That the army of migrants travel mostly by night is a well-known fact that can be verified by any one who will stand out-of-doors and listen to their chirping overhead. They seem to move in loose flocks, for there are intervals of complete silence, followed by a promiscuous chirping from many throats. Nor are these nocturnal calls all uttered by a single species, but usually a number of species seem to be travelling in company. One might say, therefore, that the feathered army moves in squads. As they travel in the dark, very little can be said about their flight; but every student has found species of birds in an early morning ramble which he could not find anywhere on the previous day, proving that they must have arrived in the night. Here is a single excerpt—many might be given—from my note-book: “On the third of March, 1894, I took a long stroll into the country, remaining in the fields until dusk; not a single meadow-lark was to be seen or heard. At daybreak next morning, however, the shrill whistle of I know not how many larks rose like musical incense from the fields and commons in the rear of my house. Depend upon it, had these lavish minstrels been in the neighborhood during the previous afternoon, they would not have escaped my attention, for they could not have kept their music in their larynxes, not they! There is a cog in Nature’s machinery lost if the meadow-larks are silent for a half day in the spring.”
In 1885 Mr. William Brewster, the well-known ornithologist, made some intensely interesting discoveries on the nocturnal flight of migrants, at Point Lepreaux Lighthouse, New Brunswick. The principal lantern, which was in the top of the tower, cast a light that could be seen fifteen miles away in clear weather. Even on dark and foggy nights this lantern would throw out a strong light to such a distance that a bird coming into the lighted area could readily be seen. On stormy nights the lighthouse seemed to possess a fatal attraction for the lost and rain-beaten birds, which would fly toward it and often dash against the glass, the roof, and other portions of the tower with such force that they fell dead or disabled. Mr. Brewster could see them approaching in the prism of light, some dashing themselves with fatal effect against the tower, but more, fortunately, turning aside or gliding upward over the roof, and then pressing on toward the west with incessant chirping. During rainy weather a larger proportion would strike the brilliant obstruction.
It is interesting to notice that different species composed the companies that passed the lighthouse. For instance, on the night of September first, seven different species of warblers and one red-eyed vireo were killed or disabled, and one Traill’s flycatcher entered the mouth of the ventilator, and came down through it into the lantern. A few evenings later, about forty per cent of the specimens identified were Maryland yellow-throats, forty per cent more red-eyed vireos, and the remaining twenty per cent were made up of two kinds of thrushes and six kinds of warblers. These figures are given to show the heterogeneous composition of the migrant army.
Mr. Brewster also found that no birds came about the lantern except on densely cloudy or foggy nights, and that they came in the greatest numbers when the first hour or two of the evening had been clear and was succeeded by fog or storm. These data would seem to prove that the birds began their nocturnal journey with the expectation of having pleasant weather, and when the fog or storm rose later in the evening, they flew lower and got bewildered by the glare of the lighthouse.
Many theories of bird migration have been proposed and argued at length, but, on the whole, I incline to Mr. Brewster’s theory that the old birds, having learned the advantage of these semi-annual expeditions, and having also determined the route by means of certain landmarks, act as aerial pilots to the army of young birds to whom the way is still unknown. Mountain ranges, river valleys, coast lines, and sheets of landlocked water doubtless serve the purpose of guide-posts to these airy travellers. Much as has been written on the subject, however, there still remains a large field for original research.
VII.
PLUMAGE OF YOUNG BIRDS.
It is surprising what odd and variegated costumes are sometimes worn by the juvenile members of the bird community. Frequently their attire is so different from that of their elders that even the expert ornithologist may be sorely puzzled to determine the category to which they belong; yet there are usually some characteristic markings, however obscure, by which their places in the avian system may be fixed. As a rule, the plumage of young birds is more striped and mottled than that of mature specimens, Nature playing some odd pranks of color-mixing in tiding a bird over from callow infancy to full-fledged life. Fashion plates in the world of bantlings would be of little account, as no fixed patterns are followed.
Some parts of the growing bird’s plumage change to the normal color sooner than others. I remember a young male indigo bird that I saw in October, whose garb, just after fledging, must have been a warm brown almost like that of the adult female; but now he had cast off a part of his infantile robes, and put on in their stead the cerulean of his male parent; his tail, rump, and the base of his wings were blue, while the rest of his plumage was brown. He made a unique and pretty picture as he sat atilt on a blackberry stem, asking me with loud Tsips to admire his quaint toilet. Early in the spring I have seen indigo birds in whose plumage the tints were quite differently blended and arranged.
What a party-colored suit the young bluebird wears! His breast, instead of being plain brick-red as in the case of the adult bird, is profusely striped with dark brown on a background of soiled white; and his upper parts, in lieu of the warm azure of riper years, are a lustrous brown curiously mottled with tear-shaped blocks of white; while his wings and tail have already assumed the normal blue of this species. In the days of his youth the chipping-sparrow also dons a striped vest, so that, if it were not for his smaller size, it would be difficult to distinguish him from his relative, the grass-finch.
My admiration was especially stirred, one midsummer day, by the dainty appearance of a small coterie of bush-sparrows flitting about on a railroad which I was pursuing on foot; a large patch on their wings was of a dark, glossy brown tint, extremely pretty, and looking precisely as if it had been painted by the deft hand of an artist. Their under parts were variously streaked with white and dusk. At first I scarcely recognized my familiar little sylvan friends; but their intimacy with several adult specimens, as well as several well-known diagnostic markings, settled the question of their identity beyond a doubt.