A Year in the Life of a Mexican Free-tailed Bat

Mexican free-tailed bats (also known as Brazilian free-tailed bats) are the most common bat found throughout Texas. In most parts of the state, Mexican free-tailed bats are migratory and spend the winters in caves in Mexico. They begin their migration to Texas in February and by early spring female bats form large maternity colonies where they will raise their young. There are only a small number of suitable sites for these large maternity colonies because the bats require high humidity and temperature levels. In June, mother bats give birth to one pup each. Male bats do not help in raising the young and form smaller “bachelor” colonies away from females.

Roosting Mexican free-tailed bats and pups. Photo: TPWD.

Bats are mammals, so the pups are born live and weigh about 25 percent of their mother’s weight. They feed from their mother’s rich milk located in mammary glands found under each of her wings.

The Mexican free-tailed bats’ milk is so rich that the pups grow fast and are ready to fly within four to five weeks of birth. It is estimated that baby Mexican free-tailed bats roost in densities of up to 500 pups per square foot. It is amazing to think that mother bats are able to find their own baby amongst thousands of pups by using their sense of smell and by knowing the sound of their pup’s call.

A Mexican free-tailed bat is in flight.

Credit: Bruce D. Taubert/Minden Pictures /Bat Conservation International

By early August, most pups are flying and foraging on their own. It is at this time of the summer when the most spectacular bat emergences often occur as the colony size might easily double. When the first cold fronts start pushing through in late October to mid-November, the Mexican free-tailed bats begin their migration to Mexico for the winter.