bird

bird Any one of c.8600 species of feathered vertebrates, which occupy most natural habitats from deserts and tropics to polar wastes. Birds are warm-blooded and have forelimbs modified as wings, hind-limbs for walking, and jaws elongated into a toothless beak. They lay eggs (usually in nests), incubate the eggs, and care for young. As a group they feed on seeds, nectar, fruit and carrion, and hunt live prey ranging from insects to small mammals, although individual species may be very specialized in their diet. Sight is the dominant sense, smell the poorest. Size ranges from the bee hummingbird, 6.4cm (2.5in) to the wandering albatross, whose wingspread reaches 3.5m (11.5ft). The 2.4m (8ft) tall ostrich is the largest of living birds, but several extinct flightless birds were even bigger. Of the 27 orders of birds, the perching birds (Passeriformes) include more species than all others combined. A bird's body is adapted primarily for flight, with all its parts modified accordingly. There are several species of large, flightless land birds, including the ostrich, rhea, emu, cassowary, kiwi, and penguin. Birds are descended from Theocodonts (reptiles), and the first fossil bird, archaeopteryx, dates from the late Jurassic period. Class Aves. See individual species