Birds are members of the class Avis, which consists of approximately 9000 species. They are mostly omnivores, carnivores and insectivores, though there are also a number of nectarivores and nut-eaters in the class.
Description[]
Birds are mostly small, and all have feathers and two legs.
Flight[]
Apart from bats, birds are the only vertebrates capable of flight. They have hollow bones to lower their weight, and large breast muscles to provide high power for the wings.