Bats, like humans and other mammals, are warm-blooded, have fur or hair, give birth to live young, and feed their newborn milk from mammary glands. Bats are the only mammals that can fly, and their wings make any of the approximate 925 living species in the world instantly recognizable. However, many variations in the basic structure of their anatomy and social lives reflects a greater degree of specialization than that of any other order of mammal
Forty-two species of bats are found in the United States, all microbats. In California, there are 23 species within 3 families - the Phyllostomidae (leaf-nosed bats; 2 species), the Vespertillionidae (plain-nosed, vespertillionid, or little brown bats; 17 species), and the Molossidae (free-tailed bats; 4 species).