Any mammal of the order Chiroptera, related to the Insectivora (hedgehogs and shrews), but differing from them in being able to fly. Bats are the only true flying mammals. Their forelimbs are developed as wings capable of rapid and sustained flight. There are two main groups of bats: megabats, which eat fruit, and microbats, which mainly eat insects. Bats are nocturnal, and those native to temperate countries hibernate in winter. There are about 977 species forming the order Chiroptera, making this the second-largest mammalian order; bats make up nearly one-quarter of the world's mammals. Although bats are widely distributed, populations have declined alarmingly and many species are now endangered.
Megabats The Megachiroptera live in the tropical regions of the Old World, Australia, and the Pacific, and feed on fruit, nectar, and pollen. The hind feet have five toes with sharp hooked claws from which the animal suspends, head downwards, when resting. There are 162 species of Megachiroptera. Relatively large, weighing up to 900 g/2 lb and with a wingspan as great as 1.5 m/5 ft, they have large eyes and a long face, earning them the name ‘flying fox’. Most navigate by sight.
Microbats Most bats are Microchiroptera: small and insect-eating. Some eat fish as well as insects; others consume small rodents, frogs, lizards, or birds; a few, vampire bats, feed on the blood of mammals. A single bat may eat 3,000 insects in one night. There are about 750 species. They roost in caves, crevices, and hollow trees. The bumblebee bat, inhabiting Southeast Asian rainforests, is the smallest mammal in the world. A new species of bat, Rhinolophus convexus, was discovered in Malaysia, at an altitude of 1,600 m in the Cameron Highlands, in 1997. It is related to the tropical horsehoe bats. In December 2001, a new bat species was discovered in Greece. It is a whiskered bat, species Myotis, and is the smallest of the species.
Many microbats have poor sight and orientation and hunt their prey principally by echolocation. They have relatively large ears and many have nose-leaves, fleshy appendages around the nose and mouth, that probably help in sending or receiving the signals, which are squeaks pitched so high as to be inaudible to the human ear.
In Britain, there are about 12 species of bat belonging to the families Rhinolophidae (the horseshoe bats, with nose-leaves) and Vespertilionidae (small bats, about 6 cm/2 1/2 in long, with plain noses). Since 1981 bats have been protected by law. However, by July 2001, there were only 4,000–6,000 horseshoe bats left in the UK.
Ancestors The difference in the two bat groups is so marked that many biologists believed that they must have had different ancestors: microbats descending from insectivores and megabats descending from primates. However, analysis of the proteins in blood serum from megabats and primates by German biologists in 1994 showed enough similarities to suggest a close taxonomic relationship between the two groups. In 2000 Japanese researchers analysing mitochondrial DNA concluded that megabats and microbats do share a common origin. They proposed that the bat order evolved 83 million years ago, and that the two groups diverged around 58 million years ago.
Biology A bat's wings consist of a thin hairless skin expansion, stretched between the four fingers of the hand, from the last finger down to the hindlimb, and from the hindlimb to the tail. The thumb is free and has a sharp claw to help in climbing. The shoulder girdle and breastbone are large, the latter being keeled, and the pelvic girdle is small. The bones of the limbs are hollow, other bones are slight, and the ribs are flattened.
An adult female bat usually rears only one pup a year, which she carries with her during flight. In species that hibernate, mating may take place before hibernation, the female storing the sperm in the genital tract throughout the winter and using it to fertilize her egg on awakening in spring. Many rainforest trees depend on bats for pollination and seed dispersal, and around 300 bat-dependent plant species yield more than 450 economically valuable products. Some bats are keystone species on whose survival whole ecosystems may depend. Bat-pollinated flowers tend to smell of garlic, rotting vegetation, or fungus.
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