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diff --git a/42739-0.txt b/42739-0.txt new file mode 100644 index 0000000..304520f --- /dev/null +++ b/42739-0.txt @@ -0,0 +1,3685 @@ +*** START OF THE PROJECT GUTENBERG EBOOK 42739 *** + + The Cambridge Manuals of Science and + Literature + + + + + THE MIGRATION OF BIRDS + + * * * * * + + + + + CAMBRIDGE UNIVERSITY PRESS + London: FETTER LANE, E.C. + C. F. CLAY, MANAGER + + [Illustration] + + Edinburgh: 100 PRINCES STREET + Berlin: A. ASHER AND CO. + Leipzig: F. A. BROCKHAUS + New York: G. P. PUTNAM'S SONS + Bombay and Calcutta: MACMILLAN AND CO., LTD. + + + _All rights reserved_ + + * * * * * + +[Illustration] + + + THE + + MIGRATION + + OF BIRDS + + + BY + + T. A. COWARD + + + + + Cambridge: + at the University Press + + New York: + G. P. Putnam's Sons + + 1912 + + * * * * * + + _With the exception of the coat of arms at + the foot, the design on the title page is a + reproduction of one used by the earliest known + Cambridge printer, John Siberch, 1521_ + + * * * * * + + + + + PREFACE + + + Any attempt to elucidate the problems connected with the + Migration of Birds must, in the present state of knowledge, contain + some theory and speculation, but the diligent observations of an + army of careful workers yearly add facts, which though they may + appear insignificant when considered alone, tend in the aggregate + to confirm or repudiate the conclusions of past workers. I have + endeavoured to bring together some of the more important theories, + and to give prominence to ascertained facts; I have also striven + to check desire on my own part to wander into realms of pure + speculation, though conscious that I have not always evidence to + support my suggestions. + + The numbers in brackets ( ) in the text refer to the books or + papers mentioned in the list at the end of the volume, which is in + no ways an attempt at a full bibliography. I have quoted freely + from the works of past and living ornithologists. To these I offer + apologies if I have misconstrued their arguments, and acknowledge + my indebtedness to those whose observations or writing have given + me light. In particular I tender thanks to Mr Wells W. Cooke for + his permission to reproduce the maps facing pp. 76, 78, 80. I have + found his writings and those of Herr Otto Herman and Mr W. Eagle + Clarke especially valuable. Mr Eagle Clarke's long looked-for book + on Migration is, as I write, still in the press; had mine been more + than a manual I should have hesitated to publish until his had + appeared. + + T. A. COWARD. + + BOWDON, CHESHIRE, + _4 November 1911_. + + + + + CONTENTS + + + CHAP. PAGE + + I. MIGRATION OF BIRDS 1 + + Definition--Variation of migration. + + II. CAUSE AND ORIGIN OF MIGRATION 13 + + Direction of passage--The potentiality of flight--Habit + of wandering--Memory--Extension of range--Influence + of Temperature--Desire for Light--Glacial Epoch--Food + Basis--Sexual Impulses--Competition. + + III. ROUTES 33 + + Route or Broad + Front--Coasting--Fly-lines--Isepipteses + --Land-bridges--Coast Lights. + + IV. THE HEIGHT AND SPEED OF MIGRATION FLIGHT 47 + + Altitude of Normal Migration--Variation in + Speed--Effect of Wind. + + V. ORIENTATION AND ROUTE FINDING 56 + + Route Finding--Use of Memory--Eyesight--Errors--Guidance + of Young--Beam Winds--Homing of Terns. + + VI. THE DISTANCES TRAVELLED BY BIRDS 65 + + The Swallow--Variation in Distances--Marking + Birds--Results--Routes of the Golden Plover--Evolution + of the Routes. + + VII. MIGRATION AND WEATHER 83 + + Knowledge of Approaching Weather--Favourable and + Unfavourable Conditions--Importance of Winds--Cyclonic + and Anticyclonic Winds--Continental Migration. + + VIII. THE PERILS OF MIGRATION 104 + + Contrary Winds--Lighthouses and Lightships--Leeward + Drift--Catastrophes. + + IX. EARLY IDEAS OF MIGRATION 114 + + Literature--Hibernation--Carriage of Small by Large + Birds. + + X. SUGGESTIONS AND GUESSES 119 + + Trans-Atlantic Migration--Ship-borne Wanderers + --Storm-blown Birds--Casual Wanderers--Swimming and + Walking. + + XI. SUMMARY 126 + + BIBLIOGRAPHY 131 + + INDEX 135 + + + + + LIST OF MAPS + + + FACING PAGE + + Map showing the range of the American Golden Plover, + with its known migration route 76 + + (From _The National Geographic Magazine_.) + + Map showing the evolution of the migration route of the + American Golden Plover 78 + + (From _The National Geographic Magazine_.) + + Map showing the evolution of the migration route of the + Eastern or Pacific Golden Plover 80 + + (From _The National Geographic Magazine_.) + + Map to show that a bird leaving Norway, near Aalsund, + might be carried round the British Islands in twenty-four + hours. The arrows indicate the actual directions + and force of wind at the times marked during a + slow-travelling circular storm in autumn 1901. + Speed of bird about twenty-five miles per hour 98 + + * * * * * + + + THE MIGRATION OF BIRDS + + + + + CHAPTER I + + MIGRATION OF BIRDS + + +Migration is the act of changing an abode or resting place, the +wandering or movement from one place to another, but technically the +word is applied to the passage or movement of birds, fishes, insects +and a few mammals between the localities inhabited at different periods +of the year. The wandering of a nomadic tribe of men is migration; +the mollusc, wandering from feeding ground to feeding ground in the +bed of the ocean, migrates; the caterpillar migrates from branch to +branch, even from leaf to leaf; the rat leaves the ship in which it +has travelled and migrates to the granary; we pack our goods, hire a +removing van and migrate to a new abode. The word migration thus applied +may be literally correct but it fails to convey the generally accepted +meaning, and the expression Bird Migration suggests periodical and +regular movement, the passage as a rule between one country and another. + +The popular application of a term does not do away with the need +of definition, especially as there are many complicated phases of +migration. The migration of birds is as a rule between the breeding +area or home and the winter quarters, but there are many migrants which +never reach breeding quarters in spring, and many others which leave the +regular breeding quarters or the place of residence in winter to perform +a very real migration under peculiar stress of circumstances. Again the +spasmodic movements of certain gregarious species, which at irregular +intervals change their location in large numbers to take up their abode +in another part of the range, is really migration, though it is now +usually described as irruption, incursion or invasion. + +Newton says (38) that bird migration is "most strangely and +unaccountably confounded by many writers with the subject of +Distribution," but the very act of the bird which extends its range, the +first step in distribution, is migration. The histories of present-day +distribution and migration are irrevocably interwoven; as Mr P.A. +Taverner remarks (51), "migration is a dispersal, and conversely, this +dispersal, as it manifests itself, is migration," whilst distribution is +the outcome of dispersal. + +Broadly speaking, all birds migrate, though the length of the journey +varies in different species, and in some cases in individuals of the +same or closely allied species, from the merest change of elevation to +a voyage almost as wide as the world itself. The sedentary red grouse +nests on the moors, often less than 1000 feet above the sea, but "when +snow-bright the moor expands" it feeds and resides in the cultivated +valley, and as shown by the committee appointed to study grouse disease, +not infrequently migrates from range to range across wide valleys. Many +tropical birds, usually considered non-migratory, are subject to short +movements, the origin and purpose of which is search for food and safe +nesting places. + +The knot breeds in countless numbers in Arctic Greenland and America, so +far north that only a handful of ornithologists have traced its home; +it travels south in summer so far as Damara Land. The Arctic tern has +a northern breeding range extending perhaps as far north as that of +any bird, and it has been taken far to the south of South America in +the Antarctic regions; if the thesis that the further north the bird +goes in summer the further south it travels in winter is correct, as +it can be proved to be with some species, some of these terns must +annually travel about 22,000 miles (21). Between these extremes are an +endless variety of distances travelled and methods of migration, with +striking differences in the performances of individuals of the same +species. Take one instance, a song thrush reared in a nest in our own +garden. We may see and recognise this bird up to the middle of July, +but what trained ornithologist can, yet, say with certainty where that +bird will be by the end of the month or in three to four months time? +We know that all through the winter there are some song thrushes near +the house, and that they are the birds which not only begin to sing +early but actually nest with us; we know too that before there is any +marked immigration of northern thrushes there is a recorded emigration +from our southern coasts, presumably of thrushes which have nested with +us, beginning towards the end of July; further we know that there is +an autumn immigration of Scandinavian or other northern song thrushes, +sub-specifically distinct to the expert eye, and some, small and dark, +whose origin is by no means proved, as well as later emigrations of +birds to the Continent or Ireland, both regular and occasioned by +exceptional weather. Will our young July thrush remain in England or +will it join one of these streams, and if so which? We do not know yet. +I repeat "yet," for the study of races, sub-species or local variations +is commanding more and more attention; the patient work of the +"splitters," scorned by the old school of "lumpers," will eventually +solve many of the problems of to-day. + +The ancients--a usefully ambiguous term--realised that birds migrated; +our immediate forefathers of two or three centuries ago realised that +certain birds vanished in winter and wondered how; and within modern +times the phenomena of migration, the "mystery of mysteries," has been +the subject of much study, speculation, and literary exposition. Indeed +a full bibliography of migration would be a considerable volume. Even +workers within the last few years have declared that certain phenomena +were beyond human understanding, only to be explained by instinct, a +word capable of most varied interpretation. In truth there is much to +learn, much to which we must still answer--we do not know; but the +speculative theory of yesterday is now either myth or fact, and the +theory of to-day may be proved true and add something to the data of +which knowledge is built. The wildest speculations, based on slender +locally ascertained facts or on no foundation whatever except the +fertility of the brain, have been offered as solutions of the mysteries; +the literature of migration is a jumble of contradictions. John Legg, in +1780, said "In relating so many instances of unparalleled credulity, I +confess I cannot suppress the irascible passion" (33), and Herr Otto +Herman, only a few years ago, pointing out the ingenious dogmas "void +of every firm foundation," says that "really it is a field in which +every thinking ornithologist may create new theses to any extent and +more or less incredible" (31). + +Herr Herman's system of "ornithophænology," the accumulation of +substantiated observations and facts, will not prove everything, but +his work in Hungary, that of Dr Merriam and Mr Cooke in America, and +of Mr W. Eagle Clarke in Britain, each aided by a numerous band of +careful workers, are striking examples of what can be accomplished. +Whatever errors future enlightenment may show in their conclusions their +ascertained facts will remain positive knowledge; theirs is not what +Herr Herman himself described as "pretended authority." + +In order to grasp the problems of migration it is necessary to get rid +of the puerile and insular aspect of the subject, namely that migrants +are merely those birds which come to us, like the swallow and cuckoo in +the spring, and those, like the fieldfare and brambling, which visit us +in winter but are not with us in summer. The complication of the subject +may be demonstrated by a rough classification of the migrants to be +observed in the British Islands. + +Arbitrary grouping of the members of an avifauna is only for general +convenience; many species are represented in more than one group. + +1. Permanent Residents: birds which remain in Britain all the year +round. These are comparatively few in number, and largely consist of +insular races of birds which perform regular and often long migration +journeys in other parts of their range. Most, if not all, perform short +migrations, in some cases only seasonal changes of altitude, spending +summer on the hills and winter in the lowlands; examples, the red grouse +and dipper. Others, like the tits and creepers are nomadic and more or +less gregarious in the colder months. Few appear to remain in the same +locality at all seasons, but possibly some of our British robins and +song thrushes, both sub-species of migratory Continental forms, may be +non-migratory. + +2. Summer Residents: birds which nest in our islands, leaving in +autumn for countries to the south, and return in spring. In addition +to the regular summer visitors, which all leave in autumn, this group +includes a number of wagtails, pipits, finches and other birds which are +represented in winter in our islands by a proportion which remain. + +3. Winter Residents: birds which nest to the north or east of our +islands and arrive in Britain in autumn, leaving in spring for their +breeding area. With birds like the fieldfare, brambling and jack snipe, +which do not nest in Britain, must be included many (for example the +robin, rook, song thrush and common snipe) which are also permanent +residents. + +4. Birds of Passage or Spring and Autumn Migrants: birds which neither +nest with us nor normally remain for the winter, but merely use the +British Islands as feeding and resting places on their journey between +the northern breeding area and the southern or eastern winter quarters. +This group is an especially difficult one, for in it must be included +such birds as dunlins and curlews, which are represented as breeding +species in Britain, and also a number of birds which apparently go no +further south than our islands in winter, and others which, though not +breeding, go no further north in summer. The actual status of these +individual birds is uncertain. In this group too we have the Greenland +wheatear, so closely allied to our familiar early migrant that, unless +the bird can be measured, its identification is uncertain. + +5. Irregular Migrants: birds which may be classed in other groups. +Some of these are really winter residents, but their visits are so +irregular that they may for convenience be classed with spasmodic or +occasional invaders, such as Pallas's sand-grouse, which arrive at +uncertain intervals in large numbers. Some of their number, during these +irruptions, usually breed and thus the bird becomes an irregular summer +resident or even, for the time, a permanent resident. + +6. Stragglers or Wanderers: birds whose occurrence in our islands is +more or less accidental, due apparently to their having lost their way +or to their ordinary wandering habits having taken them far from the +normal range of their species. Some of the rarer petrels and other +oceanic birds certainly pertain to this group, but our knowledge of +the migration routes of others is still so slender that it is unwise +to declare dogmatically that they are lost. Some too of the so-called +stragglers may have been artificially or accidentally introduced; many +"records" prove on investigation to be the aimless wandering of escaped +captive birds, whilst others are known to have been aided in their +journey and carried out of their usual course when resting on shipboard. + +When Mr Eagle Clarke was on the Kentish Knock Lightship, off the mouth +of the Thames, he found that in autumn there were continuing practically +simultaneously the following streams of migration. Immigration from +the Continent to England from east to west, and from south-east to +north-west, and passage along both lines; emigration from north to +south-south-west, and from north-west to south-east, with passage from +north to south-south-west. Birds of the same species actually crossed +paths, travelling in contrary directions (16). + +The above grouping applies to the British avifauna, but a somewhat +similar arrangement might be made of the birds of any particular area, +large or small. The grouping of birds for the study of Geographical +Distribution is of little consequence in connection with migration, +but the mapping of the world into various ornithological rather than +zoogeographical regions is of considerable importance, both for +convenience in tracing the ranges of migrants, and in the discussion +of the history of migration, which almost certainly began in the +form of short wanderings from the centres of distribution. It is of +comparatively small importance what boundaries we take for the various +regions; these depend largely upon the view of certain ornithologists as +to which groups of birds shall be considered as typical of the regions +in question. Sclater's six regions are perhaps the most universally +used. They are as follows:-- + +1. Palæarctic, embracing the whole of Europe and northern Asia. + +2. Ethiopian--Africa, Arabia, Madagascar and roughly half of the +Atlantic and Indian Oceans. + +3. Indian, including India, Further India, Southern China, the western +portion of the Malay Archipelago and the Chinese Seas. + +4. Australian, embracing Australia, New Guinea, New Zealand and the +southern Pacific. + +5. Nearctic, roughly America north of the Gulf of Mexico. + +6. Neotropical, America south of the Gulf. + +Newton suggested an alteration, a continuous northern region to be +called the Holarctic Region, which embraces almost the whole of +the Northern Hemisphere, and the division of the Australian into +Australian and New Zealand Regions. Each of these southern regions is +the winter home of some of the Holarctic birds, and it is a matter of +dispute whether many of these originated in the northern or southern +hemispheres. The value of these artificial divisions of the world is +rather in the consideration of the conditions their varied climates and +physical features present as attractions to birds in search of suitable +nesting places and food supplies. + +The study of Migration involves reference to the work of ornithologists +of the past and present, the mass of contradictory literature already +referred to, and we are repeatedly faced with the difficulty that some +particular theory about the vexed questions of the cause or origin of +migration, the height and speed at which birds travel, whether they +do or do not follow routes, how they find their way, in what order +they migrate, how and why they do or do not avoid dangers, or any +similar problem, which seems to give finality so far as certain cases +are concerned, is met by an absolute negation in other instances. The +truth seems clear; more than one factor has influence on most birds, +and different species in different places are influenced by different +factors. Elliott Coues' sweeping statement, though I strongly disagree +with the article in which it occurs, expresses much that is true. +"Isepipteses and magnetic meridians, coast-lines and river channels, +food-supply and sex-impulses, hunger and love, homing instincts and +inherited or acquired memory, thermometer, barometer and hygrometer, may +all be factors in the problem, good as far as they function; but none of +them, and not all such together, can satisfy the whole equation." + +Some of the theses may be laws or rules, but there are no rules without +exceptions, and these exceptions may become local rules. Laws regulating +migration in one area, whether it be the great continent of America, the +British Islands or the islet of Heligoland, may have little application +in other parts of the world: local evidence alone can never solve the +great problems. + + + + + CHAPTER II + + CAUSE AND ORIGIN OF MIGRATION + + +The question--What makes Birds Migrate? or what causes them to remove +from one zone to another at certain seasons, has been answered, no doubt +to the satisfaction of the respondents, in many varied ways. Closely +connected with the question of immediate impulse is the deeper, and less +easy to prove problem as to how migration originated. + +It has been dogmatically asserted repeatedly that birds invariably +breed in the most northerly part of their range, and winter in the +most southerly. Winter, when speaking of Holarctic birds, only applies +to the season in the northern hemisphere; the birds which pass south +of the equator winter in summer. Whilst accepting this as a rule, two +reservations must be made. First, that it only applies to birds of the +northern hemisphere, and secondly that it is a rule with exceptions. It +seems probable that the breeding area of some of the birds which reach +the British Islands in autumn by the so-called east and west route is +in more southerly latitudes than our islands, and certainly it seems +evident that the temperature of the winter refuge has more effect upon +the birds than its geographical position. Perhaps the statement that a +bird always nests in the coldest part of its range is more universally +correct. Even this may not be invariably the habit, but in acknowledging +it as a rule we must clearly understand that this cold district is +resorted to at the period of the year when its temperature is at its +highest. There are certain birds which breed in Australia and winter in +Oceanic islands where the temperature is cooler than in their breeding +area. + +When considering the migration of birds which summer in the extreme +north or breed in the extreme south--alas, but little is known about +the migratory habits of many southern breeders--it is comparatively +simple to offer an explanation; in the long winter months this home, +so desirable in the short weeks of daylight, is dark, ice-bound, and +foodless; it is wholly unsuited to the requirements of birds, which, +in spite of many assertions to the contrary, have never been proved to +hibernate, the only way in which animals can survive for any lengthened +period when food supply is entirely cut off. + +Birds are structurally provided with the means of escaping from the +disastrous effects of adverse circumstances; the power of flight, though +not the only way in which animals can migrate, is at the root of the +migration of birds. The advantages of the power of flight, to which also +it owes its development, include the ability to avoid active and passive +enemies, and to remove from one feeding ground to another undeterred by +the barriers which restrict the