number that will attain to reproduction and the greater
+prospect the species will have of survival. The emphasis in the one case
+lies on the fact that the area occupied must be sufficiently large; on
+the other, on its being just sufficient and no more to accommodate the
+egg. Hence the difference in the function at the opposite extremes is
+brought about, not by modifications of the instinctive behaviour which
+leads to the establishment and defence of the territory, but solely by
+modifications in the size of the area occupied, in accordance with the
+conditions prevailing in the external environment. No doubt, if we had
+the life-histories of a sufficient number of species worked out, we
+should find that the gradations were complete from the one extreme to
+the other. We are justified in thinking that this must be so because in
+many directions we can not only observe differences in the size of the
+area occupied, but can recognise a close correspondence between those
+differences and the conditions of life of the species. Thus the
+Herring-Gull occupies a comparatively small area, though one which is
+many times larger than that of the Guillemot. It requires more space
+because it not only builds a nest but rears four instead of a single
+offspring, and it can be allowed more space because the young remain in
+the nest until they are capable of sustained flight, and consequently it
+can make use of many miles of cliff from which the tide recedes at the
+base, and which on this account are denied to the Guillemot, but
+manifestly it cannot be allowed so much space as the Bunting, for then
+comparatively few individuals would attain to reproduction.
+
+Again, the Reed-Warbler inhabits swamps overgrown with the common reed,
+and in such places insect life is abundant just at the time when the
+young are hatched. But these swamps cover a comparatively small acreage
+in the breeding range of the bird, and if each pair were to attempt to
+establish dominion over an area equal, let us say, to that of the
+Willow-Warbler, the species would have but a poor chance in the struggle
+for existence. So that, in a case of this description, the supply of
+food and the comparative scarcity of breeding stations have been factors
+of like importance in the evolution of the territory.
+
+Finally we were led to inquire as to how it comes about that the extent
+of the area occupied by each individual is adapted to the circumstances
+in which the individual finds itself; and we came to the conclusion that
+the movements of the bird, subsequent to the initial act of establishing
+itself in a position, are regulated and defined by the law of habit
+formation. For example, the Warbler, in response to its inherited
+nature, takes up a position in an appropriate situation. It then
+proceeds to search for food; it makes short journeys first in this
+direction and then in that; it repeats these journeys, and gradually
+forms a habit which compels it to remain within more or less
+well-defined boundaries. But the actual distance that it traverses on
+the occasion of its first attempt must be determined by the relative
+abundance or scarcity of the particular kind of insect life which it
+requires. So that, although habit defines and in some measure helps to
+determine the boundaries of the territory, it is clear that in the last
+resort they must depend upon the nature of the conditions in the
+external environment.
+
+We have, then, the congenital basis which leads to the occupation of a
+position, and to the enmity shown by the owner of the position towards
+other individuals; and this congenital basis is found alike in many
+widely divergent forms, living under equally widely divergent
+conditions; we have acquired accommodation; and we have relationships in
+the organic and inorganic world--and the outcome of it all is a system
+of behaviour which we, who can perceive the end to which such behaviour
+is tending, are justified in speaking of as "a disposition to secure a
+territory." In the development of this system a primary value must be
+ascribed to the conditions in the external environment, for they
+determine the direction of the variations of instinctive procedure and
+of acquired habit which work towards the same goal--that of adjustment
+to the conditions of life.
+
+
+
+
+NOTE
+
+
+The following are the experiments referred to on page 181:--
+
+
+On the 14th May 1915, a nest of Blackbirds approximately four days old
+was removed at 6.45 A.M. The temperature was considerably below the
+normal, and snow lay on all the high ground in the neighbourhood. In a
+short time the birds collapsed, and at 9.15 A.M. were dead. On the 29th
+May, at 6 A.M., a second nest was removed, containing young of
+approximately the same age, and although the conditions were more
+normal, the temperature being 50 deg. F., the birds collapsed at 8 A.M.,
+and an hour later one of the brood showed little signs of life. The wind,
+however, then changed to the west, and the temperature rose one degree,
+with the result that they were still living at 11 A.M. A further
+experiment was made with Song-Thrushes on the 5th June. The wind was in
+the south and the temperature 63 deg. F. The young, approximately four days
+old, were removed at 7.25 A.M., but as they showed no signs of collapse
+at 1 P.M. I replaced the nest in the original site.
+
+
+On the 30th May, a nest of Whitethroats three days old was removed at
+7.15 A.M. The wind was northerly and the weather fine, but the
+temperature low--50 deg. F. At 8.15 A.M. the birds showed no sign of life. 
+A second experiment with this species was made on the 10th June under more
+favourable circumstances, for although the sky was overcast and the wind
+northerly, the temperature was 59 deg. F. In this case the young survived
+from 6.55 A.M. to 7 P.M.
+
+
+On the 27th May 1915, a nest of Hedge-Sparrows hatched the previous day
+was removed at 7 A.M. The temperature was below the normal, being 49 deg.
+F. At 8 A.M. the young were cold and in a state of collapse, but they
+survived nevertheless until 3.20 P.M.
+
+
+On the 7th June 1915, a nest of young Skylarks three days old was
+removed at 7.15 A.M. The temperature was 62 deg. F., and the birds survived
+until 4 A.M. the next day.
+
+
+On the 6th June 1916, a nest of Linnets just hatched was removed at 6.47
+A.M. The temperature was 51 deg. F. At 7.50 A.M. the birds were cold and in
+a state of collapse, and only survived until 8.50 A.M.
+
+
+
+
+CHAPTER VI
+
+THE WARFARE BETWEEN DIFFERENT SPECIES AND ITS RELATION TO THE TERRITORY
+
+
+We have now considered the various ways in which the territory is useful
+in furthering the life of the individual. We have seen that, in some
+cases, there is competition for stations where the egg or eggs can be
+deposited and incubated in safety; that, in others, there is competition
+for stations capable of furnishing an adequate supply of food for the
+young; and that the establishment of "territories" not only renders the
+attainment of reproduction for the individual secure, but serves so to
+regulate the distribution of pairs that the maximum number can be
+accommodated in the minimum area. This being so, the question arises as
+to whether competition for territory is strictly limited to individuals
+of the same species, or whether it may not occur also between different
+kinds of birds, providing always that similar conditions of existence
+are required. First of all I shall relate a number of facts which will
+serve to show the nature and extent of the warfare, and I shall then
+give the reasons which lead me to believe that the fighting not only
+bears some relation to the "territory," but that it is an important
+factor in contributing to the attainment of that which for biological
+interpretation is the end for which the whole territorial system has
+been evolved.
+
+Those who have studied wild life on one of the rocky headlands, which
+are so numerous round our coasts, will probably be familiar with the
+rivalry that exists between the Raven and certain birds of prey. Where
+the Raven finds shelter for its nest, there, too, the Peregrine has its
+eyrie--and so it happens that these two species are continually at war.
+Now the warfare occurs not only during the season of reproduction but
+continues throughout the greater part of the year, and can even be
+observed in the late summer or early autumn--the period when we should
+expect to find the instinct least susceptible to appropriate
+stimulation. But it is of a more determined kind early in the spring,
+and it is then that we often witness those remarkable exhibitions of
+flight, the skill of which excites our admiration. The Falcon rises
+above the Raven, stoops at it, and when it seems no longer possible for
+a collision to be avoided, or, one would imagine, for the Raven to
+escape destruction, the Raven skilfully turns upon its back and
+momentarily faces its opponent, and the Falcon with equal skill changes
+its course, passing upwards and away. The attack, however, is soon
+repeated, and though no collision may actually take place, yet the fact
+that the Raven, when it turns to face its adversary, is obliged to drop
+the stick which it carries, is not only an indication of the character
+of the struggle, but it shows that a definite end is gained--that the
+efforts of the Raven to build in that particular locality are hampered.
+But the Falcon is not the only enemy that the Raven has to face;
+Buzzards are just as intolerant of the presence of Ravens in their
+neighbourhood as the Ravens are of them, and consequently there is
+incessant quarrelling wherever the same locality is inhabited. As a
+rule, the fighting occurs whilst the birds are on the wing; the Buzzard
+rises to a considerable height, and, closing its wings, stoops at the
+Raven below, and when within a short distance of its adversary, swerves
+upwards and gains a position from which it can again attack. The
+Buzzard, however, is by no means always the aggressor; I have watched
+one so persistently harassed by a Raven that at length it left the rock
+upon which it was resting and disappeared from view, still followed by
+its rival. Thus it seems as if they were evenly matched, and, when they
+occupy the same locality, it is interesting to notice how the initiative
+passes from the one to the other according to the position occupied by
+the birds in their respective territories.
+
+[Illustration: Peregrine Falcon attacking a Raven
+
+Emery Walker ph.sc.]
+
+That there is constant warfare between the Green Woodpecker and the
+Starling is well known, the purpose of the Starling being to gain
+possession of the hole which the Woodpecker with much skill has drilled
+for itself. As far as my experience goes, the Starling is always the
+aggressor, and there is only too good reason to fear that, in the course
+of time, the Green Woodpecker will disappear as a result of the greater
+fertility and tenacity of its enemy. The Martin suffers a similar kind
+of persecution from the House-Sparrow, and here again there is reason to
+believe that the greater virility of the Sparrow will hasten the
+extinction of its rival. In cases of this description the purpose of the
+fighting is clear, and one can understand why such divergent species
+should be hostile to one another; yet others, equally remote in the
+scale of nature, are hostile when no such ostensible reason can be
+assigned for their hostility. Few birds are more pugnacious than the
+Moor-Hen, and the determined manner in which different individuals fight
+with one another is notorious. But the intolerance it displays towards
+other species is no less remarkable, and its pugnacious instinct seems
+to be peculiarly susceptible to stimulation by different individuals
+belonging to widely divergent forms. At one moment a Lapwing may be
+attacked, at another a Thrush or a Starling, harmless strangers that
+have approached the pool to drink; even a Water-Rail, as it threads its
+way through the rushes, may fail to escape detection; and, which is
+still more curious, a covey of Partridges will evoke response if they
+approach the pool too closely.
+
+Here is a curious instance of apparent waste of energy. A pair of
+Magpies built their nest in an ilex tree. Early one morning there was a
+commotion in the tree, much flapping of wings and a medley of sounds
+which told of large birds engaged in a struggle--the Magpies were
+attacking a pair of Wood-Pigeons. There was no question as to the
+genuineness of the struggle, nor any doubt as to the proximate end for
+which the Magpies were striving, for their efforts continued so long as
+the Wood-Pigeons remained in the tree, and only ceased when they had
+succeeded in driving them away.
+
+Turning next to species which are less distantly related, we find that
+instances of intolerance are more numerous and that a wider range of
+species is involved. The hostility that the Lapwing displays towards the
+Snipe calls for special remark. It often happens that the marshes or
+water meadows, that are such favourite haunts of the Lapwing, are also
+resorted to by Snipe for the purpose of securing food, or it may be even
+for the purpose of reproduction. In such places both species are often
+abundant; the meadow is divided up into Lapwings' territories, and early
+in the season the Snipe wander over it in small parties, singly, or in
+pairs. Now, if it were only on isolated occasions that the Lapwing paid
+heed to the Snipe, one would not perhaps attach any peculiar
+significance to the fact; but the pugnacious instinct of the bird
+responds to the presence of this intruder almost as freely as it does to
+that of another Lapwing. Again and again, day after day, the Snipe are
+attacked and driven off in a manner which would be fittingly described
+as persistent persecution, for the Snipe has neither the physical
+capacity nor apparently any instinctive tendency to retaliate. Thus a
+Lapwing may come suddenly upon a small party of Snipe hidden from view
+in a dyke where they are probing the ground for food; the Snipe
+immediately rise and fly away and there is momentary confusion as the
+Lapwing darts first at this one, then at that; or, espying a Snipe at
+rest at the opposite end of its territory, it will first of all run
+rapidly towards it, and then fly after it, as, with twisting flight, it
+darts hither and thither a few feet above the ground; or again, it will
+attack and rapidly pursue solitary individuals as they skim across its
+territory and attempt to settle. Is this intolerance merely an exuberant
+expression of an instinct which is serviceable in another direction? The
+behaviour of the Lapwing scarcely justifies such a conclusion, for all
+its actions denote a striving towards some end which we can describe,
+and it seems to gain satisfaction only when the ejection of the intruder
+has been accomplished.
+
+Many of the Warblers display irritation when approached by other birds
+which we should scarcely expect would arouse their hostility. The
+Hedge-Sparrow, for example, is frequently regarded with suspicion, and
+it is by no means unusual to see it attacked by so small a bird as the
+Chiffchaff. The Wood-Warbler is also pugnacious, and will even attack a
+pair of Chaffinches. Between the Tit family and some of the smaller
+Warblers there are constant exhibitions of hostility; even the Great Tit
+is liable to be driven away, but the Blue Tit is especially marked out
+for persecution, though doubtless it is well able to hold its own.
+
+The following incident will show how real is the antagonism between
+these two families. A Chiffchaff occupied the corner of a small osier
+bed, and was particularly aggressive towards other closely-related forms
+in its immediate neighbourhood. On two mornings in succession ten Blue
+Tits invaded its ground, passing from end to end of it as they wended
+their way from tree to tree in search of food. Their presence evoked the
+usual hostile response, yet, withal, aroused the fear of the Chiffchaff,
+which, at times, appeared to be swayed by conflicting impulses. Now, in
+attempting to interpret the nature of the instinct which was evoked, one
+has to be guided, in a case of this description, by the similarity of
+the response to that which can be observed on other occasions and in
+other situations when the intention of the bird is clear. And on this
+occasion the Chiffchaff betrayed all the symptoms which normally precede
+an attack; it spread its tail, quivered its wings, uttered its
+high-pitched note rapidly, hopped from twig to twig, or flew restlessly
+from tree to tree, and seemed to be prevented from attacking only by the
+number of its opponents. This, indeed, was shown by its subsequent
+behaviour, for whenever a Tit became temporarily detached from its
+companions it hesitated no longer but forthwith attacked.
+
+There are other species which are no less aggressive than the
+Warblers--the Chats for example. The Stonechat regards with suspicion
+almost any bird of its own size, and will even pursue a Tree-Pipit if it
+approaches too closely. The same is true of the Whinchat, and one would
+scarcely expect to find this bird attacking Buntings as it sometimes
+does. A Whinchat that occupied some marshy ground was constantly at war
+with a pair of Reed-Buntings; their territories were adjacent and in
+some measure overlapped, and the Whinchat drove away either sex
+indiscriminately, and was not only always the aggressor but seemed to
+be master of the situation.
+
+Coming now to kindred forms, those, that is to say, which belong to the
+same family, we find that, both in intensity and extent, the warfare far
+exceeds anything that we have thus far considered. So frequent, indeed,
+are acts of intolerance, and so readily awakened into activity is the
+pugnacious nature of the bird, that the fighting will almost bear
+comparison in volume with that which occurs between individuals of the
+same species. Between the Thrush and the Blackbird there are incessant
+quarrels early in the year, and the initiative seems to pass from one
+to the other according to the circumstances in which they are placed. If
+the territory of a Thrush is invaded the Thrush is the aggressor, and,
+conversely, if that of the Blackbird is threatened, the Blackbird
+becomes the aggressor; and so, when the territories of the two birds are
+adjacent or overlap, as frequently they do, there is constant friction,
+resulting in quarrels which attract attention on account of the
+noisiness of the birds.
+
+All the Warblers are exceedingly pugnacious, the fighting being
+especially severe between those that are very closely related. The
+Blackcap and the Garden-Warbler are constant rivals, and the scenes
+which can be witnessed when the two meet in competition are interesting
+from many points of view. The birds not only pursue and fight with one
+another, but their emotional behaviour reaches a high level of
+intensity--excitable outbursts of song are indulged in, tails are
+outspread, wings are slowly flapped, and feathers raised--in fact the
+attitudes assumed are similar in all respects to those which occur
+during the contests which are so frequent between the respective
+individuals of each species; and it would be difficult to point to any
+one item of behaviour which is not also manifest at one time or another
+during the battles between these rivals, and still more difficult to
+trace any difference in the intensity of the excitement. And if we are
+satisfied that the fighting in the one case is purposive, so, too, must
+we regard it as having some biological purpose to serve in the other.
