Popular Science Monthly/Volume 9/July 1876/Certain Phases of Bird-Life
|CERTAIN PHASES OF BIRD-LIFE.|
NOTWITHSTANDING so general an interest has been taken in studying the habits of our birds, by both scientific and amateur naturalists, there are several phases of bird-life to which little or no attention has been paid; at least scant reference, if any, has been made to them, in ornithological literature.
One such feature of bird-life is the mode of acquiring the range of flight-power characteristic of each species. A careful and long-continued study of our birds in their chosen haunts, free from all unnatural (i. e., human) persecution, has enabled me to detect but little variation in the flight-powers of the individuals of any species of bird observed—far less than in the general range of their habits: but still, such individual variation, I think, does exist. A bird is not a perfectly-adapted machine, capable of faultlessly filling its destined place in Nature, and unerringly performing everything required of it. With the simple growth of the feathers of the wing, there does not come the ability to fly. Just as creeping precedes walking, in children, this is a gradually-acquired power. The commencement may be termed "flapping," and consists in simply breaking the force of a descent; this is followed by a more effectual use of the wings, and horizontal progression, and it is some time subsequent to this that the young birds attain to the power of upward flight. This holds good of a considerable number of species, studied with special reference to their flight, as the robin, the wood-thrush, cedar-bird, cat-bird, pewee, and indigo-bird.
It is doubtful if young birds, while yet in their nests, are conscious of the use to be made of their wings. After long-continued experimenting, I find they make no use of them, in endeavoring to escape, but trust to their legs entirely, if removed from the nest, or defend themselves by pecking at the intruder. When a sufficient growth of feather has been obtained, the parent-birds, directly and indirectly, instruct them; or, perhaps more properly, force them to use their wings. So, at least, I can only interpret certain habitual actions of the parent-birds with reference to their newly-fledged young.
As an instance I will quote from my field-notes, with reference to the indigo-bird: "June 23, 1873. Found a nest of this species in a dense thicket of blackberry, and, curiously enough, within just seven paces of the railroad-track. The young birds were just ready to leave the nest. I visited the nest the next day, and saw on my approach one of the four young birds sitting on a brier-stem, about a yard from the nest. Taking a favorable position, I continued to watch the birds closely, as they were very restless and noisy. Evidently something unusual had occurred or was occurring. In a few moments I saw the hen-bird go to the nest and push one of the young birds out of the nest. It forced it from the edge of the nest, to which it clung with its feet. Once free, the little fellow struggled to keep itself up, throwing up its wings, as a child would straighten out its arms when falling. This was the initial movement that developed into flight. All of the young birds were thus forced from the nest, and I am satisfied from no outside cause, as, for the three following evenings, the young returned to the nest to roost. I spent several hours watching this brood and their parents, and the whole time was occupied, except short intervals when they were fed, in forcing the young birds from point to point, but ever keeping them from the railroad-track, over which trains passed frequently. Two days from leaving the nest they could fly six or eight yards, but always from a higher to a lower perch, and regained the more elevated branches by very short, 'jumping' flights, with a laborious flapping of the wings; but on the fifth day they could follow their parents almost any distance, and execute an upward flight with apparently the same ease. Examination of the wing-feathers on the 30th of June, as compared with a week previous, showed so slight gain in the growth of the feathers, that I believe nothing in the increased flight-power was due to their being now better fledged."
Such observations as the one noted in detail I have so frequently repeated with widely-differing species as to satisfy me that what may be termed "direct instruction" in flight is given to the young birds by their parents. "Indirect instruction" also is noticeable, in the fact that the parent-birds cease to feed their young, and so force the latter to leave the nest and follow them. Once out of the nest, they soon endeavor to walk on air, as it were, and, falling, open their wings, and, as described, thus take the initial step. This ceasing to bring the food to the young while yet in the nest is done in some instances, I judge, only to draw them from the nest; and then they feed them as before, but not as frequently, which leads the young to voluntarily move from point to point. The important fact must not be lost sight of, too, that the young birds, when once out of the nest, witness nearly every movement of their parents, and learn, undoubtedly, very much through imitation of their movements.
For these reasons, I believe the acquisition of full flight-power is gradually acquired; first there is a mere "flapping" to prevent falling; then short horizontal stages of aërial progression; finally, a steady, intelligent use of the wings, enabling the birds to execute the highest type of flight within their capabilities, i.e., upward flight.
In the case of birds of more complicated flight than those mentioned above, such as the falcons, where hovering is a necessary acquirement, the truth of the assertion that flight is gradually acquired becomes more evident from the fact (which I have very frequently verified by observation) that the young birds for some time after leaving the nest are fed by their parents. They commence procuring food for themselves by chasing sparrows; checking their moderate flight when above a thicket, they rush upon the fleeing birds, more frequently without success than with. Their first attempts at hovering are miserable failures, and it is not until autumn that they are enabled, by the complete control of their wings, to stay themselves in mid-air, and, at the proper moment, dart with unerring aim upon some luckless mouse.
