Bats (order Chiroptera with 986 species) are the only truly flying mammals, although several gliding mammals are referred to as “flying” (such as the flying squirrel and flying lemur). The “wings” of bats are double membranes of skin stretching from the sides of the body to the hind legs and tail, and are actually skin extensions of the back and belly. The wing membranes are supported by the elongated fingers of the forelimbs (or arms). Nocturnal (active at night), ranging in length from 1.5 inches (25 millimeters) to 1.3 feet (40.6 centimeters), and living in caves or crevices, bats inhabit most of the temperate and tropical regions of both hemispheres. The majority of species feed on insects and fruit, while some tropical species eat pollen and nectar of flowers, and insects found inside them. Moderate-sized species usually prey on small mammals, birds, lizards, and frogs, and some eat fish. But true vampire bats (three species) eat the blood of animals by making an incision in the animal’s skin—from these bats, animals can contract rabies.

Most bats do not find their way around by sight but have evolved a sonar system, called “echolocation,” for locating solid objects. Bats emit vocal sounds through the nose or mouth while flying. These sounds, usually above the human hearing range, are reflected back as echoes. This method enables bats, when flying in darkness, to avoid solid objects and to locate the position of flying insects. Bats have the most acute sense of hearing of any land animal, hearing frequencies as high as 120 to 210 kilohertz. The highest frequency humans can hear is 20 kilohertz.