In Bird Land :: VI. WINGED VOYAGERS.

VI. WINGED VOYAGERS.

The subject of bird migration is one of absorbing interest, presenting many a perplexing problem to the student who cares to go into the philosophy of things. Why do the birds make these wonderful semi-annual pilgrimages, and whence came the original impulse, are questions often asked. With my limited opportunities for observation I cannot hope to shed much, if any, new light on the subject; yet it seems to me that some persons are disposed to invest it with more of an air of mystery than is really necessary. There are several patent, if not wholly satisfactory, reasons that may be assigned for the migrating impulse.

As this is not a scientific treatise, the writer will not be over-methodical in presenting these reasons, but will mention them in the order in which they occur to him. If we keep in mind the invariable succession of the seasons, and that this annual rotation has continued for ages, and if we also remember that all animals are dowered by their Creator with as much intelligence as is necessary for their well-being, much of the difficulty attaching to this subject will at once disappear. Birds, like their human kinsmen, learn by experience and tutelage, and are also gifted with a sure instinct that amounts in many cases almost to reason. Take, for instance, this one fact. As the sun creeps northward in the spring, it pours a more and more intense heat upon the northern portions of the tropical and sub-tropical regions. The heat would soon become intolerable to certain birds, which have doubtless tried the experiment of spending the summer in equatorial countries; or if individuals now living have not tried it, perhaps some of their more or less remote ancestors have. That birds do make experiments is proved by the fact that several pets of mine will carefully “sample” a new kind of food offered them, and if they do not find it to their taste, will let it severely alone; nor is it any the less evident that young birds receive instruction from their elders. Thus the necessity of leaving the torrid regions as summer approaches may have been impressed on the migrating species from time immemorial.

Again, as spring advances, insect and vegetable life is revived in regions farther north, and this certainly must act as a magnet upon the birds, drawing them from point to point as the supply of food becomes scarce in the more southern localities. Then, let us suppose for a moment that all the birds did remain in the south through the summer; there would sooner or later be a bird famine in the land, for the supply of seeds and insects would soon be exhausted. Our feathered folk are simply obliged, on account of the exigencies of food, to scatter themselves over a larger extent of country. They solve the problem of food supply and demand by these annual pilgrimages to the boreal lands of plenty.

To go a little more to the root of the matter, we may easily imagine how the migrating spirit got its first impulse and gradually became evolved into a habit of something like scientific precision. If the first birds lived in tropical climates, as was probably the case, some of them, as the food supply became exhausted, would be crowded northward, or would go of their own accord, and wherever they went they would find well-filled natural larders. Having once discovered that spring replenished the north with food, they would soon learn the desirability of making periodical journeys to that part of the globe. With this constant quest for food must also be coupled the instinctive desire of most birds for seclusion during the season of reproduction,—an instinct that would naturally drive them northward into the less thickly tenanted districts. But it may be objected that many species make long aerial voyages, passing over vast tracts of country to reach their chosen summer habitats in various parts of the north; and it is well known that the same individuals will return again and again, on the recurrence of spring, to the same locality. How are these facts to be accounted for?

If we accept the glacial theory—a hypothesis pretty well established now among scientific men—we may readily conceive that, as the sun melted the ice at a greater distance in both directions from the equator, the habitable area of the earth’s surface would gradually become enlarged. For the sake of vividness let us fancy ourselves living at that period of the world’s history. Let us select a point north of the equator where a given pair of birds can live in summer. They find plenty of food there, and are comparatively undisturbed by other birds, and they therefore become attached to the place, most feathered folk having a strong “homing instinct.” When winter comes, they and their progeny are forced to retire to the south; but they do not forget their pleasant summer haunt, their Mecca in the north, and therefore, at the approach of the following spring, they obey the home impulse and hie by easy stages to the beloved spot. Some of their number doubtless find it possible from time to time to push farther northward, and thus other breeding-haunts are selected. As the glacial accumulations melt away, the whole temperate region and a large part of the frigid zone become habitable. All this takes place by a very gradual process, requiring thousands of years, thus giving ample time for heredity to infuse the migratory habit into the nature of the birds. Every new generation would learn the route and other needful details from their predecessors, and thus the process would go on in an unending circuit year by year.