+But the Garden-Warbler is not the only bird that acts as a stimulus to
+the instinct of the Blackcap; Whitethroats are often attacked, and the
+Chiffchaff is a source of irritation. Even when a male Blackcap is
+engaged in incubation, it will leave its nest on the approach of a
+Chiffchaff, and, having driven away the intruder, proceed to sing
+excitedly. At other times both male and female will combine to attack
+this small intruder.
+
+But this does not mean that the Chiffchaff suffers persecution; it is
+itself most aggressive, as is shown by the fact that it will join in the
+Blackcap quarrels and attack the combatants indiscriminately. Its
+behaviour, however, requires further consideration, especially as
+regards its relations with its nearest of kin--the Willow-Warbler; for
+here we have a mutual intolerance which is somewhat remarkable, and
+evidence of it can be found wherever the birds occupy the same ground.
+Now it can be observed that the hostility is not limited merely to
+occasional acts of intolerance, but that there is organised warfare
+lasting, it may be, for many days in succession, and that the actions of
+the birds bear the stamp of a persistent striving towards some end. On
+one occasion the Willow-Warbler may be the aggressor, on another the
+Chiffchaff, and at times it is difficult to say which of the two is
+responsible for the quarrel. In size and in strength they are equal, and
+the "will to fight" is as strong in the one as in the other, so that it
+is seldom, if ever, possible to point to this one as the victor and that
+one as the vanquished. Success or failure probably depends more upon the
+cumulative effect of many combats entailing physical exhaustion, than
+upon the issue of any one particular battle; and whilst observation
+might quite well fail to distinguish any resultant change in the
+relative positions of the birds, or any harmful effect upon their
+constitutions, yet the area occupied by this one might be sufficiently
+curtailed to prejudice the welfare of the young, or the vitality of that
+one might be seriously impaired--and we should be none the wiser.
+
+Neither the Marsh-Warbler nor the Reed-Warbler will tolerate strangers
+within the small space of ground over which they exercise dominion. Of
+the two, the Marsh-Warbler is perhaps the more pugnacious, and will
+attack any other Warbler that approaches too closely; Whitethroats are
+often pursued and driven away, and less frequently, Garden-Warblers. In
+one case, a male occupied the same ground as a Sedge-Warbler, and there
+was a constant feud between them; a willow-tree formed its headquarters,
+and this same tree seemed to be the headquarters of the Sedge-Warbler,
+so that they often met and whenever they did so they quarrelled. As a
+rule the Marsh-Warbler was the aggressor and had the mastery over its
+opponent, and when it attacked, it uttered a peculiar harsh scolding
+note, raised the feathers on its back, spread out its wings, and
+betrayed the usual symptoms of emotional excitement.
+
+On the other hand, the Sedge-Warbler is most aggressive towards other
+kindred species, and when a male happens to occupy the same ground as a
+Reed-Warbler, there are frequent battles between them and incessant
+commotion; they fly at one another and meet in the air with an audible
+clicking of bills, or pursue one another amongst the reeds, each one
+uttering its characteristic scolding note.
+
+The Tits, as a family, are notoriously pugnacious. I have seen a pair of
+Blue Tits attack a single Long-tailed Tit with great determination, and
+not only did they pursue it, but, flying at it, struck it with
+considerable force.
+
+In giving an account of the domestic economy of the Carrion-Crow, Mr.
+Edmund Selous refers to the hostility between this bird and the Magpie.
+"About a week ago," he says,[6] "I saw a Crow busily engaged in chasing
+away several Magpies, not only from three or four tall slender trees
+close together, in one of which it had its nest, but also from various
+other trees, not far off, round about. In this the Crow had a good deal
+of trouble, as the Magpies were always returning. After a time it was
+joined by another crow, which however did not take so active a part in
+the drama, nor did I see either of the two actually go to the nest,
+though I could only explain their action by supposing it was their own.
+This morning I saw the same thing reversed, for a pair of Magpies, with
+an undoubted nest, kept attacking a Crow that insisted on settling in
+one of a row of trees--also tall and slender--in which it was placed.
+Both were equally persevering--the Crow, though often chased away,
+always returning, and settling generally in the last tree of the row,
+where he would be left alone sometimes for a minute or two, but before
+long one of the Magpies flew at him, and put him to flight. The Crow
+defended itself, but not, it would seem, very successfully, and in the
+last attack upon him, made, with great spirit, in the air, a large black
+feather floated to the ground, which I made no doubt was his. Yet this
+did not drive him from the trees, and it was only on my approaching
+nearer that he finally left them. Thus we see that both species look
+upon the approach of the other to within a moderate distance of their
+nest as an intrusion."
+
+That the Rook suffers persecution from the Carrion-Crow is a
+well-established fact, and there is reason to believe that it has
+another dangerous enemy in the Hooded Crow. According to the late
+Mr. Ussher, Choughs will attack both Hooded Crows and Ravens. "I once
+saw," he says, "two Choughs energetically attacking a pair of Ravens;
+they shot up into the air and darted down on the latter, whose heavy
+flight made them helpless against their agile tormentors."
+
+Birds of prey are often hostile to one another. The Merlin is
+exceptionally pugnacious, and its boldness in attacking intruders is
+well known. When, for example, a Kestrel approaches its territory, it
+leaves the tree, bush, or rock upon which it was resting, utters its
+characteristic cry, and soars rapidly upwards; then, rising to a
+considerable height, it swoops down upon the Kestrel, and by
+alternately stooping at and chasing its opponent, drives it away from
+the immediate neighbourhood.
+
+What we have, then, to consider is, Do these battles between different
+species contribute towards the attainment of the end for which the whole
+territorial system has been evolved?
+
+Let us take the individual and see whether we can establish any relation
+between the hostility it displays towards members of other species and
+its general disposition to secure a territory. We must remember that a
+male can have no knowledge of the prospective value of its behaviour,
+nor is it likely that it has any ulterior purpose in ejecting other
+males, beyond the pleasure it derives from satisfying its impulse to do
+so. The proximate end of its behaviour is to attack, nothing more, and
+this, of course, it can only do just in so far as the intruder evokes
+the appropriate instinct.
+
+Now the arguments we shall employ will, on the whole, be similar to
+those which we made use of in the second chapter, wherein we attempted
+to ascertain the conditions under which a male becomes intolerant of
+other males of its own species, and examined more especially the claims
+of the "territory" as opposed to those of the "female." But here we
+start on firmer ground, because the one factor which introduced an
+element of uncertainty--the female--can be definitely excluded; at least
+it seems so to me, for granting even that her presence is the condition
+under which the pugnacious nature of the male is rendered susceptible to
+stimulation, it is difficult to see why a male of a different species
+should supply that stimulus, or what biological purpose could be served
+by its doing so.
+
+When dealing with the attitude of a male towards others of its kind, we
+attached considerable significance to the fact that its pugnacious
+nature gained or lost susceptibility according to the position which it
+happened to occupy. We found, it will be remembered, that the same bird
+that was pugnacious in its own territory took no further interest in its
+opponent when the boundary was passed; and, moreover, that if it
+happened to wander into an adjoining one, it made no real effort to
+defend itself when attacked, but returned forthwith to its own
+headquarters. It remains to be shown whether the rivalry between
+different kinds of birds is similarly related to the position which the
+opponents happen to occupy at the time.
+
+First, then, there is the general consideration, namely, that the enmity
+occurs for the most part just at the time when the territories are in
+process of being established. During autumn and winter, many birds of
+more or less close affinity assemble together in flocks, wherever the
+supply of food is abundant, and are then not only sociable, but, so
+there is reason to believe, are mutually helpful both in discovering the
+necessary means of subsistence which are often none too plentiful, and
+in affording protection from enemies, which, on the contrary, are often
+numerous. That the different units of which these flocks are composed
+should live on amicable terms is therefore as necessary for the welfare
+of the whole community at this particular season as that the different
+individuals of the same species should do so. But just as the sociable
+relations, which obtain between these individuals throughout the winter,
+undergo a marked change at the commencement of the breeding season, so,
+too, do different species, which habitually associate together, suddenly
+become hostile to one another. This change is coincident in time with
+the rise of the organic condition which leads to the establishment of
+territories; and the hostility continues, though in diminishing degree,
+throughout the breeding season, and dies away the following autumn.
+
+For example, different Warblers resort to the elders (_Sambucus nigra_)
+in September, and there pass much time feeding on the fruit which is
+then ripe and often abundant. In the same bush there may be Blackcaps,
+Garden-Warblers, Whitethroats, and Lesser Whitethroats, some preening
+their feathers, others searching for the berries, others again, with
+feathers relaxed, making feeble attempts to sing. Occasionally there may
+be a scuffle, perhaps between a Blackcap and a Lesser Whitethroat, or
+between a Garden-Warbler and a Blackcap, but it is of short duration and
+lacks vigour. Apart, however, from such temporary disturbances, there is
+no real rupture in their relations, and certainly nothing to lead one to
+suppose that the bickerings are determined by the functioning of any
+specific instinct. Yet only a few months previously some of them were
+constantly at war, and their quarrels betrayed symptoms of great
+persistence; and if we remember how the observed behaviour of the birds
+suggests the fact that they were striving to attain something definite,
+we shall understand the nature and extent of the change, and shall, I
+fancy, be in a better position to estimate its biological worth at its
+true value.
+
+We can find many similar examples--flocks are to be found on arable
+ground, on the water meadows, and on the mud-flats; here different kinds
+of Thrushes feed on the berries of the yew, there different kinds of
+Tits travel together in parties; hosts of Finches collect in the hollies
+to pass the night and Buntings roost together in the gorse; and, in
+fact, in whatever direction we choose to look in the autumn and winter,
+we find various birds assembled together and living on amicable terms.
+All of this changes in the spring, and the relationship undergoes a
+gradual but noticeable alteration; so much so that whereas the
+outstanding feature of bird life in the winter is sociability, that of
+the spring is hostility.
+
+So much, then, for the seasonal change of relationship; let us now turn
+to particular cases and attempt to trace the condition which accompanies
+such change.
+
+Many migrants in the spring seem to follow the course of the Severn
+during their journey northwards through Worcestershire; and where the
+river bends to the north-west at Lincombe Lock, there they leave it, or,
+rather, continue in a north-easterly direction which takes them across
+the southern end of Hartlebury Common. As I have already mentioned, this
+Common is overgrown with gorse, heather, and ling, and scattered here
+and there are a number of dwarf oak-trees and small elder-bushes. The
+situation is therefore an ideal one for the smaller migrants to rest for
+a brief time, and, from the point of view of the observer, very suitable
+because it is open and the movements of the birds can be traced for some
+distance. Turtle Doves pass over at a great height, or skim across a few
+feet above the gorse; Redstarts settle for a few minutes and then
+disappear; Tree-Pipits, Whinchats, and Willow-Warblers pass from tree to
+tree or flit from bush to bush--and all in a north-easterly direction.
+They do not sing, they are restless, and, judging by their behaviour,
+they are anxious to conceal their presence, not to make it known. Yet we
+know that when they reach their destination, as presently they will, all
+this will change; that each of them will employ every means at its
+disposal to make itself conspicuous; and that each, as far as it is
+able, will resist intrusion on the part of other species.
+
+Now the southern end of the Common is always inhabited by individuals
+belonging to one of these species, or to others of close affinity; so
+that wherever these travellers settle whilst passing across it, the
+chances are that they will find the ground occupied--and their behaviour
+under such circumstances is no less interesting than the behaviour of
+the bird upon whose ground they are trespassing. We will take the case
+of the Whinchat. It arrives from the south-west, and, flying from bush
+to bush, works its way in a north-easterly direction. In doing so it
+intrudes upon the territory of a Stonechat; and the Stonechat, becoming
+excited, flies towards it, and it retires for a short distance in the
+direction from whence it came. Here again it is followed and attacked
+and again moves on, and then, flying in a circle as if to avoid the
+territory which blocked the path, resumes its former line of flight,
+though still followed by the Stonechat, which after continuing the
+pursuit for perhaps a quarter of a mile, suddenly turns in the air and
+returns to its headquarters.
+
+It is difficult to put oneself in the place of the Stonechat or of the
+Whinchat. But even after making due allowance for the danger inseparable
+from any attempt to do so, there remains the unquestionable fact that
+whereas the impulse to attack was strong in the one, the impulse to
+defend itself was wholly lacking in the other. Yet a Whinchat, when it
+has established itself, is most pugnacious; it not only attacks every
+bird of a similar size that approaches its position, but its behaviour
+under such circumstances bears the impress of unusual determination; and
+if we were to take a male and place it in the position of the Stonechat,
+we should find that its nature would change, that the presence of the
+Stonechat would evoke a hostile response, and, conversely, that the
+instinct of the Stonechat would not be susceptible to stimulation. Hence
+it is clear that the nature of a bird when on migration is not quite the
+same as it is when its destination is reached; that the positions
+occupied from time to time during the journey carry no meaning, or,
+rather, are not brought into relation with its life in quite the same
+way as is the position which it finally occupies; and further, it is
+clear that the interest it displays in other species undergoes a
+somewhat remarkable transformation when at length its destination is
+reached.
+
+This altered nature of the migrant is a fact of some importance in
+relation to our present subject, but it does not stand alone--the same
+characteristic is observable in other phases of bird life. Some of the
+residents, the Buntings and the Finches for example, occupy their
+breeding ground very early in the year, and it often happens that the
+situations which they select are not capable of supplying them with food
+so early in the season, though at a later date food will be there in
+abundance; so that they are compelled to resort to the surrounding
+neighbourhood, and since, even there, the available supply is sometimes
+scarce or, if plentiful, limited to certain areas, they are constrained
+from time to time to join together again in flocks. Thus, for part of
+the year, they may be said to lead a double existence; for just as the
+Whinchat, that is sociable on migration, betrays a changed nature when
+it reaches its destination, so too does the nature of these residents
+change from hour to hour according to whether they are seeking food or
+occupying the breeding ground.
+
+In the newly-sown fields of grain the birds frequently find a supply of
+food. Here Yellow Buntings, Greenfinches, and Chaffinches collect from
+the surrounding neighbourhood. The majority are somewhere in possession
+of territories, and not a few are paired. Between the territories and
+the feeding ground a highway is formed by individuals passing to and
+fro. Sometimes both members of the pair leave together in order to seek
+food, at other times they separate and the male may be in his territory
+whilst the female is with the flock. Apart from occasional
+manifestations of sexual emotion on the part of a male, there is nothing
+to disturb the harmony of the flock nor anything in the behaviour of the
+birds which would lead one to suspect that, when they return, their
+nature will change and that they will be no longer sociable; and, which
+is still more remarkable, no matter how great the provocation which an
+individual, when in company with the flock, may be called upon to
+endure, its customary hostile response will fail to be elicited. An
+incident which happened in the spring of 1917 will serve to make this
+clear. A flock of some thirty Yellow Buntings, Greenfinches, and
+Chaffinches were feeding in one corner of a field which had recently
+been sown with barley. As they sought their food they wandered outwards
+into the middle of the field, and in so doing, passed across the
+territory of a Skylark. Whereupon the Skylark became excited, uttered
+its call-note rapidly, and rising a few feet from the ground, attacked
+those members of the flock that were nearest, which happened to be the
+Yellow Buntings; and so determined were its onslaughts that the Yellow
+Buntings were forced to retire. The Skylark showed no discrimination as
+to sex, but attacked both males and females, and within a few minutes
+succeeded in driving away at least two pairs. One would have expected
+that the Yellow Buntings would have made some show of resistance; one
+would have thought that the fact of being violently attacked would have
+supplied a stimulus sufficiently strong to evoke a corresponding hostile
+response: yet there was no mistaking the lack of interest that they
+displayed in the contest--they made no effort to retaliate but seemed to
+accept the situation as unalterable and left.
