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-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
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-
-Title: The Migration of Birds
-
-Author: T. A. Coward
-
-Release Date: May 19, 2013 [EBook #42739]
-
-Language: English
-
-Character set encoding: ISO-8859-1
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-*** START OF THIS PROJECT GUTENBERG EBOOK THE MIGRATION OF BIRDS ***
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-
-                    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.
-
-
-
-
-
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