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.