THE SENSES OF BATS 



By Brian Vesey-FitzGerald, F. L. S. 



[With 4 plates] 



Of all the many problems which bats set for the inquiring naturalist, 

 none has been more puzzling than that presented by their flight at 

 night: the way in which they catch the insects upon which most of 

 them feed (in the case of British bats, upon which all of them feed) 

 without colliding with objects in their path. The flight of bats is rapid 

 and the course erratic, frequently through thick woods or the narrow 

 winding passages of caves, often in total darkness. It has always 

 seemed unlikely that animals with such small eyes could see well enough 

 in the dark to fly in such surroundings without mishap. Many experi- 

 ments have been tried with captive bats to demonstrate their ability 

 to avoid obstacles which they could not see. Toward the end of the 

 eighteenth century the Italian scientist, Lazzaro Spallanzani, found 

 that bats which he had blinded could fly about a room, avoiding the 

 walls, the furniture, and silken threads stretched across their path. 

 A Swiss scientist, Louis Jurine, confirmed this and made the addi- 

 tional discovery that bats lost their ability to avoid obstacles when 

 their hearing was interfered with. Cuvier poured scorn on these 

 findings, and they were forgotten for a century and a half. All that 

 was remembered was that a blinded bat could fly perfectly surely. 

 But the uncanny ability remained, and all sorts of theories were ad- 

 vanced to account for it. It was suggested, for example, that bats were 

 very sensitive to changes in atmospheric pressure. 



Then, in 1920, Professor Hartridge suggested that bats when flying 

 in the dark were probably able to ascertain the position of obstacles by 

 means of supersonic sounds emitted by the animals and reflected to 

 their ears. Twenty years later, after the development of radar as an 

 operational system, GrifRn and Galambos working in America were 

 able to prove him correct. 



Both radar and sonar are, of course, founded on the same fact, 

 namely, that if a short burst of energy is sent out and the time taken 

 for the echo to come back is noted, then, if the speed at which the 

 energy travels is known, the distance of the object can be accurately 

 calculated. Moreover, by sending the energy down a narrow beam 



1 Reprinted by permission from Endeavour, vol. 6, No. 21, London. January 1947. 



317 



