Why do bats live in caves?
Why don't they fly into objects at night?
Most bats are nocturnal.
Most bats are nocturnal. They fly and forage for their food (bugs) at night.
This means that they need safe places to sleep during the day. Caves provide
the kind of protected shelter in which bats can thrive. Hanging 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 cave colonies. Some of these
colonies have millions of members, even up to 20 million! Carlsbad Caverns in
New Mexico once had 7-8 million, but now has about 1 million.
So, why don't bats fly into things at night? They use echolocation to locate
food and avoid obstacles. They have the ability to create and hear noises that
humans cannot hear. The sound waves bounce off of objects and back to the bat,
which can then judge the size and distance of the object. These subsonic noises
vary in length and pulse frequency, and are unique to the individual. Each bat
recognizes its own pulse reflections, or "voice," and uses 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 chaotic
amount of noise! The bats simply ignore their personal navigation systems
inside the caves. The echolocators are on, but the bats aren't listening.
If you suddenly appeared in their cave among the flying bats, they would crash
into you.
The famous bat expert, Dr. Donald. R. Griffin, called this phenomenon the
"Andrea Doria effect." The Andrea Doria sank when it crashed into another ship
out in the middle of the Atlantic ocean .
When bats are paying attention to their sonar signals, they can navigate
without crashing into things. They can identify and capture food while it is
moving. The echolocation system is designed to 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 sound-reflecting surface. 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 well-developed eyes and poorly developed echolocation.