terrestrial animal. A natural sequence +of this ability to take advantage of aerial locomotion is the habit of +wandering in search of food, more or less noticeable in all birds. The +habit of wandering led to the discovery of feeding grounds and suitable +nesting places; where these nesting places, probably at first, only +removed a short distance from the parents' nesting site, were suitable, +dispersal and an extension of the distributional area or range of the +species followed; but where the feeding area was unsuited or not so +well suited to the needs of the species, hereditary attachment to the +original home and memory of the direction of this home, or even in some +cases accidental wandering back to the more suitable locality, would +originate a migration. Coupled with this are two important factors which +would tend to make the habit periodical and regular both as regards +time and locality. The memory of the bird, call it instinctive memory +if we like, would limit the wanderings in search of food to a certain +number of places where food was most abundantly found, and the passage +between feeding area and breeding area become regular journeys, at the +seasons of the year when an increasing number of young birds in the +breeding area drove the overgrown population to seek food further from +the base, and again when the sexual impulses urged the birds to seek +secure nesting sites. The other factor is the weeding-out influence of +mistaken effort, the natural selection which leads to the survival of +the fittest. The young wanderer which reached unsuitable lands must +either wander further or perish. Judging by the juvenile mortality +amongst young birds the failures would be many, and only the successful +competitors would return to leave progeny. + +Great stress has been laid on the attachment of birds to certain nesting +sites, an undoubted fact, and it has been argued that because, in some +cases, for hundreds of years certain sites have been occupied by the +same species, it is evident that after the death of parents the young +will return to and occupy the home. This has even been put forward as +evidence that birds do not wander in search of fresh nesting sites. The +argument is not sound. It is improbable that in most cases both parents +perish in the same year. Birds of prey, and many of the cited instances +of long tenancy refer to raptorial birds, have a wonderful power of +finding a mate, male or female, to complete the hatching and rearing of +the young, when one of a pair has been destroyed. The survivor of any +pair might have the home attachment and by bringing a fresh mate create +an attachment which would be passed on from mate to mate indefinitely. +Again it must not be overlooked that certain sites present advantages +to particular species which must be evident to all in search of those +advantages; it by no means follows that the occupiers of a nesting site +are in any way related, except specifically, to those which occupied it +in previous years. + +The answer to the argument that birds do not seek fresh nesting places +and thus extend their distributional area, is evident when we consider +those species which, at the present time, are extending their range. +Within the last few years, for instance, the turtle dove and tufted duck +have begun to nest regularly in many parts of England in which they were +entirely unknown twenty or thirty years ago. The starling has spread and +in some parts is spreading still, and many other similar cases might be +cited. + +In this manner migration, as we know it to-day, may have originated, and +as Mr P. A. Taverner expressed it, "however instinctive their habit may +now be, there must have been a time when migrations were intelligent +movements, intended to escape some danger or secure some advantage" +(51). Granting this, however, as the first cause, we are only on +the threshold; the question still remains unanswered, what actually +impels the birds to seek fresh food supplies or to look for safe nesting +places? The natural answer, the cravings of nature and sexual impulses +fails to give satisfaction in every case. Wanderings in search of food +might lead in any direction, and probably did in the first place, but +now birds in the main travel south in search of food and north in search +of home, and many of them perform immense journeys, passing over or +through lands which are capable of supporting a wealth of bird-life even +in the winter months. + +The majority of Arctic birds or those nesting in high latitudes leave +before the great harvest of autumn fruits, and even our common swift +begins to depart--for all do not go at once--towards the end of July, +when insects are more abundant than at any other time of the year. Food +supply has not failed when most birds start their journey in search +of food! Again in spring, when it is claimed that the powerful sexual +impulses are sufficient reason to account for the northward journey, +hosts of sexually immature birds and of others which are apparently +mature but do not breed that spring, migrate northwards, some even +arriving before the mature birds of their own species. + +The earlier students of migration insisted that temperature was the sole +cause of change of abode; that the northern lands became unsuitable +through their falling temperature, and that the birds deserted them for +warmer climes, returning when the lands they wintered in became too hot. +As a variant of this notion, which cannot be lightly cast aside, the +suggestion was mooted that it was not cold but the lack of food during +the cold months which drove them south, and that in the Tropics, where +at one time it was thought that all migratory birds wintered, food was +scarce during the months of extreme heat. Dr. Wallace went further and +stated that the incentive to northern migration was the inability to +find sufficient soft bodied insects suitable for the nestlings in the +Tropics during summer (54). Yet there are birds which do find food +enough for their young, and some of them are insect eaters. + +Seebohm, arguing with reason that the first home of the _Charadriidae_, +was the Polar Basin (44), suggests that the desire for light +originated the idea or the action, and though this was only applied +by him to Arctic birds, others have striven to show that the longer +hours of daylight would be an advantage to all birds, even though the +difference of dark and light in the zone retired from and in that +arrived at might be inconsiderable (41). Against this must be taken +into consideration the fact that many waders and ducks, northern +breeders, feed by night or day, according to the state of the tide. +Light is not an absolute necessity to them. + +The suggestion that migration owes its origin to the Glacial Epoch, +"that supposed solution of so many difficulties," to quote Mr Gadow +(28), has had many exponents. Some take for granted that the Polar +Regions were the original home, the centre of dispersal, of all northern +birds, and consequently that migration originated in the gradual pushing +back of avian life as the ice gained more and more land each year. +During the summer, the birds, urged by an irresistible love of home, +travelled as far north as the ice allowed them, but gradually they were +driven to nest further and further south until they found refuge in the +unglaciated parts of the earth. The individuals and the species, if not +the whole families of birds, which failed to retreat, went the way of +the "thousand types." On the retreat of the ice, the birds, impelled by +a mysterious hereditary memory of home and of the good times enjoyed by +their remote ancestors, for very very many generations must have been +born under more or less sedentary conditions during the Ice Age, began +the same pushing forward each year to the limits allowed them. In this +case they travelled nearer and nearer to the original home instead of +constantly being driven further from it. + +Surely the question of original home, at any rate of the home in +pre-Glacial days, may be entirely left out of the question. No one can +ever prove that this wonderful memory did or could exist. Post-Glacial +dispersal northwards, and the foundation of migratory habits of +advancing to the new food-producing areas, suitable also for the rearing +of young, was doubtless a fact, but would have taken place in any case. +The congestion due to the increased numbers driven to a restricted area, +would involve a rebound outwards, and the uninhabited areas northward +of the refuge would be the natural bourn towards which the birds would +travel. The seasonal return of cold would drive them southwards in +winter, and the periodical migration habit would thus be originated. + +The intense love of home during the spread of glacial conditions would +tend rather towards extinction than the formation of any new habits. +The birds which possessed the greatest attachment to the particular +district would be less likely to fly from adverse conditions, and the +reduction of their numbers through the ordinary physiological changes +in habit--reduction of the number of young produced, and possibly +disinclination to pair--would inevitably end in extinction. The stronger +the attachment to home the more likely the bird to remain to the bitter +end, and if driven away by increasingly severe winters, to return +and attempt to nest in the locality which had become unsuitable for +nesting. The spread of glaciation would be gradual and so would be the +annihilation of the species, but the end would be sure. + +Birds which are cited as species which have shown this remarkable +attachment to home, have disappeared before adverse circumstances--the +great auk and the Labrador duck. + +From what little we do know about the behaviour of our summer birds in +their winter home, we may safely conclude that their habits are similar +to those of winter visitors to Britain. Only in a few species are there +two restricted areas, two abiding places or homes. The necessity of +retaining a secure home for the young and the care of these young during +their more helpless age keeps the individual birds within a certain +area during the breeding season, but at all other times the bird is +more or less of a wanderer. The variation, however, of the wanderings +is remarkable. For instance the flocks of fieldfares, redwings, and +some of the finches which come to winter in the British Islands wander +continually from feeding ground to feeding ground, remaining in one +place only so long as the food supply is plentiful. When there is a +plentiful harvest of beech-mast, chaffinches and bramblings will linger +near one clump or avenue of beeches for many weeks, but when, as often +happens, the mast crop fails, they become nomadic, and pass from place +to place in their hunt for food. They visit fields top-dressed with +manure, glean the refuse of the harvest, frequent the farm-yards, and +in early spring, visit the budding larches to prey upon their insect +pests. On the other hand golden plovers and lapwings are remarkably +local in their winter habits, and so long as the weather remains open +will frequent the same fields throughout the winter. Severe weather, +especially snow, which effectually closes their chance of obtaining +food, at once drives them away. They will migrate to the unfrozen +mud-flats of the coast, or to those parts of England, generally the +south-west, and Ireland, where the climate is normally milder, or they +will even leave our islands altogether under great stress. + +The wandering habit, except during the breeding season, is confirmed in +most birds, and experience shows that the same species of birds visit +the same districts again and again when there is some particular food +supply to attract them. Memory and experience guide them from place +to place. This regular visitation of certain food bases, being of the +greatest importance to birds which have a long period of travel or +wandering before them, tends to originate the so-called route by which +they travel. The fact that as a rule these stages are in consecutive +steps southward is surely due to the fact that the temperature is +falling in the north more rapidly than in the south. That they are not +always due south is certain. The American golden plover, as Mr Wells +W. Cooke so lucidly demonstrates, at first travels eastwards from its +home in western Arctic America to the fruit-laden lands of Labrador +and Nova Scotia, where it feeds for some time, stoking up for its long +oversea journey due south. Mr Cooke says, "It can also be said that food +supplies _en route_ have been the determining factor in the choice of +one course in preference to another, and not the distance from one food +base to the next. The location of plenty of suitable provender having +been ascertained, the birds pay no attention to the length of the single +flight required to reach it" (21). During the evolution of the route +many bases would be found which were superior to others, and skipping +and the gradual shortening of the journey from one to another would +result. The final goal, the food base which in any weather or season +provides the safe sufficiency of food, having been reached by the birds, +this becomes the winter quarters. They return to this secure retreat +each winter, instead of aimlessly wandering in search of a better, and +thus the long-distance migratory habit is formed. Heredity tends to +confirm this and it becomes an instinct. + +Any observer may verify the assertion that birds regularly visit certain +favourable food-bases by paying attention to the occurrences of birds of +passage. The study of a county, for instance, shows that certain species +show partiality for particular localities. Thus in Cheshire goldeneyes +pass through every spring and autumn, and may be met with occasionally +on any of the meres; but at Oakmere, in the Delamere district, one may +be almost certain of seeing parties of this species any time during the +periods of passage. The curlew may be heard or seen passing over any +part of the county, but only in the Delamere fields do we frequently +meet with flocks feeding in inland Cheshire. Before the winter resident +golden plovers have arrived in autumn and after they have departed in +spring, the favourite fields are regularly visited by passing flocks, +and the lower reaches of the Mersey, where the common sandpiper is rare +as a summer resident, are visited every autumn by parties of birds on +passage. Chance may lead a casual wanderer to a good food-supplying +spot, but the regularity of appearance suggests habit and memory. + +A fact which supports the theory that birds ramble far in search of +food in their winter quarters, is that in many species the winter range +is more extensive than the breeding area. Thus Mr Cooke shows that the +known breeding area of the Pacific golden plover has an east and west +extension of some 1700 miles, but in winter it ranges over an area with +an east and west extension of about 10,000 miles. The scarlet tanager, +however, has a breeding range extending for some 1900 miles across +eastern Canada and a winter home in north-western South America of only +some 700 miles in extent. + +The winter quarters, or the outermost limits of the individual but not +necessarily the specific range, having been reached, the bird spends +its time in seeking food, remaining in one place if food is plentiful, +or wandering, according to necessity or the habit of the species. +The assertion that some birds have a second breeding season in their +southern home is either unsupported by any direct evidence or is the +result of a mistake in identification; the bird which has been found +breeding has in several instances been shown to be a southern form or a +related species of the one it was thought to be. + +As the northern spring approaches, the strongest of all animal +instincts, on which reproduction and the very existence of the species +depend, overcomes all other desires, and the bird grows restless. The +hereditary instinct, the origin of which we have endeavoured to show, +urges the bird to seek the breeding area which has by degrees become so +far removed from the winter quarters. The bird returns home. + +But here is a serious difficulty urged by some writers as a powerful +argument against the sexual impulse as the great factor in the return +journey. Many of the birds which migrate northwards or homewards are +sexually immature, and others of them are undoubtedly to be classed as +"non-breeders," which means that during that particular summer they will +not be engaged in the work of reproduction; why, then, should young +birds or non-breeders migrate from the winter base. Possibly in the +early days of migration only the mature birds did return; that we cannot +state one way or the other. But it is reasonable to argue that once a +regular migration habit has become not only confirmed by heredity but a +very true advantage to the species, its influence will be felt by each +and every individual. Again it is clear that the sexual impulses, in an +undeveloped form, are appreciated by the adolescent, and in many animals +by even the most juvenile. The play of all young animals is either an +imitation or reflection of the search for food--the hunting instinct--or +the love-making and sexual quarrels pertaining to reproduction, the +pretended competition by the young for the favours of the opposite sex. +They may play at and actually perform a migration which is so closely +bound up with the life of the species. That this impulse has not always +sufficient strength to force them to perform the whole journey is +apparent from the fact that many non-breeders, young or sexually mature, +on their northward journey through our islands or along our coasts, +never reach the breeding area; the food supply on the way attracts them +more than the memory of home; they linger with us until the breeding +season is over and the return journey has begun. Knots, sanderlings, +turnstones and many other waders may be seen on passage late in June, +and some remain on our mud-flats throughout the summer; in July the tide +of migration has turned. + +It has been suggested that some of the sexually mature non-breeders may +be actually enjoying their winter during our summer; in other words that +they have bred in southern breeding-stations whilst their congeners +wintered in the same zone. This means a double breeding-area for certain +species--a possible explanation, but one hardly supported by known +facts. When a bird had so cosmopolitan a range that in the course of +its dispersal its breeding areas were separated, we almost invariably +find that the birds inhabiting these two areas are distinguishable +geographical forms or sub-species. Mr W. H. Hudson, in his "Naturalist +in La Plata" refers to the godwit, _Limosa haemastica_, which spends +the southern summer in La Plata and breeds in the north, and to birds +of the same species which winter in La Plata, arriving from supposed +breeding places to the south when the northern birds leave. Captain R. +Crawshay, author of "The Birds of Tierra del Fuego," found it in this +little known land, but speaks somewhat doubtfully of its identity; we +shall probably learn that the southern form is sub-specifically distinct +from the northern. There are other wide-ranging waders which are +suspected of having a southern nesting area, but we still await proof. + +The lack of sufficient or suitable food in the winter home during our +northern summer may also cause the exodus, but this is a difficult point +to prove when it is remembered that the winter home of every bird is +not the parched tropical land or the waterless desert. From some zones +removal must be a necessity, but in others there is food for all, so far +as man can tell. + +Dr J. A. Allen, a severe but discriminating critic of migration +theorists, says--"Migration is the only manner in which a zoological +vacuum in a country whose life-supporting capacity is a regular +fluctuating quantity, can be filled by non-hibernating animals" (51). +When in the early days of migration this periodically-supplied northern +zoological vacuum was filled to overflowing by the increased numbers of +avian inhabitants at the close of the breeding season, the natural food +supply would be taxed to its limits; the falling temperature drove some +and finally all to seek food further south, and their short migration +to lands already filled with old and young birds, caused pressure and +overcrowding further south. Further outward and usually southward +movement was necessary and the zone of stress was gradually extended, +though probably in those early days no particular species took long +passages. The winter passed and the vacuum was again provided, and the +rebound to fill it would create a slackening force all along the line; +birds would spread from congested districts so soon as food supplying +areas opened to receive them. + +Mr Taverner, arguing on these lines (51), shows that competition +would be originated in areas containing the earliest breeders, and be +severest in the most productive districts. Weaker and later breeders +would be driven out or prevented from colonizing by the stronger and +earlier species, and the evicted ones would encroach on others, forcing +them in turn to trespass on a wider circle of species. He then argues +how the gradual recession of the glacial ice would increase the possible +northward breeding area, and cause longer migration, and that this +migration would delay breeding and conversely delayed breeding would +assist the evolution of migration. + +But the lengthening of the journey might surely be occasioned in +another way, and the evolution of migration assisted apart from any +glacial influences. Each successive increase of the length of the +journey taken by the stronger and more go-ahead individuals, leading +them in advance of the bulk of southward moving and competing birds, +would be a distinct advantage to the individual and consequently to the +species. The pioneer would arrive, like the slower movers, in a land +already peopled with an avian population, but it would not have its own +fellows to add to the stress of competition; it would be ahead of the +greatest struggle. So the fittest would mould for the species the most +suitable journey both in distance and route, and the laggards would +gradually fall out of the competition. + +Dr Wallace, without destroying these arguments, has shown that the +survival of the fittest has a powerful influence. Those birds which +do not leave the breeding area at the proper season will suffer and +ultimately become extinct, and the same will happen to those which fail +to leave the winter quarters when it would be a distinct advantage to +the species to move into lands better suited for reproduction. + +It has been put forward as a serious objection to many arguments that +migration, instead of being advantageous to birds, is a danger to the +race; that the perils of the journey are greater than those occasioned +by more sedentary habits. It has even been suggested that migration is +a habit specially created to thin down