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 thin things s in its path dr robert galambos of the university of rochester medical school recounted his e experiments x peri ments in a general electric electra c science forum address at schenectady new york bats move around almost exclusively clu in complete darkness in search of food except for moon and starlight dr galambos said that means they would collide with trees bushes and fence posts unless they had some way to tell where such obstacles are located although bats have eyes they prefer 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 fence posts 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 devices for detecting the supersonic sounds of bats dr galambos continued when dr donald griffin and I 1 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 Us ui who very generously turned over to us whatever laboratory space and equipment 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 str earn of cries in which frequencies around 50 cycles were particularly strong strong the doctor explained humans cannot hear much above about cycles and as people grow older the upper limit drops lower and lower until at 60 or so a person is deaf above about cycles the bat emits a steady tat tat tat of about 30 supersonic cries a second as it cruises about in the air dr galambos said but when an obstacle lies ahead this rate just about doubles momentarily then 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 id cry in another way they tied the mouth of the animal closed and then let it fly away those gagged animals were helpless in the air but as soon as they cut the strings each bat avoided obstacles once again the physicists also found that plugged ears were as dangerous as gags for the bats the latter bumping into obstacles again fundamentally the same vocal structure produces supersonic cries in bats as produces speech in man |