MURCIELAGOS DE LA PATAGONIA

ORDEN CHIROPTERA

Clasificación

Bats are the only mammals that have true wings and flight. Bat wings are modified forelimbsth, much as are bird wings, except in the case of bats the flight surface is covered with skin and supported by four fingers, while in birds the flight surface is provided mostly by feathers and is supported by the wrist and two digits. The flight membrane usually extends down the sides of the body and attaches to the hind legs. Bats also often have a membrane called a uropatagium that runs between their hind legs and includes their tail (if they have one). Bats are the second-most species group of mammals, after rodents. The approximately 925 species of living bats make up around 20% of all known living mammal species. In some tropical areas, there are more species of bats than of all other kinds of mammals combined. Bats are found throughout the world in tropical and temperate habitats. They are missing only from polar regions and from some isolated islands.

  There are two major groups of bats, usually given the rank of suborders, Megachiroptera and Microchiroptera The Megachiroptera includes one family (Pteropodidae) and about 166 species. All feed primarily on plant material, either fruit, nectar or pollen. The remaining 16 families (around 759 species) belong to the Microchiroptera. The majority of species are insectivorous, and insectivory is widely distributed through all microchiropteran families. But many microchiropterans have become specialized for other kinds of diets. Some are carnivorous (feeding on rodents, other bats, reptiles, birds, amphibians, even fish), many consume fruit, some are specialized for extracting nectar from flowers, and one group of three species feeds on nothing but the blood of other vertebrates. Megachiropterans and microchiropterans differ in many other ways. The "megabats" are found only in the Old World tropics, while "microbats" are much more broadly distributed. Microbats use highly sophisticated echolocation for orientation; megabats orient primarily using their eyes (members of one genus are capable of a primitive form of echolocation). Megabats control their body temperature with a tight range of temperatures and none hibernates; many microbats have labile body temperatures, and some hibernate. Megabats have claws on the second digits supporting their wings (with one exception); this is never the case in microbats. Megabats have relatively simple external ears; microbats often have large and relatively complex pinnae, including an enlarged tragus or antitragus. Microbats often have dilambdodont dentition or cheek teeth whose morphology can easily be related to dilambdodont teeth; megabats have simplified cheek teeth that are difficult to interpret.

  Suborder Megachiroptera have the only Family of  Pteropodidae (Old World fruit-eating bats). Suborder Microchiroptera:  Family Rhinopomatidae (long-tailed or mouse-tailed bats), Family Craseonycteridae (bumblebee bat), Family Emballonuridae (sac-winged or sheath-tailed bats), Family Nycteridae (slit-faced or hollow-faced bats), Family Megadermatidae (false vampire bats), Family Rhinolophidae (horseshoe bats or Old-World leaf-nosed bats), Family Noctilionidae (bull-dog or mastiff bats) Family Mormoopidae (naked-backed bats), Family Phyllostomidae (New World leaf-nosed bats) Family Natalidae (funnel-eared or long legged bats), Family Furipteridae (smoky or thumbless bats), Family Thyropteridae (disc-winged bats), Family Myzopodidae (old world sucker-footed bats), Family Vespertilionidae (evening bats), Family Mystacinidae (New Zealand short-tailed bats), Family Molossidae (free-tailed bats).

Ecología

Insectivorous bats, which obtain most of their insect food while flying. Many also eat some fruit. They are of relatively small size and comprise the majority of the total bat population.
Fruit-eating bats, which feed almost exclusively on fruit and some green vegetation. No doubt they also eat some insects or insect larvae found in or on fruits. They often work together in groups, sometimes traveling long distances to fruit-bearing trees or shrubs. In some areas these bats do considerable damage to fruit grown for human consumption; however, most of them depend upon wild fruit. They are of necessity tropical bats, as they can survive only where fruit is constantly ripening. They range in size from the large, so-called flying foxes, with a wingspread of up to 1.7 meters, to those with a wingspread of about 250-300 mm.
Flower-feeding bats, which eat mainly pollen and nectar and possibly some of the insects found in flowers. They are almost exclusively small and usually have a long, pointed head and a long tongue with a brushlike tip to help them obtain their food. They are also inhabitants of the tropics or subtropics.
True vampire bats, which eat blood obtained by making a small incision in the skin of an animal while it is asleep. There are only three small species in this group. The danger to the bitten animal is subsequent contraction of virus-caused diseases, such as rabies, and secondary infection of the wound.
Carnivorous bats, which prey on other small mammals, birds, lizards, and frogs. They have a widely varied diet, however, and do not eat only animals. They are of moderate size.
Fish-eating bats, which catch fish at or near the water's surface. These bats obtain the fish by use of the feet, which are large, powerful, and equipped with hooked claws.

Most bats have only one young per year. This low reproductive rate is offset by the fact that bats live longer then most mammals of their size. Ernest P. Walker had a pet Eptesicus that attained an age of at least 13 years. The Zoological Society of London had a fruit bat for 17 years, and there are records of bats marked in the wild that lived at least 30 years. In the hibernating forms, ovulation occurs in the spring, with the breeding generally taking place the preceding fall (delayed implantation). The sperm is retained in the reproductive tract of the female during the winter. In the nonhibernating forms, ovulation and breeding occur in the spring or at favorable seasons.

Bats destroy many harmful insects and pollinate many flowers. The guano deposits found in "bat caves" are valuable as fertilizer. People eat some of the larger bats. Some animals that feed on bats are the birds of prey, snakes, and other mammals, including other bats.
The congregation of bats in caves facilitates the preservation of their bodies after death. Some of the water that drips into caves is heavily impregnated with minerals; this slows the rate of decay and, in time, helps to form a deposit over the dead bats. Ernest P. Walker encountered such a condition in a lead mine in Mexico. The mine was merely a fissure two to eight feet wide that had been worked out. On the floor of the fissure were thousands of dead bats that had recently succumbed to disease. There was little decomposition, so that a deposit of soil and suitable chemical conditions, or the dripping of water onto the dead bats, would eventually make a fossil deposit.