I have used the term "unerring," because it is customary so to characterize this act of the falcons; but, having watched, with a powerful field-glass, the hovering and darting of hawks, I have been forced to consider the term far from correct, and that not more than one-half, if as many, of the "strikes," on the part of the bird, are effectual.
Following the young birds, of any species, from the nests, and noting their movements, we find that the one prominent aim of their lives, during their first summer, is the acquisition of food. They have really nothing else to do, if we except escaping from the attacks of their enemies, and this is taught them directly by their parents. I judge that the great majority of birds that fall victims to birds of prey and carnivorous mammals are young. To return to the feeding-habits of birds. These appear to be acquired, by every bird, through imitation of the movements of the parents when in search of food; judgment as to localities, on the part of the young, and allied circumstances connected with procuring food, come by experience. Watch a restless little creeper, during these chill winter mornings (Certhia familiaris), as it flies from tree to tree, and clambers over and about the rough bark. It seems, indeed, a mere automaton, driven, and not going of its own free-will; but, if we continue our observations but a little longer, we shall find it really a discriminating creature, passing by certain trees that are to us all one with those visited. It is not chance, but a consciousness of the uselessness of search, that determines its flight to some more distant rather than a nearer tree.
As an example of the knowledge gained by young birds through imitation, let us take young woodpeckers. On leaving the nest, they accompany their parents, but are not fed by them. Like the old birds, they immediately commence to climb the trunks and branches of the trees. Having been fed with insects when in the nest, they are already able to recognize their proper food, and devour the visible insects they may discover on the outer surface of the bark. Now, was it the example set by their parents, or the peculiar construction of their bill and feet, that was the cause of their having sought the trees, and climbed over them in the peculiar manner common to their kind? I think, clearly the former. Now, merely clambering over the bark of trees would not enable them to secure sufficient food, and imitation could not extend beyond this point; but here experience comes into play, and the gradual acquirement of the whole routine is easily traced. The bark of trees is nearly always cracked, and in the crevices are more insects than on the surface, and the habit, soon acquired, of search in the cracks of the bark is the one step from searching over the exposed surface to search beneath. Imitation led the ignorant young bird to the thrifty growth of timber, and not the tangled hedge-rows. Experience taught him the accustomed haunts of those insects on which Nature bids him prey. If we go back into the remote past, and recall the ancestral woodpecker, we can with no undue use of the imagination picture to ourselves the first steps that led the good climber to find in the half-decayed bark the nourishing food abounding there; and now let us return to the present, and seek for some variation in the habits of the birds of today. As an instance, the "flicker," or golden-winged woodpecker, leaves the timber-lands, and in loose flocks, often in company with robins, wanders over pasture-fields and meadows in search of food, more especially the crickets, and not under fences do they look for them, but under the dry droppings of the cattle. Here is an instance where accident, it may be, gave origin to, and experience has confirmed into a habit, a decided variation from normal woodpecker life. Now, a young woodpecker leaving its nest June 1st, if dissociated from its kind, would never leave the woodlands, and, seeking the pasture-fields, overturn dry chips of cow-dung, in search of crickets; but such young birds will naturally follow their parents thither, and this is just the case, for the larger proportion of birds killed in October, in such localities, are the young of the preceding summer.
In conclusion, with reference to young birds, I believe they leave their nests totally ignorant, and naturally imitate their parents. What this imitation secures to them, in the way of knowledge, they perfect by experience; and this explains the variation in the habits of the same birds, so noticeable when studied in localities widely distant and greatly differing in character.
