VOICES OF EXPERIENCE 



faced with complicated navigational problems, such as 

 dodging you or a stick which you hold up in front of 

 you, you may hear the ticking suddenly increase imtil it 

 forms a faint buzz. The same thing happens just before 

 a bat makes a landing, but the audible ticks are such a 

 faint sound that it requires patience and completely 

 quiet surroundings for them to be heard. The auditory 

 basis of obstacle detection by bats was independently 

 recognized in 1932 by a Dutch zoologist, Sven Dijkgraaf, 

 who made a careful study of these faint, audible clicks 

 and noted how closely they were correlated with the 

 echolocation of obstacles. This is an example of the need 

 for care, patience, and appropriate conditions if one is to 

 notice and enjoy some of the more fascinating facets of 

 the natural world. 



Bats are not always agile and clever fliers; sometimes 

 they are sleepy and clumsy— especially when they have 

 been disturbed in the daytime. Most American and Eu- 

 ropean species tend to let their body temperature fall to 

 about that of the air in which they sleep. In winter many 

 kinds of bats hibernate in caves or other places where 

 they find temperatures only a few degrees above freez- 

 ing. At such temperatures they are completely torpid, 

 and one may easily think them dead. In between deep 

 hibernation and full activity are many degrees of activity 

 and alertness. The bats we are most likely to find and 

 have an opportunity to observe are usually those that 

 are least agile and least ready to display their full reper- 

 toire of flight maneuvers. If fully airworthy, they would 

 be xmHkely to let us watch them for long at close range. 

 Furthermore, they often seem to become tired, and when 

 chased about a room or attic they may soon become 

 clmnsy from fatigue alone. But if one takes the trouble 

 to observe bats at their best, when fully awake and in 

 top flying condition, as they are every night of normal 



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