the surplus bird population. Dr +W. K. Brooks, however, puts this idea, which is not entirely devoid of +truths, in rather a different way. "Adaptations of nature are primarily +for the good of the species--beneficial to individuals only so far as +these individuals are essential to the welfare of the species" (9). +The destruction of overabundant young, the thinning down of superfluous +numbers, may be an economic advantage. It is one thing to say that +migration has been caused to kill off a surplus, and another to show +that, once a habit has been originated and become an advantage, it will +be conducive to a greater prolificness, and that the natural sequence +of an increased birthrate, when food supply and other conditions remain +unchanged, must be an increased mortality. Thus the perils of migration +may become a boon to the species. + +The theories of C. L. Brehm (7) and Marek that birds are living +barometers, foretelling by intuition the changes of barometric pressure, +may be dismissed as purely speculative. That birds begin their journeys +during particular barometric conditions is certain, but what they know +of forth-coming weather conditions is guess-work. + + * * * * * + + + + + CHAPTER III + + ROUTES + + +The migrating bird, when passing between the breeding home and the +winter quarters, travels by what is termed its Route. The definition of +the route has caused more controversy than perhaps any other incident +of migration; the chief point at issue is whether the bird uses a +particular high road, along which all its fellows from the same area +travel, or if all birds move in what has been called a "Broad Front." +Ornithologists have been, and to some extent still are, divided into two +camps, one upholding defined routes and the other the extended or broad +front movement. + +After all the difference is merely one of degree. Even the widest +notion of the broad front, that of Gätke, who insisted, as dogmatically +as he did on most points, that the width or breadth of the migrating +host corresponded with the extent of the breeding range (29), is of +a route, bounded on the one hand by the northern or eastern and on the +other by the southern or western lines of latitude or longitude which +marked the limits of the range. The idea of a route may be narrowed down +to the extent of a wide river valley, or to a fly-line represented on +a map by a ruled line, which passes over certain ascertained places. +The absurdity of Gätke's arguments are proved by the study of his truly +remarkable book. According to him the island of Heligoland was only +remarkable in that it possessed an observer, himself, who saw marvels +unobserved elsewhere, though the same number of birds were every year +passing over any particular spot in an area which, for many species, +must have been many degrees in extent. + +Had not so much weight been placed upon, and so many arguments based +on Gätke's extraordinary statements by, unfortunately, many of our +leading British ornithologists, his theories might have been ignored. +Unfortunately he is looked upon as an authority, even an oracle, +whereas, as Dr Allen pointed out, on many points which he treats with +great positiveness his knowledge is obviously as limited as the little +field which was the scene of his life-long labours (2). Glibly he +tells of hooded crows "in never-ending swarms of hundreds of thousands" +passing across and for many miles on either side of the island; of +"every square foot of the island" teeming with goldcrests, and of "dark +autumn nights" when "the sky is often completely obscured" by the +migrants, which pass thousands of feet overhead. How did he observe the +obscured sky? Indeed he again and again declares that migration passes +unseen yet calculates the numbers observed on the darkest nights; the +illumination of the lighthouse could not be sufficient to enable him to +even guess at the numbers he mentions. After stating that "the whole +vault of heaven was literally filled to a height of several thousand +feet with these visitors from the regions of the far North," and that +a certain east to west passage extended from the Faroes to Hanover, he +concludes that "the view--that migrants follow the direction of ocean +coasts, the drainage areas of rivers, or depressions of valleys as fixed +routes of migration can hardly be maintained." + +As emphatically he maintains that most observable migration over +Heligoland is due east to west or west to east, though the birdstuffer +Aeuckens, who supplied him with much of his information, told Seebohm +that it was north-east in spring and south-west in autumn (45). Is +it not perfectly evident that the geographical position of Heligoland +makes it a convenient resting place for large numbers of migrants, for +it is certainly true that large numbers are observed there, which pass +southward and westward along the Baltic, crossing Schleswig-Holstein and +the mouth of the Elbe, or coast south along Denmark, and cross the Elbe +diagonally, _en route_ for the Dutch and French coasts and to a lesser +extent the south-east coasts of Britain? + +Coasting undoubtedly exists; birds, day migrants especially, may be +observed following coast-lines in steady flight, though a mile or less +inland no passage is visible. On the North Norfolk coast I have seen +little parties of swallows passing along the shore in spring, coasting +slowly but steadily from east to west. All day long and almost every day +for more than a week this steady flight was continued, though I never +saw any passing within sight more than a few yards out at sea, nor any +at all more than a few hundred yards inland. Evidence which cannot be +refuted shows that this habit of coasting is general, though a deeply +indented bay, an estuary or strait, is usually crossed, and by no means +always at the narrowest point. The same careful observations prove that +both narrow and wide river valleys are followed by migrating birds in +greater numbers than are ever observed passing beyond the limits of +these valleys. + +Seebohm's experience in Siberia led him to doubt the existence of +routes, but his later studies of migration in autumn at Arcachon and in +spring at Biarritz, caused him to modify his ideas. He found a gentle +but continuous stream of migrants following the coast of the Bay of +Biscay, arriving from over the Pyrenees on their northward journey, but +moving "only within a mile or two of the coast." He contrasts island +and coastwise migration; in the latter the travellers can rest at night +or take short journeys during bad weather, but in the former they must +await favourable conditions before attempting a perilous passage (45). + +On the other hand many birds undoubtedly pass over inland localities +independently of any river valley or mountain range which might +indicate a route. Even such typical coast-lovers as the maritime waders +constantly cross or pass through inland England. They are heard at +night, or met with resting or feeding on inland waters, or their bodies +are found when, on a dark night, they have collided with telegraph or +telephone wires. + +So long ago as 1886 Mr W. Brewster maintained that the breadth of the +fly-line varied according to the character of the country which was +being crossed. The migrating column, he said, might be hundreds of +miles in length, "a continuous but straggling army," which only became +a "solid stream" when travelling through some narrow pass (8). This +solid stream or army passage is, however, seldom observed when the +birds are crossing continents, especially if they are traversing a wide +area in which food is equally plentiful for miles on either side of the +direction of flight. The consolidation of their numbers appears only to +take place when, either on account of the indifferent food-supply or of +unsuitable weather conditions, the speed is accelerated. + +In America Mr Cooke proves that the Mississippi Valley is undoubtedly +utilised as a fly-line by a large number of species, but by no means +all, and his evidence, though proving the use of routes, is that +these are seldom constricted pathways but broad areas crossed in a +generally coincident direction by the birds which make use of them. +This main fly-line is however formed in America as in other places by +the convergence of subsidiary streams, and it is these tributaries, +as Herr Herman points out, which have in many instances led to error; +they have been mistaken for main routes. The main route may be compared +to the trunk of a tree, the birds following the roots from the area +in which they have been nesting or wintering, and at the end of the +journey splitting off in various directions, like the branches, to their +temporary winter or summer homes. + +The contrast in the method of travelling of different species or of +the same species under different conditions, may be realised by taking +two examples. Firstly, Mr Eagle Clarke's experiences at the Eddystone +and Kentish Knock Lightship, when birds passed during the daytime at +varying elevations, sometimes close to the waves, in twos or threes or +scores, and at night in large numbers. The other is an observation of a +"bird wave" by Mr P. Cox, during a snow storm in 1885 at Newcastle, New +Brunswick. The birds passed eastward in a column about twenty-five yards +wide, some just above the trees, others hardly visible, but the bulk in +a massed column directly over the margin of the shore, and not over the +river or meadow on either side. The movement was continuous for about +two hours. + +Dr I. A. Palmén was the great upholder of routes in the Old World, but +his routes were largely speculative; they were founded on a considerable +knowledge of migratory birds, but not sufficient to cover the vast +area mapped out (39). Until a very large band of workers, working +on similar lines all the world over, accumulate a sufficient mass of +evidence as to which birds do or do not pass their various stations, +with the times at which they appear, accurate knowledge of the routes of +birds is impossible. + +Von Middendorf collected statistics of the passage of birds in the +Russian Empire, and by reckoning the average date of arrival of a few +species at certain points of observation, worked out a number of curves +or lines which he calls "isepipteses," or lines of simultaneous arrival +(35). The result was, according to his argument, a general convergence +northwards; the birds passing through Central Siberia travelled roughly +in spring from south to north, in Eastern Siberia from south-east to +north-west, and in Europe from south-west to north-east; they converged, +in fact, upon the Taimyr Peninsula. This to some extent is doubtless +true, but Middendorf goes on to prove that the magnetic pole is situated +in this Peninsula and that the birds are drawn thither by magnetic +influence, "in spite of wind, weather, night or cloud." He calls them +"sailors of the air," possessed of an internal magnetic influence. +He supports his argument by the statement that there is a similar +convergence in North America towards the magnetic pole of the western +hemisphere. + +But all birds do not go in the direction of the magnetic poles, and many +of those which do, stop short at suitable breeding places long before +they have travelled so far north. The Taimyr Peninsula, a vast area in +the extreme north of Siberia, is each spring a "zoological vacuum"; +towards this desirable spot migrants will stream. + +Herr Otto Herman cleverly shows the absurdity of many of the reputed +routes by cartography; his map is crossed in all directions by the +routes upheld by various theorists. Birds could not possibly follow all +the directions "which authors invented for them," most of which he adds +are founded on mere supposition (31). Dr Palmén, he shows, usually +managed to avoid districts where there were no observers, but Mr Dixon +and M. Quinet made their routes follow rivers and coast lines, whether +there was evidence to support this idea or not. + +Only to a certain extent can it be safely contended that the present +route of a species is an indication of its earlier journeys, or that +the direction of original dispersal is recapitulated in the present +line of migration. Heredity, experience, and imitation would certainly +tend to preserve and confirm the general direction; the shortest and +easiest passage from food-base to food-base would become an hereditary +route, unless circumstances arose which caused a change. Mr Cooke +shows how there has probably been evolution of the route as well as +of everything else concerned with a mutable animal. The fly-line +across an arm of the sea may be lengthened if this lengthening means a +corresponding advantage in reaching the desired haven. Thus the birds +which now cross the Gulf of Mexico at its widest part, at one time +probably coasted round the Gulf, as many do still, by the land-bridge +of Mexico and Central America. The gradual straightening of this curve +would shorten the journey both in time and distance, though lengthening +the actual single flight across a portion of the sea. We can imagine +a bird arriving in autumn at the mouth of the Mississippi, at first +passing from Louisiana to Mexico, so as to save the time of travel +through Texas. Generations later the shortening of the journey, through +lengthening of the short cut, would lead the birds to Vera Cruz and +later still to Yucatan. It may be questioned, what object could the +birds have in risking an oversea voyage, away from chance of food +and hope of rest, when the land-bridge remained open for them? Each +individual or group of individuals which arrived at any particular place +a little in advance of the migrating multitudes of its own species, +or others which fed upon the same kind of food, would certainly gain +advantage, and would be the most likely to develop strong flight and the +power of endurance in its descendants; it would indeed be a winner in +life's race. + +Great weight has been placed upon the use of land-bridges and the +hereditary habit of crossing seas where these land-bridges once existed +but have been submerged during the great geological changes in the +earth's surface. Many have insisted that wherever migrants cross the sea +they do so along submerged coast-lines or over submerged land-bridges, +arguing that the gradual evolution which has made the advantageous +adoption of a habit of migration possible was unable to eliminate +the hereditary tendency to follow the exact route by which their +ancestors passed from place to place. That there have been considerable +alterations in coast-lines and in the general distribution of land +and water since the time when birds began to be migratory is indeed +probable, but unless crossing the sea means a distinct advantage it +implies the retention of a habit which would not only be useless but +might be a positive danger to the species. + +In the Gulf of Mexico and the Caribbean Sea there is evidence of perhaps +the most recent land-bridge in the chain of islands from Florida to +Venezuela, collectively known as the West Indies. Although vast numbers +of North American birds winter in South America only a few of the +species which annually pass from one continent to the other make use of +this comparatively easy passage. One might naturally conclude that the +final severance of England from the Continent was in the neighbourhood +of the Straits of Dover, yet this short passage is only used by a +comparatively small number of our migrants. + +Mr Dixon indeed argued that there is no greater barrier to migration +than even a narrow arm of the sea (26). He refers to many Continental +species which are common breeders in France but are unknown as nesting +species in the British Islands, and others which are found in England +but not in Ireland. But this is surely but an incident of distribution; +the narrow strait or even river may for a time mark the limit of +expansion of a species, just as at the present time the westward and +northward unseen barrier prevents the range of the nightingale from +spreading to districts apparently well suited for its home, and until +recently the turtle dove and great crested grebe were checked in their +northward advance. + +In the evolution of some routes land-bridges certainty appear to have +played their part, but once those bridges have ceased to influence +direction the shortening of the time occupied by the lengthening of +the single oversea flight is only a question of generations when an +advantage to a species is to be gained. + +This subject will be further dealt with in connection with the actual +passages performed by certain birds. + +The study of migration, based on observations at our lighthouses and +lightships, shows that even in the comparatively small area of the +British Islands there are certain routes followed with regularity. The +birds which pass along our western coasts of England and Wales do not as +a rule follow the shores round Cardigan Bay or along the eastward tidal +scoop of the Irish Sea towards the coasts of Lancashire; the main body +passes from Pembroke to the Lleyn Peninsula, and thence to Anglesey and +the Isle of Man, on its way to the southern Scottish shores. + +A source of possible error in the method of deduction from these results +must be taken into consideration. The observations at lightships and +lighthouses are mostly made when untoward circumstances bring the birds +within range of vision, and on dark and foggy nights cause them to +strike the light in great numbers. What is their normal course when +no great migration wave or "rush" is observed? Are the few passing +stragglers noted all that go by this route in fair weather? The same +uncertainty must be applied to the observation of passing birds in +inland localities. The immense numbers which do pass is shown by the +observation of large movements, when as occasionally happens some +check to normal migration leads an army of birds to a dangerously low +altitude, or when high winds hold up a portion of the host on our +coasts; but even these multitudes must be small compared with the +millions of birds which annually pass from zone to zone unseen. The +few or many birds we meet with, either on the coast or inland, resting +on passage, may represent a lost or wandering party of stragglers or +weaklings from a vast army which has passed over; they may or may +not be on the route or course normally followed by the majority. The +cartography of bird migration is a study in itself. + +Mr Abel Chapman, describing his experiences in the Mediterranean, +says--"For forty hours we were passing across (or beneath) the lines +of an army of migrants--say 500 miles in width; yet not a sign did we +see, save only the wreckage--the feeble that fell out by the way." On +April 10th a sudden bitter northerly gale sprang up, and two hours later +the steamer was the goal of hundreds of birds, no longer able to face +the adverse wind. These were blue-headed wagtails, swallows, martins, +pipits, wheatears, nightjars, and lesser kestrels. He thinks that the +strong ones may have passed on but all the others perished (12). + + * * * * * + + + + + CHAPTER IV + + THE HEIGHT AND SPEED OF MIGRATION FLIGHT + + +In the last chapter reference was made to the great height at which +birds may fly on migration. Certain species, even comparatively +weak-winged ones, appear normally to fly high, whilst others, often +birds with pointed wings and great aerial powers, usually proceed at low +elevations; but there is still much conjecture as to the actual altitude +reached by any migrants. + +Gätke was of opinion that we do not see much of real migration, which +is certainly correct, but there is no reason for his statement that +it normally takes place at anything like the altitudes he mentions, +30,000 feet or more, or that birds at the time of migration undergo +physiological changes which enable them to fly at immense heights and +speeds and to see clearly in the dark (29). Nor need much weight be +placed on the speculation of Lucanus, who contends that the height +of travel must be less than 1000 metres, for above that elevation +aeronautical observations show that perspective lessens. There are +actual observations which, though liable to a margin of error, are proof +of migratory flight at very high altitudes. + +Most of these observations were at first made by accident; birds were +seen through astronomical telescopes passing across the face of the moon +or sun; but recently this method of observation and several ingenious +plans of measuring height and speed have been made use of expressly to +study migration. W. E. D. Scott, at Princetown in 1880, thought that +by shape and size he could even recognise two species, _Chrysomitris +tristris_ and _Quiscalus purpureus_, which passed across his field of +vision at a height of at least half a mile above the earth (43). In +1888 Mr Frank M. Chapman published an account of similar observations; +he calculated that the birds passed at distances varying from one to +five miles, and that their altitudes must therefore have been between +600 to 1000 feet, and 3000 to 15,000 feet. He adds an important note: +"A number of birds were seen flying upwards, crossing the moon, +therefore, diagonally, these evidently being birds which had arisen in +our immediate neighbourhood, and were seeking the proper elevation at +which to continue their flight," but the direction of flight of most of +the birds which were observed was parallel to the earth's surface and +southerly. The average height was certainly far above the inferior limit +(13). + +Mr F. W. Carpenter, reviewing these astronomical calculations, says +that Verey compared the apparent size of birds with lunar features, and +considering that the small birds noticed would average 6 inches in +length, calculated a height of 2000 feet above sea-level. At Detroit, +Winkenwerde obtained estimates of a little over half a mile, and R. A. +Bray, in England, saw birds crossing the sun in September 1894 which +were invisible to the naked eye and must have been 2 or 3 miles away +(11). + +In December 1896 Mr H. H. Clayton, at Blue Hill Observatory, saw ducks +flying at a height of 958 feet. He was at the time engaged in measuring +the height and velocity of clouds, and was able to estimate the speed +of the birds at nearly 48 miles per hour. In March geese passed at over +900 feet at 44.3 miles per hour. In 1905 Prof. Stebbins and Mr Carpenter +worked out a scheme for ascertaining heights by simultaneous observation +from different points. They based their calculations only on birds which +were observed by them both, and found that these passed at various +altitudes, ranging from 1200 to 2300 feet; in the following October the +lowest altitude observed was 1400 feet, and the highest 5400. Allowing +the 25 per cent possible error, these results are of great value. + +Mr Chapman's remarks about the upward flight of some of the birds are +enlightening, for when birds start on oversea journeys they frequently +ascend to a great height. Dr Allen and others think that the ascent is +to increase the visible distance, but it may also be to reach a zone