Why do bats live in caves and why don't they fly into objects at night?

Main Idea ___________________________

Bats fly and hunt for their food at night. This means that they need safe places to sleep during the day. Caves provide the kind of shelter in which bats can thrive. When they hang from the ceiling of a cave, bats are out of reach of most of their enemies. Some of the most successful species of bats live in large groups called colonies. Some of these colonies have millions of members, even up to 20 million! Carlsbad Caverns in New Mexico once had 7 to 8 million bats, but now has about 1 million.

Main Idea _____________________________

So, why don't bats fly into things at night? They use echolocation to find food and avoid obstacles. Echolocation is a kind of sonar. Bats create and hear noises that humans cannot hear. The sound waves from the noises bounce off of objects. They come back to the bat, which can then figure out how big an object is and how far away. Each bat makes its own individual noise. They recognize their noise or "voice" and use it to avoid objects and to identify food.

Most bat colonies leave their caves more or less together, in large groups after dark. Before leaving, they fly around inside, preparing for departure. Flying around with thousands of other bats inside a cave creates a lot of noise! The bats simply ignore it, and fly into each other.

If you suddenly appeared in a cave among the flying bats, they would crash into you. Dr. Donald. R. Griffin has called this phenomenon the "Andrea Doria effect." The Andrea Doria was a ship that sank in 1956, when it crashed into another ship in the middle of the Atlantic ocean.

Main Idea _____________________________

When bats are paying attention to their echolocation signals, they can navigate without crashing into things. They can identify and catch food while it is moving. Echolocation lets them locate very small insects. Most of them are less than a centimeter in diameter. Compared to a bug, a human being is a very large, slow moving surface that reflects sound. Outside of the cave, the chance of a bat hitting a person is very slim!

There are also bats that fly and hunt for food during the day. They sleep outdoors at night in trees, under bridges and other locations. Unlike nocturnal bats, they have good eyesight and bad echolocation.