Bird

Birds are bipedal, warm-blooded, oviparous vertebrate animals characterized mostly by feathers, forelimbs modified as wings, and hollow Bones. Birds range in size from the tiny hummingbirds to the huge Ostrich and Emu. Depends on the taxonomic viewpoint, there are about 8,800–10,200 living bird species in the world, making them the most diverse class of terrestrial vertebrates.

Birds feed on nectar, plants, seeds, insects, fish, mammals, carrion, or other birds. Most birds are diurnal or active during the day, but some birds, such as the owls and nightjars, are nocturnal or crepuscular, and many coastal waders feed when the tides are appropriate, by day or night. Many birds travel long distances to utilize optimum habitats while others spend almost all their time at sea. Some, such as Common Swifts, stay aloft for days at a time, even sleeping on the wing.