summaryrefslogtreecommitdiff
path: root/31987.txt
diff options
context:
space:
mode:
Diffstat (limited to '31987.txt')
-rw-r--r--31987.txt8532
1 files changed, 8532 insertions, 0 deletions
diff --git a/31987.txt b/31987.txt
new file mode 100644
index 0000000..997320e
--- /dev/null
+++ b/31987.txt
@@ -0,0 +1,8532 @@
+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
+
+*** END OF THIS PROJECT GUTENBERG EBOOK TERRITORY IN BIRD LIFE ***
+
+***** This file should be named 31987.txt or 31987.zip *****
+This and all associated files of various formats will be found in:
+ https://www.gutenberg.org/3/1/9/8/31987/
+
+Produced by Chris Curnow, Turgut Dincer, Joseph Cooper and
+the Online Distributed Proofreading Team at
+https://www.pgdp.net
+
+
+Updated editions will replace the previous one--the old editions
+will be renamed.
+
+Creating the works from public domain print editions means that no
+one owns a United States copyright in these works, so the Foundation
+(and you!) can copy and distribute it in the United States without
+permission and without paying copyright royalties. Special rules,
+set forth in the General Terms of Use part of this license, apply to
+copying and distributing Project Gutenberg-tm electronic works to
+protect the PROJECT GUTENBERG-tm concept and trademark. Project
+Gutenberg is a registered trademark, and may not be used if you
+charge for the eBooks, unless you receive specific permission. If you
+do not charge anything for copies of this eBook, complying with the
+rules is very easy. You may use this eBook for nearly any purpose
+such as creation of derivative works, reports, performances and
+research. They may be modified and printed and given away--you may do
+practically ANYTHING with public domain eBooks. Redistribution is
+subject to the trademark license, especially commercial
+redistribution.
+
+
+
+*** START: FULL LICENSE ***
+
+THE FULL PROJECT GUTENBERG LICENSE
+PLEASE READ THIS BEFORE YOU DISTRIBUTE OR USE THIS WORK
+
+To protect the Project Gutenberg-tm mission of promoting the free
+distribution of electronic works, by using or distributing this work
+(or any other work associated in any way with the phrase "Project
+Gutenberg"), you agree to comply with all the terms of the Full Project
+Gutenberg-tm License (available with this file or online at
+https://gutenberg.org/license).
+
+
+Section 1. General Terms of Use and Redistributing Project Gutenberg-tm
+electronic works
+
+1.A. By reading or using any part of this Project Gutenberg-tm
+electronic work, you indicate that you have read, understand, agree to
+and accept all the terms of this license and intellectual property
+(trademark/copyright) agreement. If you do not agree to abide by all
+the terms of this agreement, you must cease using and return or destroy
+all copies of Project Gutenberg-tm electronic works in your possession.
+If you paid a fee for obtaining a copy of or access to a Project
+Gutenberg-tm electronic work and you do not agree to be bound by the
+terms of this agreement, you may obtain a refund from the person or
+entity to whom you paid the fee as set forth in paragraph 1.E.8.
+
+1.B. "Project Gutenberg" is a registered trademark. It may only be
+used on or associated in any way with an electronic work by people who
+agree to be bound by the terms of this agreement. There are a few
+things that you can do with most Project Gutenberg-tm electronic works
+even without complying with the full terms of this agreement. See
+paragraph 1.C below. There are a lot of things you can do with Project
+Gutenberg-tm electronic works if you follow the terms of this agreement
+and help preserve free future access to Project Gutenberg-tm electronic
+works. See paragraph 1.E below.
+
+1.C. The Project Gutenberg Literary Archive Foundation ("the Foundation"
+or PGLAF), owns a compilation copyright in the collection of Project
+Gutenberg-tm electronic works. Nearly all the individual works in the
+collection are in the public domain in the United States. If an
+individual work is in the public domain in the United States and you are
+located in the United States, we do not claim a right to prevent you from
+copying, distributing, performing, displaying or creating derivative
+works based on the work as long as all references to Project Gutenberg
+are removed. Of course, we hope that you will support the Project
+Gutenberg-tm mission of promoting free access to electronic works by
+freely sharing Project Gutenberg-tm works in compliance with the terms of
+this agreement for keeping the Project Gutenberg-tm name associated with
+the work. You can easily comply with the terms of this agreement by
+keeping this work in the same format with its attached full Project
+Gutenberg-tm License when you share it without charge with others.