+
+So far we have examined only those cases in which the pugnacious
+instinct was stimulated in one of the adversaries, and in which
+consequently the fighting seldom reached any high degree of severity. We
+must now consider some others in which each of the opponents acts as a
+stimulus to the pugnacious instinct of the other. It is here, of course,
+that we find the most violently contested battles, and it is here, too,
+that the purpose of the fighting seems clear. The persecution which the
+Green Woodpecker suffers from the Starling is well known. The purpose of
+the Starling's behaviour is clear, namely the possession of the hole
+occupied by the Woodpecker. Bird for bird, the Woodpecker is more than
+the equal of the Starling, but persistent endeavour ultimately wins the
+day. The Starlings perch close beside the hole, and, whenever the
+Woodpecker shows itself, attack with determination; and not only do they
+do so but they are assisted, so there is reason to believe, by other
+individuals or pairs in the attainment of their end, so that no matter
+how stoutly the Woodpecker defends itself, in time it is almost certain
+to be deprived of its ownership.
+
+In like manner different kinds of Woodpeckers contend with one another
+for the possession of a hole, and here the opponents are more equally
+matched. I have seen a pair of Lesser Spotted Woodpeckers endeavouring
+to drive away a Great Spotted Woodpecker. The excitement of all three
+birds was exceptional. Each of the Lesser Spotted Woodpeckers kept
+swooping in turn at their rival, sometimes in the air and sometimes when
+it was settled on the topmost branches of a dead tree, and the sounds
+produced reminded one of the piping of a flock of Oyster-Catchers in
+flight.
+
+A battle between a pair of Green Woodpeckers and a Great Spotted
+Woodpecker is worth mentioning. It occurred on the 24th of April.
+Passing through the middle of a wood, I noticed a Great Spotted
+Woodpecker fly out of a hole in an oak-tree. Shortly afterwards, a pair
+of Green Woodpeckers settled near the hole and then flew to some
+oak-trees close at hand, where they were joined by their rival and signs
+of hostility were soon apparent. Presently the Great Spotted Woodpecker
+returned to the hole and entered. Both of the Green Woodpeckers then
+flew into the tree; and one of them, settling upon the trunk, climbed
+up to the level of the hole and, when it became aware of the Great
+Spotted Woodpecker within, extended its wings fully and proceeded to
+peck viciously at its opponent. Whereupon there was a scuffle at the
+mouth of the hole and the Great Spotted Woodpecker hurriedly left. After
+this, all was quiet and the Green Woodpecker eventually descended and
+entered the hole. The Great Spotted Woodpecker, however, returned again,
+but, after fluttering around the hole, disappeared, leaving the Green
+Woodpeckers in possession.
+
+In this varied field of hostile behaviour which we have explored, one
+feature stands out prominently, namely, that the interest which a bird
+displays in other species varies not only at different seasons but even
+from hour to hour. I have used the word "nature" as equivalent to
+"interest," and I have spoken of the bird's nature changing or altering
+according to the circumstances in which it was placed. But its nature is
+its inborn constitution, and its constitution cannot change from day to
+day, still less from hour to hour. So that, in a sense, and having
+regard to strict scientific accuracy, it is misleading in this
+particular connotation to say that the bird's nature changes.
+
+[Illustration: H. Gronvold dcl. Emery Walker ph.sc.
+
+A battle between a pair of Green Woodpeckers and a pair of Great
+Spotted Woodpeckers for the possession of a hole in an oak tree.]
+
+What then does happen? The instinct of pugnacity must form just as much
+a part of the hereditary make-up of the migrant, when on migration, as
+when finally it reaches its destination; still more must it form part of
+the constitution of the Bunting when it leaves its headquarters
+temporarily and joins the flock. And, if it is there, the question
+arises as to why it does not respond. Now every instinct requires for
+its response a stimulus of an appropriate kind, and, therefore, a
+reasonable view to take would be that the necessary stimulus was
+lacking. But this is a view which we cannot uphold, because on all these
+occasions an opposing male was present--and, so far as it is possible to
+judge by observation, that is the stimulus which in the main evokes a
+hostile response. We must therefore look elsewhere than in its
+direction for a reason which will adequately explain the behaviour.
+
+Though it be true that every instinct requires for its functioning a
+stimulus of an appropriate kind, yet it is also true that the condition
+which will render it responsive must be present. What we have then to
+consider is whether the phenomena which we have explored give us any
+clue as to the particular nature of that condition. In the first place,
+we have the general fact that the hostility is not confined to a few
+species belonging to a few families, but that it is of wide
+application--birds of prey, Warblers, Woodpeckers, all supply us with
+evidence which serves to show, in greater or less degree, its nature and
+extent. Next, we found that the hostility was peculiar to a certain
+season--and that one the season of reproduction. And if the question
+were asked: What condition would then be most likely to render the
+instinct susceptible, the answer that would most certainly be given
+would be--the presence of a female. And in reply to a further question
+as to the particular nature of the stimulus to which the instinct would
+respond, we should be told--the presence of another male of the same
+species. Now the possible influence of the female on the course of the
+male's behaviour was the subject of inquiry in the second chapter,
+wherein we endeavoured to explain the hostility between males of the
+same species, and we came to the conclusion that it was not alone
+sufficient to account for the facts disclosed. Still less likely,
+therefore, is it that her presence can bear any direct relation to the
+hostility between different species, the more so since the biological
+end of securing a mate is definitely excluded. And we have something in
+the nature of proof of the correctness of this view in the fact that she
+accompanies her mate when he joins the flock, and that there his
+instinct is not susceptible to stimulation. We then proceeded to examine
+certain cases in which all the indications pointed to the fact that the
+"will to fight" was present in only one of the opponents; and we
+attached considerable importance to this circumstance, because we knew
+from experience that the same bird which seemed to lack courage, could
+at other times and in other situations be most aggressive. If then we
+ask what condition was present on the one occasion that was absent on
+the other, we have no difficulty in finding a reply--on every occasion
+on which the opponents appeared to be unevenly matched, one was in
+occupation of a territory and the other was not. And if we inquire
+further as to which of the two was the aggressor, the answer is again
+clear, namely, the bird that occupied a territory. Finally we considered
+some particular instances in which the "will to fight" was present alike
+in both opponents, and in which the battles were protracted and severe.
+
+But the fact that a bird has established a territory is not in itself
+sufficient to render its hostile nature susceptible; it must be actually
+in occupation if a response is to be elicited. We reach this conclusion
+step by step: the behaviour of the migrant, that lacks the "will to
+fight" when on migration but is pugnacious when it has secured a
+territory, shows it; the behaviour of the resident, which temporarily
+joins the flock and is there sociable, shows it; and it is shown also by
+the determination with which both opponents fight when the question of
+ownership of a station is in dispute. And of all the facts we have
+reviewed, this is perhaps the most important in relation to our present
+subject, for it demonstrates that the change from sociability to
+hostility is not merely an incident of the sexual season, not merely an
+indirect result of the functioning of the general disposition which
+leads to the establishment of a territory, but that it is intimately
+associated with the whole process, and that the particular part of the
+bird's nature which is concerned is so nicely balanced that it will
+respond under one condition and one only.
+
+Thus we are led to the only conclusion which seems consistent with the
+facts, namely that there is a relationship between the "territory" and
+the hostility.
+
+
+If we are satisfied that all this warfare is not merely an expression of
+an instinct which is serviceable in another direction, what part does it
+play in the whole scheme of reproduction?
+
+The young of many birds are delicate at birth and unable to withstand
+exposure to cold, and in the previous chapter we came to the conclusion
+that the territory was serviceable in that it provided an adequate
+supply of food in the vicinity of the nest, and thus obviated the
+necessity of the parents being absent from them for long. But manifestly
+no matter how active a male may be in driving away members of its own
+sex and kind, it will neither make its position secure, nor insure a
+supply of food for its young, so long as any number of individuals of
+different kinds are allowed to establish themselves in the same space of
+ground. On the one hand, then, we have the fact that there is constant
+strife between males of close affinity, whilst on the other, we know
+that many species require like conditions of existence and are bound to
+assemble wherever these conditions are suitable; and we can infer that
+the territory would fail to serve its purpose if no restriction were
+imposed upon the measure of such assemblies.
+
+The question then arises: Does all this warfare contribute towards the
+attainment of reproduction? Not far from my house there is a small water
+meadow, three acres in extent, which for some years has been derelict
+and is now overgrown with the common rush (_Juncus communis_) and small
+alder trees. For three successive seasons I watched the bird life of
+this meadow, and more especially the Reed-Buntings whose behaviour I was
+studying at the time. In every respect the meadow was suitable for this
+bird; there was an abundance of food and numberless situations in which
+nests could be placed. Each year all the pairs were successful in
+rearing one, if not two broods, yet the number of pairs never exceeded
+five--the first year there were three; the second year five; and the
+third year four. In addition to the four pairs of Reed-Buntings, there
+were in the spring of 1915, six pairs of Whitethroats, one pair of
+Lesser Whitethroats, four pairs of Willow-Warblers, one pair of
+Sedge-Warblers, two pairs of Grasshopper-Warblers, one pair of
+Chiffchaffs, three pairs of Hedge-Sparrows, two pairs of Tree-Pipits,
+one pair of Skylarks, one pair of Whinchats, one pair of Flycatchers,
+two pairs of Song-Thrushes, one pair of Blackbirds, one pair of
+Redstarts, three pairs of Chaffinches, and one pair of Wrens--in all,
+thirty-five pairs, whose young were mainly dependent for their living
+upon the insect life of that meadow and the ground immediately
+surrounding it. If we allow three young to each pair--and this would
+take no account of second broods--we arrive at the following result,
+namely, that one hundred and five young and seventy adults had to be
+supplied with food from that locality, which would mean, if the search
+for food were strictly limited to that meadow, that 83 square yards
+would be allotted to each individual.
+
+Suppose now that the four male Reed-Buntings had each admitted one other
+male, and that they had secured mates, what would have been the effect
+upon the whole community? The four additional pairs with their young
+would have represented twenty individuals, which would have represented
+a decrease of 8.5 square yards in the space allotted to each individual.
+The pressure of the bird population upon the means of support would then
+have been materially increased; and not only the Buntings, but the
+Warblers, Pipits, and all the rest would have suffered. But the result
+would have been the same if, instead of the four additional male
+Reed-Buntings, four males of other kinds had been allowed to enter the
+marsh, and we can multiply the number four until we arrive at a point
+when the means of subsistence would no longer have been adequate for the
+adults, still less for the young. If, then, there were nothing to
+prevent this happening, many of the birds in that marsh would have no
+chance of rearing their young successfully. Hence, if the territory is
+adequately to serve the purpose for which we believe it has been
+evolved, some provision must have been included in the system to meet
+the difficulty.
+
+There are three ways by which this may have been
+accomplished--indirectly, by increasing the size of the area occupied by
+each individual, and thereby reducing the relative number of each
+species; or directly, by rendering the fighting instinct of the bird
+susceptible to stimulation by individuals of other species; or,
+possibly, by a combination of the two. There were four pairs of
+Reed-Buntings in the marsh, and their territories covered the whole of
+it. But inasmuch as other insectivorous birds were established there
+also, and found sufficient food to maintain both themselves and their
+families, it is clear that the area these Reed-Buntings occupied was in
+excess of that which they would have required if they had been the sole
+inhabitants. And such often appears to be the case. Many a Warbler
+allocates to itself a space of ground more than sufficient to supply it
+with all that it needs; so, too, does the Finch, or the Pipit, or the
+Falcon--if we take no account of kindred species. Thus there is reason
+to believe that, by limiting the number of individuals in a given
+locality, this apparently wasteful expanse of territory is serviceable
+in that it provides against the pressure of the bird population upon the
+available means of support becoming too great. But though a reduction in
+the numerical standing of the different species would certainly follow
+from any increase in the area occupied by the respective individuals,
+and with even greater certainty would place them in a more secure
+position as regards their supply of food, yet, when we remember how
+large a number are dependent upon a supply of insect life for their
+young, we can understand that it would not alone be a sufficient
+safeguard against the dangers attendant upon overcrowding. It is here, I
+believe, that we shall find the true explanation of the hostility; it
+roughly insures that the number of pairs in any given area does not
+exceed the available means of support, and indeed it is difficult to
+imagine how such uniformity of distribution as would free the young from
+the risk of exposure could be obtained without some such control.
+
+Some birds, however, have no difficulty in finding the necessary food
+for their young, yet have great difficulty in finding a station where
+they can rear their young in safety; and the area each one occupies has
+been reduced to the smallest proportions in order that the maximum
+number can be accommodated. Here, any increase in the size of the
+territory would inevitably lead to the extinction of the race, so that
+nothing stands between failure and success except the ability of the
+bird to defend its territory. If we study the bird population at one of
+the breeding stations on the coast, we find, generally speaking, that
+each kind of bird inhabits a particular portion of the cliff; on the
+lower ledges are the Guillemots and Kittiwake Gulls; higher up are
+Razorbills and Fulmars, and at the top, where the cliff is broken and
+the face of the rock covered with turf and soil, the Puffin finds
+shelter for its egg. At the same time there is much overlapping; the
+kind of ledge that suits a Razorbill is equally suitable for a Guillemot
+or a Fulmar, and so, no matter how successful the Razorbill may be in
+establishing a territory and preventing intrusion upon it by other
+Razorbills, it will be all to no purpose if it allows itself to be
+jostled out of its position by a Fulmar. Hence, inasmuch as breeding
+stations are limited and competition for territory so severe, only those
+forms in which the fighting instinct responds freely to a wide range of
+stimuli will be in a position to maintain a footing upon the cliff.
+
+In trying to estimate the importance of the hostility in its relation to
+the territory, we must bear in mind that competition varies in different
+seasons and in different localities. The surface of the land is
+constantly undergoing modification, partly owing to human and partly to
+physical agency--forests are cleared; marshes are drained; the face of
+the sea-cliffs is altered by the erosion of the waves; here the coast
+may be locally elevated, there locally depressed; and so forth. Many of
+these changes are slow and imperceptible, many can be observed in our
+own lifetime. The timber is felled and the undergrowth cleared in some
+wood, and the following spring we notice a change in the character of
+the bird population. Migrants which formerly found in it no suitable
+accommodation now begin to appear, and as the seasons pass by and the
+undergrowth affords more and more shelter for the nests and an
+increasing supply of insect life, so their numbers increase until the
+wood becomes an important breeding station, resonant with the song of
+many individuals. But slowly the growth increases; the bushes pass into
+saplings and the saplings into trees, and the undergrowth then
+disappears just as surely as do the migrants which can no longer find
+there the conditions which they require.
+
+Or, as an illustration of the effect produced by natural agency, let me
+describe a change which has taken place in a corner of Co. Donegal. The
+promontory of Horn Head is bounded on the west by extensive sand-hills,
+100 ft. or more in height. On the southern side it is divided from the
+mainland by a channel, which narrows down to 100 yards or so in width
+where it fringes the sand-hills, and then widens out again, covering an
+area of approximately 270 acres. As far as is known in the memory of
+man, this area has always been tidal. But in recent years a change has
+taken place, and the blown sand has silted up the channel, with the
+result that this tidal area has been transformed into a brackish lake.
