Bird

Bird (class Aves), any of the 9,600 living species unique in having feathers, the major characteristic that distinguishes them from all other animals. A more elaborate definition would note that they are warm-blooded vertebrates more related to reptiles than to mammals and that they have a four-chambered heart (as do mammals), forelimbs modified into wings (a trait shared with bats), a hard-shelled egg, and keen vision, the major sense they rely on for information about the environment.

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