Due to the abundance of forms and the myriad legends and superstitions concerning them, bats have been given vernacular names in practically all languages. Most of these names are all-inclusive terms meaning simply "bat," but many are derived by combining words used for other animals. Thus, the Aztec term Quimichpapalotl means "butterfly mouse," the German Fledermaus means "flying mouse," and the French chauve-souris means "bald mice.

Comportamiento

  Most bats do not find their way about by sight. Nocturnal orientation is by means of a phenomenon known as echolocation, in which the bat emits vocal sounds through the mouth or nose as it flies. These sounds are usually above the limit of human hearing and are reflected back to the bat in flight as echoes. They enable the bat to avoid hitting obstacles when flying in darkness and to locate the position of flying insects. Bats are unable to guide themselves by their own voice when their ears are plugged. The New World bats that feed on fruit or the blood of large sleeping animals send out pulses having only about one-thousandth the sound energy of those used by bats that feed on flying insects and fish. Echolocation has been found in all the families investigated thus far. All bats can see, and some probably have good eyesight. Vision is used by the Old World fruit bats (Pteropodidae) more than by most other bats.

In addition to the high-frequency vocal sounds emitted in echolocation, bats have voices used to express emotion or for communication. Ernest P. Walker detected a vibration of the entire body, legs, and wings at 52 cps in the common big brown bat of North America (Eptesicus) and similar vibrations in other North American insectivorous bats. Apparently this vibration is under the bat's complete control and seems to occur only when the bat is resting and contented. It ceases when the bat goes to sleep. This vibration probably exists in many if not all bats, but it apparently has been overlooked by all but the few persons who have kept bats as pets. Bats also utter many other vocal sounds that humans cannot hear.

Bats shelter in caves, crevices, tree cavities, and buildings, and some sleep in exposed locations on trees. In the colder parts of their ranges in the temperate zone, bats either hibernate during winter or migrate to areas where food is available. There is a great reduction in metabolism during hibernation, so that the oxygen consumption is only about a hundredth of the normal active rate. When sleeping during the day, many bats become semitorpid and there is a great reduction in body temperature, but as they awaken their temperature rises. When asleep, a bat's oxygen consumption may be only a tenth of the active rate. Some bats thus spend much of their life in hibernation or a condition that approaches hibernation or estivation. Resting bats thoroughly groom themselves, using the tongue and the toes. Back scratching is no problem for a bat: it merely reaches up with either hind foot and scratches any portion of its back, the top of its head, its face, or its mouth. Bats do not carry bed bugs, as is often stated, though some of the parasites occasionally found on them can be mistaken for bed bugs by those unfamiliar with external parasites.

The normal position of most bats at rest is to hang head downward, though a few rest on horizontal surfaces in caves and elsewhere. Occasionally, fruit bats, while scrambling about in trees, get into a head-upward position. When a bat is hanging head downward in an elevated position, it is very easy for it to take flight by merely letting go, dropping, and spreading the wings. Bats have no difficulty in taking to flight when resting on a level surface: they leap into the air, using both arms and legs to launch themselves (the photographs used to illustrate some of the genera here are from old publications in which the animal was drawn with the head upward).

Considering their structure, it is not surprising that bats fly with their legs as well as their wings; one could say that they "swim" through the air. Photographs of bats in flight reveal that their legs work in unison with the wings, just as swimmers use their legs and arms at the same time.

Some bats pick insects off foliage or even off the ground. Probably all bats require more water or moist food than do other mammals of comparable weight, because their wings have such great evaporation surfaces in comparison with their weight.

When catching insects in flight, a bat uses the tail and wing membranes to prevent the escape of its prey. When it has an insect in its mouth on which it does not have a firm grip, the bat spreads its legs out and forward, so that the membrane is spread into an excellent lap, and bends the head forward into this apron. Thus, it keeps the insect under restraint while it manipulates it about in its mouth and renders it helpless. Bats do this in flight, when hanging up, or on a level surface. Often in this struggle they fall onto their backs, but only for an instant. They quickly right themselves, for they are superb acrobats.

Distribución - Conservación

  Bats inhabit most of the temperate and tropical regions of both hemispheres but are absent from certain remote, oceanic islands. They are not found in the colder parts of either hemisphere beyond the limit of tree growth. Among mammals, only the rodents exceed bats in number of species.

Literature

Hill, J. E., and J. D. Smith. 1984. Bats, a Natural History. University of Texas Press, Austin. 243 pp.

Koopman, K.F. 1984. Bats. Pp. 145-186 in Anderson, S. and J. K. Jones, Jr. (eds). Orders and Families of Recent Mammals of the World. John Wiley and Sons, N.Y. xii+686 pp.

Nowak, Ronald M., 1994. Walker's Bats of the World. Johns Hopkins University Press, Baltimore.

Savage, R. J. G. and M. R. Long. 1986. Mammal Evolution, an Illustrated Guide. Facts of File Publications, New York. 259 pp.

Vaughan, T. A. 1986. Mammalogy. Third Edition. Saunders College Publishing, Fort Worth. vii+576 pp.

Wilson, D. E., and D. M. Reeder. 1993. Mammal Species of the World, A Taxonomic and Geographic Reference. 2nd edition. Smithsonian Institution Press, Washington. xviii+1206 pp.

The animal web: http://www.oit.itd.umich.edu/bio108/Chordata/Mammalia.shtml

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