or +stratum of atmosphere in which flight may be more easily accomplished. +Robert Service's account of the departure of migrants from the Solway +shores, gives suggestion of high flight. They arrive often one by one +and "seem to drop literally from the clouds," but when they actually +departed it was easy to see their method. They "fly upwards and onwards, +then they hesitate, fly sideways once or twice, again attempt an upward +and onward flight, hesitate again, and down they come once more to +earth." After repeating this manoeuvre several times, "away they go +over the sea." One morning he counted sixty blackbirds in one hedge, and +others kept arriving, but, however closely he watched, he failed to see +whence they came. "They came down from the upper air, becoming suddenly +visible, sometimes three at a time." "I saw about a dozen birds thus +drop into view, but I quite failed to see any indication of the point of +the compass from whence they had come" (46). + +Gätke frequently mentions birds raining down from the sky, appearing +first as mere specks, and dropping vertically to the island, and others +when departing "with breasts directed upwards and rapid powerful strokes +of the wings, fly almost perpendicularly upwards." + +On May 24th, 1911, I watched the departure of a spoonbill from Easton +Broad on the Suffolk coast. The bird rose and soared in ever-widening +circles until it was a mere speck, even when seen through powerful +prismatic glasses; the great stretch of its wings alone enabled me to +watch it for so long. When at a great height--I will not guess what +elevation--it ceased its circling flight and made straight for the north. + +In October I saw several flocks of redwings leave the Spurn. They rose +to a great height before directing their flight southwards, although the +Lincolnshire coast was plainly visible. + +Great differences of opinion have been expressed about the speed of +migrating birds, and here again Gätke's estimates, on account of the +weakness of his arguments and his immense presumption, cannot be +seriously considered. There are but few measured speeds, and most of +these, except perhaps the ducks and geese referred to already, are of +birds travelling at low elevations. + +Many birds, especially day-migrating swallows, hooded crows and other +birds, frequently travel at slight elevations; it is not unusual to +see birds at sea flying a few feet only above the waves. Mr W. Eagle +Clarke, whose systematic observations demand the profoundest respect, +again and again urges that the direction of the wind has little effect +upon migration, but that the force of the wind may make migration +impossible. At the Eddystone, where he spent a month in the autumn of +1901, he noticed birds passing at heights varying from 20 to 200 feet, +all flying southwards. He concluded that "the wind is certainly the main +factor in migration meteorology--I am convinced that the _direction_ of +the wind is, in itself, of no moment to the emigrants, for they flitted +across the Channel southwards with winds from all quarters" (16). When +the velocity of the wind, however, was above 28 miles per hour (a fresh +breeze, force 5 on the Beaufort scale), no migration was observed. + +Allowing this, and also taking into consideration the undoubted fact +that birds are frequently held up by strong winds on the shore before +starting oversea journeys, is there any proof that they do not actually +avail themselves of fairly steady strong winds when they reach the upper +air? + +Mr F. J. Stubbs makes some useful suggestions (50). He points out that +Gätke and others imagine that a bird flying with the wind would suffer +inconvenience through the wind ruffling up its feathers. It is surely +evident that a bird supported in a moving medium could not progress at +any slower rate than that medium; the bird is not flying on one stratum +of air with another moving with a different speed immediately above it; +it is actually in a current, not on it. If the bird flies at 20 miles an +hour, and the wind or moving air is progressing at 10 miles an hour, +the bird will cover a distance of 30 miles in one hour, though the force +exerted by the bird is the force necessary for 20 miles in a calm. +Conversely, if a 10-mile air current meets it, it will unconsciously +be carried only 10 miles. If the speed of the bird is the same as the +opposing force of the wind, it will remain stationary; I have seen ducks +in a blizzard rise head to wind and fly rapidly, making no progress but +maintaining their position over the water, to which they dropped again +when the storm passed. Some black-headed gulls on the same water did not +attempt this manoeuvre, and in a few seconds had vanished down wind. +The swimmer, in a swiftly-flowing river, may hold himself in position +so long as he can swim at the same rate as the stream he is contending +with, but he cannot make headway if the speed of the water exceeds his. +He may, however swiftly the stream moves, swim in any direction, but his +actual progress will be down stream; if he aims to swim directly across, +his real course will be diagonal. + +The fact that birds fly in any direction in a wind, and when at low +elevation pay little heed to the direction of the wind, when the breeze +is light, simply means that they can fly faster than the medium they are +in; if the medium travels faster than they do, they will be carried in +it to their advantage or disadvantage. + +Even in these days of upper-air investigation we really know very little +about the speed, direction and steadiness of upper-air currents, but +we do know that at a moderate elevation--some two or three thousand +feet--the strength is usually greater than nearer the earth. + +Mr Abel Chapman, in "Wild Norway," makes this pertinent remark--"Except +by aid derived from the operation of physical laws, the nature +and extent of which are unknown to me, and by taking advantage of +'Trade-wind' circulation in the upper air, I believe that migration is +impossible for short-winged forms of sedentary habits--but that aid, +and those advantages, may facilitate, and perhaps vastly accelerate, a +process which is otherwise impossible." + +In "Bird Life of the Borders" he goes further. "Birds are warmer-blooded +than ourselves or other mammalia, and are capable of sustaining life +in rarified atmospheres where these could not. By a simple mechanical +ascent, they can reach, within a league or two, regions and conditions +quite beyond human knowledge: where, selecting favouring air-strata, +they may be able to rest without exertion; or find meteorological or +atmospheric forces that mitigate or abolish the labours of ordinary +flight, or possibly assist their progress.... It is in the upper regions +of open space where, I suggest, the final clue will be found" (12). + +A warbler flying leisurely, say at 10 miles per hour, in a current of +air which was travelling at 20 or more miles an hour, could accomplish +the journey across the North Sea--say 300 miles, in ten hours. Allowing +much higher rates of speed for strong-winged species, and greater force +of wind, some of the marvellous distances covered by migrating birds +cease to be mysterious. Prof. J. Stebbins and Mr E. A. Fath made careful +calculations from observations with the telescope, and found that birds +passed at rates varying from 80 to 130 miles per hour, and these were +the minimums, for if the birds were not flying absolutely at right +angles with the line of observation, they must have travelled a greater +distance in the time occupied between their passage of the observation +points (47). + + * * * * * + + + + + CHAPTER V + + ORIENTATION AND ROUTE FINDING + + +The question, How do birds find their way? is answered by many ingenious +and often purely speculative theories, some of which have been already +referred to in connection with the points discussed. + +Each theory, though it may apparently explain certain phases of +migration, can be answered by some exceptional difficulty which makes +it fail as a full explanation; we are driven to the conclusion that +birds possess a sense of direction, which is often, very incorrectly, +called Orientation. Biologically this term does not imply any connection +with the East, but is simply used to describe the power of finding +the way back to a certain base, or of returning home. It is a power +or sense which undoubtedly exists in many vertebrate animals and in +some invertebrates, though it is hard, in many cases, to separate or +distinguish it from memory and impression gained through eyesight. Mr +John Burroughs, one of the strongest opponents of what he calls the +"Sentimental School of Nature Study," gives in his "Ways of Nature" a +striking instance of this faculty which may serve as an example, though +the cases of dogs and cats amongst domestic animals, and of many wild +creatures finding their way, could fill many volumes. His son brought +a drake home in a bag from a farm 2 miles away, and shut it up in a +barn with two ducks for a day and a night. As soon as it was released +it turned its head homewards, but for three or four days its efforts +were frustrated. Then Mr Burroughs decided to see what the drake would +do, and to go with it to give it "fair play." The "homesick mallard +started up through the currant patch, then through the vineyard towards +the highway which he had never seen," and Mr Burroughs followed 50 +yards behind. A dog scared the bird and turned it up a lane, but after +a detour it reached the road again; it stopped to bathe in a roadside +pool, then started off again refreshed. A lane, leading in the right +direction off the main road, puzzled it, and it took a wrong turning, +but, discovering its mistake, made for the road again, but not by +actually retracing its steps. The false move seemed to put it out, for +after hesitating at the next and right turning, it actually overshot the +mark. Its companion, unable to spare time to continue the experiment, +then headed it back, and when it reached the turning again it seemed to +recognise something familiar and raced home with evident signs of joy. + +The duck was a domesticated bird, but the incident is not without +interest; the homing faculty was clearly exhibited, but it was not +infallible; the bird made a mistake. So, inexperienced young birds, +travelling instinctively by orientation may, and do, make mistakes. + +Human beings, in varying degree, possess a sense of direction, and some +a wonderful power of finding their way in strange places; it is most +marked amongst those men we choose to call uncivilised, who, indeed, +live in closer touch with nature than those of us who depend so much on +compass, map, road, train and tram; we, as path-finders, are degenerate. +Middendorf marvelled at the powers of the Samoyeds, but when he +questioned them was met by blank surprise, and the cross-question--"How +does the little Arctic fox find its way aright on the great Tundra?" + +In addition to this instinctive power, the bird has eyes and brain. We +can afford to put aside as purely speculative Middendorf's suggestion +that the bird is impelled or dragged by magnetic force, but we cannot +deny that it uses its eyes and that it has a wonderful memory; its +second journey will be easier than the first, for it will recognise +landmarks, just as the drake recognised something familiar when it +neared home. Sight, however, cannot be always necessary, for, at the +Kentish Knock Lightship, Mr Eagle Clarke noticed that birds flew so low +along the water that they could not possibly have seen their way. + +It is purely speculative to say that the young bird which travels alone, +for it seems certain that many young do travel unguided on their first +journey, has an inherited memory of the actual route to be followed, but +that it has an hereditary sense of direction, or an hereditary impulse +to travel in a certain direction, is quite another matter. The sea, to +the young bird, may be a barrier; it may wander coastwise and be lost, +or, if this is the best way, find itself at the desired haven. If the +shortest and quickest way is across the ocean, the young bird may brave +the perils and succeed, or on this trackless waste it may wander till it +sinks to the waves and be added to the long list of failures. + +Certain species summer in Greenland either in the same areas or in +areas comparatively near to one another; some of these travel in autumn +south-east, and winter in Europe or Africa, and others go south-west +into the States or South America. Most of these are distinctly eastern +or western forms, but occasionally American birds are met with in +Europe, and European in America. Probably at the start these stragglers +joined the wrong band, and travelled for company and unconsciously by +the wrong route. Birds drifted to leeward may find companions of quite +an alien tribe; others, wind-swept in this way, may travel alone to new +lands. A few pelagic South Pacific and South Atlantic petrels and other +birds have reached Europe from time to time, but theirs is an error of +too wide nomadic wandering. The wonder is not that these stragglers do +turn up, but that so few are noticed; probably the frequent mistakes +made by inexperienced or even experienced birds are speedily rectified +by nature; failure to find food or exhaustion spells death. + +Mr C. Dixon emphatically declares that each party of young birds is +accompanied by one or more older ones to act as guides--"The many +winter'd crow that leads the clanging rookery home." This is as +emphatically denied by other observers. Probably there is no regular +rule for many species, as there certainly is not for swallows, in +which the old and young birds can be easily distinguished. I have seen +bands trailing south in autumn in which all the birds were immature, +and others in which a number of young were accompanied by a few mature +birds, though, certainly, these old birds did not appear to lead. +Another assertion, that the old and young do not even travel by the +same route rather supports the idea that the young birds find their way +simply by a sense of direction, a sense liable to blunder, whilst the +old birds travel by the perfected or best route which their experience +has taught them. Martorelli wisely asserts that orientation is not +infallible, but develops with age. + +Mach-Bruer attempted to localise this sense of direction in the +semicircular canals of the ear, which are so highly developed in birds, +but Dr Allen contends that the theory has been refuted by experiments +on pigeons. Möbius urged that birds were guided in their journey by the +direction of the roll of the waves; Newton replies that though this may +be a constant direction in certain parts of the Pacific, it is most +inconstant in the stormy North Atlantic (37). + +There is a very generally accepted idea that birds prefer to travel with +the wind striking them diagonally--the "beam-wind theory," a theory, +which so far as I can see, has absolutely no sound foundation. When on +the Kentish Knock Lightship, Mr Eagle Clarke noticed, on a bad day, east +to west migrants hurrying past "as if to avoid as much as possible the +effects of the high-beam wind." + +Mr A. H. Clark worked out the long oversea and overland course followed +by the American golden plover, and showed to his own satisfaction that +the birds always travelled at right angles to the prevailing winds; +therefore, he argued, they were guided by the beam-winds; always +keeping the wind on their flanks led them aright (14). He says that if +they fly at 100 miles per hour, with a beam-wind of 30 miles per hour, +they will reach a spot 100 miles from whence they started, but 30 miles +to leeward of a line drawn at right angles to the wind. Thus, if they +rely upon the wind, their course is more or less diagonally across it +according to its strength. He maps out the supposed route according to +prevailing winds, but fails to notice that the very route he maps may +be caused simply by the leeward drift when flying on winds which are +not with them. One portion of the journey is enough to illustrate what +I mean. From Labrador to the east of Bermuda the birds fly south-east, +so, he argues, as to cross the south-west wind at right angles. But +supposing the birds headed due south, meeting the south-west wind on +their right front, they would of necessity, if the wind was strong, +drift away to the east. It is improbable that they actually aim to +strike the Bermudas, for it is only during certain weather conditions +that they visit these islands. In favourable weather the birds do not +touch the Bermudas, but continue their flight direct to South America. + +The leeward drift of birds in a strong beam-wind may be noticed during +ordinary flight; it has occasioned one of the most remarkable of +Gätke's statements. Referring to hooded crows, he says--"To escape the +disagreeable experience of having the wind (south-east) blowing through +their plumage obliquely from behind, they turn their body southward, +and appear to be flying in this direction. This, however, is not the +case. They do not make the least forward progress to the south, but +their flight is continued in as exactly a westerly course, and with the +same speed, as though the birds were moving under favourable conditions +straight forwards, _i.e._, in the direction of the long axis of the +bodies. This is shown in the most convincing manner by such bands as +happen to pass immediately over the head of the observer. + +"Besides hooded crows, many other, indeed perhaps all species, are +capable of executing a laterally-directed movement of flight of this +nature, not only under such compulsory conditions as they may encounter +during the flight of migration, but also during the ordinary activities +of their daily life" (29). He admits that he once thought it was a +drift to leeward, but that he is now convinced that it is intentional, +and is sure proof of his East to West flight. In the face of such absurd +statements as these, how can anyone quote Gätke as an authority on +migration! Yet, in recently-published books, this east to west flight +across Heligoland to Yorkshire is stated to be a proved fact, though +Mr Eagle Clarke, so long ago as 1896, showed it to be unsupported by +British evidence. + +Dr Allen, reviewing Dr H. E. Walter's "Theories of Bird Migration" +(3), cites the following experiments as strong arguments in favour of +orientation. Dr J. B. Watson took fifteen sooty and noddy terns from +Bird Key, Tortugas, and liberated them at intervals after they had been +marked. The shortest distance was 20 miles from the Key, the farthest, +Cape Hatteras, 850 miles; thirteen returned to the Key. Neither sooty +nor noddy terns range, as a rule, north of the Florida Keys, so that +it is unlikely that any of the birds had been over the route before. +They could have gained no experience, or hereditary knowledge, and as +they were released during the breeding season, there would be no marked +movement southward which they might follow, nor would they at that time +be impelled by any desire to migrate. The change of direction from the +Florida Keys, westward, to the Tortugas, occasioned by the water course +which feeding habits would force them to follow, "removes the direction +of the wind as a guiding agency, whilst the absence of landmarks over +the greater portion of the journey makes it improbable that sight was of +service in finding the way." + + * * * * * + + + + + CHAPTER VI + + THE DISTANCES TRAVELLED BY BIRDS + + +Not only do the distances of the migration paths of different species +vary considerably, from a trip of a few miles to a voyage from the +Arctic to the Antarctic, but the individuals of one and the same species +do not all travel to the same degree. + +The familiar swallow, _Hirundo rustica_, though subject to certain +geographical variations, is found throughout the Palæarctic and Nearctic +regions, nesting throughout Europe to between 63° and 70° north and in +Africa north of the Sahara, where, however, Canon Tristram found it +also wintering in the oases. South of the Sahara to the Cape it is a +winter visitor. In Asia it breeds, according to Seebohm, in Asia Minor, +Persia, Afghanistan, and western Siberia, and winters in Scinde and +western India. One form breeds in and north of the Himalayas, eastward +to China and Japan, and winters in India and Burma, and another ranges +from eastern Siberia across Behring Strait throughout North America, +so far south as Mexico. This form winters in Burma, in Central America +and Brazil, but the Mexican birds are more or less stationary at all +seasons. + +Our swallow and its congeners have an almost cosmopolitan range, +summering in the Northern and wintering in the Southern Hemisphere or +comparatively near to the Equator in the Northern. Towards the centre of +its range its migrations are either short or the bird is non-migratory. + +Mr W. L. Sclater, addressing the South African Ornithologists' Union +(42), stated that the swallow arrives at Cape Town at the end of +October, and is common from November to March; practically all have +left by the middle of April. Swallows begin to arrive from the south +in Africa north of the Sahara in the latter half of February; early +in March they reach southern Europe, later in the same month they are +in Central Europe and by the middle of April large numbers arrive in +England. Thus swallows leave South Africa actually after they have +arrived in England; the South African birds cannot be the same which are +in North Africa a month earlier! The swallow supports Seebohm's thesis +that the individuals which go farthest to the south in winter, breed +farthest north. A day-migrant and by no means a rapid one, the swallow +may be timed from place to place, and it is not presumption to suggest +that the birds which reach Britain to nest came from lands little south +of the Sahara and well north of the Equator, and that those which pass +through England and along our shores in May and even June are on their +way from Southern Africa to the northernmost limits of their range. +Mr Sclater points out one very interesting fact; when the swallow +reaches South Africa it is in ragged worn plumage, before it begins its +northward journey it passes through its one annual moult. + +Waders and shore birds which reach South Africa in autumn--the spring of +the Cape--are moulting into winter dress; before they leave they have +often assumed or partially assumed the breeding dress. When they arrive +the native South African birds are breeding, but though Mr Sclater +thinks that some nest a second time in the south, no satisfactory +evidence has ever been brought forward to support the suggestion. +These long-distance travellers not only move from a zone of moderate +temperature to a warmer one, but many of them pass through the hotter +zone to a country having a similar temperature to the one in which they +bred, thus enjoying summer but not torrid heat all the year round. + +There are birds in which the northern and southern forms are distinct. +The wheatear, _Saxicola oenanthe oenanthe_, reaches us early, sometimes +during