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------------------------------------- Bats: engineering marvels ------------------------------------- (December 30, 1997 2:18 p.m. EST)- If you can get past the notion that bats are kind of Halloween-like and scary, they are amazing creatures. As Oxford biologist Richard Dawkins says in his book, "The Blind Watchmaker," "They are like miniature spy planes, bristling with sophisticated instrumentation." Take the common small brown bat, Myotis, as an example. It catches insects using a system similar to radar. To do this, an individual bat needs to decode a world of incoming and outgoing sound waves in real time. A spy plane would require a sizable computer to decode similar information. Myotis creates the sounds needed for echoes by clicking its tongue rapidly. When one of these bats is cruising through the air, it normally emits its clicks at a rate of about 10 per second. Dawkins says this is about the rate of a Bren machine gun. At 10 per second, it's 'view' of the world is a series of frozen images, like what you might see at a discotheque that uses a strobe light. However, when the bat is closing in on an insect, the pulses go up to 200 per second. At 200 pulses per second, the bat would have a sound picture of the world similar to what our eyes would provide us when we're, for example, playing ping pong. The bat needs this better "picture" to follow an insect that's twisting and diving in its desperate attempt to shake off its predator. For the bat's echolocation system to work, the sounds need to be powerful, and they are. If they were at a frequency that we could hear, we'd find them deafening. The reason the sounds have to be loud has to do with physics. When a bat emits its cry, the sound gets diluted as it expands in all directions away from its initial source. That means that the sound is going to get very weak very fast. That, however, is only the beginning of the problem. If the sound from the bat hits an insect, it's going to bounce off the insect, also in all directions. The already weak sound bouncing off the insect is going to weaken dramatically as it gets further from the insect. By the time the sound has hit the insect and bounced backwards so that bat can hear it, the signal is extremely weak in comparison to the initial cry. The consequence of this is that the bat's ears must be extraordinarily sensitive to pick it up. This poses a whole new problem for the bat. An ear sensitive enough to pick up the weak incoming sound would be damaged by the enormously loud outgoing pulse of sound. Some bat species solve this by using muscles in their ears to switch the ears off temporarily as the sound is emitted. They then switch their ears back on again as the echoes come back in. Dawkins compares this fine tuning to the fighter planes during World War I that fired machine guns "through" the propeller. The timing of the bullets was synchronized with the rotation of the propeller so that the bullets always passed between the blades. Next time you want to feel a sense of awe at the natural world, think of the humble bat. With its ability to find its prey through echolocation, it is wondrously adapted to its niche in the world. If you'd like to help protect these amazing creatures, contact Bat Conservation International, P.O. Box 162603, Austin, TX 78716. By MITZI PERDUE, Scripps Howard News Service Copyright 1997 Nando.net Copyright 1997 Scripps Howard ------------------------------------- janet paterson / 50-9 / [log in to unmask]