58 



Special Uses of Hearing and Vision /3 : 3 



bats navigated. The present knowledge followed the construction of 

 these physical analogs. Moreover, the pulses of the bats can be detected, 



analyzed, and displayed only by 

 modern acoustic and electronic 

 techniques. In order to discover 

 the details of bat navigation, Griffin 

 and his associates had to be pre- 

 pared to apply modern physical 

 techniques. 



3. Echo-Location in Other 

 Animals 



Because bats use echo-location, one 

 might wonder if other animals can 

 also use this type of information. 

 The answer is a strong affirmative ; 

 the number of animals known to 

 use echo-location has grown rapidly 

 since 1945. The list includes birds 

 that live in dark caves, marine 

 animals, and, to a limited extent, 

 humans. It is not inconceivable 

 that certain deep-sea fish also use 

 some form of echo-location. 



Among birds, two types have 

 been shown to use auditory clues 

 when flying in dark caves. One of 

 these is the oilbird of the valley of 

 Caripe, in Venezuela, named 

 Steatornis caripensis. These birds, 

 when flying in the light, use their 

 visual system to sense their sur- 

 roundings. In the dark, either at 

 night or far within their caves, they 

 emit clicks of 1 to 1.5 millisecond duration with frequencies in the neigh- 

 borhood of 7 kc. This is lower than most bat sound pulses. How- 

 ever, bird hearing is, in general, limited to the same range as human 

 hearing, in contrast to small mammals most of which can hear frequencies 

 as high as 100 kc. Thus, it is physiologically reasonable that the oil- 

 birds should use lower frequencies than the bats. It seems physically 

 reasonable also because the oilbird, being much larger, is concerned 



Figu re 2. Photograph of a flying bat, after 

 Edgerton. After Griffin, D. R. , Listening 

 in the Dark (New Haven, Connecticut: 

 Yale University Press, 1958). 



