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Bats are mammals in the order Chiroptera. Their most distinguishing feature is that their forelimbs are developed as wings, making them the only mammal capable of flight. (Other mammals, such as flying squirrels and gliding phalangers, can glide for limited distances but are not capable of true flight). The word Chiroptera can be translated from the Greek words for "hand wing," as the structure of the open wing is very similar to an outspread human hand, with a membrane (patagium) between the fingers that also stretches between hand and body.

There are estimated to be about 1,100 species of bats worldwide: about 20% of all mammal species.

About 70 percent of bats are insectivorous. Most of the remainder feed on fruits and their juices; three bat species eat blood and some prey on vertebrates. These bats include the leaf-nosed bats (Phyllostomidae) of central America and South America, and the related bulldog bats (Noctilionidae) that feed on fish. There are two known species of bat that feed on other bats: the Spectral Bat or American False Vampire bat and the Ghost Bat of Australia.

Most microbats are active at night or at twilight. But although the eyes of most species of microbats are small and poorly developed, the sense of vision is still functional, especially at long distances, beyond the range of echolocation. Their senses of smell and hearing, however, are excellent. By emitting high-pitched sounds and listening to the echoes, the microbats locate prey and other nearby objects. This is the process of echolocation, a skill they share with dolphins and whales.

The teeth of microbats resemble those of the insectivorans. They are very sharp in order to bite through the chitin armour of insects or the skin of fruits.

The finger bones of a bat are much more flexible than those of other mammals. One reason is that the cartilage in their fingers lacks calcium and other minerals nearer the tips, increasing their ability to bend without splintering. The cross section of the finger bone is also flattened instead of circular as is the bone in a human finger, making it even more flexible. The skin on their wing membranes is a lot more elastic and can stretch much more than what is usually seen among mammals.

Because their wings are much thinner than those of birds, bats can maneuver more quickly and more precisely than birds. The surface of their wings are also equipped with touch-sensitive receptors on small bumps called "Merkel cells", which is found in most mammals, including humans. But these sensitive areas are different in bats as there are a tiny hair in the center, making it even more sensitive and detects and collects information about the air flowing over the wings. Another kind of receptor cells are found in the wing membrane in species who are using their wings to catch prey, and is sensitive to the stretching of the membrane. These cells are consentrated in the areas of the membrane where insects hits the wings when the bats capture them.

Mother bats usually have only one offspring per year. A baby bat is referred to as a pup. Pups are usually left in the roost when they are not nursing. However, a newborn bat can cling to the fur of the mother and be transported, although they soon grow too large for this. It would be difficult for an adult bat to carry more than one young, but normally only one young is born. Bats often form nursery roosts, with many females giving birth in the same area, be it a cave, a tree hole, or a cavity in a building. Mother bats are able to find their young in huge colonies of millions of other pups. Pups have even been seen to feed on other mothers' milk if their mother is dry. Only the mother cares for the young, and there is no continuous partnership with male bats.

The ability to fly is congenital, but after birth the wings are too small to fly. Young microbats become independent at the age of 6 to 8 weeks, megabats not until they are four months old. At the age of two years bats are sexually mature.

Bats vary in social structure, with some bats leading a solitary life and others living in caves colonized by more than a million bats.

The fission-fusion social structure is seen among several species of bats. The fusion part is all the individuals in a roosting area. The fission part is the breaking apart and mixing of subgroups by switching roosts with bats, ending up with bats in different trees and often with different roostmates.

Studies also show that bats make all kinds of sounds to communicate with each other. Scientists in the field have listened to bats and have been able to identify some sounds with some behavior bats will make right after the sounds are made.

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