320 ANNUAL REPORT SMITHSONIAN INSTITUTION, 194 7 



ear contracts momentarily, shutting off the squeak, and permitting 

 only the echo to be heard. 



Bats are not the only creatures with the power of echo-location. The 

 tapping of Blind Pew's stick is an example of the same process, and 

 many blind human beings develop what appears to be an uncanny 

 ability to move about without striking obstacles. Nor are bats the 

 only creatures able to hear supersonic vibrations : dogs, for example, 

 are often trained on the Galton whistle. But so far as is known at 

 present bats are the only creatures that emit supersonic vibrations 

 and guide themselves by the reflections. This important discovery, 

 however, still leaves unanswered many questions about the behavior 

 of bats, and, as is the way with important discoveries, poses a number 

 of fresh problems. 



Invariably the first question that is asked is : Why do not the bats 

 become confused between the echoes from their own squeaks and the 

 echoes from the squeaks of their neighbors? It might be thought 

 that with a large number of bats of the same species together in a cave 

 or in the roof of a church, and all uttering supersonic squeaks, con- 

 fusion would be inevitable. But it must be remembered that super- 

 sonic squeaks do not travel far, for their energy is quickly dissipated 

 in the air. It has been shown that the supersonic squeaks of bats 

 travel only about 15 feet, and that they are able to give a useful echo 

 only up to about 12 feet. In other words, provided that the bats are 

 not crammed close together, there is very little likelihood of confusion. 

 But, as everyone with any field experience of bats knows, they very 

 often are crammed close together, yet there is no confusion. It seems 

 evident that there is a difference in the frequency of the vibrations 

 made by each bat. A very slight difference in frequency would be 

 sufficient to enable each bat to recognize its own voice. 



There remain a number of problems to which no answer has yet 

 been given. First, do bats emit the supersonic squeak through the 

 mouth or the nose, or both? All the British bats are insect eaters, 

 and all, with the possible exception of the barbastelle {Barbastella 

 harhastellus) , habitually fly with their mouths open. Furthermore, 

 all the British bats capture their prey while m flight, and most of them 

 take flying insects. What happens when the bat closes its mouth on 

 catching an insect? Does echo-location cease (in which case the bat 

 must fly blind) or does its continue through the nose? We do not 

 know. In the greater horseshoe {Rhinolophus f evnvm-equinum in- 

 sulans) the epiglottis does not open into the back of the mouth as in 

 most animals, but is projected up into the roof of the mouth, fitting 

 into the rear opening of the nasal passages. It is not fixed in this 

 position, and can probably be withdrawn, but the arrangement suggests 

 that the supersonic squeaks, in the Rhinolophidae at any rate, are 

 emitted through the nose, and this suggestion receives additional 



