BAT

a member of any of some 900 species of flying mammals. Bats are the only mammals to have evolved true flight, and most species also possess an acute system of acoustic orientation, or echolocation. Most bats are insectivorous. As they consume immense quantities of insects, bats are important in the balance of insect populations and may even be instrumental in controlling some insect pests. Certain bats also feed on fruit, pollen, and nectar, and vampire bats in tropical America feed on the blood of mammals and large birds. These bats sometimes serve as carriers of rabies. Bats are found worldwide. The United States is known to have 15 genera, totalling 40 species of bats. While in the West they are the subject of unfavourable myths, in the Orient bats are often considered to be good luck symbols. In the tropics, where they are particularly abundant, bats attract considerable attention by their noisiness, guano (droppings), and odor, as large colonies of bats can infest houses and public buildings. Two suborders divide the bat order: the Megachiroptera (flying foxes and Old World fruit bats) and the Microchiroptera (distributed worldwide). The Megachiroptera are visually oriented-only one genus, Rousettus, possesses an acoustic orientation ability-and in many ways skeletally primitive. The Microchiroptera all possess the ability to orient and even hunt by acoustic means. It is not known whether the two have a common origin. Bats vary greatly in size. The largest of the flying foxes, Pteropus vampyrus, has a wingspread of as much as 1.5 m (5 feet), while the wingspread of Kitti's hognose bat (Craseonycteris thonglongyai) is about 15 cm (6 inches). Bats also display variety in colour, fur texture, and facial appearance. The wings of bats are an evolutionary modification of the forelimbs. The fingers (not including the thumb) are greatly elongated and joined by a membrane extending from the forearm and upper arm down the side of the body to the ankle or foot. The thumb ends with a claw. Most bats also have a two-layer membrane of darkly pigmented, naked skin extending between their legs. The bat's muzzle is often rodentlike or foxlike. The external ear projects forward and is usually very large and often highly mobile. Many bats also have a nose leaf, which consists of skin and connective tissue that either surrounds the nostrils or flaps above them. It is thought that the nose leaf influences sound production for echolocation. The bat's neck is short, the chest and shoulders well muscled and large, and the hips and legs slender. Except for the wing membranes, bats are well furred in shades of gray, tan, brown, or black on the back and in lighter shades ventrally. Among species that roost in the open, mottled or speckled fur and variations in coloration are common. Bats affect the natural order by predation and by pollination and seed dispersal, which they aid by their feeding habits. Only the vampire bats of tropical America pose a serious problem to man; among livestock they can transmit rabies in cattle. The guano deposits of insectivorous bats have long been used for agricultural fertilizer. The sexual cycles of entire bat populations are synchronized so that most of the mating activity occurs over a period of a few weeks. Gestation ranges from six or seven weeks to five or six months. Pregnant female bats of many species migrate to special nursery roosts. Bats generally bear one young, although the big brown bat (Eptesicus fuscus) can bear twins and the red bat (Lasiurus borealis) bears a litter of one to four. Infants are born nude or with light fur and are often blind and deaf for a short period after birth. They nurse for five or six weeks or for as long as five months, depending on size and suborder. By two months of age most Microchiroptera are adult-sized. Indiana bats (Myotis sodalis) hibernating on a cave roof. Nearly all bat species roost during the day and forage at night. This gives carnivorous bats, vampires, and perhaps fishing bats an advantage over sleeping prey and also protects bats from predators, sun, and high temperatures. Bats generally prefer isolated roosts such as caves, crevices, burrows, or buildings. Some bats, however, roost outdoors on trees or rocks. Usually bats are found in clustered colonies ranging from a few dozen to hundreds of thousands of individuals. Predation is not a serious threat to bats, and disease, starvation, and accidents appear to take small tolls. Some bats are known to have lived more than 20 years. Isolated roosts, nocturnal activity, and a generally colonial way of life are factors that contribute to the longevity of bats. In those bats that use echolocation, short high-frequency sound pulses are produced that reflect from objects in the vicinity. The bats listen to the returning echoes and are able to locate prey and obstacles. Highly sensitive ears and greatly developed integration of vocal and auditory centres of the brain are required for this feat. The sound pulses may also be used for communication between bats. any member of the order Chiroptera, the only mammals to have evolved true flight. This ability, coupled with the benefits deriving from their system of acoustic orientation (so-called bat sonar), has made the group a successful one in numbers of species and individuals. About 900 species are currently recognized, belonging to some 174 genera. Many species of bats are enormously abundant. Observers have concluded, for example, that some 100,000,000 female Mexican free-tailed bats (Tadarida brasiliensis mexicana) form summer nursery colonies in Texas, where they produce about 100,000,000 young in five large caves. Adult males of this species, although equal to the females in numbers, may not range as far north as Texas. (Individuals of the species also range widely throughout tropical America.) Thus, bats of one species alone number at the very least in the hundreds of millions of individuals. Additional reading G.M. Allen, Bats (1939, reissued 1967), a comprehensive view by a naturalist; K.C. Andersen, Catalogue of the Chiroptera in the Collection of the British Museum, 2nd ed., vol. 1, Megachiroptera (1912, reissued 1966), definitive taxonomy of the Megachiroptera; R.W. Barbour and W.H. Davis, Bats of America (1969, reprinted 1979), comprehensive coverage of North American bats, distribution, natural history, photographs, and taxonomy; A. Brosset, The Biology of the Chiroptera (1973; originally published in French, 1966), the most complete, up-to-date review of all bats; R.G. Busnel (ed.), Animal Sonar Systems, 2 vol. (1967), the most recent important symposium on echolocation and related systems; R.B. Davis, C.F. Herreid II, and H.L. Short, Mexican Free-Tailed Bats in Texas (1962), the most complete published survey of a given species of bats; M. Eisentraut, Aus dem Leben der Fledermuse und Flughunde (1957), a review of European bats by an important student of bat natural history and physiology; K. Faegri and L. van der Pijl, The Principles of Pollination Ecology, 3rd rev. ed. (1979), the role of bats in pollination; D.R. Griffin, Listening in the Dark: The Acoustic Orientation of Bats and Men (1958, reprinted 1986), an authoritative summary of echolocation, and Echoes of Bats and Men (1959), a paperback introduction to echolocation; A. Novick and N. Leen, The World of Bats (1969), a review of bat behaviour and ecology with action photographs; L. van der Pijl, Principles of Dispersal in Higher Plants, 3rd rev. and expanded ed. (1982), the role of bats in dispersal of seeds; D.R. Rosevear, The Bats of West Africa (1965), an important compilation on the bats of a particular range; H. Saint Girons, A. Brosset, and M.C. Saint Girons, "Contribution la connaissance du cycle annuel de la Chauve-souris Rhinolophus ferrum-equinum (Schreber, 1774)," Mammalia, 33:357-470 (1969), an extensive study of the biology of one European bat species; J. Verschuren, Ecologie, biologie, et systmatique des Cheiroptres (1957), the primary work on the ecology of bats; B. Villa-R., Los murcielagos de Mexico (1966), an important compilation of knowledge on the bats of Mexico; W. Wimsatt (ed.), The Biology of Bats (1970), the definitive current work on bat biology. Alvin Novick