the second week in March, and speedily settles down to nest. +Towards the middle or end of April a brighter larger bird appears, the +Greenland wheatear, _Saxicola oenanthe leucorrhoa_, which was recognised +in Greenland, Iceland and eastern North America before it was seen +that both forms occurred in Britain. This larger bird loiters through +Britain, for its northern home is not ready for it until the Arctic +spring. We know it breeds farther north than our wheatear, but its +winter range is not fully worked out. The smaller bird is found in north +and north-western Africa, and the larger form farther east, even south +of the equator on the eastern seaboard, and probably, when we know more +about the range of the two we shall find that the form breeding farther +north, winters farther south. + +The folly of laying down the law on the strength of the knowledge of +the habits of a few species is shown by the study of the movements +of American birds. Mr Cooke shows that as a rule "the migration is a +synchronous southward movement of the whole species" in autumn, "the +different groups of individuals or colonies retaining in general their +relative position." The black and white creeper _Mnistitta varia_ breeds +from South Carolina to New Brunswick, nesting in the south in April and +reaching the northern limits in the middle of May. In the middle of July +old and young birds have been seen at Key West, 500 miles south of the +breeding range, and towards the end of August they have reached the +north coast of South America. The New Brunswick birds cannot be ready +to leave before the middle of July, and Mr Cooke allows them fifty days +for the trip, bringing them to the Gulf States in September; he argues +that this is proof that the earlier migrants must have been birds from +the southern part of the range. Black-throated blue warblers, _Dendroica +coerulescens_, reach Cuba at about the time that others of the same +species are arriving in North Carolina; the first, he concludes, are +birds from the southern Alleghanies and the others from northern New +England or beyond (20). Other species illustrate the same order which +he calls "normal," but show that it is not an invariable rule. + +Southern-bred Maryland yellow-throats, _Geothlypis trichas_, reside +throughout the year in Florida; those in the middle districts of the +range migrate for a short distance only, whilst the Newfoundland +birds pass over the winter home of their southern relatives to the +West Indies. The palm-warblers of the interior of Canada travel 3000 +miles to Cuba, passing through the Gulf States early in October; those +from north-eastern Canada travel later and slowly and settle in the +Gulf States, after a journey of only half the distance. He sums up +wisely--"No invariable rule, law, or custom exists in regard to the +direction or distance of migration.... Each species presents a separate +problem, to be solved for the most part only by patient, pains-taking +observation and by the recognition of sub-species." + +The order in spring is yet unproved. "With many birds ... the first +individuals to appear in spring at a given locality are supposed to +be old birds that nested there the previous year." These are followed +by those which nested a little farther north, followed later by those +whose homes are in the most northerly part of the range. "If, then, +for any species, the southern nesting birds lead the van in both fall +and spring migration, and the near guard in each case is composed of +northern breeding birds, it follows that some time between October +and April a transposal of their relative positions occurs; and that +the more southern birds pass over the more northern ones, which delay +their migration, knowing that winter still holds sway in their summer +dominions." It is not known where this transposal takes place, nor +whether the northern birds remain in winter quarters till the southern +birds have passed, or start a slow migration, during which the southern +birds pass over them. Later another transposal occurs; the northern +birds cross the southern part of the range, passing birds which are +already nesting. "Spring migration seems to be therefore for some +species a game of leapfrog--the southern birds first passing the +northern, and the northern passing them in turn" (20). + +The custom, now fortunately becoming widespread, of marking birds +by affixing a numbered metal ring to one leg, may help to elucidate +this and many other problems, but until a large number of results are +collected it is unwise to draw conclusions. Almost every month the +recovery of some of these marked birds is noted in the scientific +journals, but so far, beyond indicating the minimum distance travelled +by individuals, little can be proved. It is, however, plain that birds +do not invariably act as they ought to do if they obeyed all the laws +which have been invented for them. A few records or results may be +quoted, but any suggestions from these must be treated as suggestions +only; many more must be forth-coming before we can say, proved. + +The white stork, _Ciconia alba_, has been systematically ringed in +Rossitten in East Prussia, in Denmark and in Hungary for some years, and +Mr A. L. Thomson gives a brief summary of the interesting results up to +date, in "British Birds" for May, 1911. Ten young birds, taken during +their first autumn journey, show a general south-easterly trend through +Europe. Three east Prussian storks were obtained in Syria, one in the +April after it was marked, the other two in April and July of the second +year; another was taken in Palestine, and one Hungarian stork in Syria. +In the May of the year following that in which it was marked in Prussia +one was obtained at Alexandria. In their first autumn Prussian storks +have been recorded from near Lake Chad in October, from Rosaires on the +Blue Nile in the same month, and from the Victoria Nyanza at the end of +November. A ringed bird is reported from German East Africa, but full +details are wanting, but one shot at Fort Jameson in north-east Rhodesia +in December 1907 had only been hatched in Pomerania a few months before; +it left the nest on August 19th and began its journey south on or about +the 26th. In its first winter a Prussian bird was shot in the Kalahari +Desert. + +Seven Prussian and about a dozen Hungarian birds have been obtained +in winter quarters in the Transvaal, Natal, and other parts of south +Africa, and one in German south-west Africa; one, recovered in the July +following the summer in which it was marked, was possibly a weakling +bird which had failed to make the return journey. Storks which had +returned are recorded in their first, second and third summer; most of +them having been found within a few miles of their birthplace. One bird, +marked as a nestling near Brunswick in 1906 was reported in June 1908 +from Sorquitten in East Prussia, over 430 miles away. Mr Thomson, from +his reference to this being roughly in the same latitude but reached +by a different "line of flight," suggests that it is an exception; +this will be shown when some hundreds more cases have been collected. +It may, however, be found that some birds deliberately launch forth in +search of new homes, though at present it looks more like a bird which +on approaching the breeding area had banded itself with the wrong local +body of travellers. + +A bird marked at Cassel in western Germany has been recorded from +Barcelona in Spain; this so far single record may indicate that storks +get lost, that there is no regular direction, or that there is more than +one, a south-westerly as well as a south-easterly route. That too, we +hope, will be shown in the future. + +That much will be learnt from storks is evident, but the lessons will +be only general; each migratory species must be treated separately, and +to some extent this is being done. In the opening chapter I mentioned +the uncertainty about the behaviour of any individual song thrush, +merely as an example. So far, the few records of marked song thrushes +add to rather than solve this problem. Years ago the song thrush was +looked upon as a permanent resident so far as Britain was concerned. +Then it was found to be migratory even in Britain, and it was suggested +that each song thrush performed a short migration, southern British +birds leaving the country, northern British retiring to winter in the +south of England, and northern European birds replacing these as autumn +immigrants. The study of local races quickly altered this opinion; it +was guessed that in Britain there was a sedentary insular race and a +migratory passage race; others, however, saw that some of our home-bred +birds left in autumn. What do we find? A song thrush, marked as a +nestling in July in Northumberland, is found in November in Durham; +another one, marked in Berkshire travels to Norwich and is recorded in +November, but a third, born in Aberdeen takes an autumnal flight of at +least 1500 miles and is found in Portugal. Evidently we cannot yet frame +any rule for our British-bred birds. + +It is said that home-bred lapwings are somewhat sedentary, and that the +large winter flocks are composed of Continental immigrants. The frequent +westward migration of lapwings during exceptionally severe winter +weather has led to the supposition that these birds fly for refuge, +under these circumstances, to Ireland. This is true, so far as it goes, +but a lapwing marked as a nestling near Stirling has been found in the +south of France, and two others in Portugal, whilst five have been +recovered in Ireland. + +The results of marking sea-birds are interesting, showing that the +young birds often wander northward in search of food before there is +any marked autumnal southward migration. Terns and black-headed gulls +have been found a month or more after they have left the nest to the +north of their breeding colonies in Cumberland and mid-Wales. A bird +from Ravenglass was taken in its first January in Brittany. Rossitten +black-heads have been shot in the Isle of Wight and in Breydon in +Norfolk. + +This may only mean that the young blackhead is a confirmed wanderer +in search of food, but the few results with woodcocks, marked as +British-bred nestlings, are puzzling. They have been known to linger in +the neighbourhood of their home until November, and have been found in +Portugal only a month later. Birds marked at Tyrone have been found so +far apart as Cornwall, Harrow and Inverness; what route for the Irish +birds can be guessed at? + +Birds marked as adults present further problems, but also provide +interesting evidence. Hooded crows, captured on migration in spring at +Rossitten and then released, have been recovered in autumn actually +in the same place and in other localities in Germany, and one marked +in October was taken two years later, in spring, in Finland. The sum +of these records of crows proves one thing conclusively--the fallacy +of Gätke's due east to west and west to east flight, and supports a +coastwise migration for this species. + +Adult teal, captured in decoys, ringed and released in South Denmark +in September and October, were taken in November and December in +Hampshire, Suffolk and the Moray Firth, whilst others from the same +place were recorded from other parts of England and Ireland, from +western France, Holland, the south of Spain and the north of Italy. +Fly-lines, if followed, are divergent and complicated. Four young herons +were marked in one nest in Denmark; one was recorded in Holstein in +June, and another in Mecklenburg in July; the third was killed near +Salisbury in Wiltshire in October, and in the following February the +last was obtained in the north-west of France. Two from another nest +were recovered in Denmark, one in July and the other in February, twelve +months after birth. Another heron reached Andalusia by August. In each +case where there was indication of a direction it was south-westerly. +Many more records might be mentioned, but these are sufficient to show +the value of the method and the present insufficiency of results. + +Many of these records show that the speed of the migrating birds, even +in spring, is not great. Mr Cooke proves that most species in North +America travel slowly through the districts where food is plentiful +and during the earlier part of the journey northwards only a few miles +are covered per day; they travel with the slowly advancing vernal +wave, but, as we shall show in the next chapter, many species actually +outstrip it, and travel from warmer to colder climates. + + [Illustration: Map showing the range of the American Golden Plover, + with its known migration route. + + (From _The National Geographic Magazine._)] + +By the kind permission of Mr Cooke I am able to reproduce three of his +maps, illustrating the longest known distance travelled by any bird in a +single flight, and the probable evolution of this extraordinary oversea +voyage (21). This long journey, roughly 2500 miles at a flight, is +used in autumn by several species of American shore birds, and the +particular species most easily recognised, is the American golden +plover, _Charadrius dominicus_, which differs but little from our _C. +pluvialis_. An important point to notice is that the route followed in +the fall is not the one used by the bird in spring, an undoubted proof +that all routes are not identical with the original line of dispersal +of the species. Nor is the route directly from the north to the south, +though there is plenty of evidence to show the fallacy of the notion +that all birds move in this one direction. + +The golden plover nests along the Arctic coasts of North America from +Alaska to Hudson Bay. So soon as the young are able to take care of +themselves the birds migrate south-east to Labrador, where for some +weeks they fatten on the autumn harvest of fruits. A short journey +across the Gulf of St Lawrence brings them to Nova Scotia, where they +gather before starting on their oversea flight. The eastward trip to +the food-supplying districts is support of the idea that a route is +originated by passage from food-base to food-base, rather than by any +hasty rush from the dangers of approaching winter. The birds start south +from Nova Scotia for South America! + +During this long oversea journey, which Mr G. H. Mackay thinks, with +reason, may be undertaken under favourable conditions at a speed of from +150 to 200 miles an hour by birds with such magnificent power of flight, +the plovers may meet with many different winds. The Cape Cod sportsmen +look for them if the wind is strong from the north-east; the Barbados +gunners expect them when there is squally weather from the south-east, +but when westerly breezes are blowing they will pass so far as 400 miles +east of the Bermudas. Only when the wind is adverse and strong do the +plovers visit the Bermudas or even stop at any of the northern Lesser +Antilles, 600 miles from the coast of South America. In favourable +weather they neglect any of these "emergency stop-overs" and hasten on. +In the Guianas the birds rest and feed, but they soon move on. Across +the Brazils their actual route is uncertain, but they have been met +with in Amazonia, and are known to winter in Argentina, and, it is +suspected, in eastern Patagonia. + + [Illustration: Map showing the evolution of the migration route + of the American Golden Plover. + + (From _The National Geographic Magazine._)] + +The return migration is, so far as it is known, in a steady northerly +direction, rather north-west across Bolivia towards Central America. +From Yucatan they cross the Gulf to Texas, then slowly travel up the +great Mississippi highway and across Canada to their northern breeding +grounds. "Its round trip has taken the form of an enormous ellipse with +a minor axis of 2000 miles and a major axis stretching 8000 miles from +Arctic America to Argentina." + +The following is Mr Cooke's suggestion of the origin of this great +ellipse. Towards the close of the glacial era, when the ice began to +recede, the Florida peninsula was submerged and only a small area in the +south-east of the States was free from ice. Plover attempting to follow +up the retreating ice were confined to an all-land route from Central +America through Mexico to the western part of the Mississippi Valley. +As the east gradually became uncovered the route would be extended to +the north-east, until the area stretching to the Great Lakes was fit +for bird-habitation. As the route lengthened and the power of flight +developed, there would be a tendency to shorten the line by cutting off +some of the great curve (No. 1) through Mexico and Texas, and a short +flight across the Gulf (No. 2) would be gradually lengthened, until the +present spring route, then also the autumn route (No. 3), was attained. +As Canada opened out, the routes in spring and autumn diverged; in +autumn the fruits of Labrador were an attraction, but the Chinook winds +made the country east of the Rockies more suitable for spring migration; +the fall route tended eastward (No. 4), the spring route remained +unchanged. When the fall route had worked eastward to the Gulf of St +Lawrence (No. 5), shortening took place in the same way from the great +westward curve, culminating in an ocean flight, short at first (No. 6) +and later extended, the total distance shortened, until the present +route was attained (No. 7). + +This reasoning, sound enough, helps to a more difficult problem--how +the Pacific golden plover, _Charadrius fulvus_, found its way to the +Hawaiian Islands, where numbers of the birds winter annually. Roughly +the islands are 2000 miles from California, 2400 from Alaska, whence +the birds fly, and 3700 miles from Japan. Mr Cooke scouts the idea that +any bird flies aimlessly out to sea to find a new winter home, and the +chance colonisation by a storm-swept party is as improbable; if this did +occur it is hardly likely that they would at once depart, in a single +season, from ancient habits and carve out an entirely new migration +route. Probably the origin of the route is as follows. The bird breeds +on the northern shores of eastern Siberia from the Liakof Islands to +Behring Strait, and on the Alaskan side south to the northern base of +the Alaska peninsula. It winters on the mainland of south-eastern Asia, +in eastern Australia, and throughout the Oceanic Islands from Formosa +and the Liu Kiu Islands on the north-west to the Low Archipelago in the +south-east. + + [Illustration: Map showing the evolution of the migration route + of the Eastern or Pacific Golden Plover. + + (From _The National Geographic Magazine._)] + +It is fairly certain that the original route would be roughly north and +south, between Siberia and southern Asia. In time the species spread +eastward in winter, to Australia and to islands farther east, whilst the +breeding area extended to Alaska. If these extensions took place before +any cutting off of corners in the route, Alaska birds would travel +11,000 miles to reach the Low Archipelago, only 5000 miles in a direct +air-route (No. 1). Probably shortening began early among the Pacific +islands, from the northern islands to the Asiatic coast, and finally to +Japan (No. 2). From Palmyra the flight to the nearest of the Marshall +Islands is 2000 miles; thence a journey, provided with several possible +rests, of 3000 miles would bring them to Japan. A thousand-mile drift +through strong winds might cause the birds to reach Hawaii, whence they +would find a chain of islands which would help them, and render the +last flight to Japan no longer than the one they had been accustomed to. +Having once reached the Midway Islands the shortening of the route would +be carried on again by lengthening the oversea journey northwards until +the Aleutian Islands were discovered (No. 4). The present route, now +followed in spring and autumn (No. 5), would be the natural climax of +this long evolution. The two golden plovers, sub-specifically distinct, +nest little more than a hundred miles apart; their migrations and winter +homes are as different as they could be in any two widely divergent +species. It is one of the most striking of the ascertained facts in the +distribution and habits of birds. + + * * * * * + + + + + CHAPTER VII + + MIGRATION AND WEATHER + + +In previous chapters it has been necessary to refer repeatedly to the +connection between migration and meteorology; either the relation of +periodic movements to the rotation of seasons, or the influence directly +or indirectly of weather conditions upon normal and abnormal migration. +That there is an overruling relation between the advance of spring and +the passage to northern breeding quarters, and the gradual cooling in +autumn and the retreat to winter quarters is, of course, evident, but +it must not be held, as contended by the early students of migration, +that this is the sole factor which regulates migration. The actual +relationship between the weather and the movement of birds is far more +complicated than one would imagine, and the stimuli of continental or +overland travelling differ from those of a cross-sea flight. + +In the British Islands most of our larger movements are at their start +or their finish, or both (so far as our area is concerned), oversea +passages, and unless the weather be absolutely favourable, birds do not +undertake these voyages. No one has added more to our knowledge of +the connection, in what we may term British migration, than Mr Eagle +Clarke, but it must not for a moment be imagined that his conclusions +and the data from which he arrived at them are purely insular. The +British Islands are merely the field of observation, the centre of the +field, of the movements of Holarctic birds which travel regularly or +occasionally through Britain. Mr Clarke points out repeatedly that in +studying the phenomena it is the conditions at the point of departure +not at the point of arrival--generally the point of observation--which +are important. + +The oft-repeated assertion that birds can foretell the nature of +approaching weather--that they are living barometers--is not supported +by any satisfactory evidence, but it is certain that on many occasions +the weather into which they have passed in moving from one zone to +another has not only retarded, checked, or exhausted them, but has +proved fatally disastrous. During the westward rushes in winter, +when exceptionally severe weather has cut off the food-supply of +ground-feeding birds, observers who have seen the birds moving in +front of the storm have maintained that they had felt its approach and +retreated in time. The truth seems to be that the birds start so soon +as the supply is cut off but in many cases speedily outstrip the storm. +When these exceptional winter migrations take place the birds in the +lowlands of Lancashire and Cheshire move westward towards Ireland, and +are observed at different points along the North Wales coast. They are +sometimes seen travelling in a snow-storm and sometimes in advance +of it. In eastern Cheshire I have seen parties of lapwings passing +over westward just in advance of snow, which when it