+What has brought about the change is not easy to determine. There is
+evidence, however, of a slow alteration of the level of the shore-line;
+for in the midst of the sand-hills, situated 150 yards or so from the
+present sea-margin, and running parallel with it, there is an
+accumulation of pebbles some 3 feet high by 4 feet deep. This raised
+beach is now separated from the Atlantic by sand-drifts of considerable
+height, and consequently there are some grounds for believing that
+secular elevation is taking place, which, if it be the case, will
+account for the change in progress. Now the effect on the bird
+population can be seen even now, and will doubtless become more apparent
+as the years pass by. Sand-Martins used to find plenty of places to
+breed amongst the sand-drifts, and moreover do so still. But their
+nesting sites are constantly changing and disappearing, and the
+breeding-place of one colony, that was situated in the bank of a stream
+twelve years ago, is now buried 10 feet or more below the surface of the
+sand. The area that was once tidal, but is now a brackish lake, is fed
+by mountain streams, and as the fresh water predominates, so in course
+of time will it become fringed with vegetation; and instead of the
+flocks of Curlew, Dunlin, and other waders that, at low water, resorted
+there to feed, Coots will fight with one another for the possession of
+territories, and the Wild Duck will teach her young to seek their food.
+
+In whatever direction we turn, we find that many breeding grounds are
+subject to incessant change. Ancient haunts disappear, new ones come
+into being, a change which makes life impossible for this bird, as
+likely as not benefits that one, and so on. There is no stability. Hence
+in any given district each recurring season there must needs be a large
+number of individuals which are obliged to seek new stations, and if
+there were no control over their distribution, if each one were free to
+establish itself wherever it chanced to alight, this locality might be
+overcrowded and that one deserted; and, bearing in mind how many species
+there are that require similar conditions of existence, we can infer
+that the successful attainment of reproduction would become impossible
+for many of those individuals so long as each species was indifferent
+to the presence of the others. On the other hand, if there were no
+control over the range of the intolerance, the smaller bird would have
+no chance in competition with the larger, and it is doubtful whether the
+larger would gain an advantage commensurate with the energy it would
+expend in ridding its area of the smaller. I have described battles in
+which the opponents were only distantly related; for instance, the
+Moor-Hen will attack almost any bird--Partridge, Lapwing, or
+Starling--that approaches its territory even temporarily. Nevertheless
+the antagonism between kindred forms is more prevalent, and, as a rule,
+characterised by more persistent effort; and thus it seems as if the
+susceptibility of the fighting instinct has its limitations, the degree
+of the responsiveness being dependent upon the affinity of the
+opponents.
+
+Suppose now that we take an area inhabited by a number of different
+species requiring like conditions of existence, divide it into three
+sections, and imagine that in one they were all sociable, that in
+another they were all hostile, and that in a third those which were
+closely related were intolerant of one another. Let us suppose further
+that each one of them was represented by the full number of individuals
+that the law of territory would allow. In the first section an
+individual would establish itself, and, becoming intolerant of its own
+kind, would exercise dominion over an area roughly sufficient, providing
+conditions were normal, to insure an adequate supply of food for its
+young. But it would take no account of other species, and since any
+number might occupy the same ground, the fact of its having established
+a territory would not alone suffice to render its supply of food
+secure. Success in the attainment of reproduction would then become
+largely a matter of chance, depending upon the number of individuals
+that happened to settle in this place or in that. In the second section
+there would be perpetual warfare; for whereas the appropriate organic
+condition which leads to pairing arises in different species at
+different times, fresh claimants to occupied ground would constantly be
+appearing, and the efforts of the inhabitants to preserve their
+boundaries intact would have to be maintained throughout the whole
+period of reproduction; and while the stronger or more persistent forms
+would be more likely to breed, they would do so at the expense of their
+young, to which they would be unable to devote proper attention, and
+with an expenditure of energy that would reflect itself upon the future
+of the race. But the conditions of life in the third section would be
+such as would be more likely to yield good results. The relations of the
+different members of the community would be more evenly balanced, for a
+male would only be called upon to compete with those of its own size and
+strength. Thus, on the one hand, accommodation would be so divided as to
+secure the breeding of the maximum number of individuals with the
+minimum of expenditure of energy, whilst on the other, any undue
+pressure upon the available means of subsistence would be prevented.
+
+There can be no question that in the latter section a higher percentage
+of individuals would succeed in rearing offspring. And so, by reason of
+the fighting instinct being more susceptible or less susceptible
+according to the affinity of the opponents, a control is established
+which, while preventing unnecessary extension of warfare, allows for
+sufficient extension to render the biological end secure.
+
+
+These, then, are the facts--this the conclusion which can be drawn from
+them. It may, however, be said of these facts, as it has been said, with
+even less justification, of the battles between individuals of the same
+species, that they do not afford evidence of genuine hostility. No doubt
+there are many naturalists who could supplement these facts with others
+in which the conflicts resulted in bodily injury, or terminated fatally,
+or at least were of a more determined kind. But I have already drawn
+attention to the fact that, so long as a definite result is attained,
+the severity of the struggle and the amount of injury inflicted are
+matters of small moment. Let us, however, run over the substance of the
+argument, and then briefly refer again to this point of view.
+
+After enumerating instances of hostility, sufficient in number, so it
+seemed, to constitute reasonable ground for the belief that they had a
+part to play in the life-history of the individual, the two questions we
+set ourselves to examine in this chapter were: Is there any circumstance
+in the life behaviour of the individual with which the hostility can be
+definitely related; and, will the hostility lead to the securing of a
+greater measure of success in the attainment of reproduction?
+
+Many different species assemble together in winter and roam from place
+to place in search of food. But in spring their behaviour undergoes a
+remarkable transformation; they avoid one another and become
+quarrelsome, so much so that whereas the outstanding feature of the
+winter is sociability, that of the spring is hostility. With this
+general fact before us, we proceeded to investigate this change of
+behaviour still further. First of all we took the case of a migrant,
+and, comparing its behaviour, as it journeyed, with that when finally it
+reached its destination, we found that the bird which was notoriously
+pugnacious when in occupation of a territory betrayed no interest in
+other species as it travelled to the accustomed breeding ground. Not
+only so, but even though it was attacked, we found that its pugnacious
+instinct still failed to respond. Here, however, it may be contended,
+and with reasonable justification, that in the interval which elapses
+before the ultimate destination is reached, some change in the organic
+condition of the bird may occur which will account for its altered
+behaviour; or, it may be urged, with no less justification, that whereas
+on migration the bird is unpaired, when the destination is reached it is
+probably in possession of a mate and is therefore quarrelsome. Now, at
+the most, the interval can only be a matter of a few days, and it is
+unlikely that organic changes sufficient to bring about so important an
+alteration of behaviour could occur in so short a time, still less
+likely that they could be timed to come into functional activity just at
+the moment when the bird reaches its breeding ground. And with regard to
+the suggestion that the change can be accounted for by the presence of a
+mate, we shall do well to remember not only that males as a rule precede
+the females by some days, but that a male may even remain in its
+territory, mateless, for some weeks, and yet display hostility.
+
+Nevertheless the case of the migrant did not, by itself, afford
+sufficient evidence upon which to base any conclusion. We therefore
+inquired into the behaviour of some of the residents at a corresponding
+period. The Bunting served as an illustration. Early in the season it
+establishes a territory, and because food is then scarce it is forced to
+seek it elsewhere than on the small plot of ground which it has
+acquired; and so it makes its way to some spot where the supply is
+abundant, and there, meeting with other species bent on a similar
+errand, forms with them a flock. Part of its time is then spent in the
+territory and part on the feeding ground, and between these two points a
+highway is formed by the bird passing constantly to and fro. But the
+attention which it pays to other species is very different on these two
+occasions--when in the territory it is intolerant of strangers, but when
+it accompanies the flock it displays no interest in their movements.
+From hour to hour its nature seems to change. But, as we saw, the inborn
+constitution of the bird cannot change, and therefore we came to the
+conclusion that an explanation of the altered behaviour was to be found
+in the fact that the pugnacious instinct is only rendered susceptible
+under a certain condition. So that all the evidence tended to confirm
+the impression which we had gained from the course of events in the life
+of the migrant, namely, that the hostility bears a direct relation to
+the occupation of a territory.
+
+Finally we were led to inquire whether the hostility was serviceable in
+promoting the welfare of the individuals. We saw that many different
+species require similar conditions of existence, that ancient breeding
+haunts disappear and that new ones come into being, and that in the
+ordinary course of events such species must often assemble in the same
+area for the purpose of reproduction. So that even though a male might
+be successful in protecting its ground from intruders of its own kind,
+yet it might still fail to rear offspring, just because it happened to
+choose a position in which other kindred forms had gathered. Hence if
+the territory is adequately to serve its purpose, some control over the
+local distribution of species is of paramount importance. Nevertheless,
+if all the different forms that require similar conditions of existence
+were intolerant of one another in a like degree, the smaller bird would
+have no chance in competition with the larger. This, however, is not
+the case. Some, as we saw, arouse little or no animosity in others, in
+fact the more closely related the rivals, the more responsive their
+pugnacious nature seems to become.
+
+To return now to the view that the fighting is not really serious, but,
+on the contrary, that it is either vestigial and has no longer any part
+to play in furthering the life of the individual, or that it is a
+by-product of the seasonal sexual condition to which no meaning can be
+attached. First, there is the relationship with the territory, and this,
+it seems to me, is a fact of some importance; for if the fighting were
+merely an exuberant manifestation of sexual emotion, one would expect to
+find it occurring under all conditions, and not merely under one
+particular condition in the life of the bird. The hostility is too
+widespread, however, and too uniform in occurrence for us to suppose
+that it has no root in the inherited constitution of the bird; and if it
+served some useful purpose in the past, the instinct might still
+persist, so long as it were not harmful. Thus the view that the
+behaviour is vestigial is not perhaps unreasonable. But manifestly it
+makes no difference whether it be vestigial or a by-product of sexual
+emotion, whether the battle be fierce or so trivial as to appear to us
+to be more in the nature of "play," so long as some change in the
+relative prospects of the opponents is the result.
+
+For us, then, the main consideration lies in the question: Is the
+behaviour serviceable now in furthering the life of the individual?
+Whether the evidence which we have examined affords sufficient ground
+for the belief that the hostility is genuine and has a part to play in
+the whole scheme of reproduction, each must judge for himself.
+
+
+
+
+CHAPTER VII
+
+THE RELATION OF THE TERRITORY TO MIGRATION
+
+
+Coincident in time with the growth of appropriate conditions in the
+environment, organic changes take place rendering certain instincts
+susceptible to stimulation; and the stimulus being applied, the Warbler
+leaves the country wherein it had passed the winter and finds its way
+back, with apparently little difficulty, to the district in which it was
+reared or had previously reared offspring. What is the nature of these
+changes and of the impulse which is first brought into functional
+activity; whence comes the stimulus; and what directs the bird on its
+journey--these are all different aspects of one great problem, the
+problem of migration. I do not propose to discuss all these various
+aspects, for indeed I have no suggestions to offer which are in the
+least likely to be helpful, but I seek rather to ascertain whether the
+phenomena which we have explored bear any relation to the problem as a
+whole; whether, that is to say, the competition for territory and all
+that appertains to it can have supplied the conditions under which, in
+the process of time, this complex and definite mode of behaviour has
+evolved.
+
+We are sometimes told that we must seek the origin of migration in the
+physical changes that have occurred in the ancient history of the
+earth--in glacial conditions which gradually forced birds to the south,
+or in the "stability of the water and mobility of the land" which
+brought about a gradual separation of the feeding area from the breeding
+area--and which continued for a sufficient length of time to lead to the
+formation of an instinct, and that the instinct persists because it is
+serviceable in promoting the welfare of the race. But when we consider
+the lapse of time, and the changes that must have occurred in the
+character of the bird population--the appearance of new forms and the
+disappearance of the old, the ebb and flow of a given species in a given
+area--and bear in mind that, notwithstanding this, the migratory
+instinct, if not stronger, is assuredly no less strong, and the volume
+of migration, if not greater, is assuredly no less; in short, that the
+whole phenomenon is progressive rather than retrogressive, we shall find
+the view that the instinct owes its origin to conditions which no longer
+exist, receives but little encouragement.
+
+I doubt not that, throughout the ages, geological changes have been an
+important factor in directing or limiting the scope of migration, and
+moreover are so still; just as climatic changes and the relative
+abundance or scarcity of enemies have influenced the course of its
+evolution. These are all contributory factors operating in the external
+environment. But there are, besides, internal factors which form part of
+the inherited constitution of the bird, and, being passed on from
+generation to generation, afford the conditions under which migration is
+constantly being renewed. It is, I believe, in this field of organic
+change and relationship that the conditions of origin must be sought.
+
+Just as the moth in passing from the rudimentary to the perfect
+condition runs through a series of changes, each one of which is marked
+by a typical behaviour response adjusted to meet some particular
+circumstance in the external environment, so the annual history of a
+bird displays an ordered routine, each phase of which can be observed to
+correspond with one of the successive changes in the environment. In
+almost every direction, we find that this routine is characterised, in
+broad outline, by great uniformity; so much so that, providing we know
+the history of one species, we can forecast with no small degree of
+certainty the general course of behaviour of other members of the
+family. But only the _general_ course. There is endless variation in
+just the particular way in which the behaviour is adapted to meet the
+needs of particular species--the major details may be said to be
+specific, the minor details varietal.
+
+Now it is that part of the behaviour routine which has reference to the
+relationship between one bird and another upon which, for the time
+being, I wish to dwell; for the interest that A displays in B is by no
+means always the same--it changes according to the season, and this
+change can be observed to be uniform throughout a wide range of species.
+
+In winter, in whatsoever direction we turn, we observe not only that
+different individuals but that different species also collect together
+in flocks. And since food at that season is not always easy to obtain,
+and, moreover, is only to be found in certain situations, which are
+limited both in number and extent, it would seem that such assemblages
+are in the main determined by accident. No doubt the abundance or the
+scarcity of food does determine the movements of birds, and hence to
+that extent may be held to account for the flocks. But we shall but
+deceive ourselves if we think that it is the sole or even the principal
+reason, or that the situation is in no wise affected by internal
+factors. The behaviour of the individual in relation to the flock bears
+ample testimony to the presence of a gregarious impulse which derives
+satisfaction from the fact of close association.
+
+As an illustration, let us take a bird whose movements are easily
+watched, and in whose hereditary constitution the impulse to which I
+allude seems to be strongly implanted--the Curlew. When the breeding
+season is over, Curlew leave the mountain and the moor and return to
+the coast or tidal estuaries for the remainder of the year. Here, at low
+water, they find an abundant supply of food--crustaceans amongst the
+sea-weed upon the rocks, and lobworms (_Arenicola piscatorum_) in the
+mud as the tide advances or recedes. But when the tide is full, they
+retire to those parts of the shore that remain uncovered--to isolated
+rocks, or to sand-dunes, or it may even be to pasture-land in the
+neighbourhood. During this period of repose large numbers of individuals
+gather together on a comparatively small space of ground. They are not
+constrained to do so by any shortage of accommodation, nor by any
+question relative to food, nor, for the matter of that, by any
+circumstance in the external environment; they are brought together
+solely, this at least is the impression that one gains, by some
+inherited impulse working towards that end. And their subsequent course
+of behaviour tends to confirm that impression. For if we watch the
+gathering together of the different units of which the flock is
+composed, and study more particularly the emotional manifestation which
+accompanies their arrival and departure, we shall find that the coming
+of a companion arouses some emotion which is expressed by a vocal
+outburst that sweeps through the flock.
+
+Now each call, and the Curlew has a great variety, is not only peculiar,
+generally speaking, to certain occasions, but is accompanied by a
+specific type of behaviour, whence we can infer in broad outline the
+type of emotion which is aroused. Thus we come to recognise fear, anger,
+or sexual emotion, by just the particular sound which is emitted. But
+even if we are going too far in referring particular calls to particular
+emotions, we can, without a doubt, divide them into two broad
+categories--those which are pleasurable and those which are the reverse.
