Protection Of Birds By Color
( Originally Published Ealry 1900's )
THE problem of safety, as we learned some time ago, put a premium upon a bird whose color helped him to pass unobserved. It was a very pretty theory, but we are to see how it works in practice. When we think of the red and blue and yellow birds we know, it seems hard to realize that they are included in any such design; when we think of the odd-colored ornaments that birds wear, bands, crescents, stripes, and patches, often of the most brilliant hues, we fail to understand why such markings are not a sure clue to discovery; when we recollect how unlike the different sexes of the same bird often are, and how frequently young birds are very dissimilar to their parents both in colors and in markings, we must think that it is a poor law that does not apply to all the birds of one species, but explains the plumage of one age or sex, and leaves the others still unaccounted for.
We cannot go into all the details of this subject, — even men of science are agreed to dispute about them, but we can at least notice among the birds of our acquaintance instances where their color helps to conceal them from our eyes. If all our sparrows, for example, had blue or red backs, how much more readily we should discover them; for sparrows have a way of staying near the ground, either directly upon it, or in low bushes, or about fences, where a bright colored back and breast would serve to distinguish them instantly. Now most of our common sparrows, we find, are dull-colored little birds varied with stripes about the back, breast, and head that seem to blend with the colors of the earth and with the grass stems they live among.
But the sparrows have cousins, like the grosbeaks, cardinals, and buntings, that are among our gayest birds, brilliant in red, blue, yellow, and striking combinations. Are these ground-birds? Not at all, they swing and sing among the tree-tops where there are green leaves about them and blue sky for a background, and the keen edge of their own color is, as it were, taken off. I have often thought, seeing an indigo bird swinging on the top of a balsam fir, that he was just the proper weather-vane for such a tree, his rich blue coat with peacocky hints of green seeming to stand exactly between the clear blue of the sky and blue green of the fir tree. And in the case of so brilliant a bird as the male scarlet tanager, the brightest color possible, unrelieved by any shading, there seems to be an advantage taken of the law of complemental colors which makes you see scarlet after gazing too steadily at green, or green by looking too intently upon scarlet. He cannot be hidden, and yet you do not see him among the leaves much more quickly than you would a duller-colored bird.
Another thing that has struck me is that the brightest-colored birds are found most often near civilization. You do not find the orioles and grosbeaks and tanagers so abundant away from farms and gardens. Why this is so I cannot tell you now; all we wish to infer from it is that their colors evidently do not expose them to so much danger that they avoid men; in some way they either blend with their surroundings or are able to take care of themselves in spite of their brilliant plumage. They are the birds that most of all plunge into the midst of blossoms and frolic in the snowy drifts of apple and cherry blooms.
Another family of our gayest birds, the warblers, are quite commonly tricked out with yellow and green. In watching them, I have sometimes noticed how much yellow there is in the green foliage, how they accord with leaves just opening or with leaves just fading. This is scarcely color protection, but it is color harmony, which is much the same thing.
The dull-mottled coloring of the owls, we may suppose, lias less to do with their hunting by night than with their lying still by day, when in shape and color they often much resemble dead and broken branches such as abound in a forest. An owl alighting on the top of a dead stub will seem to be a part of it, he sits so stiff and shapeless, and looks so square-headed. Nearly all the sandpipers, snipe, and other shore birds are streaked or dotted upon the back with brown and buffy like the light grass stems and the dark background behind them, a coloring which often protects the sandpiper, especially the mother bird upon the nest, from observation. But the plovers, which are nearly related to the sandpipers, have plain-colored backs, so that they come under a different protective device. They are less spotted than the sandpipers, and often have dark bands, bars, or marks about the breast and head that may help to efface the outline.
When you have opportunity, notice how much the backs of nighthawks and whippoorwills look like some of the dark-spotted, night-flying moths that lie still by day under brown leaves and upon tree trunks. In the same way, these birds that hunt during the hours of dark and twilight, and crouch upon the ground or upon the branch of a tree during the day, closely resemble the surface they alight on. The back of the woodcock is quite similarly mottled. The back and sides of grouse and quail are also protectively colored.
