ECHOES OF BATS AND MEN 



Orientation Sounds of Bats 



Bats make a variety of vocal sounds; for example, 

 when disturbed they squeak and chitter. But we are in- 

 terested primarily in the sounds they use in flight to gen- 

 erate useful echoes that tell them about objects at some 

 distance. These orientation sounds are all of high fre- 

 quency, though they overlap slightly the range of human 

 hearing to produce the very faint audible ticking we have 

 discussed. But most of the sound energy emitted by fly- 

 ing bats lies at frequencies from 10 to 150 kc in different 

 species, and I will describe only one or two examples 

 of orientation sounds that have been measured from a 

 few typical kinds of bats. 



One of the simplest acoustic patterns is that used by 

 the horseshoe bats, an insectivorous group that lives in 

 Europe, Asia, Austraha, and Africa. They use orienta- 

 tion sounds of nearly a single frequency, which may be 

 anywhere from 60 to 120 kc, depending on the species. 

 The individual sounds last only a small fraction of a 

 second, usually from 50 to 100 miUiseconds, but this is 

 much longer than the duration of other bats' sounds. 

 The name horseshoe bat refers to a complicated se- 

 ries of folds or membranes surrounding the nostrils and 

 the mouth with two roughly concentric rosettes which 

 vaguely resemble a horseshoe when viewed from in 

 front. The German zoologist Franz P. Moehres has 

 shown recently that the horseshoe serves as a small horn 

 to concentrate the emitted sound into a narrow beam 

 which is swept back and forth as the bat scans its sur- 

 roundings. Bats have a habit of hanging head downward 

 by the hind feet, and the horseshoe bats have especially 

 flexible hip joints. They can pivot through almost a 

 complete circle as they scan with their beam of high- 



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