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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 begin to form large maternity colonies where they will raise their young.

There are only a small number of suitable sites for these large maternity colonies which require high humidity and temperature levels. In June, mother bats give birth to one pup. Male bats do not help in raising the young and form smaller bachelor colonies. 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 babies grow fast and are ready to fly within five to six weeks of birth. It is estimated that baby Mexican free-tailed bats roost in densities of up to 500 babies 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.

By mid-August the pups begin flying. It is at this time of the summer when the most spectacular bat emergences often occur as the colony size might easily double.

Mexican free-tailed bats can fly up to 100 miles round trip in an evening looking for food. They are built for speed with short fur and long narrow wings and can fly up to 60 miles per hour with a tail wind. They have been observed feeding up to 10,000 feet while searching for food.

Mexican free-tailed bats are very important for keeping crop pests in check as they can eat up to two-thirds of their body weight in insects each night, especially while lactating and feeding young. With the large numbers of agricultural pests they eat, research has demonstrated that these bats can save farmers up to two applications of pesticides per year.

When the first cold fronts start pushing through the Texas Hill Country in late October to mid-November, the Mexican free-tailed bats begin their migration back to Mexico.

In 1995, the Texas State Legislature named the Mexican free-tailed bat as the "state flying mammal."


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