+
+1.D. The copyright laws of the place where you are located also govern
+what you can do with this work. Copyright laws in most countries are in
+a constant state of change. If you are outside the United States, check
+the laws of your country in addition to the terms of this agreement
+before downloading, copying, displaying, performing, distributing or
+creating derivative works based on this work or any other Project
+Gutenberg-tm work. The Foundation makes no representations concerning
+the copyright status of any work in any country outside the United
+States.
+
+1.E. Unless you have removed all references to Project Gutenberg:
+
+1.E.1. The following sentence, with active links to, or other immediate
+access to, the full Project Gutenberg-tm License must appear prominently
+whenever any copy of a Project Gutenberg-tm work (any work on which the
+phrase "Project Gutenberg" appears, or with which the phrase "Project
+Gutenberg" is associated) is accessed, displayed, performed, viewed,
+copied or distributed:
+
+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
+
+1.E.2. If an individual Project Gutenberg-tm electronic work is derived
+from the public domain (does not contain a notice indicating that it is
+posted with permission of the copyright holder), the work can be copied
+and distributed to anyone in the United States without paying any fees
+or charges. If you are redistributing or providing access to a work
+with the phrase "Project Gutenberg" associated with or appearing on the
+work, you must comply either with the requirements of paragraphs 1.E.1
+through 1.E.7 or obtain permission for the use of the work and the
+Project Gutenberg-tm trademark as set forth in paragraphs 1.E.8 or
+1.E.9.
+
+1.E.3. If an individual Project Gutenberg-tm electronic work is posted
+with the permission of the copyright holder, your use and distribution
+must comply with both paragraphs 1.E.1 through 1.E.7 and any additional
+terms imposed by the copyright holder. Additional terms will be linked
+to the Project Gutenberg-tm License for all works posted with the
+permission of the copyright holder found at the beginning of this work.
+
+1.E.4. Do not unlink or detach or remove the full Project Gutenberg-tm
+License terms from this work, or any files containing a part of this
+work or any other work associated with Project Gutenberg-tm.
+
+1.E.5. Do not copy, display, perform, distribute or redistribute this
+electronic work, or any part of this electronic work, without
+prominently displaying the sentence set forth in paragraph 1.E.1 with
+active links or immediate access to the full terms of the Project
+Gutenberg-tm License.
+
+1.E.6. You may convert to and distribute this work in any binary,
+compressed, marked up, nonproprietary or proprietary form, including any
+word processing or hypertext form. However, if you provide access to or
+distribute copies of a Project Gutenberg-tm work in a format other than
+"Plain Vanilla ASCII" or other format used in the official version
+posted on the official Project Gutenberg-tm web site (www.gutenberg.org),
+you must, at no additional cost, fee or expense to the user, provide a
+copy, a means of exporting a copy, or a means of obtaining a copy upon
+request, of the work in its original "Plain Vanilla ASCII" or other
+form. Any alternate format must include the full Project Gutenberg-tm
+License as specified in paragraph 1.E.1.
+
+1.E.7. Do not charge a fee for access to, viewing, displaying,
+performing, copying or distributing any Project Gutenberg-tm works
+unless you comply with paragraph 1.E.8 or 1.E.9.
+
+1.E.8. You may charge a reasonable fee for copies of or providing
+access to or distributing Project Gutenberg-tm electronic works provided
+that
+
+- You pay a royalty fee of 20% of the gross profits you derive from
+ the use of Project Gutenberg-tm works calculated using the method
+ you already use to calculate your applicable taxes. The fee is
+ owed to the owner of the Project Gutenberg-tm trademark, but he
+ has agreed to donate royalties under this paragraph to the
+ Project Gutenberg Literary Archive Foundation. Royalty payments
+ must be paid within 60 days following each date on which you
+ prepare (or are legally required to prepare) your periodic tax
+ returns. Royalty payments should be clearly marked as such and
+ sent to the Project Gutenberg Literary Archive Foundation at the
+ address specified in Section 4, "Information about donations to
+ the Project Gutenberg Literary Archive Foundation."
+
+- You provide a full refund of any money paid by a user who notifies
+ you in writing (or by e-mail) within 30 days of receipt that s/he
+ does not agree to the terms of the full Project Gutenberg-tm
+ License. You must require such a user to return or
+ destroy all copies of the works possessed in a physical medium
+ and discontinue all use of and all access to other copies of
+ Project Gutenberg-tm works.