+And we need have no hesitation in placing the particular call to which I
+allude in the first of these two categories, not only on account of the
+nature of the sound produced, but because the activities which are
+aroused are not such as normally accompany irritation. This is well seen
+if the behaviour of different individuals be closely observed. After
+resting on one leg for some time, first one and then another is seized
+with cramp, and running a few yards in an ungainly way, bumps up against
+its companions as if it had not full control over its movements. Its
+behaviour produces irritation which is expressed by a vocal outburst,
+and followed by actions the meaning of which is clear. Moreover, the
+call is taken up by other individuals and sweeps over part of the flock
+as does the greeting. But the nature of the cry is entirely different
+from that which greets the arrival of a companion--humanly speaking it
+is a passionate and impatient utterance, the height of displeasure. The
+arrival, then, acts as a stimulus to something in the inherited
+constitution which is expressed in, and presumably is satisfied by, this
+vocal outburst; and, since the bird that arrives joins also in the
+chorus, there is reason to think that the impulse which determines its
+movements is similar to that which is temporarily aroused in the flock.
+
+Apart, however, from the evidence derived from the affective aspect of
+the operation of the instinct, the general course of behaviour lends
+support to the view that the assemblies are determined by internal
+factors, and are not merely the outcome of circumstances in the external
+environment. Observe, for example, the manner in which the flock is
+built up. Single individuals are content to rest alone so long as no
+assembly is in sight, but they are drawn towards their companions
+directly the opportunity arises, just as surely as the smaller
+aggregation is drawn towards the flock; and so, as the flock increases,
+it gradually absorbs all the lesser flocks and smaller parties, for the
+greater the flock the greater the attraction seems to be; and different
+individuals appear to gain some satisfaction from being in close bodily
+contact with one another.
+
+When the Curlew flies to that part of the mud-flat which is first
+exposed by the receding tide, and there associates with others, it does
+not then do so because it has any interest in its fellows, nor because
+they serve as an attraction, but because it is constrained by hunger--in
+other words, the association is determined by accident. But when, during
+periods of repose, it sees a flock, flies to it, and takes up a position
+in the midst of it, it does so not because suitable accommodation is
+lacking--not therefore because of external constraint--but because it
+derives some pleasure from satisfying something in its organic complex.
+We speak of this behaviour and of the emotion which characterises it as
+the _gregarious instinct_: by which we mean that the inherited nature of
+the Curlew, as a tribe, is so constituted that, given the appropriate
+internal conditions and adequate external stimulation, every individual
+will respond in a similar manner--that is, the behaviour is primarily
+determined by racial preparation. This is what we mean by the
+_gregarious instinct_ biologically considered. We may resolve our own
+experience in relation to the crowd into its simplest constituents,
+project our own primitive feelings into the Curlew, and say that the
+bird feels uneasiness in isolation and satisfaction in being one of the
+flock. But in truth we know nothing, save by analogy, of the correlated
+psychical state. All the knowledge we possess is derived from a study of
+the objective aspect of the behaviour, which in simple terms may be
+expressed thus: the individual is drawn towards its companions; there is
+a relation between the size of the flock and the strength of the
+attraction; and all Curlew behave similarly under similar circumstances.
+
+This instinct controls the movements of many birds from early autumn to
+the commencement of the breeding season. And so powerful is the control
+that the individual is suppressed and its activities subordinated to the
+welfare of the community as a whole. Flocks of Waders roam about the
+tidal estuaries in search of food, and different kinds of Gulls assemble
+there and preen their feathers or sleep; Warblers alter their mode of
+life, and in the osier bed, or amongst the elders, seek their food
+together in peace; Finches, Buntings, Pipits, and Wagtails, though food
+is everywhere abundant, gather themselves together respectively into
+bands which, as winter approaches, grow into flocks and even into
+composite flocks; and as the Warblers leave for the south, so their
+places are filled by flocks of Thrushes and Finches from the north. In
+whatever direction we turn, when the days begin to shorten, it is the
+community, not the individual, that thrusts itself upon our attention;
+and throughout the winter continues to be the outstanding feature of
+bird life.
+
+With the approach of the breeding season we witness that remarkable
+change which I have endeavoured to make clear in the previous
+chapters--the disintegration of the flock and the reinstatement of the
+individual. Instead of continuing with the flock, the individual now
+goes forth to seek the appropriate breeding ground; and having arrived
+there, is not only content to remain in isolation, but so behaves that
+isolation is insured. Intolerant of the approach of a stranger,
+intolerant even of the approach of the very members of the community
+whose companionship was previously welcomed, it not only fights to
+maintain the position it has selected, but fights indeed for the
+possession of ground already occupied, and, until reproduction is
+completed, asserts its individuality and exercises dominion over its
+territory. What, then, is the prospective value, biologically
+considered, of the changing interest that A displays in B, and to what
+will such changes lead? These are the questions to which we will now
+direct inquiry.
+
+The annual life-history of a bird is in broad outline conditioned by
+two powerful and at first sight opposing impulses--the one to live in
+society, the other to live solitary. But, manifestly, a bird cannot be
+governed by opposing impulses. It has but one character, within which,
+according to the season and the circumstances, different impulses
+predominate. But these impulses, no matter how different they may appear
+to be, have their respective parts to play in furthering the life of the
+individual. Hence they cannot oppose, though they may conflict, if the
+resultant behaviour contributes towards survival.
+
+The majority of birds live to-day in constant danger from predatory
+species, and that this danger was still greater in bygone ages there can
+be but little doubt. A curious mode of behaviour of the Curlew,
+Whimbrel, and Godwit demonstrates this, for it must be the outcome of
+the necessity for constant watchfulness. Whilst resting with its head
+turned back and its beak buried in the feathers of the mantle, the bird
+constantly moves the axis of its body, so that an observer, if placed in
+a direct line behind it, sees at one moment the right eye and at another
+the left. No movement of the feet or of the legs is perceptible, and the
+shifting of the body continues whether the eyes are open or closed. This
+body movement enables the bird to survey a much larger area of ground
+than it would otherwise be capable of doing, and thus adds to its
+security. As far as my experience goes, the movement is less evident
+amongst the members of a flock than when an individual is resting alone,
+or even with a few companions, which may be due to the fact that since
+some members are always awake and watchful, a bird of prey would have
+more difficulty in approaching a flock unawares than it would have in
+approaching a single individual. With the greatest ease a Sparrow-Hawk
+can pick up a Thrush as it feeds on the meadow by itself, but if it
+attempts to seize one of a flock, the chances are that its approach is
+signalled and that its prey escapes. And not only do the different
+members give warning one to another of the approach of danger, but they
+also combine to harass or even to drive away an enemy. So that there can
+be no doubt that the gregarious instinct is serviceable in promoting the
+welfare of the race, and has, as its end, the preservation of the
+individual in order that it may take its share at the appropriate time
+in procreating its kind.
+
+In winter, then, the individual loses its individuality and is
+subordinated to the welfare of the community, whilst in spring it
+regains its individuality, and all its inherited instincts which then
+come into operation lead to its isolation from the flock. The impulse to
+seek isolation is dependent upon internal organic conditions which are
+peculiar to a certain season; whereas the gregarious impulse depends
+upon internal organic conditions which inhere at all times, though its
+functioning is inhibited by the functioning of the former impulse. The
+evidence which leads to this conclusion is to be found in the fact that
+a male often deserts its territory temporarily and joins the flock,
+where it remains at peace with its companions--an aspect of behaviour
+which we have discussed on various occasions. The former impulse becomes
+dominant in the spring owing to its innately superior strength; the
+latter becomes dominant in the autumn because the organic condition
+which determines the functioning of the former then subsides. The
+impulse to seek the appropriate breeding ground and to dwell there would
+seem to be the strongest of all the impulses save one--the sexual.
+When, however, I speak of the sexual, I refer to the actual discharge of
+the sexual function, which is the consummation of the whole process. But
+the territory and all that appertains to it is part of that process--the
+search for the breeding ground, the dwelling there, and the intolerance
+of intrusion are but different stages, each one of which must have an
+impulse peculiar to it; and since the completion of the sexual act can
+only be successfully accomplished providing that success is attained at
+every stage, the probability is that, of the impulses concerned, one is
+neither more powerful nor less powerful than another.
+
+So that we have two impulses operating at different seasons and guiding
+the behaviour into widely divergent channels. But though the proximate
+end to which the behaviour is directed is apparently different, there
+are not two biological ends in view, but one--the attainment of
+reproduction; and the changes that we witness are not contrary but
+complementary, and their prospective value lies in the circumstance that
+they contribute towards the preservation of the race.
+
+If, then, every male is driven by inherited impulse to seek the
+appropriate breeding ground each recurring season; if, having arrived
+there, it is driven to seek a position of its own; if, in order to
+secure isolation it is obliged to attack other males or to ward off the
+attacks of intruders; if, in short, success can only be attained
+providing that the inherited nature is so adjusted that the bird can
+accomplish all that is here demanded--what will be the general result?
+That the individual will rear its offspring in safety and that they will
+inherit the peculiarities of their parents, enabling them, in their
+turn, to procreate their kind; all this will certainly follow. We are
+not concerned, however, at the moment, with the direct effect upon the
+individual, but with the consequences that will accrue to the species as
+a whole.
+
+Now certain facts are presented to observation which enable us not only
+to understand the nature of the change that is wrought in the history of
+the species, but to foreshadow, with no small degree of certainty, the
+extent of that change. I suppose that it has come within the experience
+of most of us to observe, at one time or another, the ebb and flow of a
+given species in a given district. Some favourite haunt is deserted for
+a year, or for a term of years, and is then revisited; or, if it is
+always occupied, the number of inhabitants fluctuates--plenty of pairs
+in this season, only a few in that. Many intricate relationships, both
+external and internal, contribute towards this state of affairs.
+Fluctuation in a downward direction, or temporary extinction, is brought
+about by changes in the physical world, by changes in the available
+supply of food, by the increase of enemies, or by adverse climatic
+conditions; whilst fluctuation in an upward direction, though due
+indirectly to a combination of circumstances in the external world
+favourable to the survival of large numbers of individuals, is directly
+determined by the impulse to seek isolation. As individuals of
+different species establish themselves, and form kingdoms and lesser
+kingdoms, we can watch the gradual quickening into life of moorland and
+forest and we can observe the manner in which it all comes to pass.
+Males that for weeks or months have lived in society, drifting from
+locality to locality according to the abundance of food or its scarcity,
+now set forth alone and settle first here and then there in search of
+isolation. Lapwings settle in the water meadows, and, finding themselves
+forestalled, pass on in search of other ground; Blackbirds arrive in a
+coppice or in a hedgerow and, meeting with opposition, disappear; and
+the Curlew, wandering with no fixed abode but apparently with a fixity
+of purpose, searches out the moorland where it can find the particular
+environmental conditions to which its inherited nature will respond. In
+fact, wherever we choose to look, we can observe in a general way the
+gradual appropriation of breeding ground; and if we fix our attention
+upon particular males, we can watch the method by which success or
+failure is achieved.
+
+On more than one occasion I have watched the efforts of Reed-Buntings to
+appropriate territories in a marsh that was already inhabited. Sometimes
+their efforts met with success, at other times with failure. In the
+former case, the males, whose ground was intruded upon, were severally
+forced to yield part of their holding and were thus left in possession
+of a smaller area. The success of the intruder seemed to depend upon
+persistent determination, rather than upon superior skill in battle.
+Recently I had an opportunity of observing the intrusion of a male
+Willow-Warbler upon ground already occupied. By persistent effort it
+succeeded in appropriating one half of the territory of its rival. The
+intruder occupied some trees on the outskirts of the territory it was
+invading, and used them as a base from which it made repeated efforts to
+enter the ground of its rival. These efforts were time after time
+frustrated. No sooner did it leave its base than it was seen and
+intercepted, or else attacked; and no matter from which direction it
+attempted to effect an entrance, its efforts, for a time, were all to no
+purpose. The fighting was of a determined character, and after each
+attack the owner of the territory showed signs of great excitement, and,
+sitting upright upon a branch, spread and waved its wings, which is the
+specific emotional manifestation during the period of sexual activity.
+Eventually the intruding male succeeded by persistent effort in
+appropriating part of the occupied ground.
+
+Thus we can actually witness the efforts of the individual to isolate
+itself from members of its own kind, and can observe the immediate
+consequences that follow from success or from failure. And from these
+consequences we can infer that, within a certain range but in accordance
+with the relative abundance of the species that dwell in it, every
+corner of the available breeding ground will be explored and every
+situation that evokes the appropriate response will be occupied.
+Moreover, since the annual dispersion is not merely a repetition in this
+season of that which occurred in a previous one, a progressive increase
+in the area occupied will follow. Yet, if the majority of species desert
+their breeding ground so soon as reproduction is ended, how can this be?
+An answer to the question will be found in the fact that a bird has an
+innate capacity to return to the neighbourhood of its birthplace, or to
+the place wherein it had previously reared offspring--which means that
+the results of prior process persist as the basis and starting-point of
+subsequent process.
+
+Bearing then in mind that the seeming peace in bird life around us in
+the spring is but the expression of transitory adjustments in the
+distribution of individuals and of species; bearing in mind how
+widespread is the search for isolation each recurring season, how
+frequently the search leads to competition and competition to failure,
+and how failure implies a renewal of the search; bearing in mind that
+situations, which appear to be eminently suitable for breeding purposes,
+are passed by year after year and remain unoccupied, just because, for
+reasons which have yet to be ascertained, the environment fails to
+supply some condition which is essential if the inherited nature of the
+bird is to respond--can there be any doubt that the general result of
+the functioning of the disposition will be expansion; or, since no limit
+is placed upon it from within but only from without--that is, by
+unfavourable circumstances in the external world, that the expansion
+will not merely be in one direction but in every direction?
+
+If now, when reproduction is ended, all the impulses relating to it die
+away, and the gregarious instinct again predominates, what are the
+consequences to which this change will lead? Just as the consequences
+which flow from the functioning of the former impulse are accessible to
+observation, so likewise can we observe the change that is wrought by
+the latter impulse. The process is a gradual one. Less and less
+attention is paid by the individual to intruders, more and more is it
+disposed to pass beyond its accustomed limits. Little by little,
+accompanied by its young or without them, as the case may be, the bird
+deserts its territory and wanders out into the wilderness. Here it
+associates with others, and finds in them a new interest and, I doubt
+not, a new enjoyment. All this we can observe as it takes place. But
+just as there is an innate capacity to seek, in the spring, the place
+where the pleasures of breeding had formerly been enjoyed, so we are
+bound to infer the existence in the adult of an innate capacity to
+revisit the former area of association; and this capacity will
+strengthen and confirm the gregarious instinct and set the direction of
+the general course of movement.
+
+We have seen, then, that the interest displayed by one bird in another
+changes with the seasons; we have seen that it is so modified as to be
+in useful relation to different environmental circumstances; as far as
+possible we have traced out the consequences, and have reached the
+conclusion that the change of behaviour must, on the one hand, lead to
+expansion, and on the other, to contraction; and we have seen that this
+conclusion is in accord with the facts of observation--that is the
+general result of our inquiry into the functioning of the two powerful
+impulses, the impulse associated with the disposition to secure a
+territory and the gregarious impulse.
+
+
+The phenomenon of migration embraces a number of separate problems, each
+one of which presents features of great interest and of still greater
+difficulty. On some of these problems I do not intend to touch; I seek
+only to ascertain whether the impulses that are concerned in the
+securing of a territory, and in the search for society, bear any
+relation to the problem as a whole. I hold that the origin of migration
+is not to be found merely in conditions peculiar to a remote past, but
+that the conditions inhere in the organic complex of the bird, and are
+thus handed down from generation to generation. Starting with this
+assumption I examined the behaviour which normally accompanies the
+seasonal life-history of the individual, and found, in that behaviour,
+manifestations of cyclical change leading to definite biological
+consequences. I now propose to inquire whether those consequences are
+such as might, in the course of time, give rise to the seasonal change
+of abode.
