BIRD MIGRATION.
The migration of birds is a subject that has excited the attention of naturalists of all nations from very early times, and many theories have been advanced to account for the mysterious periodical movements that take place among the feathered tribes, although it can hardly be said there is one which fully explains these movements. Some writers affirm that they are entirely due to temperature; others, that they are caused by a want of food; while others, again, assert that they are traceable, within certain limits, to a hereditary impulse which guides birds in following lines of flight over seas where at one time all was land.
There can be no doubt that originally, birds, like other animals, were actuated to a great extent in their periodical shiftings by the main considerations of food and temperature. As familiar examples of this, we have only to remember that species which are reared within the Arctic Circle are compelled to quit their birthplaces as soon as the brief summer is past—their haunts becoming wrapped in snow, and their feeding-grounds converted into a dreary expanse of ice; while in our own country, every one knows that swallows and other soft-billed birds are obliged to leave us at the close of autumn, and repair to climes where there is not only greater warmth but abundance of insect life, on which their subsistence depends.
Another theory, however, may be adverted to, as showing the phenomena in a more suggestive and poetical light—namely, that put forward by the aged Swedish poet Runeberg, who believes that birds, in undertaking their vast and toilsome journeys, are solely influenced by their longing for light. When the days become shorter in the north, birds make up their minds to go southwards; but as soon as the long northern days of summer set in, ‘with all their luminous and long-drawn hours,’ the winged hosts return to their old haunts. There is evidently something in this theory, because, in the case of the insectivorous birds, there is little diminution of food in their southern hunting-grounds to compel them to seek a change; and even with regard to marine birds, it seems quite possible that fishes and other migratory creatures in the sea on which they prey are influenced to a great extent by some such impulse as this theory indicates. The longing after light, moreover, is well exemplified in imprisoned plants, which, though firmly rooted in the ground, instinctively strain towards the light, and spread upwards in search of an outlet from the surrounding darkness. The Swedish poet, therefore, may, after all, be nearer the truth than some naturalists are willing to allow.
But whatever may be the true theory, it is certain that at the close of each summer, whether it be within the Arctic Circle or in the temperate region of Britain, where observations are now being made, vast flights of birds are seen passing southwards, and again in early spring proceeding northwards, with unvarying regularity; and it has consequently become a matter of considerable interest to ornithologists, as well as to naturalists at large, to record such observations as may help to throw light upon the question as to what species share in the general migration and how their movements appear to be influenced.
In Chambers’s Journal for December 1876, a suggestion was made that the light-keepers of our lighthouses might be enlisted in the cause of science by making notes of their observations concerning birds and other animals, as by that means new facts would certainly be added to our stores of knowledge; and Messrs J. A. Harvie Brown and John Cordeaux—two well-known ornithologists—subsequently undertook of their own accord the circulation of carefully prepared schedules among the keepers of lighthouses and lightships situated on the English and Scottish coasts, with a view to investigate the migratory movements of birds. The results, which were both interesting and valuable, were published in the Zoologist for 1880, but were immediately thereafter reprinted in a convenient form for reference. Subsequently, it was found that the scheme was somewhat beyond the limits of private enterprise, and application for aid was therefore made to the British Association at its meeting at Swansea, in the autumn of the same year. This led to the appointment of a Committee of Naturalists, whose Report, issued in 1881 (London: Sonnenschein and Allen), was so encouraging, that when the Association again met at York, a larger Committee was appointed, and a wider interest given to the investigations by their extension to the coasts of Ireland. A subsequent Report on the migration of birds, containing a mass of interesting information on the points referred to, has recently been issued as the work of this Committee; and judging from its contents, it may reasonably be expected that the results of such investigations will become more and more important as the work proceeds.
From the returns given by the light-keepers, it would appear that birds, prior to crossing the ocean, follow closely the coast-line in their journeyings, and that during the two periods named, a continuous stream passes to and from their summer quarters, broken, it may be, by a sudden change of wind or other vicissitude of weather, and thus causing ‘throbs’ or ‘rushes,’ as they have been termed, but steady as a rule—the hereditary impulse being too powerful to admit of anything but a temporary deviation or delay on these great highways of migration.
