B. change their feathers (molt), in general, once a year, and the colors of the plumage in many cases vary much in summer and winter. The change of color, how ever, often takes place without change of feathers, and in B. which molt both in spring and autumn, the autumn molting is much more complete than that of spring. The gayest plumage of ninny 13. is assumed at the breeding-season, with which, also, the song of B is connected. See SONG or Bums. The plumage of the male is, in general, mere gay than that of the female, all the young at first resembling the female iii plumage. The plumage usually characteristic of the male is occasionally assumed by the female, and most frequently by females which have become unlit for the ordinary functions of their sex.
The brain in B. differs in some important respects from that of mammalia (see BRAIN). presenting resemblances to the brain of reptiles and fishes; but it is of largo size, often larger than even in quadrupeds. The manifestation of intelligence is not, however, usually so great in 13. as in quadrupeds. Their nest-building, their migrations (see BIRDS OF PASSAGE), .and many other things of greatest interest, must be ascribed to instinct.
In the geographical distribution of B., the limits of species arc not so exactly cumscribed by mountains, seas, and rivers as in other classes of animals, their pOwers of flight enabling them to pass over these obstacles. Yet some species, and even groups, are found exclusively in certain regions: thus humming-birds are all American, pen gmins are found only in the southern seas, and B. of paradise are confined to New Guinea and the neighboring islands. See SPECIES.
The free movements of B. through seemingly boundless space, the joyous song of many, and the characteristic tones of all—their brilliant colors, their lively manners, and their wonderful instincts—have from the earliest ages made a strong impression on men's minds, and in the infancy of intellect gave rise to many peculiar and mysterious associations with this class of creatures. Hence the flight of B. was made the founda
tion of a particular art of divination. See AUGURIES and AUSPICES. Religion borrowed many of its symbols from them, and poetry many of its ornaments.
In an economical point of view, B. are very important. The flesh and eggs of almost all 13. may be eaten, although those of B. of prey and of fish-eating- 13. are generally reckoned unpleasant. Their feathers are employed for various purposes of use and ornament; their dung is valuable for manure, and guano (q.v.) is nothing else than the accumulated dung of sea-fowls. Many B. are extremely useful in preventing the multiplication of insects and worms, and compensate in this way for the misehief which they occasionally do in fields and Domestic poultry are a :mime of considerable profit, upon account of their eggs, flesh, and feathers. See Pori.re.v. Some kinds of B. of prey have been tamed, and trained to the use of the sportAnon. See FALCONRY.
About 5000 existing species of B. are known. As to their systematic arrangement, see ORNITHOLOGY.
The order of B. presents in the dodo (q.v.) a remarkable and instance of the recent extinction of a species, and even of a genus. It is also a remarkable and interesting fact that the greater part of the remains of extinct B. hitherto discovered are those of land-birds destitute of the power of flight, like the dodo, and the still existing ostrich, cassowary emu, and apteryx. A particular interest is attached to those of the gigantic dinornis (q.v.) of New Zealand. See nest article.