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diff --git a/42739-8.txt b/42739-8.txt deleted file mode 100644 index 956b2ea..0000000 --- a/42739-8.txt +++ /dev/null @@ -1,4073 +0,0 @@ -The Project Gutenberg EBook of The Migration of Birds, by T. A. Coward - -This eBook is for the use of anyone anywhere at no cost and with -almost no restrictions whatsoever. You may copy it, give it away or -re-use it under the terms of the Project Gutenberg License included -with this eBook or online at www.gutenberg.org - - -Title: The Migration of Birds - -Author: T. A. Coward - -Release Date: May 19, 2013 [EBook #42739] - -Language: English - -Character set encoding: ISO-8859-1 - -*** START OF THIS PROJECT GUTENBERG EBOOK THE MIGRATION OF BIRDS *** - - - - -Produced by Chris Curnow, Sue Fleming and the Online -Distributed Proofreading Team at http://www.pgdp.net - - - - - - - - - - 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. 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