This species is small and gray-brown with long, narrow wings and a tail that extends well beyond the membrane between the legs. Individuals weigh 8-12 g and have short ears that almost join at the midline of the forehead. Wingspread is approximately 300 mm, total length is 90 to 105 mm and the forearm is 36 to 46 mm long.
Brazilian free-tailed bats range from southern Oregon and Nebraska to South America. In Colorado, this species seems confined to the southern half of the state. Previously the Brazilian free-tailed bat was considered only a wanderer in Colorado, but it is now known to be a summer resident.
The Brazilian free-tailed bat roosts in caves and mines and is often found in man-made structures. The animals are highly social. In Arizona, New Mexico and Texas, nursery colonies of 10 to 20 million individuals have been reported. Males generally form small colonies farther north, although a colony in Colorado has an estimated population of as many as 250,000 individuals. This bat does not hibernate in Colorado. The species is highly migratory and travels south to Mexico and Central America for winter. There may be distinct migratory pathways. Some apparently live to be 15 years old, but most have a considerably shorter life span. Predators include owls, kestrels, various hawks, raccoons, skunks and snakes.
Brazilian free-tailed bats breed on their winter ranges. Gestation is 90 to 100 days, and a single young is born in mid-June or early July. Although most young are born south of Colorado, a few are produced here. At birth, infants weight 25 percent of the mother's weight, about 2.5 to 3 g. For many years it was believed that mothers in colonies of hundreds of thousands or even several million females probably did not nurse their own young, but simply fed the first young to grasp the nipple. However, it has now been demonstrated that females locate their offspring by auditory and olfactory cues. Young begin to fly at about 5 weeks and are weaned shortly thereafter.
This bat eats mostly small moths, although beetles, bugs, mosquitoes and wasps are also taken. The large population of this species in south-central Colorado consumes tons of insects each year. The bats forage high over large open areas, leaving their roosts in a flight formation that resembles a long plume of dark smoke. They may forage up to 40 miles from their day roosts.
Populations of this species are declining across their wide range. Reasons for the decline seem to be disease, pesticide poisoning and human disturbance of nursery colonies. As other bats, this valuable species deserves continued respect, study and protection.