ECHOES OF BATS AND MEN 



first begins to increase. This varies from flight to flight, 

 even for a single individual, but the average of numerous 

 measurements with several sizes of wire gave the follow- 

 ing results. 



These distances are considerably greater than one 

 would guess from the bat's flight behavior. Ordinarily 

 it flies along a fairly straight course and swerves only in 

 the last few inches to avoid a wire. Yet the increasing 

 pulse rate shows that it has already detected the wires 

 and reacted to them at the distances shown in the table. 

 If no wire is in place, there is no increase in the rate of 

 the orientation chirps. Of course, a bat might be aware of 

 the wires at still greater distances than the table shows, 

 but it gives no sign of such awareness that we yet have 

 learned to recognize. The important point is that even 

 such small wires as those 0.18 millimeters in diameter 

 are detected at some distance, not merely at the last pos- 

 sible moment to avoid colUsion. It is also interesting to 

 note that small wires produce only a small increase in 

 pulse rate. Actually the bat is moving so fast (ap- 



94 