Let us turn our attention now to adult birds; and, with reference to them, I would refer particularly to two phases of their life-habits that have interested me exceedingly. The first of these points is the ingenuity so frequently displayed in procuring food. By the exercise of ingenuity, I mean instances of the attacking bird (in cases of birds of prey) being at first outwitted by the pursued, and, after repeated efforts availing nothing, ceasing its aggressive movements; then considering the causes of failure, planning a new method of action, and, having correctly judged the difficulties, finally succeeding. This, at least, is the manner in which I interpret the following instance:
While out watching our winter birds, January 22d of this year, I was caught in quite a hard shower, and sought shelter under a group of three large, dense cedars. Like myself, driven in from the adjoining meadows by the increasing rain, came a dozen or more sparrows, which, settling among the branches, commenced dressing their feathers and twittering cheerily. In a few moments after came, with a rush and loud chirp, a gay cardinal. If the sparrows did not acknowledge his presence with a low bow, each, at any rate, took a lower branch, leaving him on his elevated perch like a monarch on his throne. But he was fated to be molested, for, scarcely had he become fairly settled, and his feathers smoothed, when a sparrow-hawk rushed through the tree, with a zigzag movement, endeavoring to seize him or one of his attendant sparrows. Failing in this, the hawk hovered about a few moments, giving the scattered birds time to return, which they quickly did, when, with a similar rush, he again scattered them. One little snow-bird was so thoroughly frightened that it lit upon my shoulder, as though seeking safety under the brim of my hat. The third effort of the hawk failing, he came back immediately and seated himself at a little distance from the top of the tree, and close to the main stem. I remained nearly motionless, but with upturned face, and could plainly see the bird, although fortunately I escaped notice. One thing in particular attracted my notice: the bird was very much exhausted, "out of breath," as we should say of ourselves, and, with his beak open, he panted violently. This satisfied me that the efforts to capture prey are not accomplished with the ease sometimes supposed. As the rain was increasing, and the wind considerable, the sparrows again collected in the tree; and now the hawk rushed out instead of in, and bore a luckless sparrow in his claws.
I think that we have here all that I claimed, when speaking of ingenuity on the part of adult birds in seeking their food. There was in the above instance a painful consciousness, at first, of failure to secure the desired prey; there was a determination to succeed, in spite of failure at the start, and a correct determination of the cause of failure, coupled with the invention of a plan by which the difficulties might be overcome. What more should be required to demonstrate that the mental powers of lower animals differ from those of man solely in degree?
Again, let us consider a case of ingenuity displayed by a bird in successfully avoiding an enemy. Here there is more cause to be surprised at the result, inasmuch as there was no cessation of the attack, to give the pursued bird time for considering how best to act under the circumstances; but, while fleeing for life, it matured a plan of escape that happily succeeded. This instance of ingenuity on the part of a pursued bird I have already related (Land and Water, March 2, 1872), but, considering it more remarkable than any other that has occurred to my knowledge, and having witnessed a repetition of it, two years later, I again relate it, in preference to other instances I have noted, bearing upon the same subject. The case is that of a "king-rail" (Rallus elegans), which my spaniel flushed in open ground, the grass not being tall enough to conceal it. The bird trusted wholly to running, and kept clear of the dog; frequently it "doubled," and seemed to enjoy the chase; but, evidently becoming somewhat fatigued, as shown by the nearer approach of the spaniel, it ceased doubling, but, running in a straight line some distance, it allowed the dog to get within a foot or more, when it jumped, with a single flap of its wings, a foot or more from the ground; then dropping down quickly behind the dog, it turned and ran in the opposite direction, gaining considerable ground before the impetuous spaniel could check its speed, turn about, and follow. Here, again, as we would express it, in describing any human experience, "the circumstances of the case were taken into consideration" by the pursued bird, and, without taking to flight, as would seem the more natural act, it surmounted the difficulties, and effected its escape. I can conceive of no other way of explaining this action of the rail-bird, than by admitting that a train of thought passed through the brain of the bird—that it thought, "If I can gain time, I am safe," just as any pursued person would think that, if he could reach some spot, be heard, etc., he would be safe. And, while yet running at great speed, the bird thought of an ingenious plan, by which it did gain time, and reached the reedy creek-bank in safety.
It might be argued that a single act of a bird, at some one time, and under peculiar circumstances, does not constitute a habit—that it simply chanced to do so and so; but a second occurrence of the kind would result differently. It must be remembered, however, that where a bird is noticed in its natural haunts, once, even if for more than an hour—which is an unusually long observation—there are weeks when this same bird is unseen, and therefore what its acts may be are absolutely unknown. For this reason, an ingenious act of a bird may be frequently repeated, and almost certainly is. Indeed, our ignorance of bird-life is so great, that what seem to us "curious instances," because but seldom witnessed, are frequently daily occurrences, and ordinary features of the bird's life. It can scarcely have escaped the notice of close observers of our winter birds, that their comparative abundance is only during clear, pleasant weather, when they will be as lively and restless as spring birds in early summer, and that during the winter certain localities, as the southern outlooks of wooded hillsides and such sheltered spots, are those where these hardy species "most do congregate." During a mild day, at some such spot, we can almost delude ourselves into thinking that spring is coming; but on the morrow a fierce wind rattles the bare branches above you, clouds of stinging dust, or driving snow, fill the chilled air, and not a bird is to be seen or heard, the cheery sights and sounds of yesterday having given place to a dreariness most drear. One question now arises, and we naturally ask, "What has become of the birds, so lately here?"
