Chambers's Journal of Popular Literature, Science, and Art, Fifth Series, No. 31, Vol. I, August 2, 1884

No. 31.—Vol. I.
Price 1½ d.
SATURDAY, AUGUST 2, 1884.
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.