It seems strange that while such movements are taking place, persons resident but a few miles inland may be unaware of the winged multitudes that in this way pass within a short distance of their homes. Yet a great deal of information may be gathered by close observers who are willing to visit the seacoast at daybreak about the time the birds are on the move. The present writer well remembers seeing large flights of birds of different species arriving in early spring on the shores of East Lothian for a succession of years. Among these, the swallows were conspicuous even at some distance out at sea, the main body passing northwards in undeviating flight, while numerous detachments left it and came landwards, to people the haunts in the country which they had occupied the previous year. The same was observed in the case of wheatears, redstarts, and golden-crested wrens—the last-named being particularly interesting from their tiny size. Occasionally goldcrests would come in great numbers, and immediately on alighting, would flutter in the morning sunlight among the rocks and walls near high-water mark in search of insect prey, paying no heed to the presence of any one watching their motions. Again, in the autumn months, buzzards, owls, and woodcock would arrive simultaneously, and pitch upon the rocks at low water, as if glad to touch the nearest land; and even wood-pigeons (supposed by the country folks to come from Norway), which delight only in dense woods and fertile fields, and which suddenly appear in vast numbers in severe British winters, settled in crowds upon the stony beach without any preliminary survey of the ground. Observations like these can be made on almost any part of the east of Scotland, and it is gratifying to find them verified in a remarkable degree by the returns from the light-keepers, which not only show the closeness with which birds follow the coast-line, but also indicate the points of land from which they speed seawards in their adventurous flight. Thus, it is found that arrivals and departures take place at Spurn Point and on the coast of Forfarshire—the inference being, if the theory of a former land-communication be true, that an ancient coast-line must have extended east or north-eastward probably from Holderness to Southern Scandinavia and the mouth of the Baltic. There is also reason to believe that similar points of arrival and departure exist in the north-east of Aberdeenshire, judging from the occurrence of so many rare birds, whose presence there at the migration season can hardly otherwise be accounted for.
Among other interesting facts brought to light by the present series of investigations we find that, with very rare exceptions, young birds of the year migrate some weeks in advance of the parent birds, and that the appearance on our coasts in autumn of many species, such as the wheatear, fieldfare, redwing, hooded crow, goldcrest, and woodcock, may almost be predicted to a day. The punctuality, indeed, with which certain birds return to us in the fall of the year is remarkable—one species regularly taking precedence of another according to the time required for their self-dependence. Shore-birds apparently reach this stage earlier than land-birds, as it has been observed that the young of the knot, gray plover, godwit, and sanderling—birds which nest in very high latitudes, and are the last of the migrants to leave in spring—are amongst the first to come to our shores.
The most interesting of all the stations from which returns have been sent is the small rocky island of Heligoland, situated in the North Sea, about forty miles from the mouth of the Elbe. Here the tired wing of many a feathered wanderer finds a resting-place. Lying almost directly in the line of migration, the island has been periodically visited by birds in incredible numbers, many of them belonging to species of extraordinary interest. Attracted by the lighthouse, which occupies the highest point of the island, and throws out on dark nights a blaze of light ‘like a star of supreme brightness,’ many thousands of birds of all kinds pitch upon its treeless surface, where they have scarcely any shelter from the weather, and where they become at once a prey to the wants of the islanders, who capture them in vast numbers, and use them as food. Mr Cordeaux, in an interesting communication to the Ibis for 1875, states, that on the evening of the 6th of November 1868, three thousand four hundred larks were captured on the lantern of the lighthouse before half-past nine o’clock; and on the same evening, subsequent to that hour, eleven thousand six hundred others were taken—making a total of fifteen thousand. For this holocaust of these charming songsters, no words of deprecation are strong enough, though their capture was probably regarded as a lawful addition to the larder of the captors, and probably such visitations had been so regarded ever since the lighthouse had begun to lure the poor creatures to an untimely fate! In this way also, no doubt, many a feathered rarity was consumed.
Fortunately for science, however, this little island has numbered amongst its resident population an observer of rare intelligence, Mr H. Gätke, whose leisure hours have been employed for nearly thirty years in registering the occurrence of the birds which have either made the rock a temporary resting-place or been seen crossing it in their migratory flight. Mr Gätke first visited Heligoland as an artist; but having secured an official appointment there, he afterwards made the island his permanent home. During the interval, he has collected and preserved with his own hands upwards of four hundred species—a collection containing examples of the avi-fauna of the four quarters of the globe. Strange as it may appear, birds have touched here whose proper homes are wide as the poles asunder—birds from the burning plains of India and the arctic lands of desolation. The Far West, too, has contributed its land and water birds; and from the barren steppes of Siberia, tiny warblers have joined the moving throng. As instances of the abundance of what are called ‘British birds,’ mention may be made of flights of buzzards numbering thousands which passed over the island on September 22, 1881; while flocks of equal numbers rested on the cliffs, and a ‘great flight’ of hooded crows, which crossed in the same direction. As for the starling—a bird which has become extraordinarily plentiful in this country during the last thirty years—it is referred to as making its appearance in a ‘great rush,’ which no doubt accounts for a flock, recorded some time afterwards as coming from the east, by a light-keeper on the English coast, ‘estimated to contain a million starlings, making a noise like thunder, darkening the air.’ All these birds were doubtless of Scandinavian origin, and had in the case of each species travelled in a compact body along the coast-line until they reached North Germany, where they had to some extent become broken up, many of the birds being induced to alter their flight westwards in the direction of the British coasts. As a natural consequence, the earliest observers of their arrival in this country would be the light-keepers at Spurn Head on the Yorkshire coast; and the records from this station show that the buzzards and hooded crows at least, reached us from Heligoland in somewhat less than twenty-four hours.