reached the East +Cheshire fields, started the local lapwings after their relatives from +farther east. + +During regular migration birds start in favourable weather but +frequently meet with unfavourable weather before their arrival at the +point aimed at; most of the bird "disasters" at the lighthouses and +lightships, and more occasionally inland, can be explained in this way. + +In his digest of the observations at lighthouses and lightships Mr +Eagle Clarke shows that spells of genial weather are favourable and +that during these spells migration is even flowing and continuous +(15). Slightly unsettled conditions have little effect, but an +increase of the irregularities accelerates migration. Sooner or later +cyclonic disturbances interrupt regular movements, and, if these are +extraordinary, act as barriers, either holding the birds in one place or +forcing a hurried departure or "rush." Favourable weather immediately +following a check or "hold up" often causes a rush; a sudden fall in +temperature may force large numbers of birds on in autumn or retard them +in spring. Temperature, he declares, is the main controlling factor +in all extraordinary movements, other meteorological conditions being +suitable. + +In the autumn migration to Britain, the chief movements take place when +a large and well-defined anticyclone has its centre somewhere over +Scandinavia, with gentle gradients in a south-westerly direction over +the North Sea. Coincident with this we usually find cyclonic conditions +prevailing to the west of the British area, with low-pressure centres +off the west or south-west of Ireland. The weather is clear and cold, +with light variable airs over Scandinavia, but in Britain the sky is +overcast, and the wind easterly and moderate to strong; not infrequently +these conditions mean fog on our eastern coasts. If the birds leave +Scandinavia under favourable conditions they may be met by the +approaching cyclonic system, which usually, though by no means always, +travels in a north-easterly direction across the Atlantic. Migration +is thus checked, but a return of favourable anticyclonic conditions +starts the birds again, often with a fresh impulse in the shape of +falling temperature. When the anticyclonic area is exceptionally +large, extending from the Scandinavian peninsula in a south-westerly +direction and embracing the whole of the British Islands, simultaneous +immigration and emigration may be witnessed. + +Cyclonic spells are not always unfavourable to migration. In spring, +when they are of a mild type with soft rain and warm winds following +after a cold anticyclonic period, a northward movement is frequent. + +Mr Eagle Clarke says that the importance of winds is overstated, but +as an incentive only. The direction of the wind has no influence as an +incentive but its force is an important factor; in a strong wind a bird +may be blown out of its course. Birds will not start in a high wind +but may pass into the influence of strong winds which may affect both +progress and direction. He adds that particular winds usually prevail +during the season of great autumn movements, which are not incentives +but are the result of pressure distribution which is favourable to +migration. These are usually north-east to south, but a westerly wind +would serve as well, but it indicates a pressure distribution which is +fatal to migration between north-west Europe and Britain--cyclonic areas +to the north-east and east of our area. + +All this, no doubt, is perfectly true. It is founded on the analysis of +a huge number of carefully recorded observations, and upon a general +knowledge of migration which few can ever hope to equal. Mr Clarke +understands his subject. It appears, however, to me that he may put +rather too much weight upon the barometric influence, and too little +on one side of the wind question. Are we yet in a position to say that +birds do not make direct use of certain winds? It may be that the use +of the prevailing winds at migration time is far more unconsciously +intentional (if such an expression can be used) than is at first +apparent. + +One or two points must be kept well to the front which are often ignored +by observers. Firstly, very much visible migration is abnormal; that +is to say, most of the incidents of passage which are noticeable, +especially observations at the lightships and lighthouses, are during +spells of weather which are described as unfavourable; it is the +"hold-ups," checks, and "rushes," which attract attention far more than +the even-flowing normal migration. + +Mr J. Tomison, in his valuable notes on observations made at Skerryvore +(52), shows that in ordinary clear weather birds pass at a great +height, beyond the power of vision. He proves this by instances of +the diurnal passage of redwings, birds which are generally supposed +to migrate at night, and undoubtedly do so frequently. He heard the +well-known passage-note in the daytime, but with the naked eye could +see no redwings; he found them with the telescope and later discovered +others which were passing above the range of normal vision. Mr +Eagle Clarke, commenting upon the extraordinary numbers of rare and +exceptional visitors which are noticed on many islands--Fair Island, +the Flannens, the Isle of May, and Heligoland may be taken as a few +examples--says that it is their detached position and comparatively +small size which makes these islands so useful to the observer. The same +variety of birds and greater numbers reach larger islands and tracts of +land, but they are unobserved when they are thinly distributed and not +massed or confined in a small area. "With all our great army of trained +observers," he declares, "we in Britain see only an infinitesimal number +of the migrants which visit our shores ..." and "this is especially the +case on the mainland." + +During an anticyclone there is a descending movement of air currents +from a centre of high pressure in all directions, and these currents +or winds are deflected "clockwise" in the northern hemisphere; and +when cyclonic conditions prevail the air currents are directed inwards +towards a low-pressure central area, rotating spirally at the surface +of the earth in the direction contrary to the hands of a watch. In the +southern hemisphere the directions are reversed. A cyclonic system is +usually carried forward by great drift winds like eddies upon a swift +stream, in the North Atlantic as a rule from south-west to north-east. + +Do we really know the force and direction of the winds at a high +altitude during these movements? Are we not merely guessing at the +real aerial conditions by the movements near the earth at the time +of the departure of the birds? Is it fair, if I am right that the +meteorological observations are founded upon only those observed at +comparatively low altitudes, to lay down laws as to the particular +conditions which are favourable or unfavourable, or the particular winds +which are used or avoided? The direction of the wind may be the same +up to a great height, many thousand feet, or it may vary within 500 +feet of the earth. Nearly fifty years ago, when Glaisher made his great +ascents, he sometimes met with three or four currents moving in opposite +directions. The more recent upper air investigations show that though +as a rule the wind at various elevations is in the main from one point +of the compass, its degrees vary considerably, and its force at the +various heights shows remarkable differences. Generally the force rises +to about 5000 feet, but there is no invariable rule. I tabulate a few +examples taken more or less at random from the Weather Reports for 1908. +The altitudes above the ground are measured in metres, roughly converted +into feet; the letters indicate the direction of the wind, the figures +its speed in miles per hour. The last one in the table, observations +made at Brighton on September 20th, is particularly useful. The +conditions on this date were anticyclonic, and favourable to migration. +At 400 feet above the sea the wind was blowing at 5 miles an hour; at +between 5000 and 6000 feet its force was 20 miles per hour. What then +would happen to a bird leaving Brighton for say the Spanish Peninsula? +If it flew at 20 miles an hour towards the French coast about Dieppe, +it would meet the wind blowing at 5 miles an hour, and take between +five and six hours to reach the coast, head to wind. If it rose to the +height of 3000 feet it would meet a wind blowing at the same speed as +it was flying, and it could make no headway. If, however, it flew in +a south-westerly direction the more it turned westerly the farther it +would drift down channel towards Normandy or Brittany, and be carried +out to sea! But this is exactly what would not have happened, for on +this date a feeble cyclonic system was approaching from the Atlantic and +extending its area of influence over southern England. In the Channel +the bird would meet westerly winds which would bring it safely to the +Brittany shores, or if it missed them, to the western shores of the Bay, +where the wind was actually from the north. I mention this merely to +show that apparently unfavourable winds may be really favourable. + +--------+-----------+--------+---------+----------+----------+----------+ + | | Ground |100 mtrs.|500 mtrs. |1000 mtrs.|1050 mtrs.| + Date. | Station. | Level. |(330 ft.)|(1660 ft.)|(3320 ft.)|(5000 ft.)| +--------+-----------+--------+---------+----------+----------+----------+ +Jan. 2 |Petersfield| NE by E| ... | ENE | E by N | E ½ N | + | | | | 30 | 50 | 13 | + | | | | | | | + " 2 | Glossop | E by N | ... | E | E by S | ... | + | 1100 ft. | 8 | | 15 | 30 | | + | | | | | | | + " 3 |Pyrton Hill| ENE | ... | E by N | E | ... | + | 500 ft. | 14 | | 35 | 53 | | + | | | | | | | + " 4 | " | NE by E| ... | ESE | E by S | E by S | + | | 10 | | 25 | 25 | 30 | + | | | | | | | + " 11 |Petersfield| S by E | ... | S | SW by W | SW by W | + | | | | 10 | 3 | 5 | + | | | | | | | +April 9 | " | SE | ... | N by W | ... | N ½ W | + | | | | 7 | | 20 | + | | | | | | | + " 8 | Glossop | N | ... | N by W | NW by N | W | + | | | | 9 | 16 | 7 | + | | | | | | | + " 30 | " | S | S by E | S | W by N | ... | + | | 14 | 27 | 30 | 46 | | + | | | | | | | +May 16 | " | WSW | W by S | W by S | W | W by N | + | | 16 | 26 | 27 | 29 | 33 | + | | | | | | | +Sept. 5 | " | WSW | W by S | W by S | W by N | W by N | + | | 12 | 15 | 17 | 21 | 23 | + | | | | | | | + " 7 | " | S by W | SSW | SSW | SW | ... | + | | 9 | 16 | 20 | 33 | | + | | | | | | | + " 10 | " | NW by N| NW by N | NW by N | NW | NW | + | | 8 | 16 | 21 | 34 | 36 | + | | | | | | | + " 20 | Brighton | ESE | SSE | S | SSE | SSE | + | 380 ft. | 5 | 5 | 15 | 20 | 20 | +--------+-----------+--------+---------+----------+----------+----------+ + +--------+-------------+------------+--------------+-------------+ + | 2000 mtrs. | 2500 mtrs.| 3000 mtrs. | 3500 mtrs. | + Date. | (6660 ft.). | (8320 ft.).| (10,000 ft.).|(11,660 ft.).| +--------+-------------+------------+--------------+-------------+ +Jan. 2 | ENE | NE | NE by N | NE by N | + | 23 | 22 | 18 | 25 | + | | | | | + " 2 | | | | | + | | | | | + | | | | | + " 3 | | | | | + | | | | | + | | | | | + " 4 | ESE | SE by E | SE by E | | + | 35 | 20 | 15 | | + | | | | | + " 11 | N by W | NW | NNW | N1/2W | + | 9 | 8 | 7 | 11 | + | | | | | +April 9 | N | NW1/2N | NW by W | ... | + | 14 | 9 | 12 | | + | | | | | + " 8 | NE | N by E | W by N | NNE | + | 6 | 8 | 8 | 9 | + | | | | | + " 30 | | | | | + | | | | | + | | | | | +May 16 | WNW | | | | + | 36 | | | | + | | | | | +Sept. 5 | W by N | | | | + | 28 | | | | + | | | | | + " 7 | | | | | + | | | | | + | | | | | + " 10 | | | | | + | | | | | + | | | | | + " 20 | | | | | + | | | | | +--------+-------------+------------+--------------+-------------+ + +--------+-------------+-------------+-------------+-------------+ + | 4000 mtrs. | 4500 mtrs. | 5000 mtrs. | 6000 mtrs. | + Date. |(13,320 ft.).|(15,000 ft.).|(16,700 ft.).|(20,000 ft.).| +--------+-------------+-------------+-------------+-------------+ +Jan. 2 | NE by N | | | | + | 23 | | | | + | | | | | + " 2 | | | | | + | | | | | + | | | | | + " 3 | | | | | + | | | | | + | | | | | + " 4 | | | | | + | | | | | + | | | | | + " 11 | E1/2N | E by S | E by NE | ENE | + | 8 | 14 | 13 | 14 | + | | | | | +April 9 | NW by W | W by N | | | + | 18 | 20 | | | + | | | | | + " 8 | NW | SSW | NNW | SW | + | 1 | 3 | 5 | 7 | + | | | | | + " 30 | | | | | + | | | | | + | | | | | +May 16 | | | | | + | | | | | + | | | | | +Sept. 5 | | | | | + | | | | | + | | | | | + " 7 | | | | | + | | | | | + | | | | | + " 10 | | | | | + | | | | | + | | | | | + " 20 | | | | | + | | | | | +--------+-------------+-------------+-------------+-------------+ + +Under ordinary circumstances are we justified in saying that birds make +use of the winds blowing with a certain force at the point of departure, +or that they ignore them? Certainly we cannot judge by either the force +or direction of the wind at the point of arrival, as Mr Clarke points +out. The bird may have dropped into most adverse currents. + +In Hungary, where migration has been very carefully studied, we find +evidence supporting Mr Clarke's theory, and yet giving it a slightly +different complexion. Low atmospheric pressure, depression (the warm +cyclonic conditions of spring) very often shows the greatest rate in +the arrival of the swallow. If there is a centre of depression west of +Hungary, and its path is directed north or north-east, swallows appear +in crowds. The fair side of the depression, with its warm southerly +winds, is therefore favourable. A list of twelve other birds, which also +appear in spring under these conditions in greatest numbers, is added. +The "bad" side, with cool northerly winds causes delays in the arrival +of these thirteen species. The depressions often have a sphere of +influence extending so far as North Africa, so that birds, on the fair +side, can cross the Mediterranean with southerly winds all the way (31). + +I have endeavoured to show that often the force of wind is greater +at a high than a low altitude, and there is ample evidence to prove +that birds fly at a great height when conditions are favourable. Birds +usually leave Scandinavia when there are descending currents flowing +outwards from the centre of high pressure; is it wild speculation to +suggest that it is the southward flowing currents, which are also +deflected westwards, upon which the birds intend to travel? Thus the +bulk of the Scandinavian birds might not touch Britain at all, but +those which started upon light to moderate north-east to easterly winds +from the western shores of Norway would be helped to Britain. Mr Clarke +mentions that when he was at Fair Island, north-west to westerly winds +did not stop migration from the north, but is it certain that the birds +did travel in or against these westerly winds? May they not actually +have travelled on the "good side" of the cyclonic system, with these +very winds carrying them towards Fair Island? their actual visible +approach from the north does not prove that they had travelled all the +way in this line. + +On September 22nd, he says--"The favourable meteorological conditions +of yesterday--fine weather and moderate south-east breezes,--has had a +marked effect, for to-day goldcrests are swarming everywhere." But what +does he mean? Favourable to him as an observer or to the goldcrests? +Surely the birds did not aim for Fair Island; were not these weak-winged +birds probably making for the south, when the south-east wind caught +them and drifted them to the west? Fair Island was a refuge, but hardly +the objective of their flight (17). + +Compare this with Cordeaux's notes of another goldcrest immigration, +this time to the Lincolnshire coast (23). On October 13th the wind was +north to north-east in the afternoon, light but increasing in force, the +weather clear and bright--a few birds arrived. They had started under +favourable circumstances. Shortly after midnight on the morning of the +14th, the wind got full east, with quite half a gale and heavy beating +rain, continuous to the morning of the 16th; the nights were very dark. +"During this time the immigration was immense," and most of the birds +were goldcrests. Cordeaux's idea that these were not normal immigrants +but birds which were passing probably from north-east to south-west, +when the easterly gale caught them, is probably correct. + +I have referred to birds starting at a high elevation. Service says +that in normal departure from the Solway, most birds mount to a high +altitude, but "a strong beam wind will bring the birds--even those of +strongest power--down to 200 to 500 feet of the surface, and it is +interesting to see whole flocks with heads turned almost completely to +wind, and yet travelling along at nearly their normal speed, at right +angles to their position" (46). Mr Tomison mentions rooks, daws and +hooded crows driven to Sule Skerry by south-east winds in March, leaving +two days later in a westerly gale. They, at any rate, did not object to +a strong wind which was in the right direction. + +I have mentioned Mr F. J. Stubbs' paper on the "Use of Wind" (50), +and I believe that there is much more in it than is actually proved by +low-level observations. I doubt if birds always intentionally make use +of strong winds, currents which would carry them for great distances +at a considerable speed, but the preliminary ascent may be to search +for these currents. Cyclonic and anticyclonic winds, even when at +an altitude of some thousands of feet, would carry them easily, and +probably it is the wind-borne individuals, parties, or even hosts, +which drop for a refuge to the first island they see when carried far +from their migratory path. They are carried rather than drifted from +their pathway, borne in the moving current whether they wish it or +not. Provided that the cyclonic winds are fairly steady in direction +and force, sweeping round and inwards towards their centre, we may in +imagination trace the pathway of our so-called lost wanderers to far +distant islands; without many more upper-air observation stations, we +cannot actually prove the route. + +But even putting aside the high altitude idea, and confining our +route-tracing to the known courses of air currents, we shall find +immense difficulty in mapping out the actual course of any bird on +any particular day. The study of some of the publications of the +Meteorological Committee, such, for instance, as the "Life History of +Surface Air Currents," by Shaw and Lempfert, published in 1906, shows +the great variation in the pathways, speeds, and formation of these +systems; a bird which accidentally entered a cyclone would unconsciously +alter its actual track and speed very many times before it passed beyond +the area of influence. + +I am indebted to Mr Stubbs and Mr Herbert Taylor of King's College, +London, for some interesting mathematically worked-out routes of birds, +travelling at a given speed in a cyclone rotating at given speeds and +moving at a fixed rate; these show great variation both in direction and +speed according to the time and place of entering the system. The track +of the bird is, of course, influenced by its own rate of progress, by +the speed of the rotating currents, and by the rate at which the whole +system moves in any direction. Thus a migrant passing south and coming +within the influence of a cyclone which is moving north-east at a high +rate of speed, say 40 miles per hour, will, if it enters towards the +northern limits of the system, be at first retarded by the conflicting + forces of the easterly winds, the trend towards the north-east of +the rapidly travelling cyclone and its own southward flight. If it is +flying faster than the speed of the cyclone it will drift westward but +gradually approach the low pressure centre. After passing this its +course will at once change and its speed will be accelerated towards the +east. + + [Illustration: + + Map to show that a bird leaving Norway, near Aalsund, might be + carried round the British Islands in twenty-four hours. The arrows + indicate the actual directions and force of wind at the times marked + during a slow-travelling circular storm in autumn 1901. Speed of + bird about twenty-five miles per hour.] + +Even violent storms move at varying rates, and it is conceivable that +a bird leaving Scandinavia on favourable anticyclonic winds might at +once come into the influence of a large, slowly-moving, circular storm, +with a low-pressure centre to the west of Ireland, and might, if the +air currents were strong, be carried westward at first, then south and +finally eastward, so that it would actually pass round the British +Islands. I have taken this exceptional case from the actual course of a +storm, which varied between forces 9 and II on the Beaufort Scale (say +an average of 50 miles per hour) but only travelled slowly eastward at +about 17 miles per hour. In some cases the storm centres are nearly +stationary for many hours. + +It is easy to appreciate Herr Herman's statement that spring immigration +in Hungary is accelerated on the good side of a mild cyclone; the +direction of the bird, of the circulating air currents and of the whole +system may be coincident. Given a low-pressure centre west of the Bay of +Biscay, spring migration would be accelerated through Spain and France +towards Britain. + +Mr Stubbs points out that the pathways of several birds, or parties of +birds, which started at different hours, would be divergent, for they +would come within the influence of winds blowing in various directions +according to the position of the system; this he argues is contrary to +the accepted idea of routes. This, however, entirely depends upon what +we mean by a route, as I endeavoured to show in an earlier chapter. The +journey from point to point is a route, although the bird may be drifted +many miles in one direction or another on the way; it is only when the +bird fails to reach its objective, a suitable breeding place or winter +station, that the route is a failure. + +The frequent occurrence of rare birds, some of them almost or quite +unknown elsewhere in Britain, on out-of-the-way islands, has led to +strange theories. One is that there are regular fly-lines over Fair +Island, the Flannens, St Kilda and elsewhere, similar to the one which +is said to pass over Heligoland. Mr Eagle Clarke's long expected book +will contain the ideas of the man who is best able to theorise on this +point; I write, now, with the feeling that his knowledge may lead me +to alter my ideas. The suggestion I can offer at present is that there +are ornithologists directing their attention to these spots which, +through geographical position and isolation, are the likely refuges +for wind-borne migrants. Also that the accidental departure from the +directions aimed at by the birds is, where wind and barometric systems +are so variable, far more frequent than is usually suspected. Direct +routes are doubtless aimed at, but only accomplished under favourable +conditions for the whole journey; migration is less infallible than we +have been led to think. It