When a Mexican free-tailed bat travels to BCI's Bracken Cave each summer, it joins millions of its closest friends.


Mexican Free-Tailed Bat (Tadarida brasiliensis)

When a Mexican free-tailed bat travels to BCI’s Bracken Cave each summer, it joins millions of its closest friends. When they arrive at the cave, there are 8-10 million bats there, but the number grows to 15-20 million once the babies are born. The cave’s annual maternity population is one of the world’s largest known mammal gatherings.

Located less than 20 miles from downtown San Antonio, BCI’s Bracken Cave Preserve is a protected sanctuary used for research, education, and bat viewing. At one point, a developer wanted to build 3,500 homes right in the bats’ flight path, but BCI and conservation partners including The Nature Conservancy worked to purchase the land, ensuring the bats plenty of room to roam.

Here are five fascinating facts about the cave and its batty inhabitants:

1) Beginning in late February or early March every year, female bats who are expecting pups fly to the cave after spending the winter in Mexico or further south. In mid-June, they give birth to their babies, almost doubling the cave’s population. Once the pink, hairless pups are born, they cluster in a nursery creche with up to 500 bats per square foot!

2) Pups have to master their flying skills and echolocation system quickly at one month old, dodging the millions of other bats learning how to fly. If they collide or fall, there are millions of dermestid beetles on the cave floor, waiting to gobble them up.

3) With nearly 20 million bats in one cave, the line-up to go insect hunting at night is impressive. It can take 3 or 4 hours for everyone to have a turn to emerge each night during the March to November season.

4) Mexican free-tailed bats have no problem traveling for a good meal. They can fly more than 100 miles each night to find insects.

5) Bracken Cave isn’t the only place hungry Mexican free-tailed bats congregate. More than 100 million come to Central Texas each year, eating a combined total of up to 1,000 tons of insects every night. They are a farmer’s best friend, gobbling up agricultural pests, like army cut-worm moths and cotton bollworm moths.

Learn more about this batty bunch by reading about BCI’s Bracken Cave work or consider planning a 2021 visit to see the cave, which will be available for private events, group visits, and Member Bat Flights for BCI members.