A Bat's Cave: A Dark City - Reading Passage

Bat Rush Hour

Just before the sun sets in South Central Texas, the summer sky comes alive. It’s the time when Mexican free-tailed bats exit their home in Bracken Bat Cave. “For more than two hours they leave the cave and spiral higher and higher into the air,” says biologist Gary F. McCracken.

At first, only a few bats fly out of the cave’s dark opening. Then hundreds and thousands more swirl out. Soon a huge cloud of as many as 20 million bats has formed in the dark sky. The flapping bat wings make a whooshing sound. Finally, the Mexican free-tailed bats fly out of sight.

A Supersize Cave

Bracken Bat Cave is huge—large enough to house the 20 million bats that roost there. Its entrance, a big hole in the ground, leads to a dark underground city. Unlike a human city that has many buildings, the cave is just one giant room, nearly 100 feet (30 m) wide.

During the day, the Mexican free-tailed bats rest and sleep safely in this giant city. They hang upside-down from the cave’s jagged ceiling. Hooked claws and special tendons in their feet let them cling to the stony ceiling without tiring. In this position, they can hide from predators such as snakes or quickly launch into flight when it’s time to feed.

On a Mission

The group that leaves Bracken Bat Cave each night is so large that it can be tracked by radar. Radar is commonly used to predict weather by following moving objects, such as raindrops, in the sky. “To radar, the millions of bats emerging from their cave look like a huge storm,” says Gary F. McCracken. Where are all these bats going?

Gary has learned that the bats leave Bracken Bat Cave to hunt insects in the surrounding area. How does he know this? The radar can also detect the billions of bugs that swarm the Texas sky.

The bats will eat about 200 tons (181 metric tons) of these bugs in one night. These insects, mostly moths and beetles, can destroy crops, so many farmers are glad to have the bats around.

Winged Hunters

How do bats catch insects? As they soar high into the air, the bats use their wings to scoop prey into their mouths. All bats have almost hairless wings, which are like hands but with webbing to connect their fingers.

Since it’s dark when they hunt, bats use echolocation to find their prey. In this process, bats send out high-pitched sounds that travel in waves. These sound waves bounce off objects and return to the bats as echoes. Bats can determine the size and shape of an object and how far away it is by listening to the echoes.

The Future

Protecting bat habitats is a good way to help keep these animals safe. Some bat conservation groups have built special gates at cave openings. The gates prevent people from disturbing sleeping bats.

Another way to help bats is for people to build bat houses. These homes not only give the bats a safe place to live, but many farmers now put these up to attract bats because they eat insects that can destroy their crops. More bats mean that there will be fewer insects to destroy human food. Scientists are hoping these efforts will keep bats safe and help their dark cities thrive for years to come.