3 : 2/ Special Uses of Hearing and Vision 



57 



TABLE I 

 Echo-Location Comparisons 



The bat is far inferior to radar and sonar in other respects, particu- 

 larly in its ability to distinguish shapes. Bats apparently could not dis- 

 tinguish solid objects in the shape of a cross from others in the shape of a 

 circle, although all were large compared to the minimum sizes the bat 

 detected. Furthermore, insectivorous bats will chase pebbles thrown 

 into the air just as readily as they pursue moths. 



Various families of bats differ in their anatomy and their use of echo- 

 location. There is no simple relationship between the range of hearing 

 and the pulses used. All bats can hear from 30 cps to 100 kc or higher 

 according to electrophysiological data. However, the largest bats 

 depend on visual information and lack a "sonar" system. Certain 

 Central American bats emit very high frequency pulses; these are pure 

 tone pulses, in the range of 80-120 kc, and of comparatively low intensity. 

 Other bats use pulses whose frequencies decrease to as low as 20 kc. One 

 species, Rousettus aegyptiens, the Egyptian tomb bat, emits a pulse whose 

 frequency goes from 100 kc to 6.5 kc each pulse. Some types of bats 

 emit their pulses through their mouths, others through their nostrils, 

 and still others can use either. Many species of bats have specially 

 shaped external ears which act as directional receiving horns, and 

 others have bizarre nose forms which act as horns for the emitted signal. 

 Figure 2 shows an insectivorous bat. 



Before the development of radar and sonar, it was hard to guess how 