+
+- You provide, in accordance with paragraph 1.F.3, a full refund of any
+ money paid for a work or a replacement copy, if a defect in the
+ electronic work is discovered and reported to you within 90 days
+ of receipt of the work.
+
+- You comply with all other terms of this agreement for free
+ distribution of Project Gutenberg-tm works.
+
+1.E.9. If you wish to charge a fee or distribute a Project Gutenberg-tm
+electronic work or group of works on different terms than are set
+forth in this agreement, you must obtain permission in writing from
+both the Project Gutenberg Literary Archive Foundation and Michael
+Hart, the owner of the Project Gutenberg-tm trademark. Contact the
+Foundation as set forth in Section 3 below.
+
+1.F.
+
+1.F.1. Project Gutenberg volunteers and employees expend considerable
+effort to identify, do copyright research on, transcribe and proofread
+public domain works in creating the Project Gutenberg-tm
+collection. Despite these efforts, Project Gutenberg-tm electronic
+works, and the medium on which they may be stored, may contain
+"Defects," such as, but not limited to, incomplete, inaccurate or
+corrupt data, transcription errors, a copyright or other intellectual
+property infringement, a defective or damaged disk or other medium, a
+computer virus, or computer codes that damage or cannot be read by
+your equipment.
+
+1.F.2. LIMITED WARRANTY, DISCLAIMER OF DAMAGES - Except for the "Right
+of Replacement or Refund" described in paragraph 1.F.3, the Project
+Gutenberg Literary Archive Foundation, the owner of the Project
+Gutenberg-tm trademark, and any other party distributing a Project
+Gutenberg-tm electronic work under this agreement, disclaim all
+liability to you for damages, costs and expenses, including legal
+fees. YOU AGREE THAT YOU HAVE NO REMEDIES FOR NEGLIGENCE, STRICT
+LIABILITY, BREACH OF WARRANTY OR BREACH OF CONTRACT EXCEPT THOSE
+PROVIDED IN PARAGRAPH F3. YOU AGREE THAT THE FOUNDATION, THE
+TRADEMARK OWNER, AND ANY DISTRIBUTOR UNDER THIS AGREEMENT WILL NOT BE
+LIABLE TO YOU FOR ACTUAL, DIRECT, INDIRECT, CONSEQUENTIAL, PUNITIVE OR
+INCIDENTAL DAMAGES EVEN IF YOU GIVE NOTICE OF THE POSSIBILITY OF SUCH
+DAMAGE.
+
+1.F.3. LIMITED RIGHT OF REPLACEMENT OR REFUND - If you discover a
+defect in this electronic work within 90 days of receiving it, you can
+receive a refund of the money (if any) you paid for it by sending a
+written explanation to the person you received the work from. If you
+received the work on a physical medium, you must return the medium with
+your written explanation. The person or entity that provided you with
+the defective work may elect to provide a replacement copy in lieu of a
+refund. If you received the work electronically, the person or entity
+providing it to you may choose to give you a second opportunity to
+receive the work electronically in lieu of a refund. If the second copy
+is also defective, you may demand a refund in writing without further
+opportunities to fix the problem.
+
+1.F.4. Except for the limited right of replacement or refund set forth
+in paragraph 1.F.3, this work is provided to you 'AS-IS' WITH NO OTHER
+WARRANTIES OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO
+WARRANTIES OF MERCHANTIBILITY OR FITNESS FOR ANY PURPOSE.
+
+1.F.5. Some states do not allow disclaimers of certain implied
+warranties or the exclusion or limitation of certain types of damages.
+If any disclaimer or limitation set forth in this agreement violates the
+law of the state applicable to this agreement, the agreement shall be
+interpreted to make the maximum disclaimer or limitation permitted by
+the applicable state law. The invalidity or unenforceability of any
+provision of this agreement shall not void the remaining provisions.
+
+1.F.6. INDEMNITY - You agree to indemnify and hold the Foundation, the
+trademark owner, any agent or employee of the Foundation, anyone
+providing copies of Project Gutenberg-tm electronic works in accordance
+with this agreement, and any volunteers associated with the production,
+promotion and distribution of Project Gutenberg-tm electronic works,
+harmless from all liability, costs and expenses, including legal fees,
+that arise directly or indirectly from any of the following which you do
+or cause to occur: (a) distribution of this or any Project Gutenberg-tm
+work, (b) alteration, modification, or additions or deletions to any
+Project Gutenberg-tm work, and (c) any Defect you cause.
