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THE BUILDING OF THE NEST
THERE are probably very few children who are not more or less familiar with birds' nests, for they are not by any means confined to the country, but are to be found in the shade trees of every village street, to say nothing of the old-time lilac hedges, gooseberry bushes, and homely shrubbery of fifty years ago. Even in our large cities there are some few birds brave enough to make their homes in or very near the busiest thoroughfares. As an instance, it was not so long ago that a yellow-breasted chat — a shy bird — nested in the yard of the Pennsylvania Hospital, at the corner of Eighth and Spruce Streets, Philadelphia, and soon learned to mimic many a familiar street sound. Such instances as these were more common before the unfortunate blunder of introducing the English sparrow. But it is in the country only that we find boys really posted in the matter of nests, and I wish I could add that they always adopt the rules of "hands off" when these nests come under their notice. It means far more mischief than most people think to disturb a nest, and so let every boy decide that he will not be guilty of such wanton cruelty. This, however, does not shut off every boy and girl in the land from studying these nests, and a more delightful subject can never come under youthful investigation.
What is a bird's nest? Every one knows, after a fashion, and yet few have ever considered how much that bunch of twigs, hollow in a tree, or hole in the ground really means. Like so much that is familiar, we glance at it in a careless way and never stop to consider its full significance. Except in a very few instances, a bird's nest is never the result of a single individual's labor. Even if but one bird does all the work, there has previously been a decision reached by two birds as to where the nest shall be placed, and how much this means! At once we are brought to consider that an interchange of thought has taken place. The pair have discussed, literally, the merits and drawbacks of the situation, and have had in mind not only their own safety, but that of their off-spring. The fact that they make mistakes
at times proves this. Were this not the case, or if nests were placed hap-hazard in any tree or bush or anywhere on the ground, bird enemies would have a happy time for a short season, and then birds, like many of the world's huge beasts, would become extinct. On the contrary, birds have long since learned to be very careful, and their ingenuity in this apparently simple matter of choosing a nest site is really astonishing. This, too, has resulted in quickening their wits in all directions, and the bird that is really a booby is scarcely to be found.
Birds suffer at times from their misjudgment or over-confidence, and this, it must be added, reflects upon us. The instances are numberless where birds have quickly learned that certain people love them, and they lose all fear. Again, naturally very timid birds soon learn when they are free from persecution. The writer frequently passes in the cars by a zoological garden on the bank of a river, and has been impressed with the abundant illustration of birds' intelligence to be noticed there. The crows have learned that fire-arms are not allowed to be used anywhere near, and so they fearlessly hop about not only the enclosure of the garden, but the many tracks of the railroad just outside, showing no timidity even when the locomotives rush by. Stranger still, wild ducks gather in the river almost directly under the railroad bridge, and do not always dive out of sight as the trains pass by, and I have never seen them take wing, even when the whistle blew the quick, short, penetrating danger signal.
To come back to their nests: birds have other enemies than man to guard against, and so are never in a hurry in the matter of determining where to build. Time and again a location has been discovered to be unsuitable after a nest has been commenced, and the structure abandoned. I have observed this many times. Indeed, my own curiosity has led the birds to move, they not quite approving my constant watching of what was going on. I well remember seating myself once in a shady nook to eat my lunch, and being almost attacked by a pair of black-and-white tree-creeping warblers. Their actions were plainly a protest against my staying where I was, and on looking about, I found that I had almost sat upon their nest, which was then just completed, but contained no eggs. I visited the spot the next day and found a single egg; but my coming was a mistake, for the birds now believed I had sinister designs, and abandoned their new-made home.
