Mexican Free-Tailed Bats
Author: Bruce Neville
A smallish bat with a tail that extends noticeably beyond the tail membrane. Among the free-tailed bats, this is the only species in which the ears do not meet at the center of the forehead. The ears are fairly large. The upperparts vary from reddish to very dark brown; the underparts are slightly lighter. The ears and membranes are blackish.
The Mexican Free-tailed Bat occurs in suitable habitat throughout New Mexico . It occurs throughout the southern portion of the United Stataes, along the Gulf and Atlantic coasts as far north as Virginia, and extending to northern Colorado, Utah, and California in the Great Plains and western mountains. The species extends southward into South America . Most of the New Mexican population migrates southward in the winter, though a few may be present throughout the winter in the largest colonies.
Mexican Free-tailed Bats occur in piñon-juniper woodlands, grasslands, and deserts to elevations of about 6000 feet. They occur rarely to elevations of 8200 feet in New Mexico. They roost in a variety of caves and fissures in both natural rock formations and artificial structures, such as bridges or buildings, both abandoned and occupied.
Mexican Free-tailed Bats feed on flying insects that it catches on the wing. Moths are among the most abundant prey items.
Reproduction and Development:
Mating occurs on the wintering ground, and females are pregnant when they return to New Mexico in the spring in April. They give birth to a single young, called a pup, after a gestation estimated at 90 days. All of the females in a colony give birth within a period of just a few days in mid-June. Pups are deposited in large groups in certain parts of the colony and are not carried by their mother during the feeding flight. Females returning to the colony find their own pups among the many pups and returning adults of a large colony. The pups grow quickly and are almost the size of the adults by the age of one month, when they are capable of joining the nightly feeding flights. Mexican Free-tailed Bats have been known to live for 11 years.
Mexican Free-tailed Bats hang from the ceiling of their roosts and take flight by dropping into the open space below. The bats emerge in groups from their roost shortly before dark. Each bat leaving the roost follows the preceding individual, resulting in an emerging swarm. On returning, they frequently approach at high speeds, dropping from high altitudes, “braking” just at the entrance to the roost. The hind feet have long stiff hairs that are used for grooming.
The calls of the Mexican Free-tailed Bat are audible to humans as loud chips.
Bats generally spend the day in various refuges, such as caves or the eaves of buildings, where they hang head downward. During cold weather, bats may become torpid, enter true hibernation, or migrate to warmer areas.
Mexican Free-tailed Bats are important in the control of insect populations.
Populations are considered to be stable.
Species: Tadarida brasiliensis
Burt, William Henry; and Richard Philip Grossenheider. 1976. A Field Guide to the Mammals, 3rd ed. (Peterson Field Guide Series; no. 5). Boston : Houghton Mifflin, 289 p., 47 plates
Cockrum, E. Lendell; and Yar Petryszyn. 1992. Mammals of the Southwestern United States and Northwestern Mexico. Tucson : Treasure Chest Publications, 192 p.
Findley, James S. 1987. The Natural History of New Mexican Mammals. Albuquerque : University of New Mexico Press, 164 p.
Findley, James S.; Arthur H. Harris; Don E. Wilson; and Clyde Jones. 1975. Mammals of New Mexico . Albuquerque : University of New Mexico Press, 360 p.
Related Terms: Chordata, Mammals, Chiroptera, Bats