Greg Cross, age 10, of Enid, Oklahoma, for his question:
Are bats really blind?
The little brown bat wakes up when the sun goes down and gets ready to fly outdoors in search of his supper. In the dim, dusky twilight he can see as well as you can ¬and perhaps a little better. However, his bright little eyes are dazzled by the daylight. He rarely if ever comes forth when the sun is high in the sky. If he did, his eyesight would not help him very much. Besides, there are daytime prowlers around and his favorite insect food is not to be found until after the sun goes down.
Blind as a bat is a very old expression, invented by people who thought that the little brown bat cannot see where he's going. Surely those people failed to watch him flying through the twilight air, dodging a crowd of his cousins and never colliding with them or with any object in his path. Or did they suspect that the little aerial acrobat did not depend on his eyesight to guide his expert maneuvers? It's not likely, because those people had never heard of radar. True, though the bat sees as well as most people do in a dim light, he does not depend entirely on his eyesight. But only recently did we discover that he had his own built in radar system.
As a matter of fact, his ancestors were using radar ages before our ancestors learned to read and write. His vision is adjusted to dim twilight and to the dark caves and crannies where he dozes during the bright daylight hours. He is fond of company and often his cave is crowded with sleeping cousins, hanging upside down from cracks in the roof and ledges on the walls. Sometimes their slumber is disturbed by a loud noise. Then hundreds of furry fliers wake up and zoom around in the pitch black darkness. Not one of them crashes into a wall or collides with a cousin. Even if dozens of ropes dangle from the ceiling they dodge between them without a mishap.
No person or animal has the vision to perform such feats. The bat succeeds because he uses his sounding system of fast echoes. For this he needs a most unusual voice and pair of super sensitive ears. His voice sounds like a series of rather faint high pitched squeaks. Actually each squeak goes up into supersonic frequencies ¬ above the range of human ears. These supersonic notes bounce off solid surfaces and return to the bat as supersonic echoes. His ears catch the echoes and in a flash his brain relays orders to dodge this or that object in his path. This built in biological system works like the mechanical radar system we use to detect distant objects by returning echoes.
Sound is vibrating energy and we rate it in frequencies of so many vibrations per second. Human ears hear sound frequencies up to about 20,000 vibrations per second. The bat's voice squeaks up to supersonic frequencies of 50,000. And the talented creature can distinguish between his own echoes and those of other bats even when hundreds of flying relatives are using their radar systems in a dark cave.