56 



Special Uses of Hearing and Vision /3 : 2 



It is interesting to compare the physical characteristics of a bat with 

 radar and sonar equipment. The table on page 57 lists some data for 

 radar and sonar systems of World War II, and the insectivorous bat, 

 Eptesicus fuscus. It is clear that the bat compares favorably with the 

 sonar and radar systems. 



2 



I 





 I 

 2 



MYOTIS LUCIFUGUS 



2 



I 



2 L 



EPTESICUS FUSCUS 



Figure I. Photographs of oscilloscope traces of the sound 

 pressure pulses emitted by two different species of bats. The 

 time markers are in milliseconds. After D. R. Griffin, Listen- 

 ing in the Dark (New Haven, Connecticut: Yale University 

 Press, 1958). 



The bat is superior to the radar and sonar systems in some respects. 

 When the insect-hunting bat is far above the ground it emits only long 

 pulses at a comparatively slow repetition rate, that is, 50 millisecond 

 pulses, five times per second. As it approaches its prey, the pulse length 

 shortens to two milliseconds and the repetition rate increases to 200 per 

 second. This makes maximum use of its available facilities. 