+
+
+Section 2. Information about the Mission of Project Gutenberg-tm
+
+Project Gutenberg-tm is synonymous with the free distribution of
+electronic works in formats readable by the widest variety of computers
+including obsolete, old, middle-aged and new computers. It exists
+because of the efforts of hundreds of volunteers and donations from
+people in all walks of life.
+
+Volunteers and financial support to provide volunteers with the
+assistance they need are critical to reaching Project Gutenberg-tm's
+goals and ensuring that the Project Gutenberg-tm collection will
+remain freely available for generations to come. In 2001, the Project
+Gutenberg Literary Archive Foundation was created to provide a secure
+and permanent future for Project Gutenberg-tm and future generations.
+To learn more about the Project Gutenberg Literary Archive Foundation
+and how your efforts and donations can help, see Sections 3 and 4
+and the Foundation web page at https://www.pglaf.org.
+
+
+Section 3. Information about the Project Gutenberg Literary Archive
+Foundation
+
+The Project Gutenberg Literary Archive Foundation is a non profit
+501(c)(3) educational corporation organized under the laws of the
+state of Mississippi and granted tax exempt status by the Internal
+Revenue Service. The Foundation's EIN or federal tax identification
+number is 64-6221541. Its 501(c)(3) letter is posted at
+https://pglaf.org/fundraising. Contributions to the Project Gutenberg
+Literary Archive Foundation are tax deductible to the full extent
+permitted by U.S. federal laws and your state's laws.
+
+The Foundation's principal office is located at 4557 Melan Dr. S.
+Fairbanks, AK, 99712., but its volunteers and employees are scattered
+throughout numerous locations. Its business office is located at
+809 North 1500 West, Salt Lake City, UT 84116, (801) 596-1887, email
+business@pglaf.org. Email contact links and up to date contact
+information can be found at the Foundation's web site and official
+page at https://pglaf.org
+
+For additional contact information:
+ Dr. Gregory B. Newby
+ Chief Executive and Director
+ gbnewby@pglaf.org
+
+
+Section 4. Information about Donations to the Project Gutenberg
+Literary Archive Foundation
+
+Project Gutenberg-tm depends upon and cannot survive without wide
+spread public support and donations to carry out its mission of
+increasing the number of public domain and licensed works that can be
+freely distributed in machine readable form accessible by the widest
+array of equipment including outdated equipment. Many small donations
+($1 to $5,000) are particularly important to maintaining tax exempt
+status with the IRS.
+
+The Foundation is committed to complying with the laws regulating
+charities and charitable donations in all 50 states of the United
+States. Compliance requirements are not uniform and it takes a
+considerable effort, much paperwork and many fees to meet and keep up
+with these requirements. We do not solicit donations in locations
+where we have not received written confirmation of compliance. To
+SEND DONATIONS or determine the status of compliance for any
+particular state visit https://pglaf.org
+
+While we cannot and do not solicit contributions from states where we
+have not met the solicitation requirements, we know of no prohibition
+against accepting unsolicited donations from donors in such states who
+approach us with offers to donate.
+
+International donations are gratefully accepted, but we cannot make
+any statements concerning tax treatment of donations received from
+outside the United States. U.S. laws alone swamp our small staff.
+
+Please check the Project Gutenberg Web pages for current donation
+methods and addresses. Donations are accepted in a number of other
+ways including including checks, online payments and credit card
+donations. To donate, please visit: https://pglaf.org/donate
+
+
+Section 5. General Information About Project Gutenberg-tm electronic
+works.
+
+Professor Michael S. Hart was the originator of the Project Gutenberg-tm
+concept of a library of electronic works that could be freely shared
+with anyone. For thirty years, he produced and distributed Project
+Gutenberg-tm eBooks with only a loose network of volunteer support.
+
+
+Project Gutenberg-tm eBooks are often created from several printed
+editions, all of which are confirmed as Public Domain in the U.S.
+unless a copyright notice is included. Thus, we do not necessarily
+keep eBooks in compliance with any particular paper edition.
+
+
+Most people start at our Web site which has the main PG search facility:
+
+ https://www.gutenberg.org
+
+This Web site includes information about Project Gutenberg-tm,
+including how to make donations to the Project Gutenberg Literary
+Archive Foundation, how to help produce our new eBooks, and how to
+subscribe to our email newsletter to hear about new eBooks.
generated by cgit v1.2.3 (git 2.25.1) at 2026-01-17 01:04:12 +0000