MOLOSSIDS
Free-tailed Bats
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MOLOSSIDS Free-tailed Bats |
| PHYLUM: Chordata | CLASS: Mammalia | SUBCLASS: Eutheria | ORDER: Chiroptera | SUBORDER: Microchiroptera | FAMILY: Molossidae |
| Genera: Tadarida | Biology | Ecology | Behavior | Distribution Conservation | Tadarida |
| Specie: brasiliensis | |||||
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Molossids are known as free-tailed bats, because their bony tail extends to the end of a
well-developed tail membrane, and considerably beyond. They often crawl backwards when on
the ground, using their tail as a sort of "feeler." Molossids are small to
moderately large bats, with forearms ranging from around 27 mm to approximately 86 mm in
length. Their muzzles are usually short and broad, and they often have wide, fleshy lips
that may have folds or creases. Many have a distinctive pad over their noses; this pad is
often endowed with odd bristles with spatulate tips. Most free-tailed bats have relatively
short but broad ears. The tragus is tiny, but opposite it, an antitragus is unusually well
developed. All species have long, narrow wings, apparently adapted for fast but relatively
unmanueverable flight in open places. Their wing and tail membranes are unusually tough
and leathery. Molossids also have short, strong legs and broad feet. Like their nose pads,
molossids' feet are well endowed with sensory bristles (also with spatulate tips). They
are excellent climbers, perhaps because they launch themselves for flight from a
considerable height above the ground. Because of their long, narrow wings, they must
attain considerable speed before they can develop enough lift to fly. They accomplish this
by falling some distance from their roost or take-off point. Molossids generally have short, even velvety fur. Most are black or brown, and many species have distinctive reddish and brownish or blackish color phases. All members of the family are insectivorous, catching their prey on the wing. Their roosting habits range from solitary to living in immense colonies of millions of bats, usually in caves. In the neighborhood of these large colonies, molossids may consume enormous numbers of insects. Approximately 85 species of molossids are placed in around 12 genera. Technically, molossids can be recognized by a combination of the following characters: long tail, tip of tail free of uropatagium tragus tiny, antitragus conspicuous no noseleaf 3rd phalanx of the 3rd finger is cartilaginous for most of its length no postorbital processes premaxillae with or without palatal branches dilambdadont teeth dental formula 1/1-3, 1/1, 1-2/2, 2-3/3. The fossil record extends to the late Eocene. Mosossids have the length of Head and body length is 40 to approximately 130 mm, tail length is 14-80 mm, and forearm length is 27-85 mm. The tail projects far beyond the free edge of the narrow tail membrane, hence the common name "free-tailed bats" for this family. The short body hair has a velvetlike texture. In one genus (Cheiromeles) the hair is so short that the animal appears to be naked. Some species of Tadarida have an erectile crest of hairs on the top of the head. The coloration is usually brown, buff, gray, or black. Some species, particularly in the genus Molossus, have two color phases. The head is rather thick and the muzzle is broad and obliquely truncate, usually with a scattering of short hairs having spoon-shaped tips. The eyes are small. The ears are thick and rather leathery, variable in size and form, and often united across the forehead and directed forward. A tragus is present. The nostrils usually open on a pad, the upper surface of which is often adorned with small hornlike projections. There is no nose leaf. The lips are large; in some genera the upper lip is furrowed by vertical wrinkles. Throat glands are often present. The wings are long, narrow, thick, and leathery. The legs are short and strong, and the foot is broad. Curved, spoon-shaped bristles are present on the outer toes of each foot; these are used by the bat in cleaning and grooming its fur.
