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Show Bats Employ 'Radar' To Dodge Obstacles When Flying in Dark The flying bat at night employs "natural radar" to avoid colliding with trees and other obstacles The little animal sends out cries, too shrill to be heard by the human ear, that help it to locate things in its path. Dr. Robert Galambos of the University of Rochester medical school recounted his experiments in a General Electric science forum address at Schenectady, New York. "Bats . move around almost exclusively ex-clusively in complete darkness" in search of food "except for moon and starlight," Dr. Galambos said. That means they would collide with trees, bushes and fenceposts. unless they had some way to tell where such obstacles are located. Although bats have eyes, they prefer pre-fer to live and feed in darkness. The method used by the flying bat depends on the production of sound and the analysis of echoes. As the bat flies through the air, it emits a constant stream of high-pitched cries, which permeate the space in front of the animal. If there are any obstacles out there, like tree branches or fenceposts, the sound is reflected or echoed back. The bat hears these echoes, changes Its course, and flies into regions which are echo-free. Physicists have invented electronic elec-tronic devices for detecting the supersonic sounds of bats. Dr. Galambos continued. "When Dr. Donald Griffin and I were asking ourselves whether bats produced a supersonic cry, we took the problem to Prof. G. W. Pierce, the expert in supersonic sound at Harvard U,, who very generously turned over to us whatever what-ever laboratory space and equipment equip-ment we required. "The instrument we needed most was a so-called sonic amplifier, a device which converts supersonic sounds into audible ones. With it we were able to show that so long as bats fly, they emit a constant stream of cries in which frequencies around ' 50,000 cycles were particularly strong," the doctor explained. Humans cannot hear much above about 20,000 cycles. And as people grow older, the upper limit drops lower and lower, until at 60 or so, a person is deaf above about 6.00C cycles. "The bat emits a steady 'tat-tat-tat' of about 30 supersonic cries s second as it cruises about in the air," Dr. Galambos said. "But when an obstacle lies ahead, this rate just about doubles momentarily, ther drops back to 30 again when the obstacle is passed." Dr. Griffin and Dr. Galambos watched about a hundred bats and also experimented further to show the importance of the supersonic cry in another way. They tied the moutb of the animal closed and then let ii fly away. Those gagged animals were helpless in the air. But as soon at they cut the strings, each bat avoided obstacles once again. The physicists also found thai plugged ears were as dangerous as gags for the bats, the latter bumping bump-ing into obstacles again. Fundamentally Funda-mentally the same vocal structure produces supersonic cries in bati as produces speech in man. |