is, too, an evolving habit, strengthened by +those which survive its perils, now as it was in its early days. + +During a long overland journey, winds will probably have less influence, +though for rapid passages high flights certainly appear to be not +uncommon. There is, however, another aspect of the connection between +migration and weather which we have hardly touched, migration synchronal +to the change of season. Mr Cooke shows that in North America the push +forward in spring is not in most species so soon as the weather permits; +they do not actually move on the spring wave. Many warblers which nest +in the Great Slave Lake region in an average temperature of 47°, linger +in the Tropics, and reach New Orleans when the temperature is about +65°F. Then they hasten northwards, outstripping the advancing spring, +finding in Minnesota a temperature of about 55°, and 52° in Manitoba, +and gain another 5° on the season by the time they reach their home. +Thus they continually reach colder weather as they travel north. + +The American robin, _Turdus migratorius_, moves more sedately; it takes +seventy-eight days for its 3000 mile trip, whilst spring takes some ten +days less to cover the distance. But the individual robins may advance +more quickly; it is the robin as a species which takes this time to +cover the area of distribution. The isotherm of 35°F., corresponding +to the beginning of spring migration, advances north at the rate of 3 +miles per day from January 15th to February 15th; 10 miles a day is the +average for the next month, and 20 for the following month. But along +the eastern foothills of the Rockies, isotherms travel faster than in +corresponding latitudes farther east; spring rushes to this western +land. In mid-April to mid-June--the height of migration--the southern +portion of the Mackenzie Valley has about the same temperature as the +region of Lake Superior 700 miles farther south. This, coupled with the +diagonal course of the birds across the fast-moving region of spring, +exerts a powerful influence upon migration; the earliest robins reach +southern Iowa on March 1st, and travelling northward at about 13 miles +per day, find in central Minnesota a temperature similar to the one +they left. Those which breed near Lake Superior increase their speed +to a daily average of 25 miles, and arrive at latitude 52°, when the +temperature is still about 34°. The isotherm, however, has reached +central Athabasca, and the Mackenzie Valley and Alaska robins double and +quadruple their daily average on the north-west diagonal to keep pace +with the spring (19, 20, 21). + +Instances worked out in America and elsewhere might be quoted to show +how some species forge ahead and others lag behind the vernal wave. +Each species needs separate tracing in its routes and times and habits, +but on the whole the movements have relation to the changes in seasonal +temperature. In autumn the journey varies according to the time of +starting. Early fall migrants, and indeed the majority of autumn +migrants all the world over, travel more slowly than in spring; they are +neither impelled by sex-impulses nor the need to escape from failing +food supplies. A little later the supply does slacken and with it the +temperature cools, and if the changes are sudden southward migration +is accelerated. Migration, however, is such an advantageous and +well-established habit that it usually begins before hurry is necessary, +and the birds loiter southward, feeding as they go. + +Mr Cooke shows that in spring, weather seldom influences the start +from the winter home, but the _average_ weather conditions regulate +the _average_ rate of northward advance and the date of arrival at the +breeding home (22). + + * * * * * + + + + + CHAPTER VIII + + THE PERILS OF MIGRATION + + +The dangers to which migratory birds are subjected during their journeys +are but little less than those which would befall them if they remained +in unsuitable zones. During long oversea passages fatigue and hunger +weed out the weaklings, sudden storms and adverse winds strike them +where no land is near, and they are carried often far from the goal +they aimed at. Predatory birds accompany them, taking toll _en route_, +and predatory man waits for the tired wanderers with gun and net. Shore +birds may rest upon the waves; sandpipers have been seen feeding as +they walked upon the drifting weed of the Sargasso Sea, and steamers +and other vessels frequently provide a rest for weary birds; but what +happens to the many which find no haven? "Woe to the luckless warbler +whose feathers once become water-soaked!--a grave in the ocean or a +burial in the sand of the beach is the inevitable result," says Mr +Cooke. A storm on Lake Michigan during spring migration piled many +birds along the shore, and in the wider Gulf of Mexico many hundreds +of passage birds were seen to fall into the water when caught, but 30 +miles from land, by a violent "norther." Other similar sudden disasters +have been recorded off our British coasts, even so far back as 1786, +when, as quoted by Southwell, a Newcastle collier passed through water +off the Suffolk shores black with vast numbers of drowned woodcocks. + +During normal migration birds may be brought to a lower elevation by +strong contrary winds, or they may be bewildered by fogs and cloud and +dropped nearer the surface; it is then that the travellers meet with +disaster at our coastwise lights. + +Mr Tomison records some of his experiences of migration at Skerryvore +(52). He never saw a bird at the windows when the moon was shining, +and on clear nights the passing crowds go on without a pause. But on +hazy nights, with an easterly wind and drizzle, or during fogs, if +large numbers of migrants are passing, hundreds may be seen flying in +all directions, "all seemingly of the opinion that the only way of +escape out of the confusion--is through the windows of the lantern." +On one September night, when he was standing on the balcony, he likens +the appearance of the birds to a heavy fall of snow. "Thousands were +flitting about; hundreds were striking against the dome and windows; +hundreds were sitting dazed and stupid on the trimming paths; and +scores falling to the rocks below, some instantaneously killed, others +seriously injured, falling helplessly into the sea." On the following +night when many fieldfares, redwings, thrushes and other birds were +passing, he says--"Sometimes we use the terms hundreds and thousands +without thinking what these figures mean but on this occasion when I say +thousands were killed I do not exaggerate in the slightest." + +Mr W. Brewster's account of his experiences at the Point Lepreaux +lighthouse (8), shows that similar disasters occur in Canada and the +States, as indeed they do wherever there are passages of birds. On a +foggy evening in September 1885 "as soon as the sky became overcast +small birds began to come about the light--with the advent of the fog +they multiplied tenfold in the course of a few minutes" and many struck. +"About the top of the tower, a belt of light projected some thirty yards +into the mist by the powerful reflectors; and in this belt swarms of +birds, circling, floating, soaring, now advancing, next retreating, +but never quite able, as it seemed, to throw off the spell of the +fatal lantern.... Dozens were continually leaving the throng" of birds +which had flown to leeward, "and skimming towards the lantern. As they +approached they usually soared upward, and those which started on a +level with the platform usually passed above the roof.... Often for a +minute or more not a bird would strike. Then, as if seized by a panic, +they would come against the glass so rapidly ... that the sound of the +blows resembled the pattering of hail." During his stay no birds came to +the light except during dense cloud or fog, and they came in greatest +numbers when an hour or two before the fog the sky was clear. + +The experiences of Eagle Clarke, Seebohm and others who have spent +migration seasons at lighthouses might be quoted, but these two give a +vivid description of what regularly takes place when weather conditions +are unfavourable. Steady white lights are the most fatal to migrants, +revolving lights, if white, are struck by some birds, but red lights +seldom attract the passers. Mr Eagle Clarke thinks that birds are +actually decoyed from their path and arrested in their course by the +action of the lights; he says that a change from white to red lights at +the Galloper Lightship stopped bird attraction. + +On the mainland a new high building or tower, new telegraph wires or +other erections, until their presence is familiar, take toll of passage +birds. + +Mr R. M. Barrington has for years collected information from the Irish +lighthouses and light-vessels; some of his results were added to the +work of the British Association Committee, and some he published himself +(5). He emphasises the fact that these phenomena depend largely upon +weather, and therefore are not trustworthy indications of the density +at any time or place of migration. Out of 115 song thrushes killed at +the lights and sent to him, 80 per cent struck during the fourth and +first quarters of the moon, and the same rule holds good for other +species. The intimate relation between the lunar phases and the number +of examples killed was shown by statistics from 1888 to 1894. Out of 673 +specimens received only 116 were killed when the moon was more than half +full. + +Apart from fog or cloud, birds may fail to hit the land aimed at, either +through accidental divergence from correct direction or wind drift. In +November 1884 Mr Barrington received information of large numbers of +rooks passing simultaneously at the Tearaght and Skelligs Lights--island +stations 20 miles apart and each 9 miles off the Kerry coast. The birds +arrived in continuous flocks from the westward--the open Atlantic--and +passed in an easterly and landward direction; they came in small parties +and in flocks numbering two or three hundred, on many days between the +2nd and 25th of the month. A few birds were noticed at the same time at +stations on the south and east Irish coasts, and all alike making for +the land. From similar observations made in other years he concludes +that these were portions of hosts which had overshot the mark, and +failing to find land had turned back. The weather charts, he adds, +show no sufficient reason for the birds to have been blown out of their +course by storms. + +The weather charts, as I have pointed out, do not indicate the force +or direction of the wind at high altitudes; I suggest that these birds +were carried rather than blown out of their way by strong currents at a +higher altitude than recorded on the charts, and that having left the +air currents they descended to the elevation of about 700 or 800 feet at +which most of them were flying when they were observed making for the +land. + +On the night of March 29th to 30th, 1911, the south-eastern extremity of +Ireland experienced a remarkable rush of migrants, and the local papers +were full of the avian disaster, for large numbers of birds struck +the lights as well as buildings and other objects in inland towns. Mr +Barrington collected information (4), and found that most of the birds +were starlings, though thrushes, blackbirds, and redwings were numerous. +He received specimens of woodcock, water-rail, snipe, dunlin, meadow +pipit, wheatear, goldcrest, starling, song thrush, redwing, blackbird, +black redstart, robin, skylark, and stonechat, whilst some thirteen or +fourteen other species were said to have been recognised, amongst them +oyster-catcher and wild duck. The area affected lay south-east of a line +drawn across country from Balbriggan to the Old Head of Kinsale, with +a coast line of some 200 miles; most of the birds noticed inland were +at towns on the rivers Suir, Barrow, and Nore. The flight was mostly +north-east, and at the lights offshore, towards the land. Mr Barrington +gives the following explanation. After crossing the Channel the coast +of Wexford was reached and the stream divided, some going north along +the east coast and others westward along the south coast, but changing +their direction when they reached the wide mouth of the Barrow. The +flocks which passed Lucifer Shoals, 10 miles offshore, proceeded north +without touching Wexford. Northerly and easterly winds had prevailed for +weeks prior to the 29th over France and the British Islands, and birds +would be held up in southern Europe; the milder coastwise temperature +of western France, he thinks, would cause them to take a more westerly +course than usual. On the morning of the 29th the wind changed to the +south at Valentia, Pembroke and the Scilly Islands, and there was an +average rise of 7° in temperature at French stations. This rise and the +southerly wind liberated the birds, but as the wind continued north-east +or east in England they "decided" to take a longer and more exhausting +course than usual, pass to Ireland and then turn north-east. The change +took place exactly on the last day of the last quarter of the moon--the +darkest night for travel. A bank of fog and drizzle met them off the +Irish coast, and baffled and weary they were attracted by the lights, +not only on the coast but in the inland towns they passed. + +In the main I think Mr Barrington's explanation is correct, but even if +the birds were gathered farther west than usual, which I doubt, it was +the north-east wind which had drifted them, and the word "decided" is a +bold one to use when dealing with the behaviour of birds. Easterly winds +would drift them westward, and the striking Ireland was accidental; it +was the safety of the many, as well as the deathblow to the comparative +few. On the night of the 31st I received news of this visitation, and +later found that similar movements, without disaster, were noticed +on the north coast of Wales and in Cheshire. On the nights of the +30th and 31st birds in large numbers passed over Bangor and the Menai +Straits; amongst them were golden plover, and the next day these birds +with fieldfares and redwings were more abundant than before in the +mid-Cheshire fields. On the night of April 2nd, from dusk to midnight, +a large passage occurred over Mere in Cheshire, where curlew, golden +plover, oyster-catcher and wild duck were recognised by their calls, +and at the same time a passage was observed at Old Colwyn on the Welsh +coast. I do not even suggest that these were the same birds which passed +over south-eastern Ireland, but their presence within so short a time, +indicates the volume of the movement. + +Welsh papers recorded an "Extraordinary feathered catastrophe" at +Pwllheli in Cardigan Bay which occurred on the night of March 17th, +1904, in which "thousands" of birds fell dead and dying upon the town +and shore. The journalistic description was lurid, but I am able to +give the explanation sent to me by a friend who was an eye-witness. The +night had been dark and foggy, and in the morning he found "scores of +dead starlings, redwings, thrushes and blackbirds lying on the beach at +high-water mark." During the night a steamer had been loading setts at +the quarry at the Gimlet Rock, a large outcrop outside the harbour, and +the artificial light used had been one of the powerful oil flares. The +fog-bewildered birds were led astray and had struck masts, rigging, and +rock in their confusion. + +During a big fire in Philadelphia on March 27th, 1906, Mr W. Stone saw +large numbers of birds passing in its illumination, and many passed +too near and fell into the blaze; he picked up a few half-burnt song +sparrows and juncos. + +Blizzards on continents, and to a less extent snow-storms in our +islands, account for the death of thousands of travellers. And even +in most favourable weather birds fall exhausted. During a stay on the +Yorkshire coast in autumn, when migration was even-flowing and unchecked +by adverse weather, I found several goldcrests which had reached land +only to die, and though most birds came in without showing signs of +fatigue, a few larks and starlings were so tired that they made little +effort to escape when approached. + +Ornithological literature supplies many accounts of more or less similar +disasters to migrating birds, but these are enough to show that the +perils of migration are not exaggerated. + + * * * * * + + + + + CHAPTER IX + + EARLY IDEAS OF MIGRATION + + +The evolution of the study and knowledge of migration is an interesting +subject, dealt with more or less completely by several writers. In a +manual it is impossible to treat it fully. That the Greek poets--Homer +and Anacreon for instance, and the writers of Jeremiah and Job, knew +something about the regular movements of birds is evident, nor is it +surprising that in lands like Greece, Egypt and Palestine the passage of +birds should be noted and directly connected in the popular mind with +the seasonal changes. + +In a measure similar observations and conclusions may be traced in +the history or traditions of most peoples, but in a northern detached +area, such as the British Islands, there is a marked tendency to +overlook passage and note only arrival and departure, mostly of summer +birds. Early observers noticed the swallow and cuckoo when they had +actually come, and missed them when they had gone, but they failed to +grasp whence they came or whither they went. Interchange of ideas with +inhabitants of other lands was limited, and few early travellers were +philosophers, at any rate so far as migration was concerned. In Germany, +however, the Emperor Frederic II. realised in the thirteenth century +many truths concerning migration (27), but in Britain uncertainty or +myth held sway until the end of the eighteenth century. Herr Herman, +reviewing the variation in thought, says--"But as in other fields, this +period is followed by a time of decadence, a natural consequence of +departing from immediate experience." + +British, and many Continental observers too, saw when birds had come +and in autumn that they had gone. Early swallows and martins were +always met with near water, and were watched dropping to roost in the +reed beds, as they always do in autumn before departure. Next morning +none was visible. Certainly then they had vanished to hibernate in the +water. The discovery of masses of torpid swallows, dead or dying, by +no means an unknown thing when birds are overtaken by sudden falls in +temperature in autumn or by a severe setback in the spring, was to these +puzzled men confirmation of their theory of hibernation. Other details +of the many stories of swallow hibernation are due to exaggeration or +to misconception. In the second half of the eighteenth century a fierce +discussion waged for and against hibernation, and many, including +Geoffroy St Hilaire and Montagu, sat on the fence, admitting that it +might be possible with some species and probably was with swallows. +Later some Americans produced "evidence" in favour of avian hibernation, +and even Mr Charles Dixon, in his earlier book at any rate, did not +think it impossible (25). The only argument in favour of hibernation +is that it is a habit resorted to by other vertebrates to escape the +consequence of exposure to severe temperatures. The arguments against it +are that not a single instance of avian hibernation will stand the light +of reason and investigation, and that birds are provided with the means +of escaping from the cold zone and certainly use these means. There +are flightless birds, but they all live in climates in which they can +exist at all seasons. As Seebohm puts it--"The hibernation of birds is a +theory, the evidence in support of which has completely broken down. The +migration of birds is a fact, as completely authenticated as the fact of +their existence." + +Dr Derham's "Physico-Theology" appeared in 1737 (24), and contained +some sound reasoning about migration, though he was a little puzzled +with the many hibernation stories. In 1780 an anonymous pamphlet--"A +Discourse on the Emigration of British Birds," flouted the theory of +winter sleep in no measured terms (33). This pamphlet was, at first, +attributed to George Edwards, and the 1811 edition has his name on the +title, but Mr A. C. Smith shows that the real writer was a comparatively +unknown man, John Legg. Legg must be looked upon as one of our first +real students of migration. It is Legg who refers to a pamphlet which +appeared in 1740 in which it was seriously argued that swallows migrated +annually to the moon. + +All this time, from 1736 onwards, the family of Marsham in Norfolk, had +been quietly recording observations on the arrival of migrants, each +generation continuing the work. The accumulated results have been used, +and will be used again, in studying the science of "ornithophænology." + +A myth, founded on mistaken observation as well as upon mere speculation +was, and to some extent still is, that the larger migrants assist the +passage of the weaker ones. How else, is still asked, can weak-winged +species cross the sea? It was an old legend when J. G. Gmelin heard it +from the Tartars in 1740; each crane they told him took a corncrake on +its back. There are men who know the corncrake well, who believe to-day +that the bird must skulk unseen through the winter, for they assert it +is quite incapable of lengthy flight. It is useless to argue with them; +the only answer is that it not only can, but regularly does perform a +long double journey; its range extending from northern Europe to South +Africa. In 1911 I handled a water-rail, a bird with short rounded +wings like those of the corncrake, which had struck the lantern of a +lighthouse with great violence. Its smashed head was nearly severed from +its body. + +Herr Otto Herman's "Recensio critica automatica" (31) supplies much +information about the literature on bird migration, and the strange +divergence of opinion on nearly every point. It is carried up to the +beginning of the twentieth century, but much of the valuable work done +in America is altogether neglected. + +A short bibliography is given at the end of the present volume, +including the more important works on the subject and a few of the +papers in periodical publications referred to in this manual. + + * * * * * + + + + + CHAPTER X + + SUGGESTIONS AND GUESSES + + +Several important migration phenomena have hardly been touched upon in +the previous pages; a few words about these may not be out of place. + +There is no doubt that now and again American species are met with in +Europe, and European in America, though there is no evidence of direct +regular trans-Atlantic passage, except from Greenland. The appearance of +these birds has been explained in several ways, the general notion being +that it is impossible for a bird to fly unaided across the Atlantic, say +over 3000 statute miles, without rest. In considering the question we +are met with various points on which we still lack knowledge. + +We know that strong-winged waders can accomplish 2500 miles, apparently +without a rest, and that if rest is necessary these birds