Another important post of observation is the lighthouse on the Isle of May, in the Firth of Forth,[1] from which one of the reporters has obtained records of species of more than ordinary interest, the intelligent keeper there having sent him no fewer than seven closely filled schedules, principally referring to autumn migrations. Seventy-five species have already been identified from this station; but in addition to these, numerous entries refer to ‘small birds’ of various descriptions, regarding which and other accidental visitors, more will be known as the investigations proceed, arrangements having been made for the preservation and transmission to the mainland of all the species that occur at the station. The occurrence of the blue-throated warbler here—a very rare bird in Britain—suggests the possibility of other interesting forms being sent from this locality.
In summarising the material received, the compilers of the Report confess that the migrations of seagulls are most erratic and difficult to tabulate. In certain years, however, these are unquestionably regulated by the movements of the fish upon which they feed. The late Professor MacGillivray has recorded that, in the winter of 1837, a flock of seagulls computed to contain not short of a million birds made its appearance in the Firth of Forth; and it must be within the recollection of at least one of the reporters that in 1872-3 similar if not even greater numbers visited the firth, the most common species being the kittiwake and lesser black-backed gull. In this memorable invasion, unusual numbers of glaucous and Iceland gulls made their appearance, birds of such note among ornithologists as to be marked objects when they do occur; and the entire assemblage was suggestive of a migration controlled by the movements of fishes—the waters of the firth being at that time swarming with sprats. The ‘catches’ of the local fishermen were so heavy as to necessitate their sale at a trifling sum per cartload to the neighbouring farmers, for the purpose of manuring their fields.
There is not much, we apprehend, to be gathered from the appearance of skuas, petrels, long-tailed or ice ducks (Harelda glacialis), and other species whose haunts are exclusively marine, as their occurrence inshore signifies in nearly all cases continued rough weather at some distance from land. There are no seafaring creatures, indeed, that delight more in storms than ice-ducks and petrels; for them, the huge green waves or churned masses of foam have no terrors; they are for the time being at home amid the wildest waters—the petrels on the one hand flitting silently over the turbulent billows, rising as they advance, and falling in their wake with contemptuous ease; the ducks, on the other hand, careering aloft during a sudden blast, and sounding their bagpipe-like notes, as if deriding the war of elements. Very different is the experience of the tender songsters that traverse the dreary waste of waters; sorely tried in their powers of flight, they are not unfrequently caught by adverse gales and driven hundreds of miles out of their course, to be finally swallowed by the pitiless waves.
In connection with this subject, and as bearing upon the question of former land-communications, reference may be made to an extremely interesting paper on the Migration and Habits of the Norwegian Lemming, read before the Linnæan Society of London by Mr W. D. Crotch in 1876. In this communication, Mr Crotch shows that the lemming, which is a small rat-like animal, occurring in abundance in many parts of Norway, assembles periodically, although at irregular intervals, in incredible numbers, and travels westwards until the seacoast is reached; after which, on the first calm day, the vast multitude plunges into the Atlantic Ocean, ‘and perishes, with its front still pointing westwards.’ Such a voluntary destruction in the case of a single species is perhaps nowhere else to be found in the history of migratory animals, and it seems difficult to understand how the annihilation of so many migratory hordes through a ‘suicidal routine’ should not ultimately lead to their extinction. Mr Crotch tells us that no survivor returns to the mountains; indeed, so formidable is the migration and its effects upon the poor fugitives, that we are told by Mr Collett—a Norwegian naturalist—of a ship sailing for fifteen hours through ‘a swarm of lemmings which extended as far over the Trondhjems fiord as the eye could reach.’
Mr Crotch rightly, we think, concludes that land existed in the North Atlantic Ocean at no very remote date, and that when dry land connected Norway with Greenland, the lemmings ‘acquired the habit of migrating westwards for the same reasons which govern more familiar migrations.’ The inherited tendencies, therefore, of this little creature are opposed to the so-called instinct which impels quadrupeds as well as birds to change their quarters in quest of food and warmth, unless we conclude, with Mr Crotch, that in the case of the lemming, such instinct has persistently failed in its only rational purpose.