Society

Mexican free-tailed most common bat found in Texas

The Brazilian free-tailed bat, otherwise known as the Mexican free-tailed bat, is the most common bat found in the state. In 1995, the State Legislature named it the “state flying mammal.”

The Mexican free-tailed bat is best known for its large colonies in several caves, known as “guano caves,” in Central Texas and the Hill Country, where up to 104 million bats may live. These caves have been used by the bats for over100years. The largest is Bracken Cave near San Antonio, where 20 million bats roost during the summer. The Congress Avenue Bridge in Austin is another famous roosting site. They are migratory, flying back to Mexico, Central and South America in late fall for the winter. They come back to Texas in February.

The bats live year-round in East Texas, mainly in old buildings, usually with less than one hundred bats living at each site. Interestingly, for every town in the bats’ range, which is most places in Texas, there will be at least fifteen roosts per 5,000 human population. This has earned them the nickname “house bat,” because they don’t have problems living in close proximity to humans.

In migrating colonies the bats you see are mainly female. Most males will not migrate, but spend their lives down south. When the females begin arriving in Texas in February, they are already pregnant. So, the guano caves in Texas are basically maternity caves. Of the small number of males that do make the journey, they will stay long enough to breed, then fly to bachelor colonies to spend the summer, as they do not help in rearing the young.

Each female gives birth to one pup in June. The pups are naked and flightless. The mother’s place their babies in certain areas of the cave, in densities of up to 500 babies per square foot. The mother will come to her baby several times during the day to nurse (the mammary glands are under each wing). The mother finds her baby by its smell and knowing its cry.

The babies are left in the cave while the mother hunts. The only time the mother will move her baby is if the cave is disturbed.

A few predators, like snakes, raccoons, and owls frequent the roosts because mothers won’t rescue babies that fall to the cave floor.

Come August the pups are full grown and can find their own food. By this time the cave is extremely crowded. The colony size has more than doubled. The mothers will abandon the cave to the youngsters and may actually leave Texas at this time.

Most babies survive. These bats can live up to 11 years in the wild.

The free-tail bat is a medium sized bat with a wingspan of 12 to 14 inches, big ears, and fur that ranges from dark brown to reddish to almost black. They are called “freetailed” because their tails are free of a membrane that most bats have.

They are built for speed, with long, narrow wings allowing them to fly up to sixty miles per hour.

The bats are great for pest control. They fly up to 100 miles round-trip looking for insects. They can eat up to twothirds of their body weight in insects per night. It has been proven that they can save farmers up to two applications of pesticides per year.

They eat moths, beetles, flying ants, and June bugs. The bats eat 6,000 to 18,000 metric tons of insects per year.

When they emerge after sunset, they spread out in several directions, leaving the cave at speeds of up to 35 miles per hour.

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El Camino Real Master Naturalists:

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2010-06-03 digital edition



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