EARTH SCIENCE > BIOLOGICAL CLASSIFICATION > ANIMALS/VERTEBRATES > BIRDS
Birds, of the class Aves, are warm-blooded craniates with a body covering
of feathers; typically with forelimbs modified as wings for active flight.
They are free living (most can fly) in all terrestrial and surface water
habitats; some are capable of swimming underwater.
Burns, David M. Animal World. 1980. Octopus Books Ltd. London.