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| Molossid bats roost in caves, tunnels, buildings, hollow trees, foliage (at least Molossus), the decayed wood of logs (reported for Molossops), the crevices of rock cliffs, and holes in the earth (reported for Cheiromeles). They also shelter under bark and rocks and often under the corrugated iron roofing of human-made structures; they prefer the high temperatures, up to 47° C and above in such places. A characteristic strong musky odor generally permeates their retreats. Some species live in groups of hundreds of thousands or even millions, others associate in smaller groups, and some forms are solitary. The colonial species generally return to their favored haunts year after year. Nyctinomops femorosaccus and Eumops perotis have been found roosting together in a crack in a large granite boulder; the two genera were segregated, the Nyctinomops hanging in the higher, narrower part of the crevice and the Eumops sheltering in the lower, wider part. | |||||
| The
large summer groups of T. brasiliensis are basically maternity colonies, consisting
mainly of females. In the southeastern United States such colonies usually number over
1,000 bats, but in the southwest there may be millions of individuals in a single cave.
During the 1960s about 100 million T. brasiliensis occupied 13 caves in Texas, and
an estimated 25 million to 50 million bats were in Eagle Creek Cave in Arizona.
Considering only sheer numbers, there was no larger concentration of mammalian life known
to exist. Some males are always present in the large nursery colonies, but most tend to
gather in relatively small groups nearby. Summer male colonies usually to number only
10-300 bats in the southwestern United States. It is possible that some males do not even
migrate northward for the summer, as a group of 40,000 was discovered in late June in
Chiapas, Mexico. In late summer, after the young are full-grown, the sexes begin to
reassociate. Most other species are not known to be as gregarious as T. brasiliensis.
For example, T. australis seldom is found in groups of more than 10.The members of
this family tend to be active throughout the year. The northernmost species may be
inactive for short periods during the winter, but there is no definite evidence of true
hibernation. Rather, these species usually make local movements or, as in Tadarida
brasiliensis of the New World, a seasonal migration. Compared with the flight of many
insectivorous bats, their flight is swift and relatively straight. They fly with their
mouths open and send out ultrasonic sounds. The diet consists of insects, often
hard-shelled forms. These bats usually have one young per litter and one litter per year. Two young are born on rare occasions, and Molossus ater, in Trinidad, possibly has two litters per year. Two successive pregnancies have been reported in a female Tadarida from Africa. Breeding generally takes place just before ovulation in late winter and spring. There may be partial or complete segregation of the sexes in some species. |
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| This family of 16 genera and 86 species is found in the warmer parts of the world, from southern Europe and southern Asia south through Africa and Malaysia and east to the Fiji Islands, and from the central United States south through the West Indies, Mexico, and Central America to the southern Argentina (Patagonia). | |||||
Species of
Tadarida:
Coloration in the genus ranges from reddish brown to almost black. Tadarida is characterized by wrinkled lips, deep anterior palatal emargination, relatively thin jaws, and a third upper molar with an N-shaped occlusal pattern. Most species have ears that are joined by a band of skin across the top of the head. In T. brasiliensis and T. aegyptiaca the ears are separated, but not so widely as in Mormopterus, and are large and forward-facing as in other Tadarida Habitat varies considerably. African species live in either
forest or open country and generally are reported to roost in trees and buildings. In
Venezuela, most T. brasiliensis roosting in houses. T. brasiliensis roosts
in buildings on the west coast and in the southeastern United States, and mainly in caves
in the southwest. Colonies of the latter species may make spectacular mass exits from
their caves after sunset and then fly up to 65 km to foraging areas. The diet consists
mostly of small moths and beetles. Based on radar observations in the southwest
researchers determined the average speed of groups of T. brasiliensis to be
40 km/hr (7-105 km/hr) and the average maximum altitude to be 2,300 meters (600-3,100
meters). Some populations of this species also make lengthy migrations. That maternity
colonies began assembling in the southwestern United States in April and disappeared by
mid-October. That populations in California, western Arizona, and southern Arizona made
only localized movements in the spring and fall, or relatively short migrations to the
south or west. Populations from central Arizona to Kansas and Texas, however, migrated
deep into Mexico, sometimes traveling over 1,600 km. Less is known about southeastern
populations. There is descripted a colony of 20,000 T. brasiliensis in New Orleans
that existed for at least 35 years, moving to an unknown location in the fall and then
returning in the spring. Literature and references cited 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. 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.
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