Page:Popular Science Monthly Volume 30.djvu/623

Rh about the matter, it would become very hungry during the long polar day.

The orders of night-birds are not very numerous, and only a few plant-feeders are known among them; but many species are represented among the darkness-loving forms, constituting groups like the owls among the birds of prey and the night-swallows, or in single species, like the strigops and apteryx of New Zealand. In the great family of the waders the stone-curlew, the bittern, the snipe, and others are nocturnal, while the black skimmer and the stormy petrel, among the swimmers, partially exhibit the same peculiarity. Those among these birds which have best adapted themselves to the nightlife, however little they may otherwise be related to one another, exhibit a number of peculiarities in bodily structure. The eyes of all of them have undergone some obvious modifications. They are large, capable of considerable widening of the pupil, and otherwise especially differentiated in the elements of the retina. A degree of uniformity also prevails in the disposition of the plumage of all these forms; it is monotonous in its coloring, brownish or greenish gray, but never striking or lively, and this for closely related reasons. First, by means of these dull and therefore protective colors night-birds are enabled to live nearly hidden during the day, and are thereby saved from many disturbances and annoyances; and, secondly, because, in the nature of things, sexual selection, determined by the coloring of the feathers, can not exert any modifying influence upon them. What use has the male night-swallow for beauties which the female can not appreciate? The plumage of the real night-birds is also peculiarly soft and dense, so that their movements in the air are almost perfectly noiseless, and so ghost-like in their silence that they are regarded with superstitious awe by the natives of almost every land.

The food itself of birds is of the most diversified character. While some of the tribe are omnivorous, others appear to be adapted to special kinds of food. Usually forms may be distinguished which feed either exclusively on animal or on vegetable meats, or on both. With most birds the last is, in a greater or less degree, the case. Even the so-called "noble" birds of prey occasionally eat berries and herbs when compelled by necessity. Only a few classes of the animal kingdom, perhaps only those which live entirely in the depths of the sea, fail to contribute of their bodies and lives to the repasts of birds; but vertebrates and insects are their favorite game. One bird will eat only living game which it has caught itself, another only carrion, and a third both. Falcons, eagles, hawks, and owls feed upon living, usually warm-blooded creatures; and, while the presence of these may in some cases be regarded as a calamity, it may in other cases be looked upon as a benefit. Alturn, by examination of the hair-balls of indigestible remains of food ejected through the mouth, found that the smaller owls are of the highest advantage in agriculture on