THE LANGUAGE OF ECHOES 



weighing only 3.5 grams, caught mosquitoes at such a 

 rapid rate before our very eyes that after 15 minutes' 

 hunting its weight had increased by 10 per cent to 3.85 

 grams. These particular mosquitoes weighed about 

 0.002 gram each. The bat had no possible way of gain- 

 ing weight during these 15 minutes of closely observed 

 himting, aside from the weight of the mosquitoes caught. 

 It drank no water and ate nothing else. It probably lost 

 a little weight by the evaporation of water while breath- 

 ing; therefore, it caught more than 0.35 gram of mos- 

 quitoes. 



Dividing the weight gain by the weight of a single 

 mosquito shows that at least 175 mosquitoes were 

 caught in 15 minutes, or more than one every 6 seconds. 

 This was also approximately the number of obvious 

 mosquito-chasing maneuvers that we could count dur- 

 ing this hunting spree. There is every reason to believe 

 that similar rates of insect capture are commonplace 

 events in the nightly activities of millions of these bats 

 and their relatives all over the world. Of course, it is not 

 always mosquitoes that are eaten; almost any kind of 

 insect that is locally available and is not too big seems 

 welcome. Sometimes moths up to an inch in wingspread 

 are taken, but at other times these bats capture insects 

 much smaller than mosquitoes. In one instance a smaU 

 gnat weighing only 0.0002 gram was found stiQ unswal- 

 lowed in the mouth of a bat killed while it was hunting. 



This maneuvering to capture one insect every 6 sec- 

 onds is what makes the flight of bats appear so erratic. 

 Far from being feeble fliers buffeted about by air cur- 

 rents, they are expert fliers engaging in the difficult in- 

 terception of flying insects. Their percentage of successes 

 must be very high indeed. Certainly they are doing vastly 

 better than simply flying around with their mouths open. 

 Even when mosquitoes are particularly abundant, their 



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