During the winter of 1874-'75 (the coldest except one—1835−'36—since 1780), I endeavored to determine to what extent these birds sought shelter, and the character of it, not only as a protection against severe storms, but as regular winter quarters, i. e., for roosting-places. I was led to do this from the fact that these winter residents, as the bluebird, the cardinal redbird, and the titmouse, do not roost in the trees, as in summer, and it seemed probable that, seeking warmer quarters in ordinary weather, they should seek shelter from severe storms, and not temporarily migrate to some point beyond the limits of the storm; not only this, but that some spot is selected early in the season as such roosting-place and refuge, and occupied as such throughout the season. So far as my observations extend, I was correct in my surmises.
I have, on my farm, a deep "gully," or ravine, thickly wooded, and with overhanging banks, extending a considerable portion of the entire length. This overhanging earth is held in place, partly by the character of the soil, and more by the roots of the trees growing near the margins of the gully. In this locality, under the overhanging earth, in some instances at a distance of three feet from the open ground, I found the snow-birds, song and chipping sparrows, occasionally a flock of cedar-birds, the arctic snow-bird, and horned larks, roosting; and, judging from the amount of excreta upon the ground, this had been the accustomed roosting-place for many weeks. A little before sundown, during January, I would find these birds, some or all of them, congregating in the adjoining fields and in the trees of the gully, and quite suddenly they would all disappear. Searching every possible hiding-place, I finally found them as above described. If the following day proved very cold or stormy, many of them would remain in their snug retreat, the arctic visitors being the first to venture out. The birds just mentioned all build open nests, either in trees or upon the ground. On the other hand, the titmouse, nuthatch, brown tree-creeper, and bluebird, all of which build nests in hollow trees, or sheltered spots of that character, I found regularly roosted in the hollow trees, or in the outbuildings of the farm. The cardinal redbirds, however, which nest in trees and brier-patches, usually took refuge in dense cedars, to roost, but sought other shelter during severe storms. For instance, during the remarkable windstorm of February 9th, when the air was filled with dust, and the thermometer ranged from 3° to 41° Fahr., no ordinary shelter could protect our resident birds. During the day not one was to be seen flying. I found the cardinal redbirds—a pair of them—had taken shelter in a large, hollow tree, and with them was quite a large number of titmice, a brown tree-creeper (Certhia familiaris), and several sparrows. I do not doubt but that the earth-shelter already described had proved inadequate, and that the birds usually roosting there had sought more sheltered spots. However, I did not have the courage to face the wind, and see for myself, if such was the case.
During the present winter I have found that some, at least, of our winter birds utilize the very excellent shelter afforded by the nests of our bank-swallows. February 20th, a bright, clear day, I passed by a high, steep cliff of compact sand and clay, much frequented by these swallows during summer. I noticed there chipping-sparrows and a bluebird sunning themselves, each at the opening of a nest. On driving them away I found that they circled about for a few moments, and returned. On passing the cliff again, some hours later, I saw these birds, and several others, some at the openings of the nests, and others flitting about, quite in the manner of swallows. I could not reach the nests, to determine if they had been much occupied during the winter, but do not doubt but that such was the case.
I have not found, however, any shelters constructed by birds for such purpose solely, except in the case of the introduced English sparrow, which builds quite an elaborate and very warm roosting-nest. During the early frosts of autumn and prevalence of cold rain-storms, occurring before the ordinary date of migratorial departure, the nests used in spring and summer are, I know, used as roosting-places, but I have not detected any refitting of them for this purpose. Considering this, it would be natural for birds to build new structures for winter use, and in the sparrow we have an instance of it, and, I presume, the abundance of natural shelter has alone prevented the gradual acquirement of this habit by our winter birds.
Having familiarized one's self with the various phases of bird-life, as it occurs in the open fields, dense thickets, along secluded streams, and in shady forests, one can scarcely conclude otherwise, if happily he has not entered upon his studies with some preconceived notion, than that these wild and wary falcons, timid sparrows, fiery little wrens, and cautious waterfowl, are creatures that, like man himself, are thrown upon the world dependent upon their own exertions, guided by their own reasoning powers. There are no prearranged rules which, when birds leave their nests, they must strictly follow, to exist. Given that knowledge which comes through direct and indirect instruction from the parent-birds, and a young bird, having the world before it, exercises just those mental powers that man exercises, but limited just so far as its own wants are less than man's wants as man. Finally, in the chance occurrence of some peculiar habit have we not a trace of the former mode of life of some far-distant ancestral form; and, in the undeniable irregularity of all habits, can we not discern unmistakable indications of the gradual adoption of every habit, just as the various specific forms themselves gradually emerged from the archaic creature that, appearing in the dim past, foreshadowed the gigantic condor of the Andes, and the petulant humming-birds of our summer gardens?