THE LANGUAGE OF ECHOES 



from the loudspeaker every time the bat broadcasts one 

 of its high-frequency chirps. 



When this "listening" apparatus is used in some spot 

 where bats do their insect hunting, we notice that one 

 cruising past on a straight course several feet above the 

 ground sounds like the slow putt-putt-putt-putt of a lazy, 

 old gasoline engine. Often it will fly straight past with 

 Uttle or no change in this rhythm, but if its attention is 

 attracted either to a real insect or to a decoy, such as a 

 pebble tossed up in front of it, then there is a marked 

 increase in the rate of the orientation sounds. Sometimes 

 this is a slight increase in rate, but if the pursuit is serious, 

 involving drastic maneuvers such as sudden turns, wing- 

 overs, or sharp dives, then the translation resembles the 

 acceleration of a motorcycle engine. On occasion it rises 

 to a real crescendo with the individual clicks coming so 

 close together that for human ears they fuse into a whin- 

 ing buzz reminiscent of a chain saw. Such crescendos 

 occur just when the bat is closing in on an elusive moving 

 target, strong evidence against the idea that all location 

 and tracking are done simply by listening to the sounds 

 of the insect's wingbeats. In this case one would expect 

 the bat to keep relatively quiet when near an insect so 

 as to hear the faint buzzing of the insect's wings. Instead 

 it fills the air with an extremely rapid series of chirps 

 that would seem to interfere severely with any process of 

 passive Ustening. 



Precision of Echolocation 



Another important aspect of bats' use of echoes for 

 rapid and precise navigation is the small size of objects 

 which can be detected and the distances at which detec- 

 tion can occur. The only feasible tests yet devised have 

 involved wires or strings rather than small isolated ob- 



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