The method of building, of course, varies as much as the patterns of nests. Even when the same materials are used, they are differently treated, and a nest of sticks only may in one case be merely thrown together, as it were, while in another they are so carefully interlaced that the structure is a basket, and holds together if held by the rim only. Another, the same in general appearance, would immediately fall to pieces if similarly treated. A reason for this is discoverable in some cases, but not in all. If we examine a great many nests, the rule will hold good, I think, that where they are very loosely put together, the locality is such that no natural disturbing causes, as high winds, are likely to bring disaster. Until I studied this point the occurrence of exceedingly frail nests was ever a matter of surprise, for it is to be remembered that the same species, as a cat-bird or cardinal red-bird, does not build after a uniform fashion, but adapts its work to the spot chosen for the nest. It would be very hazardous to say that a nest was built by this or that bird, unless the builder was seen in possession.
So difficult is it to watch a pair of birds while building, that the method of their working is largely to be guessed at from the work itself, but by means of a field-glass a good deal can be learned. It would appear as if a great many twigs were brought for the foundation of a nest, such as a cat-bird's or song-sparrow's, that were unsuitable. I have occasionally seen a twig tossed aside with a flirt of the head very suggestive of disappointment. The builders do not always carry with them a distinct idea of what they want when hunting for material, and so labor more than would be necessary if a little wiser. Very funny disputes, too, often arise, and these are most frequent when wrens are finishing their huge structures in a box or some corner of an out-building. A feather, or a bit of thread, or a small rag will be carried in by one bird and tossed out by the other with a deal of scolding and "loud words" that is positively startling. But when the framework of any ordinary open or cup-shaped nest is finally completed, the lining is not so difficult a matter. Soft or yielding materials are used that to a greater or less extent have a "felting property," and by the bird's weight alone assume the shape desired. This is facilitated by the bird in two ways: the builder sits down, as if the eggs were already laid, and with its beak pushes the loose material between it and the framework, and tucks odd bits into any too open crevices. While doing this, it slowly moves around until it has described a complete circle. This brings to light any defect in the outer structure, and the bird can often be seen tugging away at some projecting end, or its mate, outside of the nest, rearranging a twig here and there, while the other bird — shall I say? — is giving directions.
Surprise has often been expressed that the common chipping sparrow can so neatly curl a long horse-hair into the lining of its little nest. It cannot be explained, perhaps, but we have at least a clue to it. One end of the hair is snugly tucked in among stouter materials, and then, — I ask the question only, — as the bird coils it about the sides of the nest with its beak, does it break or dent it, or is there some chemical effect produced by the bird's saliva? The hairs do not appear to be merely dry-curled, for in that case they would unroll when taken from the nest, and such as I have tried, when just placed in position, retained the coiled condition when removed. But old hair, curled by long exposure to the air and moisture, is often used, and this is far more tractable. When we come to examine woven nests, such as the Baltimore oriole and the red-eyed vireo, as well as some other small birds, build, there is offered a great deal more to study, for how they accomplish what they do, with their only tools their feet and beak, is not wholly known. That the tropical tailor-bird should run a thread through a leaf and so bring the edges together and make a conical-shaped bag, is not so very strange. It is little more than the piercing of the leaf and then putting the thread through the hole. This is ingenious but not wonderful, because not difficult; but let us consider a Baltimore oriole and his nest. The latter is often suspended from a very slender elm or willow twig, and the bird has a hard time to hold on while at work. One experienced old oriole has for years built in the elm near my door, and occasionally I have caught a glimpse of him. I will not be positive, but believe that his first move is to find a good stout string, and this he ties to the twig. I use the word "tie" because I have found in many cases a capitally-tied knot, but how the bird, or birds, could accomplish this I cannot imagine. Both feet and beak, I suppose, are brought into play, but how? To get some insight into the matter, I once tied a very long string to the end of a thread that the oriole had secured at one end and left dangling. This interference caused some commotion, but the bird was not outwitted. It caught the long string by its loose end and wrapped it over and over various twigs, and soon had a curious open-work bag that served its purpose admirably. The lining of soft, fluffy stuffs was soon added. This brought up the question as to whether the bird ever ties short pieces together and so makes a more secure cable that gives strength to the finished nest. In examining nests, I have seen such knots as might have been tied by the birds, but there was no way to prove it. That they do wrap a string several times about a twig and then tie it, just as a boy ties his fishing-line to a pole, is certain. With my field-glass I have followed the bird far enough to be sure of this. When at work, the bird, from necessity, is in a reversed position, — that is, tail up and head down. This has an obvious advantage, in that the builder can see what is going on beneath him, and shows, too, how near the ground the nest will come when finished; but it sometimes happens that he gets so absorbed in his work that a person can approach quite near, but I never knew him to become entangled in the loose ends that hang about him.