+
+We are apt to think of migration in terms of the Warbler that enlivens
+our hedgerows in the spring after travelling hundreds of miles from the
+south, or of the Redwing that comes from the far north and seeks its
+food during the winter on the meadows, or perhaps of the American Golden
+Plover that each year covers a vast expanse of ocean in its journey from
+its breeding ground. The length of the distance strikes the imagination
+and constrains us to focus attention upon the extremes.
+
+But migration is of much wider significance than is here represented. I
+sit beside the River Severn in April and watch Swallows, Tree-Pipits,
+and Yellow Wagtails passing in twos and threes, in small parties, or it
+may be in small flocks; and I observe that while some establish
+themselves in the neighbourhood, others pass on. Or I watch
+Herring-Gulls returning to the breeding station at Bolt Head, an endless
+stream of individuals coming from the east as far as eye can reach;
+following them for some miles inland I see them still, first as specks
+upon the horizon, then passing beside me as they beat their way slowly
+against the strong south-westerly winds, and finally disappearing from
+view in the direction of the cliffs. Or again, I watch Buntings and
+Finches deserting the flock and seeking stations in the marsh, or
+amongst the furze-bushes on the common, or in the spinneys. In each case
+the proximate end of the behaviour is alike--wherein then lies the
+difference? Only in the distance which separates the territory from the
+area in which the birds formerly associated. And intermediate between
+the extremes, I doubt not, if we had a sufficient body of observations,
+that we should find numerous gradations, the lesser merging step by step
+into the greater. Is the Swallow a migrant and the Herring-Gull not; is
+the Tree-Pipit a migrant and the Bunting not; must a bird cross many
+miles of sea or of land before it can be considered a migrant; is the
+length of the distance traversed a criterion of migration? Surely not.
+The distance traversed is merely a collateral consequence of the process
+as a whole.
+
+The annual life-history of a bird presents, as we have seen, two
+distinct phases--the one in which the individual dominates the
+situation, the other in which it is subordinated to the welfare of the
+community. Let us take these two phases separately and endeavour to see
+how they may have influenced the seasonal movements; and first let us
+take the more important of the two, namely that one which is directly
+concerned in the continuance of the race.
+
+In this phase we must consider the three factors to which allusion has
+already been made:--(1) the internal impulse, (2) the innate ability to
+return to the former breeding ground, (3) the conditions in the external
+environment. These three work in close relation and, as I shall
+endeavour to show, lead to important results.
+
+(1) If there were nothing in the inherited nature beyond an impulse to
+seek the breeding ground, if, that is to say, when the appropriate
+locality were reached, the bird took no further interest in the
+developing situation, the attainment of reproduction would become
+largely a matter of chance. A male in a congested district, having no
+incentive to seek fresh ground, would remain inactive until a female
+happened to cross its path and stimulate its sexual impulse, when its
+activity would take another form. Hence some districts would be
+over-populated, whilst others would remain unexplored. But the system of
+reproduction does not consist merely of a search for the breeding
+ground, and of the discharge of the sexual function; it is a much more
+complex business, yet withal more complete. Nothing is left to chance;
+the end is attained step by step; and each successive stage marks the
+appearance of some specific factor which contributes towards the success
+of the whole. We start with the appropriate organic condition under
+which, when adequate stimulation is provided, the disposition to secure
+a territory comes into functional activity. Within the field of this
+disposition we can distinguish certain specific impulses. In sequential
+order we have the impulse to seek the breeding ground; the appropriate
+situation which gives rise to an impulse to dwell in it; and the act of
+establishment which supplies the condition under which the impulse to
+drive away intruders is rendered susceptible to stimulation. Grouping
+these impulses, for the convenience of treatment, under one general
+heading, I speak of an impulse to seek isolation. It implies some kind
+of action with some kind of change as its correlated effect; and from it
+there flows a ceaseless energy directed towards a definite end which for
+us, who can perceive its prospective value, is isolation in an
+appropriate environment. The emphasis here is on "isolation," for it
+involves competition, and there cannot be competition without some
+change in the relative positions occupied by different individuals; so
+that in each recurring season there will be not only a re-arrangement of
+ground formerly occupied but an arrangement of ground formerly deserted.
+
+(2) That the older birds return to the locality wherein they had
+formerly reared offspring, and the younger to the neighbourhood of their
+birthplace, was always deemed probable. But in recent years evidence
+which cannot be rebutted has been supplied by the marking of birds. This
+evidence, details of which can be found in the summary of results
+published annually by Mr. Witherby in _British Birds_, demonstrates that
+the adult frequently returns not only to the same locality in which it
+formerly bred, but even to the same station; that it does so year after
+year; that this mode of behaviour is not peculiar to one sex; and that
+many of the young breed in the locality in which they were reared. Such
+being well-established facts, we can infer the existence of an innate
+ability to revisit the place wherein the enjoyment of breeding, or of
+birth, had formerly been experienced. Of its nature we know little or
+nothing. It would almost seem as if there must be some recollection of
+past enjoyment, but all that can be definitely asserted is--that past
+experience somehow becomes ingrained in the life of the individual and
+determines present behaviour. What, however, is of importance to us at
+the moment is not the _ad hoc_ nature of the bird, but the biological
+consequences to which the behaviour leads. For if, on the average,
+individuals return to their former haunts, it follows that the annual
+dispersion will not be merely a repetition in this season of that which
+had occurred in a previous one, but that the little added this year will
+become the basis for further additions in the next. The innate ability
+is handed down from generation to generation, and, in so far as it
+contributes to success, is fostered and developed by selection; and the
+modifications of behaviour to which it leads, since the results of prior
+process in the parent persist as the basis and starting-point of
+subsequent process in the offspring may in a sense also be said to be
+handed down.
+
+(3) The conditions in the external world may be organic or inorganic. By
+organic I mean the conditions which depend upon the number of
+competitors or enemies by which a bird is surrounded. The competitors
+may include other species which require a similar environment; and the
+enemies, species which prey upon it, or animals which take its young or
+its eggs. They vary in different seasons, in different districts, and
+in nature and extent--the success of one species leads to the failure of
+another, and the multiplication of the Jay or of the Magpie robs us of
+many a songster.
+
+By inorganic I refer to the changes in the climate and in the surface of
+the earth. The nourishment of the young depends upon a regular supply of
+food, and the supply of food depends upon the climate which alters in
+different periods; in one decade the temperature falls below, whilst in
+another it rises above, the normal, and, as the insect life fluctuates,
+so there is fluctuation in the bird population. The changes in the
+surface of the earth are manifold. Little by little the alder (_Alnus
+glutinosa_) overspreads the marsh. Young shoots spring up here and
+there, in a few years grow into bushes, and in a few more years are
+trees; and the dense masses of rush which seemed to choke their growth,
+yielding their position of importance, slowly disappear. And where
+formerly the _Orchis latifolia_, _Orchis mascula_, and _Juncus communis_
+grew in mingled confusion, nothing but water, moss, and the spreading
+roots of alder cover the ground. As the rush disappears, many birds that
+for generations have inhabited that marsh must seek accommodation
+elsewhere. Ancient breeding haunts thus disappear, new ones come into
+being, and even those which appear to be permanent are almost
+imperceptibly changing.
+
+Now the bird inherits a nervous system, which works under internal
+excitation and external stimulation. Given the appropriate organic
+condition and adequate stimulation, and the impulse to seek isolation
+comes into functional activity. What the organic condition is and how it
+arises we do not exactly know; all we know is that organic changes do
+take place in the breeding season, that these changes profoundly modify
+character, and that they correspond with the seasonal growth of the
+sexual organs. And with regard to the question of stimulation, we have
+again to confess to much ignorance, although certain facts are presented
+to observation which seem to indicate the direction in which the
+stimulus lies. For example, it is well known that abnormal climatic
+conditions influence behaviour; we see migrants retracing their flight
+along the very course they travelled a short time previously--driven
+headlong by the blizzard, that at least is what we say. But if the wind,
+instead of being cold and from the north, is warm and from the west, do
+they retrace their flight? I have not found it so. And if there be no
+wind and the temperature is low, are they still affected? Again, I have
+not found it so. When, as we commonly say, they fly before the storm,
+some change takes place in their organic complex, some new impulse
+receives stimulation or the former one lacks it. If, after Lapwings have
+established themselves in their territories, the weather becomes
+exceptionally severe, the birds collect together again in flocks and
+revert to their winter routine; and under similar circumstances,
+Buntings fail to sing and temporarily desert their territories. In such
+cases it is clear that the impulse to seek isolation ceases for a time
+to dominate the situation. The inference, therefore, is that atmospheric
+changes bear some relation to the functioning of the instinct; but
+whether it be temperature, or humidity, or the direction and velocity of
+the wind, or a combination of two or more of these factors that supplies
+the stimulus, we cannot tell.
+
+The appropriate organic condition and the stimulus have then still to be
+determined, and we must pursue our inquiry from the point at which the
+impulse comes into functional activity. We will take a simple case, and
+one free from complication.
+
+Let us suppose that there is an area bereft of bird life, if it can be
+so imagined, but in proximity to other inhabited areas. Into this area,
+whilst in search of isolation, let us imagine that a Yellow Bunting
+finds its way. After the manner of its race it establishes a territory
+and occupies, let us say at a low computation, half an acre of ground.
+It then obtains a mate, breeds, and rears offspring, two of which we
+will assume are males. Reproduction ended, the birds desert the area,
+and in the following spring, when the impulse again asserts itself,
+parents and offspring seek again their former haunts. We now have three
+males, each of which occupies half an acre, and each of which rears two
+offspring--that is the position at the close of the second year. In the
+third year the number will have increased to nine and the area occupied
+to 4-1/2 acres; and so on in succeeding years, until by the beginning of
+the eleventh year, we have 59,048 Yellow Buntings occupying 29,524-1/2
+acres or 46 square miles. This, then, will be the result of the
+operation of the impulse, providing that all the individuals survive and
+that no complications supervene.
+
+But of course complications are numerous, some of which retard while
+others accelerate the rate of expansion. These complications arise from
+various sources--in the first place from natural enemies which prey upon
+the birds or upon their eggs; in the next place from climate which, if
+it happens to be unfavourable, may mean that food is scarce and that
+only a small percentage of the young survive; and lastly from
+rivals--and by rivals I mean closely related forms that require a
+similar station and similar food--which, by occupying available ground,
+may check expansion, or, by forcing a continuation of the search, may
+widen it.
+
+Now when individuals fail as many do fail in their initial attempt to
+secure territory, the activity of the impulse still persists, and there
+is no control over the direction in which the bird continues to wander
+whilst in search of its end. Some therefore seek in this direction,
+others in that; some wander inwards into inhabited areas and fail to
+find accommodation, or, according to the relative strength of their
+impulse, perhaps succeed and so set free a new competitor, others wander
+outwards into country uninhabited by the species. These latter we will
+call "pioneers." They may find accommodation within a comparatively
+short distance of their base, or they may come into competition with
+rivals and fail, not necessarily on account of any congenital weakness
+of ability, but because being warned by an alien song, they may be
+precluded from coming into contact with just the environing conditions
+which can supply the stimulus and allow behaviour to run its further
+course--and so be obliged to extend their search into remoter districts.
+But it must not be overlooked that they will be placed in a most
+advantageous position so far as the attainment of reproduction is
+concerned. In their search for territory they will meet with little
+opposition and will be free to select whatsoever ground they will; and
+be free also from intrusion by neighbouring males, which is so frequent
+in occurrence and continues for so long in congested areas. Moreover, in
+thinly populated districts, the pressure upon the available means of
+support will not be so great, neither will natural enemies be so
+plentiful; and since the offspring, guided by prior experience, return
+to the neighbourhood of their birthplace, the advantages thus gained
+will be shared by the succeeding generation. It follows, then, that the
+range of a species will not always be continuous, will not, that is to
+say, proceed by a series of successive steps, but that sometimes in this
+direction and at other times in that, the chain of territories will be
+interrupted and different individuals separated by distances of greater
+or lesser extent. New colonies will thus come into being; and as the
+unlimited increase of the population over limited areas gradually
+reintroduces into them the struggle for territory, new centres of
+distribution, where the process will repeat itself and from which
+expansion will proceed afresh, will be formed. Hence, though it is
+clearly impossible for the progeny of one pair of Yellow Buntings to
+overspread the whole of the 46 square miles, it is by no means
+impossible for the limits of their range to exceed even those limits
+within the eleven years.
+
+To sum up our knowledge regarding this phase. Of the organic condition
+which renders the impulse responsive to stimulation we know very little;
+and though certain facts of observation seem to indicate the direction
+in which the stimulus is to be found, we must here again confess to much
+ignorance. So far as can be seen, however, the impulse to seek isolation
+with its correlative territory, leads to constant modification in the
+breeding range of most species. The occupation of the small space of
+ground which each individual requires, the extent of which has been
+gradually adjusted to suit the needs of different species, results in
+expansion not only in one direction but in every direction, and not only
+in one season but in every season. And if there were no complications in
+the external world this expansion would proceed, as we have seen, with
+astonishing rapidity. But complications, some of which are favourable
+and others unfavourable, are numerous, and it is difficult to estimate
+their importance or to indicate their precise effect; the former,
+however, accelerate the rate of expansion, whilst the latter retard it.
+Those individuals that wander outwards and seek territory on the
+outskirts of the range we have called "pioneers." They will have
+advantages over others that, wandering inwards, seek isolation in
+congested districts, and will succeed where the latter fail; and since
+there is in the young an innate ability to return to the district
+wherein they were reared, the advantages so gained may be said to be
+handed on from generation to generation.
+
+Let us now turn to the contra-phase, and endeavour to ascertain whether
+the gregarious instinct bears any relation to the seasonal desertion of
+the breeding ground. The conclusion at which we have already arrived
+regarding this instinct is that it forms part of the inherited nature of
+most species; that its functioning is suppressed when a bird is actually
+in occupation of a territory; and that it is serviceable in promoting
+the welfare of the individual. We cannot of course observe the instinct.
+What we observe, when reproduction is ended, is a change in the
+relations of different individuals; instead of arousing mutual
+hostility, they attract one another, from which we infer the existence
+of something which determines their conduct, and this "something" we
+speak of as an instinct.
+
+To what does this change lead? Let us suppose that there is an area
+inhabited by one species; that the number of inhabitants has reached the
+maximum that the means of sustenance will allow; and that the season of
+reproduction is drawing to a close. The position will then be as
+follows. All the available breeding ground is divided into territories;
+each territory is occupied by one unit, the family, and each individual
+is able to fend for itself; changes both internal and external begin to
+take place, the gregarious instinct comes into functional operation, and
+the supply of food diminishes--that roughly is the position. The
+internal factor operates so that the sight of this individual or the
+call of that, instead of evoking hostility as heretofore and keeping
+different units apart, proves now an irresistible attraction; so that in
+place of a number of individuals evenly dispersed over the whole of this
+area, a small number of flocks of various dimensions are stationed at
+certain points, which points are determined partly by experience, partly
+by the supply of food, and partly by accident. This implies for each
+individual some movement in some direction. But since the population of
+this imaginary area has reached the maximum, and the supply of food,
+though limited in distribution, is nevertheless plentiful, such
+movements will be irregular and will proceed in no definite direction.
+
+Now let us suppose that the breeding range extends and that fresh ground
+is occupied by pioneers. When reproduction and the rearing of broods are
+ended and the gregarious instinct becomes dominant, these pioneers, or
+at least some of them, will revisit the area wherein formerly they
+associated with companions. Their offspring, however, though they will
+have the inherited impulse and the innate tendency, will not have the
+experience; how then will they behave? There can be no doubt that some
+will accompany the older birds, and, being led by them, will share the
+experience of a former generation; nor any question that others will
+collect together in the neighbourhood of their birthplace and, if their
+impulse is satisfied, will remain there so long as food is to be found.
+Thus the gregarious instinct, working in close relation with acquired
+experience, will on the one hand lead to the formation of organised
+movements in certain directions, whilst on the other it will lead to the
+formation of new areas of association which will follow in the wake of
+the expansion.
