BIRDS AND THEIR DAILY BREAD. 601 



ticular 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 repre- 

 sented 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 night- 

 life, however little they may otherwise be related to one another, ex- 

 hibit 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 espe- 

 cially differentiated in the elements of the retina. A degree of uni- 

 formity 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 Tast 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 king- 

 dom, 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. Altum, 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 ac- 



