Free-Tailed Bats and Mastiff Bats: Molossidae

Physical characteristics: Also called the Mexican free-tailed bat, Brazilian free-tailed bats are small to medium in size, with a total head and body length of approximately 3.8 inches (9.5 centimeters).

Geographic range: Brazilian free-tailed bats are found in the southern half of the United States, as well as Mexico, Central America, South America to southern Chile and Argentina, and much of the Lesser and Greater Antilles.

Brazilian free-tailed bats may roost in colonies of millions of bats. These are some of the largest colonies of mammals in the world. (John Hoffman/Bruce Coleman Inc. Reproduced by permission.)

Habitat: Brazilian free-tailed bats are primarily found in arid and semi-arid habitats. They are also found in urban areas, moist forests, and grassland areas. These bats roost in caves, mine tunnels, tree hollows, and under bridges. They also are frequently found in and around buildings.

Diet: These bats feed on a range of insects, including moths, beetles, weevils, mosquitoes, flying ants, and leafhoppers.

Behavior and reproduction: Brazilian free-tailed bats are best known for their immense roosting colonies. While roosts of several dozen have been found, these bats also roost in colonies that reach the millions. A colony that lives in Bracken Cave, Texas, makes up the largest colony of mammals in the world, with an estimated twenty million individuals in this summertime maternity colony. They fly high above the ground when foraging for prey, except when sweeping over a body of water to drink.

Mating among these bats is considered promiscuous (prah-MISS-kyoo-us), meaning males and females mate with more than one other bat. Females bear a single offspring once a year in May to July. In maternity roosts where millions of bats are packed tightly together, mothers are able to identify and nurse their own young.

Brazilian free-tailed bats and people: Many of the insects these bats eat are considered pests by humans. These bats are also known carriers of rabies.

Conservation status: Many of the large colonies have declined dra-matically in numbers. The IUCN lists Brazilian free-tailed bats as Near Threatened. ∎