The oriole at times offers us a wonderful example of ingenuity. It occasionally happens that too slight a twig is selected, and when the nest is finished, or, later, when the young are nearly grown, the structure hangs down too low for safety or sways too violently when the parent birds alight on it. This is a difficulty the bird has to contend with, and he has been known to remedy it by attaching a cord to the sustaining twigs and tying them to a higher limb of the tree, thus securing the necessary stability.
A more familiar evidence of the intelligence of birds is when the vireos are disturbed by the presence of a cow-bird's egg in their nest. To get rid of it, they often build a new floor to the nest, and so leave the offending egg to spoil. But there is displayed here an error of judgment that I am surprised to find. The birds that take this trouble certainly could throw the egg out, and, I should think, preserve their own eggs, which invariably are left to decay when a new structure is reared above the old. I believe even three-storied vireos' nests have been found.
There is one common swallow that is found well-nigh everywhere, which burrows into the sand; and when we think of it, it seems strange that so aerial a bird should build so gloomy an abode for the nesting season. This bank swallow, as it is called, selects a suitable bluff, facing water, and, with closed beak, turns round and round with its head to the ground, thus boring a hole big enough to crawl into. It turns into a gimlet for the time, and uses its beak as the point of the tool. This is odd work for a bird that almost lives in the air; and then think, too, of sitting in a dark cave, sometimes six feet long, until the eggs are hatched. On the other hand, the barn swallow makes a nest where there is plenty of light and air, and is a mason rather than a carpenter or miner. The mud he uses is not mere earth and water, but is made more adherent by a trace of secretion from the bird's mouth; at least, my experiments lead me to think so. To build such a nest would be slow work did not the two birds work together and carry their little loads of mortar with great rapidity. They waste no time, and use only good materials, for I have noticed them, when building, go to a quite distant spot for the mud when a pool was directly outside of the barn in which they were building. To all appearance the nest is of sun-dried mud, but the material has certainly undergone a kind of puddling first that makes it more adherent, bit to bit, and the whole to the rafter or side of the building. Again, these swallows have the knack of carrying a little water on the feathers of their breasts, I think, and give the structure a shower-like wetting from time to time. At last the structure "sets" and is practically permanent.
There are birds that build no nests, like the kill-deer plover and the woodcock, and yet they exercise a faculty of equal value intellectually; for to be able to locate a spot that will be in the least degree exposed to danger is a power of no mean grade. The kill-deer will place its eggs on sloping ground, but somehow the heaviest dashes of rain do not wash out that particular spot. There are sand-pipers that lay their eggs on a bit of dead grass, just out of reach of the highest tides. As we look at such nests, we conclude that the birds trust a great deal to good luck; but, as a matter of fact, the destruction of eggs when in no nests, or next to none, is very small. Why, on the other hand, wood peckers should go to such an infinity of trouble to whittle a nest in the firm tissue of a living tree, when a natural hollow would serve as well, is a problem past finding out. I have even seen a woodpecker make a new nest in a tree which already contained one in every respect as good.
Going back to the fields and thickets, it will be seen that birds, as a rule, desire that their nests should be inconspicuous, and their efforts are always largely in this direction in the construction. The foliage of the tree or bush is considered, and when not directly concealed by this, the nest is made to look marvellously like a natural production of the vegetable world, as the beautiful nest of our wood pee-wee or the humming-bird shows. These nests are then not merely the homes of young birds, but are places of defence against a host of enemies. The parent birds have no simple task set before them that can be gone through with mechanically year after year. Every season new problems arise, if their favorite haunts suffer change, and every year the birds prove equal to their solution.