After the foregoing was written, my attention was called to the following quotation from Dr. J. A. Allen’s valuable paper on the “Origin of the Instinct of Migration in Birds.” The extract is taken from an article by Frank M. Chapman, published in “The Auk” for January, 1894: “Nothing is doubtless more thoroughly established than that a warm temperate or sub-tropical climate prevailed down to the close of the Tertiary epoch, nearly to the Northern Pole, and that climate was previously everywhere so far equable that the necessity for migration can hardly be supposed to have existed. With the later refrigeration of the northern regions, bird life must have been crowded thence toward the tropics, and the struggle for life thereby greatly intensified. The less yielding forms may have become extinct; those less sensitive to climatic change would seek to extend the boundaries of their range by a slight removal northward during the milder intervals of summer, only, however, to be forced back again by the recurrence of winter. Such migration must have been at first ‘incipient and gradual,’ extending and strengthening as the cold wave receded, and opened up a wider area within which existence in summer became possible. What was at first a forced migration would become habitual, and through the heredity of habit give rise to that wonderful faculty which we term the instinct of migration.” The reader’s attention is also directed to Mr. Chapman’s own article in the number of “The Auk” indicated.

It may be asked why some species remain in torrid and temperate climates, while others wing their way to the far north, even beyond the boundary of the Arctic Circle. My answer is, There is some Power that has wisely arranged all these matters, either by gradual development or by an original creative fiat. Every species is made to fit with nice precision into its peculiar niche in the creation. Perhaps Bryant suggests the true explanation in his poem entitled “To a Waterfowl”:—

“There is a Power whose care

Teaches thy way along that pathless coast,

The desert and illimitable air,

Lone wandering, but not lost.”

This may seem like begging the question; yet, to my mind, it is impossible to develop a philosophy of the universe without assuming an original creative Intelligence. True, the laws of evolution will account for many of the details, and birds, like men, are empowered in a large measure to work out their own destiny; but somewhere there must be a Power that has infused into Nature all these wonderful potentialities of development. Involution must precede evolution.

But this is speculation. Account for them as we may, the facts are evident. Within the circle of my own observation there is abundant proof of this varied but wise adaptation in Nature. There, for example, is the tiny golden-crested kinglet, which remains here all winter, no matter how severe the weather, and seems to be the embodiment of good cheer; whereas the brown thrasher, a bird many times as large, would be likely to perish in the first snow-squall. Then, when spring arrives, Master Kinglet hies to the north for the breeding-season, while Monsieur Thrasher comes up from the south and becomes my all-summer intimate.

Another matter of intense interest concerning bird migration is that the migrants which winter farthest north are, as a rule, the first to arrive in the spring at their summer homes or vernal feeding-grounds. For instance, in the latter part of March or the beginning of April, while the thrashers, cat-birds, and others which winter in our Southern States, are arriving in New England, New York, Pennsylvania, and Ohio, the warbler army, which spends the winter in the West Indies, Yucatan, and Central America, is just crossing over from those countries to the southern borders of the United States.

When autumn comes, experience has taught the migrants that their only safety lies in making their way to the south before cold weather sets in; for many of them certainly do start on this voyage long before winter drives them from their northern haunts. In my opinion, they are gifted with sufficient reason—call it instinct, if you like—to do this, and I do not think they are moved by an uncontrollable impulse which acts upon them as if they were mere automata.

Portions of the migrating army often overlap. For example, the juncos and tree-sparrows are winter residents in my neighborhood, but very frequently they remain here a month or more after the earliest arrivals from the south. Presently, however, they grow nervous, flit about uneasily, trill little snatches of song, inure themselves to flight by longer or shorter excursions about the country, and then join the northward procession en route for their breeding-haunts in British America. With regret I bid them adieu, but find compensation in the knowledge that their places will be supplied by a brilliant company of summer residents.

One of the strangest features of migration is the fact that a bird will sometimes make the voyage from north to south, and vice versa—or a part of the voyage—alone, at least as far as companionship with individuals of its own kind is concerned. Whether this is done advertently or inadvertently I am unable to say, but the fact cannot be disputed. In the spring of 1892, as noted in another chapter, a hooded warbler was flitting about a gravel bank in a wooded hollow, and although I scoured the country for miles around day after day, I never met another bird of this species. The little Apollo in feathers was so gentle and familiar that surely his mates would not have escaped my notice had there been any in the neighborhood. Why he preferred to travel alone, or in company with other species rather than his own kin, might be an interesting problem in avian psychology. A little farther down the glen a single mourning warbler was also seen at almost the same date. His companions had probably wished him bon voyage, and left him to strike out in an independent course through the trackless ocean of air.

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.

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