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.
 Related
Web Sites |
-
Bats
Bibliography - This Web site from the California
Academy of Science provides a bibliography of books,
children's books, videos, and World Wide Web resources
about bats.
-
Bat
Conservation International -
"BCI's mission is to teach people the value of
bats, to protect and conserve critical bat habitats,
and to advance scientific knowledge through research."
BCI's Web site provides a wealth of information about
bats, such as publications for students and teachers,
projects, facts, a catalog of books & gifts, and
bat links.
|
 Further
Reading |
- Griffin,
Donald R. Listening in the dark: the acoustic orientation
of bats and men. New Haven, Yale University Press, 1958.
415 p.
- Wilson,
Don E. Bats in question : the Smithsonian answer book.
Washington, The Smithsonian Institution, 1997. 168 p.
- Leen,
Nina. The world of bats. New York, Holt Rinehart
and Winston, 1969. 171 p.
|
 For
more print resources...
Search on "bat
and species," "bats and sonar," or "bat and
nocturnal"
in the Library of Congress Online
Catalog.
|
Image from USDA
Agriculture Research Service Sci4Kids.
[Different
species of bats, with details of heads, wing and teeth structure]
/ Fournier, sc. ; N. Remond, imp. [published between 1836 and 1849].
Rare Book and Special
Collections Division, Library of Congress.
Federal
Music Project presents the comic opera "Die fledermaus"
- "The bat" by Johann Strauss [poster]. Music
Division, Library of Congress.
|
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