+
+We have assumed, in the imaginary case which we have just taken, that
+the conditions in the external world are such as enable the birds to
+endure throughout the year--in short, that there are no complications
+regarding the supply of food. But we must bear in mind that so long as
+conditions are favourable during the period of reproduction, which is of
+short duration, the breeding range can continue to expand, and that
+therefore, in the course of centuries, regions will come to be occupied
+wherein, owing to alternations of climate or physical changes in the
+surface of the earth, food will be impossible, or at any rate difficult
+to obtain at certain seasons. Hence there will come a time when the area
+of association ceases to follow in the wake of the expansion, and the
+breeding area begins to diverge from the subsistence area.
+
+How, then, is the gulf between these two areas to be bridged? We can of
+course say that those individuals which, in virtue of some slight
+variation of hereditary tendency, return to regions where food is
+plentiful will survive; whilst others, less well endowed, will perish.
+We can state the position in some such general terms, and doubtless
+there would be truth in the statement, but it does not carry us far; we
+wish to know more of the nature of the tendency, and of the manner in
+which it has evolved. Well now, in this new situation which arises, two
+things are apparent--that the struggle for existence becomes a struggle
+for the means of subsistence, and that anything in the inherited
+constitution of the bird which can be organised to subserve the
+biological end in view becomes of selection value. So long as food can
+always be procured in the new areas of association, the individuals that
+behave in accordance with ancestral routine gain thereby no particular
+advantage; but directly the breeding range extends into regions where
+the supply fluctuates, traditional experience becomes a factor in
+survival, and those individuals that come under its influence will, on
+the average, be more likely to endure and so to procreate their kind and
+maintain the tradition. Let it once be granted that there is an innate
+capacity to retain in later phases of routine the experience gained in
+earlier phases, and it is difficult to see how traditional guidance can
+be refused recognition as a factor in the developing situation. But only
+_a_ factor, and by no means the most important one; for observation has
+shown that the young are capable of performing the return journey
+without guidance. Something therefore _is_ inherited, some impulse
+which comes into functional activity at a specified time, and leads the
+bird to set forth in a given direction.
+
+There are no grounds for supposing that the experience of one generation
+forms any part of the hereditary equipment of subsequent generations. In
+what direction then are we to look for the congenital factor? What is
+given is an inherited tendency to co-operation and mutual help, and an
+innate capacity to make use of the results of experience. The inherited
+tendency, as we have seen, leads on the one hand to the formation of new
+areas of association, whilst on the other, since it is the means of
+bringing isolated individuals into contact, it leads to experience being
+handed on from generation to generation, which, in its turn, results in
+a certain amount of backward movement along the line of expansion. It
+forms part of the hereditary equipment of many species, and is
+serviceable in promoting the welfare of the individual. Moreover, there
+is reason to believe that its origin dates back to an early period in
+the evolution of the higher forms of life; and if in the subsequent
+course of evolution it could have been so organised as to serve a double
+purpose, so much the more reason would there have been for its survival.
+In what does the instinct consist? Is it merely that the sight of this
+individual or the call of that proves at some particular moment an
+irresistible attraction, or does the appropriate organic condition give
+rise, as is generally supposed, to some preceding state of uneasiness?
+In the former case, the temporarily isolated individual or colony would
+have but little chance of sharing in the benefits which mutual
+association confers upon the associates; in the latter, the feeling of
+discomfort would lead to restlessness, and would thus bring the bird
+into touch with the environing circumstances under which instinctive
+behaviour could run its further course. So that it is probable that the
+movements of each individual, prior to its becoming a unit in the flock,
+are not accidental but are determined in some measure by racial
+preparation.
+
+Now if the fundamental assumption of the doctrine of the struggle for
+existence be true, the gregarious instinct will not be quite alike in
+all the members of different broods, nor even in each member of the same
+brood; that is, variation will occur in all possible directions. And we
+shall not, I think, exceed the limits of probability if we assume that
+different individuals vary in the persistency with which they strive to
+attain their unknown end, and in the direction in which they travel in
+pursuit of it. So that in each generation they will fall into three
+classes: (1) those which are inert, (2) those which wander along the
+line of expansion, (3) those which wander in other directions. If then
+the struggle for life at this particular juncture in the evolution of
+the breeding range is a struggle for the means of subsistence, the
+members of these three classes will not be in a like satisfactory
+position so far as the competition for food is concerned. Those in the
+first class--_i.e._, those in which the activity feelings are weak--will
+neither gain the benefits which arise from mutual help, nor will they
+have much prospect of enduring through the season of scarcity. Those in
+the third class will, it is true, derive some assistance one from
+another, and so be in a better position to discover what food may be
+available; but inasmuch as they will remain in regions where the climate
+alternates and the supply of food is liable to fall below the minimum
+required, the chances are that a high percentage will fail in the
+struggle for existence. We come now to those in the second class, and it
+is upon them that I wish more particularly to focus attention. The
+initial movement in their case will be in the direction from which
+outward expansion has all along taken place. Within a comparatively
+short distance they will reach districts where the species is plentiful,
+and here, associating with others that have some traditional experience,
+they will be guided by them and will find themselves in regions where
+food is plentiful. Hence in each generation those will survive that,
+owing to some congenital variation of their instinct, seek satisfaction
+for their impulse in a direction which brings them under the influence
+of tradition. And though at first but slight and not in themselves of
+survival value, such variations, since they coincide with modifications
+of behaviour due to acquired experience, will be preserved and in the
+process of time so accumulated as to be capable of determining the
+direction and extent of the movement.
+
+But the young Cuckoo deserts this country many weeks after its parents,
+and there is no reason to suppose that it lives in society when
+eventually its destination is reached; and the young Falcon passes to
+the south, and is certainly not gregarious--how then can we explain
+their behaviour in terms of something which they show no signs of
+possessing? I do not wish to make light of a difficulty which
+admittedly, at first sight, is a grave objection to the view that the
+gregarious instinct has been operative in the manner here claimed for
+it. It must, however, be borne in mind that this instinct, though
+originally developed to serve the purpose of mutual protection, supplies
+the material upon which evolution works when the extension of the
+breeding range creates a situation requiring readjustment on the part of
+the organism to new conditions of life; and that those variations which
+can be so modified as to be in useful relation to the new environmental
+circumstances are seized upon by natural selection and, being
+transmitted, form the foundation of a specific inherited response, no
+longer dependent upon, though operating in close relation with the
+primitive response whence originally it sprang. Thus the primordial
+instinct becomes so organised as to serve a secondary purpose, that of
+rendering secure a means of access to a certain food supply. In the
+course of evolution species were bound to arise which, owing to some
+peculiar conditions, derived greater advantage from living solitary than
+from living in society. Does it then follow, because such species
+manifest no inclination to live in society, that the instinct never has
+played any part in their lives? Or because the primary purpose has
+lapsed, does it follow that the secondary no longer exists?
+
+
+Let me recapitulate the principal considerations which I have discussed
+in this chapter.
+
+Though I have been advancing a theory, and though I have taken much for
+granted, yet it will, I think, be admitted that both the theory and what
+has been taken for granted rest on observational grounds. As our
+starting-point we have a bird whose inherited nature alternates
+according to the season, and in whose nature we can distinguish two
+contra-phases--the one to live in society, the other to live solitary.
+While both have their part to play in furthering the life of the
+individual, for biological interpretation there is only one end, the
+prospective value of which is the continuance of the race. We may say
+that the latter phase is the more important of the two because it is
+directly concerned with reproduction. But we shall make a great mistake
+if we attach peculiar importance to one phase, or to one mode of
+behaviour within that phase, or to one action within that mode of
+behaviour; for if there is one thing certain it is that the whole is an
+inter-related whole in which each part depends for its success upon that
+which precedes it.
+
+In that phase in which the territory is the central feature of the
+situation, the struggle for existence is in operation in its acutest
+form; all the congenital and acquired capacities of the bird--pugnacity,
+song, capacity to utilise in later phases the experience gained in prior
+phases, all these are organised to subserve an end--a proximate
+end--which in its simplest terms may be described as "isolation."
+Isolation is then the first step in the process of reproduction, and any
+individual that fails to make it good, fails to procreate its kind. But
+isolation implies separation, and the degree of separation varies in
+different species, from the few square feet of cliff required by the
+Guillemot to the few square miles of barren moor over which the
+Peregrine exercises dominion. One species must occupy sufficient ground
+to enable it to secure food for its young; another requires sufficient,
+but no more, upon which to deposit its egg; and a third must secure a
+position for its nest within the community. Hence it follows that the
+degree of separation varies with the conditions of existence. Since,
+however, the conditions in the external world are constantly changing
+according to the relative abundance or scarcity of enemies, the rise or
+fall of rivals, the physical changes in the earth's surface, and the
+alterations of climate, it is clear that isolation can only be obtained
+with difficulty, and that the competition for it must be severe. Some
+individuals therefore fail to breed, whilst others, perhaps because
+their impulse is stronger, persevere and seek stations elsewhere. What
+are their prospects of finding them? By extending the field of their
+activities, they will wander into districts remote from the scene of
+competition, districts where not only food is plentiful but where
+enemies and rivals are scarce; and to these pioneers, if to any, success
+in reproduction will most certainly be assured. But not only is it they
+who will benefit; their offspring also, when the time comes for them to
+take their part in the maintenance of the race, will share in the
+success of their parents, for even though they may not escape
+competition from individuals of closely related forms, they will meet
+with but little from those of their own kind. Now species which live
+throughout the year in the vicinity of their territory are comparatively
+few, the majority are obliged to wander in search of food so soon as
+reproduction is ended, and their behaviour is determined not only by its
+abundance or scarcity, but also by the powerful gregarious impulse which
+waxes in proportion as the instincts connected with reproduction wane.
+If, then, when the sexual instinct again becomes predominant, the
+experience of the former season nowise affects their movements, little
+or no progress will be made in the expansion of the range. But just as a
+certain entrance into the bush and pathway through it, when once made
+use of in the process of building, becomes so firmly established as to
+form the sole highway to and from the nest, so likewise, when the
+impulse to seek isolation repeats itself, the bird is constrained to
+seek the neighbourhood wherein it had experienced the enjoyment of
+breeding or of birth. Thus the little that is added one year becomes the
+basis for further additions in the next, and new centres of distribution
+are continually being formed from which expansion proceeds anew.
+
+Now as the range gradually extends into regions where the climate
+alternates and food at certain seasons is consequently scarce, the
+distance between the customary area of association and that of
+reproduction must perforce widen. The question then arises: How will the
+young that have no experience find their way to regions wherein they can
+endure? The forces which may have been organised to subserve the end in
+view are three: (1) Acquired experience, (2) tradition, (3) the
+gregarious instinct. The pioneer that carries the range a little further
+forward starts from a base where it has associated with companions and
+found food plentiful; and when the impulse to live in society again
+asserts itself, it not only repeats its former experience but hands on
+the habit thus acquired to those of the next generation that happen to
+accompany it. Granting, however, that by successive increments in the
+distance traversed, traditional guidance may in time accomplish much, it
+cannot account for all the known facts, it cannot at any rate explain
+the fact that in some cases the inexperienced offspring finds its way to
+the food area without guidance. Something, therefore, _is_ inherited.
+And my suggestion is this: That the gregarious instinct, the ancient
+origin of which we can infer from its manifestation in so many and
+diverse forms of life, supplies the material upon which evolution works;
+that variations of the initial impulse, at first slight and not in
+themselves of selection value, in so far as they coincide in direction
+with modifications of procedure due to experience or tradition, are
+preserved; and that, in the process of time, they are so accumulated as
+to form a specific congenital endowment determining a definite mode of
+behaviour.
+
+
+  FOOTNOTES:
+
+  [1] June 1915, R. M. Barrington.
+
+  [2] _Dictionary of Birds_, p. 556.
+
+  [3] _Social Psychology._
+
+  [4] _Manual of Psychology._
+
+  [5] _Ibis_, April 1918.
+
+  [6] _Zoologist_, 1912, p. 327.