The outline of a bird is often more readily recognized than a spot or color would be; we see the familiar line, and infer that it belongs to a bird, therefore many of the bird's ornaments are a protection against discovery. " This makes, for instances, the mallard's dark green head tend to detach itself from his body and to join the dark green of the shady ledge, or the ruby of the humming-bird to desert him and to appear to belong to the glistening flower he is searching." In this way, bright or strongly contrasting crown patches, throat patches, necklaces, and collars may be seen to have a use other than mere ornament, and crests often help to conceal birds by disguising familiar outlines. The cedar bird and the ruffed grouse are experts in evading notice by throwing themselves into strange attitudes and erecting their crests. Curves are what betray the bird; broken outlines or stiff lines conceal him. Therefore the ruffed grouse, when in a tree, lays all his feathers flat, stands stiffly at his greatest height, with his neck stretched as far as he can reach or crooked sharply at an angle. I have stood within two yards of a ruffed grouse, in fair sight, and that not many years since, and have decided that he was a very strange branch on a willow bush, before it flashed upon me what I was looking at.
The most beautiful arrangement for protective color is also the commonest, and though nearly every bird and animal profits by it, no man ever discovered it until a few years ago. It is called the "law of gradation." Nearly every bird, you know, is lighter on the breast than on the back, and it is almost a rule that birds not uniformly colored, like the crow and the blackbirds, shall be white or gray or buffy along the belly and beneath the tail, even if they have dark breasts and throats. Why this is so, is as simple as it is interesting.
Every bird, standing in his usual positions, cuts off a portion of the light that falls from above and so casts a shadow on his own breast and under surface. We do not see the shadow, we do not know of its existence, but it is there. If the bird's breast were the same color as his back, the shadow, making it appear darker than it is (that is, darker than the back), would bring out the line of the breast sharply against the background. The shadow on a light breast cancels the effect of light upon a dark back and causes the outline to blend with the back-ground.
Nothing could be simpler than the experiment by which Mr. Abbott H. Thayer, the artist who painted the " Madonna Enthroned " and other well-known pictures, proved his discovery of this " law of gradation " to a large number of scientists. Any child can perform the experiment with very little trouble. We quote from the original report of the experiment: Mr. Thayer placed three sweet potatoes, or objects of corresponding shape and size, horizontally on a wire a few inches above the ground. They were covered with some sticky material, and dry earth from the road on which they stood was sprinkled over them so that they would be of the same color as the background. The two end ones were then painted white on the under side, and the white color was shaded up and gradually mixed with the brown of the sides. When viewed from a little distance these two end ones, which were white below, disappeared from sight, while the middle one stood out in strong relief and appeared much darker than it really was. Mr. Thayer explained that terrestrial birds and mammals which are protectingly colored have the under parts white or very light in color, and that the color of the under parts usually shades gradually into that of the upper parts. This is essential in order to counteract the effect of the shadow, which otherwise, as shown by the middle potato, makes the object abnormally conspicuous and causes it to appear much darker than it really is. Some of the witnesses could hardly believe that the striking difference in the visibility of the three potatoes was entirely due to the coloring of the under side, and Mr. Thayer was asked to color the middle one like the two others in order that the effect might be observed. Mr. Thayer complied with the request, painting the under side of the middle potato white, and shading the white up into the sides as in the case of the others. The effect was almost magical. The middle potato at once disappeared from view. A similar experiment was tried on the lawn. Two potatoes were painted green to resemble the green of the grass above which they were suspended. One was painted white on the under side and at once became invisible when viewed from a little distance, while the other showed plainly and seemed very dark, the shadow, superadded to the green of the under side, making it remarkably conspicuous. The experiments were an overwhelming success."
Try this experiment yourself and then notice how al-most invariable is this law of gradation by which Nature helps the birds and beasts to escape detection, however gayly they are colored.