can swim and +rise from the waves. We know, too, that there is regular passage between +Greenland and Europe. We do not know how long a bird can, without rest +and food, sustain flight; we do not know the speed it can travel when +aided by favourable winds, nor to what extent even passerine birds may +rest upon the water. My friend Mr J. A. Dockray, when punting in the +Dee estuary, has often seen birds alight to rest on his punt, and once +saw a tired thrush settle repeatedly on the water and finally safely +cross the estuary. There are several instances recorded of passerine +birds alighting upon and rising again from the water. + +We do not know the extent of Greenland as a summer breeding home of +birds; the growing knowledge of this vast continent proves that its +summer avifauna is much larger than we thought, and that western and +eastern forms inhabit adjacent breeding areas; the possibility of birds +banding with the wrong set of travellers is greater than was suspected. + +It is urged that the western shores of Scotland and Ireland should +receive these stragglers, but that the records of American birds +are fewer from these coasts than from the eastern shores and even +Heligoland. The best island route, however, would lead birds to join +the travellers from Scandinavia which pass by the safer eastern route +than the one round the western wind-swept shores of Ireland. Even this +reputed scarcity may be error, for how many reliable watchers are there +compared with the immense length of this wave-indented coastline? How +easy for a straggler to be overlooked! Mr S. F. Baird, in his paper on +the "Distribution and Migration of North American Birds," is emphatic +that the transfer of American birds to Europe is entirely due to the +agency of winds carrying them from their course (6). Mr A.L. Butler +met with snow-buntings in mid-Atlantic travelling east, and Mr J. +Trumbull supplies information about many passerine birds--especially +snow-buntings and wheatears--seen in September and October at various +points between Canada and the British coasts (53). Some joined ships +but others made no attempt to do so, even at 54° north 44° west. + +Unfortunately there is the negative evidence of fraud, for when +unscrupulous dealers found that the public would give high prices for +rare birds, a trade in American skins began. It is not impossible that +even Gätke was victimised. Error or even accidental fraud may be taken +into account. Some years ago I heard that a hawk-owl had been killed +in Cheshire, at an inland port on the Ship Canal; I traced the bird, +the American species, but discovered that it had been captured on an +east-bound steamer in the Straits of Belle Isle, and had only died or +been killed when the vessel reached the coaling station at Partington, +where the taxidermist who received it thought it had been taken. A Cape +pigeon, which I saw in the flesh, reported as shot in Lancashire, I +found had been brought home in cold storage. + +Birds may be carried on shipboard. When the "Mauretania" was between +400 and 500 miles out from New York, bound eastward on June 15th, 1911, +a curlew came on board and remained for three days, leaving when the +Irish shores were sighted on the 18th. My informant, an experienced +wildfowler, failed to catch the bird, but described it as like our +curlew. Probably it was the American _Numenius longirostris_, but +amongst the Irish curlews it would easily remain unrecognised. + +When a seabird appears inland the usual explanation given is +"storm-blown," but increasing knowledge shows the frequent fallacy of +this idea. The Manx shearwater, for instance, is a regular migrant, and +the examination of the dates of the records of so-called "storm-blown" +birds found in inland localities, shows a remarkable regularity; the +majority are met with between the end of August and the end of the first +week in September. Not only do the birds move south in the early days of +September but many, usually at any rate, cross England; the weaklings +fall out and are found. Is it possible that some of these collapses of +passing birds are due to more than mere physical fatigue? Aviators have +discovered the existence of "wind pockets" or "holes in the air," where +the resistance of the air appears suddenly to fail; what is the effect +on a flying bird which suddenly enters one of these pockets? + +The lesser black-backed gull also crosses England in large numbers; its +movements are more noticeable than those of the herring gull, common +gull, or even of the inland nesting and inland feeding black-headed gull. + +Recent investigation has added the yellow-browed warbler, the +blue-throat, and many other "rare," or "casual" passerine birds to the +list of regular British birds of passage; evidently they have been +overlooked before. Even the crossbill, so long classed as a spasmodic +invader, is now seen to be a regular bird of passage to Britain, though +in varying numbers, and quite independently of the sub-specific form +which is always with us. + +The wanderings to our islands of southern petrels and other oceanic +birds has occasioned much surprise. Take two examples of the genus +_Oestrelata_, one _O. brevipes_ taken at Borth in 1889, and _O. +neglecta_ in Cheshire in 1908, the known breeding range of both being in +the western Pacific; pelagic wanderings might lead a bird anywhere, but +it is conceivable that investigation may show that the breeding area is +wider than is supposed and that these species have stations even in the +South Atlantic. + +Some writers affirm that birds only migrate on the wing, but the journey +by sea of many species is varied in method. Those very regular migrants, +the puffins and guillemots, which the light keepers assure us leave and +return to their stations almost at fixed dates, move by slow nautical +stages, swimming and feeding as they go. On May 2nd, 1911, I watched +a red-throated diver slowly travelling north; it actually travelled +farther beneath the surface than either by swimming or flying, so long +as I had it in view. The penguin's migrations cannot possibly be on +the wing. Dr Brooks rightly contended that the periodic assemblage of +wandering sea-birds at their "rookeries" is true migration, regular +as the almanack, although the feeding area is immense and the birds +do not reach home by any single path. Seebohm tells us of young bean +geese migrating in full moult, marching in an army to the interior of +the Tundra, and Mr W. H. Hudson, in "Birds and Man," relates a pathetic +story of a pair of upland geese in southern Buenos Ayres. His brother +saw them in August, the early spring of South America, leaving the +plains where they had wintered to breed in Magellanic islands. The main +flocks had departed, but these two birds, the female with a broken wing, +were steadily moving south, the male taking short flights and waiting +for her, as if to urge her on, and the female walking. "And in this +sad, anxious way they would journey on to the inevitable end, when a +pair or family of carrion eagles would spy them--and the first would be +left to continue the journey alone." + + * * * * * + + + + + CHAPTER XI + + SUMMARY + + +Migration owes its origin to the potentiality of flight, enabling +birds to advantage themselves by extended dispersals, which through +heredity become instinctive, regular and periodical. Geological changes, +especially the passing away of the glacial epoch, only influenced by +opening up new lands for summer colonisation, but climatic conditions +prevented these lands from becoming permanent abodes and fostered the +habit of periodical migration. Whatever the original home or centre +of distribution may have been, the dispersal from it was towards new +lands with a retreat towards the food-supply when these lands became +untenable. Fluctuating food-supply, love of home, sexual impulses, +desire for light, varying temperature, and other factors, all have more +or less influence, but the force exerted by any or all depends upon +the species operated upon and the locality in which it resides. The +present route followed or method of migration is little guide to the +history of past migration; during the evolution of present-day migration +alterations may have been occasioned by environment and changing +conditions. As Seebohm puts it, "The desire to migrate is a hereditary +impulse, to which the descendants of migratory birds are subject--a +force almost, if not quite, as irresistible as the hereditary impulse to +breed in the spring" (44). + +The route is simply the course followed between the breeding area and +winter quarters; it is more or less restricted by the size of the area +in which food is to be found; it is usually the most direct way from one +food-base to the next, in a general direction from the seasonal bases. +Most birds move between north and south, but migrations are regularly +followed in other directions by some species. + +Routes may follow coast-lines, these providing visible landmarks, and +also, for many species, plentiful food; islands, capes, estuaries and +inlets are landmarks, asylums, food-bases, and sites for congregation +and departure for cross-sea passages; at these places migration is +often specially noticeable. Overland routes may suggest "broad front" +migration, when there are no particular restricting influences and the +species have no special need for hurry. Migration at great elevations +and at high rates of speed is proved, but the highest and quickest +possible is as yet unascertained. It may also, under other conditions, +be performed at low elevations and very slowly. It is probable that +strong air-currents at a high elevation materially assist rapid and +lengthened migration. Force not direction of wind influences birds +moving at a low elevation. + +Birds possess a certain power of orientation, a homing instinct, +which need not be called a sixth sense. Brain and eyes assist in the +development of this power; birds have an excellent memory. Young birds +lose their way more frequently than is generally supposed; variations +in routes are explained in many cases by these errors. Young may or may +not be guided by experienced adults; orientation is not infallible but +develops with age. + +There is apparently no truth in the assertion that birds travel by +choice against a head wind or in a beam wind; a moderate wind behind, +on which they are carried, is most favourable. Leeward drift through +contrary winds explains many normal and abnormal routes, and the +occurrence of unexpected species in unexpected places. The distance +travelled not only varies according to species but in individuals of +the same species; the thesis that the most northerly breeder winters +farthest south does not always hold good. + +Much may be learnt by the careful registration of arrivals and +departures of migratory birds, and by the marking of birds. +Ornithophænology, the science of migration study, as carried on at +present in many countries, would be materially assisted by some better +method of international registration and interchange of ideas. + +In conclusion I would urge the value of the study, citing Herr Herman's +reasons put before the International Ornithological Congress in 1905. +The solution of the problem is in the interest of science, and therefore +of intellectual progress, teaching us the great part which migratory +birds play in the scheme of nature. The millions of birds which wander, +season after season, from one zone to another, represent an enormous +aggregate of labour, by flight and search for food, acting on "the +organic life of nature as does the regulator of a steam-engine, at +one time accelerating, at another retarding." Full insight into the +essence of the work done by birds will give us a correct notion of their +usefulness or injuriousness to man, and lead us to rational action for +their protection. + +Whilst fully agreeing with Herr Herman I would go further. We live in +an age when aerial locomotion has become important, and will be more +and more important in the future. Every lesson we can learn from the +successes or failures of these most perfect aerial navigators must be of +use. + +But putting aside economic and utilitarian considerations, there is to +some of us a greater stimulus to solve the problems of nature. With +the birds, and the insects and plants upon which they feed, we share +a common heritage, and the more we learn of the life of these, our +fellow workers, the nearer we approach solution of the great riddle of +the Universe, the mysterious law-abiding scheme of Nature. The book +of knowledge to which we may add some iota is marred with mystery, +superstition and error, but each proved fact cleanses its pages. +"Facts," says Laing, "are the spokes of the ladder by which we climb +from earth to heaven." + + * * * * * + + + + + BIBLIOGRAPHY + + + 1. ALLEN, J. A. Cooke's _Some New Facts about the Migration + of Birds_, _Auk_, xxi., 1904, 501. + + 2. ---- Gätke's _Heligoland_, _Auk_, xiii., 1896, 137. + + 3. ---- Walter's _Theories of Bird Migration_, _Auk_, xxv., 1908, 329. + + 4. BARRINGTON, R. M. "The great rush of Birds, etc." _Irish + Nat._, xx., 1911, 97. + + 5. ---- _The Migration of Birds as observed at Irish Lighthouses + and Lightships_, London, 1900. + + 6. BAIRD, S. F. "The Distribution and Migration of North + American Birds." _Amer. Jnl. Science and + Arts_, 2, 1866, xli. + + 7. BREHM, C. L. "Der Zug der Vögel," _Isis_, 1828, _Naumannia_, + 1855. + + 8. BREWSTER, W. "Bird Migration." _Mem. Nuttall Orn. Club_ + Cambridge, Mass. No. 1, 1886. + + 9. BROOKS, W. K. _The Foundations of Zoology_, New York, 1899. + + 10. _Bulletin of the British Ornithologists' Club. Reports on + Migration_, vols. xvii., xx., xxii., xxiv., + xxvi., 1906-1910. + + 11. CARPENTER, F. W. "An Astronomical Determination of the + Heights of Birds," _Auk_, xxiii., 1906, 210. + + 12. CHAPMAN, ABEL. _Bird-Life of the Borders_, 2nd edit., London + 1907. + + 13. ---- F. M. "Observations on the Nocturnal Migration of + Birds," _Auk_, 1888, 37. + + 14. CLARKE, A. H. "The Migration of Certain Shore Birds," + _Auk_, xxii., 1905, 134. + + 15. CLARKE, W. E. "Bird Migration in Great Britain." _Report + of the British Association_, _London_, 1896. + + 16. ---- "Studies in Bird Migration," _Ibis_, 1902, 246, 1903, 112. + + 17. CLARKE, W. E. "The Birds of Fair Island; Native and + Migratory." _Ann. Scot. Nat. Hist._, 1906, 4. + + 18. COOKE, W. W. "Distribution and Migration of North + American Shorebirds." _U.S. Dept. Agric. + Biol. Survey_, Bull, 35, Washington, 1910. + + 19. ---- "Routes of Bird Migration," _Auk_, xxii., 1905, 1. + + 20. ---- "Some New Facts about the Migration of Birds." _U.S. + Dept. Agric. Year Book_, 1903, 371. + + 21. ---- "Our Greatest Travellers." _Nat. Geog. Mag._, 1911, 346. + + 22. ---- "The Migratory Movements of Birds in Relation to the + Weather." _U.S. Dept. Agric. Year Book_, + 1910, 379. + + 23. CORDEAUX, J. "Migration in the Humber District," _Zool._, + 1892, 418. + + 24. DERHAM, W. _Physico-Theology_, London. 1737. Lect. delivered + in 1711-12. + + 25. DIXON, C. _The Migration of Birds_, London, 1892. + + 26. ---- _The Migration of British Birds_, London, 1895. + + 27. FREDERICK II., (Emperor). _De Arte Venandi cum Avibus_, + Ed. Schneider, 1788, (Rhea. ii.. 1849). + + 28. GADOW, H. F. "Migration," _Encyclo. Brit._, 11th Edit., + Cambridge, 1911. + + 29. GÄTKE, H. _Heligoland as an Ornithological Observatory_, + Trns. Rosenstock. London, 1895. + + 30. HERMAN, O. "A.M.O.K. Ornithophænologiæ anyaja," + _Aquila_, 13, 1906, xx. + + 31. ---- _Recensio Critica automatica of the Doctrine of + Bird-Migration_, Budapest, 1905. + + 32. LAIDLAW, T. G. "Reports on the Movements and Occurrences + of Birds in Scotland during 1902 and + 1903." _Ann. Scot. Nat. Hist._, 1903-4. + + 33. (LEGG, JOHN). _A Discourse on the Emigration of British + Birds_, London. 1795. (Salisbury, 1780, and + London 1811, the latter under name of + George Edwards.) + + 34. LINNÉ. C. _Dissertatio migratione Avium._ Upsaliae, 1757. + + 35. MIDDENDORF, A. T. VON. _Die Isepiptesen Russlands Grundlagen + zur Erforschung der Zugzeiten und + Zugrichtungen der Vögel Russlands_, St + Petersburg, 1853. + + 36. MENZBIER, M. "Die Zugstrassen der Vögel im Europäischen + Russland." _Bull de la Soc. Imp. d. Nat._, + Moscou, 1886, 291. + + 37. NEWTON, A. _A Dictionary of Birds_, London, 1893-1896. + + 38. ---- "Migration," _Encyclo. Brit._, 9th Edit., London. + + 39. PALMÉN, I. A. _Om foglarnes flyttingsvägar_, Helsingfors, 1874. + + 40. ---- _Über die Zugstrassen der Vögel_, Leipzig, 1876. + + 41. SCHÄFER, E. A. "On the Incidence of Daylight as a determining + factor in Bird Migration." _Nature_, + 1907, 159. + + 42. SCLATER, W. L. "The Migration of Birds in South Africa." + _S. African Orn. Union_, 1906, II., 14. + + 43. SCOTT, W. E. D. "Some Observations on the Migration of + Birds." _Bull. Nuttall Ornith. Club_, vi. 97. + + 44. SEEBOHM, H. _Geographical Distribution of the Family + "Charadriidae,"_ London, 1888. + + 45. ---- _The Birds of Siberia_, London, 1901. + + 46. SERVICE, R. "Bird Migration in Solway." _Ann. Scot. + Nat. Hist._, 1903, 193. + + 47. STEBBINS, J. and FATH, E. A. "The use of Astronomical + Telescopes in determining the speeds of + Migratory birds." _Science_ (New York), + xxiv., 1906, 49. + + 48. STEJNEGER, L. "Do Birds Migrate along their Ancient Immigration + Routes." _Condor_, vii., 1905, 36. + + 49. STONE, W. "Bird Waves and their Graphic Representation," + _Auk_, 1891, 194. + + 50. STUBBS, F. J. "The Use of Wind by Migrating Birds." + _Mem. and Proc. Manchester Lit. and Phil. + Soc._, vol. 53, 1909. + + 51. TAVERNER, P. A. "A Discussion of the Origin of Migration," + _Auk_, xxi., 1904, 322. + + 52. TOMISON, J. "Bird Life as observed at Skerryvore Lighthouse." + _Ann. Scot. Nat, Hist._, 1907, 20. + + 53. TRUMBULL, J. "Notes on Land Birds observed in the North + Atlantic and the Gulf of St Lawrence." + 1904. _Zoologist_, 1905, 293. + + 54. WALLACE, A. R., _Nature_, x., 1874, 459. + + 55. WHITLOCK, F. B. _The Migration of Birds_, London, 1897. + + + In addition numerous notes in the following periodicals + have been consulted:--_Annals of Scottish Natural History_, + _Auk_, _British Birds_, _Condor_, _Emu_, _Field_, _Ibis_, _Irish + Naturalist_, _Naturalist_, _Nature_, _Zoologist_. + + + + + INDEX + + + ALLEN, J. A., 29, 34, 49, 61, 64 + + American Golden Plover, 24, 61, 77 + + ---- Robin, 102 + + Anacreon, 114 + + Anticyclones, 89 + + Arctic Tern, 3 + + + BAIRD, S. F., 120 + + Barometric Influence, 88 + + BARRINGTON, R. M., 108, 109, 111 + + Beam Wind, 61, 96 + + Black and White Creeper, 68 + + Blackbird, 50, 109, 112 + + Blackheaded Gull, 75 + + Black Redstart, 109 + + Black-throated Blue Warbler, 69 + + Bluethroat, 123 + + Brambling, 7, 22 + + BRAY, R. A., 49 + + BREHM. C. L., 32 + + BREWSTER, W., 37, 106 + + BROOKS, W. K., 32, 124 + + BURROUGHS, J., 56 + + BUTLER, A. L., 121 + + + Cape Pigeon, 121 + + CARPENTER, F. W., 48, 49 + + Chaffinch, 22 + + CHAPMAN, A., 45, 54 + + CHAPMAN, F. M., 48, 49 + + _Charadrius dominicus_, 77 + + _Charadrius fulvus_, 80 + + ---- _plurialis_, 77 + + _Chrysomitris tristris_, 48 + + _Ciconia alba_, 71 + + CLARKE, A. H., 61 + + CLARKE, W. E., 6, 9, 38, 51, 59, 61, 64, 84, 85, 87, 88, 89, 94, + 95, 100, 107 + + CLAYTON, H. H., 49 + + Common Tern, 75 + + COOKE, W. W., 6, 24, 25, 38, 41, 68, 69, 77, 79, 80, 101, 103, 104 + + CORDEAUX, J., 96 + + Corncrake, 117 + + COUES, E., 12 + + COX, P., 39 + + CRAWSHAY, R., 29 + + Crossbill, 123 + + Curlew, 8, 25, 111, 122 + + + _Dendroica coerulescens_, 69 + + DERHAM, W., 116 + + Dipper, 7 + + Disasters at lights, 85, 105, 106 + + DIXON, C., 41, 43, 60, 116 + + DOCKRAY, J. A., 120 + + Dunlin, 8, 109 + + + EDWARDS, G., 116 + + + FATH, E. A., 55 + + Fieldfare, 7, 22 + + FREDERIC II., 115 + + + GADOW, H. F., 20 + + GÄTKE, H., 33, 34, 47, 50, 51, 52, 62, 63, 121 + + GEOFFROY ST HILAIRE, 115 + + Geographical Distribution, 2, 10 + + _Geothlypis trichas_, 69 + + Glacial Epoch, 20 + + GLAISHER, 90 + + GMELIN, J. G., 117 + + Goldcrest, 95, 96, 109, 113 + + Goldeneye, 25 + + Golden Plover, 23, 24, 25, 26, 61, 77, 80, 111 + + Great Auk, 22 + + Great Crested Grebe, 44 + + Guillemot, 124 + + + Hawk Owl, 121 + + HERMAN, O., 5, 6, 38, 40, 99, 115, 118, 129 + + Hibernation, 115, 116 + + _Hirundo rustica_, 65 + + Homer, 114 + + Hooded Crow, 51, 75, 97 + + HUDSON, W. H., 28, 124 + + Hudsonian Godwit, 28, 29 + + + Isepipteses, 39 + + + Jack Snipe, 7 + + + Knot, 3, 28 + + + Labrador Duck, 22 + + Land-bridges, 42, 43 + + Lapwing, 23, 74, 85 + + LEGG, J., 5, 117 + + Lesser Black-backed Gull, 123 + + _Limosa haesmastica_, 28 + + LUCANUS, 47 + + + MACH-BRUER, 61 + + Manx Shearwater, 122 + + MAREK, M., 32 + + MARSHAM family, 117 + + MARTORELLI, G., 61 + + Maryland Yellowthroat, 69 + + Meadow Pipit, 109 + + MERRIAM, C. H., 6 + + MIDDENDORF, A. T. Von, 39, 58 + + _Mnistitta raria_, 68 + + MÖBIUS, K., 61 + + MONTAGU, G., 115 + + Moon-phases, 108 + + Moult, 67 + + + NEWTON, A., 2, 11, 61 + + Nightingale, 43 + + Noddy Tern, 64 + + Non-breeding birds, 27, 28 + + _Numenius longirostris_, 122 + + + _Oestrelata brevipes_, 123 + + ---- _neglecta_, 123 + + Orientation, 56 + + Ornithophænology, 6, 117 + + Oystercatcher, 109, 111 + + + Pacific Golden Plover, 26, 80 + + Pallas's Sand-grouse, 8 + + Palm Warbler, 69 + + PALMÉN, I. A., 39 + + Penguin, 124 + + Puffin, 124 + + + QUINET, A., 41 + + _Quiscalus purpureus_, 48 + + + RED GROUSE, 3, 7 + + Red-throated Diver, 124 + + Redwing, 22, 88, 109, 111 + + Ringing, 71-76 + + Robin, 7, 8, 109 + + Rook, 8, 97 + + Rushes, 85, 88 + + + Sanderling, 28 + + SCLATER, P. L., 10 + + SCLATER, W. L., 66 + + SCOTT, W. E. D., 48 + + SEEBOHM, H., 19, 35, 36, 66, 107, 116, 124 + + SERVICE, R., 50, 96 + + Skylark, 109, 113 + + SMITH, A. C., 117 + + Snipe, 8, 109 + + Snow Bunting, 121 + + Song Thrush, 4, 7, 8, 73, 74, 109, 112 + + Sooty Tern, 64 + + Spoonbill, 50 + + Starling, 17, 109, 112, 113 + + STEBBINS, J., 49, 55 + + STONE, W., 112 + + Stonechat, 109 + + STUBBS, F. J., 52, 97, 98, 100 + + Submerged Coastlines, 42 + + Swallow, 36, 51, 65, 94 + + Swift, 18 + + + TAVERNER, P. A., 2, 17, 30 + + TAYLOR, H., 98 + + Teal, 76 + + Thomson, A. L., 71 + + TOMISON, J., 88, 97, 105 + + Trans-Atlantic Migration, 119 + + TRISTRAM, Canon, 65 + + TRUMBULL, J., 121 + + Tufted Duck, 17 + + _Turdus migratorius_, 102 + + Turnstone, 28 + + Turtle Dove, 17, 44 + + + Upland Goose, 124 + + + VEREY, A. S., 48 + + + WALLACE, A. R., 19, 31 + + WALTERS, H. E., 64 + + Water-rail, 109, 117 + + WATSON, J. B., 64 + + Wheatear, 67, 68, 109, 121 + + White Stork, 71 + + Wild Duck, 109, 111 + + Wind Pockets, 122 + + Wind Speed Tables, 92, 93 + + WINKENWERDE, H. A., 49 + + Woodcock, 75, 109 + + + Yellow-browed Warbler, 123 + + + + + Transcriber's Note: Although most printer's errors have been + retained, some have been silently corrected. Some spelling and + punctuation, capitalization, accents and formatting markup have + been normalized. Paragraphs which were split by illustrations, have + now been rejoined. + + + + + +End of the Project Gutenberg EBook of The Migration of Birds, by T. A. Coward + +*** END OF THE PROJECT GUTENBERG EBOOK 42739 *** |