+
+
+
+
+  INDEX
+
+
+  Acquired experience, 300
+
+  Adjustments, transitory, of distribution, 275
+
+  Alarm notes, 119
+
+  Arrival, advantages and disadvantages of late, 33-44
+
+  Assemblies in winter, 262, 263
+
+  Assembly grounds, 173
+
+  Attainment of reproduction, 171
+
+
+  Barrington, R. M., on the sex of migrants, 25
+
+  Battle between two male Cuckoos, 82
+
+  ---- between two Moor-Hens, 86, 92, 93, 94
+
+  ---- ---- Pied Wagtails, 86
+
+  ---- ---- Raven and Buzzard, 217
+
+  ---- ---- Raven and Peregrine, 216
+    law of, 13,19
+
+  Behaviour routine, 262
+
+  ---- sexual, 3
+
+  Bickerings, 96
+
+  Birthplace, return to, 43, 50
+
+  Blackbird, 87, 182, 222, 244
+
+  Blackcap, 81, 156, 224, 230
+
+  Black Grouse, 63
+
+  Black-tailed Godwit, 53
+
+  Boundaries, 1, 5
+
+  ---- conflicts for retention of, 7, 62
+
+  ---- disputes as to, 1
+
+  Brambling, 124
+
+  Breeding ground, search for appropriate, 270, 271
+
+  ---- range, extension of, 291-92
+
+  ---- site, acquirement of, 3
+
+  ---- stations, evolution of, 15-19
+
+  ---- ---- repeatedly visited long before nesting-time, 64
+
+  ---- territory, 2, 3, 7
+
+  ---- ---- evolution of, 18
+
+  ---- ---- foundation of, 7
+
+  ---- ---- innate capacity to return to former, 279-81
+
+  Bridled Guillemot, 64
+
+  Brooding, 180
+
+  ---- impulse, 191
+
+  Bunting, Cirl, 28, 140
+
+  ---- Corn, 28
+
+  ---- Reed, 28, 68, 69, 85, 104, 132, 158, 160, 244
+
+  ---- Yellow, 28, 30, 47, 64, 140, 159, 162, 183, 187, 188, 189,
+    235, 236, 286
+
+  Buzzard, 217
+
+
+  Capacity, innate, to return to former breeding territory, 279-81
+
+  Carrion Crow, 226
+
+  Chaffinch, 28, 31, 32, 33, 45, 87, 103, 156, 159, 235, 236, 244
+
+  ---- Donegal, 160
+
+  Change of breeding quarters owing to unsuitableness, 50
+
+  Chiffchaff, 49, 51, 80, 139, 140, 221, 224, 244
+
+  Cirl Bunting, 28, 140
+
+  Clarke, W. Eagle, _Studies in Bird Migration_, 24
+
+  Cleanliness of nest, 180
+
+  Cliff-breeding species, 63
+
+  Climatic changes, alteration of routine, due to, 284
+
+  ---- changes, food dependent on, 283
+
+  ---- conditions, influence of, 20
+
+  Communities, 202
+
+  ---- birds after breeding-season remain in, 265-67
+
+  Competition, female, for males, 13
+
+  Complexity of strife, 84-85
+
+  Conflicts between males during the mating period, 74, 86
+
+  ---- between males during the nesting period, 87
+
+  ---- for areas, 10, 11, 13, 62
+
+  ---- of Ruff, 54
+
+  ---- sexual, 10
+
+  Congenital disposition, 135
+
+  Contests between males for possession of females, 80
+
+  Coot, 61
+
+  Corn-Bunting, 28
+
+  Corncrake, 39
+
+  Crow, Carrion, 226, 227
+
+  Crow, Hooded, 202
+
+  Cuckoo, 52, 82, 144, 296
+
+  ---- restricted breeding area, 52
+
+  Curlew, 119, 138, 140, 250, 262, 263, 265, 273
+
+
+  Danger warnings, 269
+
+  Darwin, C., _Descent of Man_, 35
+
+  ---- on the arrival of males before females, 35
+
+  Defence of territory, 6
+
+  Development, sexual, 6
+
+  Disposition, congenital, 135
+
+  ---- functioning of, 74
+
+  ---- inherited, 5
+
+  ---- to defend the territory, 73-118
+
+  ---- to mate, 27
+
+  ---- to remain in a particular place in a particular environment, 6
+
+  ---- to secure a territory, 6, 20-72
+
+  Distribution, adjustment of, 275
+
+  Dove, Turtle, 126, 232
+
+  Dunlin, 250
+
+
+  Emotional behaviour, 53, 82, 114
+
+  ---- manifestation, 90, 283
+
+  ---- response, 26
+
+  Enemies, 282
+
+  Energy, waste of, 219
+
+  Environment, 6
+
+  ---- and food, 56
+
+  ---- changes of, 283
+
+  ---- external, conditions in, 279, 282
+
+  Equipment, hereditary, 6
+
+  Evolution of breeding stations or territory, 15, 19
+
+  ---- of the territory, 176
+
+  ---- of the voice, 163
+
+  Existence, struggle for, 294
+
+  Experience, acquired, 300
+
+  Experiments, removal of nests for, 181, 185, 190, 213, 214
+
+  Exposure, its effect on nestlings, 180
+
+  External environment, conditions in, 279, 282
+
+
+  Falcon, 48, 71
+
+  Feeding grounds, neutral, 125 in communities, 70
+
+  Females, fighting amongst, 109-118
+
+  ---- sexual impulse of, 13
+
+  Fieldfare, 124
+
+  Fighting instinct, 79, 82
+
+  Flight, emotional behaviour of Godwit during, 53
+
+  Flocks, in winter, birds collect together in, 262
+
+  Flycatcher, 244
+
+  Food, procuring of, 5
+
+  ---- abundance, or scarcity of, its relation to prosperity of young,
+         15, 16
+
+  ---- its bearing, on the movement of flocks, 262
+
+  ---- rearing of young dependent on rapid and regular, 179, 195
+
+  ---- supply, proximity to, necessary for rearing young, 179, 195
+
+  Fortuitous mating, 174
+
+  Fowler, Ward, on the value of communities, Rooks, 202
+
+  Fulmar, 121, 247
+
+  Functional activity, 259
+
+  ---- instinct of Reeve, 173
+
+  Functioning of the disposition, 275
+
+  ---- of the primary dispositions, 100
+
+
+  Garden Warbler, 223, 225, 230
+
+  Gaetke, H., _Birds of Heligoland_, 24
+
+  ---- on the absence of song in birds on Heligoland, 124
+
+  ---- on the early arrival of Guillemots on Heligoland, 64
+
+  Godwit, emotional behaviour of, during flight, 53
+
+  ---- Black-tailed, 53
+
+  Grasshopper Warbler, 39, 131, 139, 153, 155, 187, 244
+
+  Greenfinch, 28, 33, 140, 235, 236
+
+  Gregarious instinct, 20, 61, 141, 265-66, 269, 276, 289, 290, 291,
+    296, 300
+
+  Grouse, Black, 63
+
+  Guillemot, Bridled, 64
+
+  ---- Common, 63, 64, 121, 192, 195, 206, 211, 247
+
+  ---- Ringed, 64
+
+  Gull, Common, 119
+
+  ---- Herring, 210, 278
+
+
+  Habit formation, law of, 8, 62, 65, 66, 67, 205
+
+  Hawfinch, 28
+
+  Headquarters, 176, 206, 207, 274
+
+  ---- restricted, 8, 9, 30, 50, 58, 64, 127
+
+  Hedge-Sparrow, 213, 221, 244
+
+  Hereditary equipment, 6
+
+  Herring-Gull, 210, 278
+
+  Hooded-Crow, 202
+
+  Hostility and territory, relationship between, 242
+
+  House-Sparrow, 218
+
+
+  Imitation, vocal, powers of, 156, 157, 161
+
+  Impulse, internal, 279
+
+  ---- to brood, 191
+
+  Inherited disposition, 5
+
+  Instinct, fighting, 79-82
+
+  ---- gregarious, 20, 61, 141, 265, 266, 269, 276, 289, 290, 291, 296,
+         300
+
+  ---- migratory, 37
+
+  ---- of song related to establishment of territory, 125
+
+  ---- sexual, reawakening of, 4, 18
+
+  Instinctive response, 180
+
+  Instincts susceptible to stimulation, 259
+
+  Internal impulse, 279
+
+  Internal stimulation, 62, 123
+
+  Interpretation of battles, 75
+
+  Intolerance of other birds, 218, 219
+
+  Intrusion resented, 274
+
+  Isolation, impulse to seek, 288
+
+  ---- of male, 12, 62, 65, 73, 81
+
+  ---- of male during breeding season, 267, 272, 273, 275, 281
+
+
+  Jay, 87, 156, 283
+
+
+  Kestrel, 228
+
+  Kittiwake, 116, 200, 247
+
+
+  Lapwing, 58, 59, 61, 62, 64, 84, 103, 104, 126, 189, 190, 220, 251, 284
+
+  Lapwing, life-history of, 58-61
+
+  Late arrival, advantages and disadvantages of, 33-44
+
+  Law of battle, 74, 75, 86
+
+  Lesser Whitethroat, 230, 244
+
+  Linnet, 156
+
+
+  M'Dougall, Dr, _Social Psychology_, 77
+
+  Magpie, 219, 283
+
+  Males arrive before advent of females, 24
+
+  Marsh-Warbler, 39, 40, 52, 81, 132, 140, 153, 155, 156, 165, 225
+
+  Martin, 201, 218
+
+  Mating, difficulties of, 172
+
+  ---- fortuitous, 174
+
+  Maximum number supportable in a given locality, 49
+
+  Meadow-Pipit, 188
+
+  Meeting places for antics, 54, 63
+
+  Mental Image, 77
+
+  Merlin, 227
+
+  Migration, 3-4
+
+  ---- distance no criterion, 279
+
+  ---- its relation to territory, 259
+
+  Migration, origin of, 260, 277
+
+  ---- phenomenon of, 277
+
+  Migratory instinct, 37
+
+  ---- species more highly specialised than resident species, 56
+
+  Missel-Thrush, 21
+
+  Mobility of the land and stability of the water, 260
+
+  Moor-hen, 61, 85, 103, 218, 250, 251
+
+  Morgan, Professor Lloyd, on instinctive behaviour, 74
+
+  ---- on emotional behaviour, 114
+
+
+  Nest, cleaning of, 180
+
+  ---- construction of, 3
+
+  Nests, removal of, for experiments, 181, 185, 190, 213, 214
+
+  Neutral feeding grounds, 62, 125
+
+  ---- ground, 98
+
+  Newton, E., on the arrival at breeding stations of males before female,
+    24, 35
+
+  Nightingale, 39, 156
+
+  Notes of alarm, 119
+
+  ---- of anger, 119
+
+  ---- of recognition, 139
+
+  ---- of warning, 119, 139, 141, 145, 151, 153
+
+
+  Offspring, rearing of, 3, 4
+
+  Organic change, sexual, 92, 123
+
+  ---- changes, 65
+
+  ---- condition of Reeve, 173
+
+  Owl, Wood, 156
+
+
+  Paired for life, 55-56
+
+  Parental instinctive response, failure of, 185
+
+  Partridge, 87, 218
+
+  Persecution, Carrion Crow and Magpie, 226
+
+  Persecution, Carrion Crow and Rook, 227
+
+  ---- House Sparrow and Martin, 218
+
+  ---- Lapwing and Snipe, 220
+
+  ---- Raven and Buzzard, 217
+
+  ---- ---- and Peregrine, 216
+
+  ---- Starling and Woodpecker, 218, 237
+
+  Persistency to remain in territory, 68
+
+  Pied-Wagtail, 86, 155
+
+  Pigeon, Wood, 219
+
+  Pipit, Meadow, 188
+
+  ---- Tree, 51, 188, 189, 222, 244, 278
+
+  Polyandrous females, 144
+
+  Predatory species, 268
+
+  Promiscuous pairing of Ruffs, 172
+
+  Proximity to food-supply necessary for rearing young, 179, 195
+
+  _Psychology, Manual of_, 1
+
+  Puffin, 63, 116, 200
+
+  Pugnacious instinct, 87-109
+
+  Pugnacity, 11, 62
+
+  ---- of females to obtain mates, 109-118
+
+  ---- of males, prior to mating-season, 77-81
+
+  ---- of Moor-Hen, 218
+
+
+  Racial preparation, 41, 43, 46, 67, 205, 206, 266
+
+  Rail, Water, 218
+
+  Raven, 48, 202, 216
+
+  Razor-bill, 63, 64, 200, 247
+
+  Readjustment of territory, 146
+
+  Rearing of offspring, 3, 4
+
+  Red-backed Shrike, 39, 50, 51, 156
+
+  Redbreast, 47
+
+  Redshank, 139
+
+  Redwing, 124
+
+  Redstart, 230, 244
+
+  Reed-Bunting, 28, 68, 69, 85, 104, 132, 156, 158, 160, 244, 246, 273
+
+  Reed-Warbler, 49, 51, 68, 81, 132, 140, 152, 153, 211, 225
+
+  Reeve, 171
+
+  Relation of song to the territory, 119-68
+
+  ---- of territory to migration, 259
+
+  ---- of territory to the system of reproduction, 169-214
+
+  Relationship to a territory, 169
+
+  Reproduction, 14, 15
+
+  ---- and territory, 169-214
+
+  ---- attainment of, 2, 6, 37
+
+  ---- goal of, 6
+
+  Ringed Guillemot, 64
+
+  Robbery of territory, 104-107
+
+  Rock-formation, suitability for Guillemots nesting on, 196
+
+  Rook, 202, 227
+
+  Routine behaviour, 262
+
+  Ruff, 54, 63, 172
+
+  ---- meeting places for conflicts, 54
+
+  Ruffs, promiscuous pairing of, 172
+
+
+  Savi's Warbler, 139
+
+  Sedge-Warbler, 25, 44, 152, 226, 244
+
+  Selous, E., on the life-history of Ruffs and Reeves, 172
+
+  ---- on meeting places for conflicts and antics, 54
+
+  ---- on the meeting places of Black Grouse, 63
+
+  Service, Robert, on flocks of unmated Sedge-Warblers, 44, 45
+
+  Sexual behaviour, 3
+
+  ---- conflicts, 10
+
+  ---- development, 6
+
+  ---- function, discharge of, 2, 3, 26
+
+  ---- impulse of females, 13
+
+  Sexual instinct in the migratory male, 26
+
+  ---- of Reeve, 173
+
+  ---- ---- reawakening of, 4, 18
+
+  ---- life of birds, 1
+
+  ---- maturity, males arrive at, before females, 36
+
+  ---- organic change, 92, 123
+
+  ---- selection, 166
+
+  Shag, 121
+
+  Shrike, Red-backed, 39, 50, 51, 156
+
+  Skylark, 188, 236, 244
+
+  Snipe, 153, 156, 219, 220
+
+  Sociability when not paired, 125, 126
+
+  Song, as an aid in searching for a mate, 12
+
+  ---- its influence on mating, 167
+
+  ---- origin of, 138
+
+  ---- relation to reproduction, 123
+
+  ---- relation to territory, 119-168
+
+  ---- volume of, influenced by age, seasonal sexual development,
+         or isolation, 166
+
+  Song-Thrush, 222, 244
+
+  Sparrow, House, 218
+
+  Sparrow-Hawk, 269
+
+  Spring, at approach of, birds lose their shyness, 138
+
+  Stability of the water and mobility of the land, 260
+
+  Starling, 217, 218, 237, 251
+
+  Stimulation, internal, 62, 123
+
+  ---- question of, 284
+
+  Stonechat, 87 187, 188, 189, 222, 233, 234
+
+  Stout, Dr, _Manual of Psychology_, 1, 77
+
+  Struggle for existence, 294
+
+  Susceptibility to position, 96
+
+  Swallow, 21, 156, 278
+
+
+  Territory, 1, 5
+
+  ---- adjustment of, 10
+
+  Territory and reproduction, 169-214
+
+  ---- breeding, 2, 3, 7
+
+  ---- dates of acquisition of, 33
+
+  ---- defence of, 6
+
+  ---- desertion of, after rearing young, 276
+
+  ---- disposition to defend, 73-118
+
+  ---- disposition to secure, 6, 20-72
+
+  ---- establishment of, 74, 285
+
+  ---- evolution of, 176
+
+  ---- failure to secure, 286
+
+  ---- fights for, 10, 11, 13, 62
+
+  ---- ownership of, 189
+
+  ---- possession of, a stimulus to song, 136
+
+  ---- its relation to migration, 259
+
+  ---- its relation to reproduction, 169-214
+
+  ---- readjustment of, 147
+
+  ---- restriction of, advantageous for mating, 172
+
+  ---- restricted, 8, 9, 30, 50, 58, 64
+
+  ---- separate for male and female Cuckoo, 144
+
+  ---- song, its relation to the, 119-68
+
+  ---- temporary desertion of, 28, 35, 58, 59
+
+  ---- and hostility, relationship between, 242
+
+  Thrush, Song, 222, 244
+
+  Tit, Blue, 221, 226
+
+  ---- Great, 221
+
+  ---- Long-tailed, 226
+
+  Tradition, 300
+
+  Tree-Pipit, 51, 188, 189, 222, 232, 244, 278
+
+  Turtle-Dove, 126, 232
+
+
+  Union of sexes, 12
+
+  Ussher, H. B., on the hostility between Choughs and Hooded Crows
+    and Choughs and Ravens, 227
+
+
+  Vocal Imitation, 156, 157, 161
+
+  Voice calls of Curlew, 263
+
+
+  Wagtail, Pied, 86, 155
+
+  ---- Yellow, 278
+
+  Wanderings from land, Guillemots, 193
+
+  Warbler, Garden, 223, 225, 230
+
+  ---- Grasshopper, 39, 131, 139, 155, 187, 244
+
+  ---- Marsh, 39, 40, 52, 81, 132, 140, 155, 156, 225
+
+  ---- Reed, 49, 51, 68, 81, 132, 140, 152, 153, 211, 225
+
+  ---- Savi's, 139
+
+  ---- Sedge, 25, 44, 152, 226, 244
+
+  ---- Willow, 25, 47, 50, 51, 80, 91, 140, 187, 211, 232, 244, 273
+
+  ---- Wood, 50, 51, 132, 221
+
+  Warfare between different species and its relation to the territory,
+    215-58
+
+  Warning notes, 119
+
+  ---- of danger, 269
+
+  Water Rail, 218
+
+  Wheatear, 25, 51
+
+  Whimbrel, 140
+
+  Whinchat, 39, 50, 51, 81, 222, 232, 233, 234, 244
+
+  Whitethroat, 25, 50, 68, 69, 124, 140, 182, 187, 189, 190, 213, 230,
+    244
+
+  ---- Lesser, 230, 244
+
+  Wild Duck, 250
+
+  Will, the, to fight, 102
+
+  Willow-Warbler, 25, 47, 50, 51, 80, 91, 140, 187, 211, 232, 244, 273
+
+  Winter assemblies, 262-63
+
+  Witherby, H. F., in _British Birds_, on the return to former
+    breeding-ground, 281
+
+  Wood-Owl, 156
+
+  Wood-Pigeon, 219
+
+  Wood-Warbler, 50, 51, 132, 221
+
+  Woodpecker, Lesser Spotted, 237
+
+  ---- Great Spotted, 237, 238
+
+  ---- Green, 20, 71, 156, 208, 218, 237
+
+  Wren, 244
+
+
+  Yellow Bunting, 28, 30, 47, 64, 140, 159, 162, 183, 187, 188, 189,
+    235, 236, 286
+
+  Young die in nest from exposure, 184, 185
+
+
+
+PRINTED BY OLIVER AND BOYD, EDINBURGH, SCOTLAND
+
+
+
+
+
+End of Project Gutenberg's Territory in Bird Life, by H. Eliot Howard
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