VOICES OF EXPERIENCE 



was available for converting underwater sound to audi- 

 ble, airborne sound, porpoises were found to be posi- 

 tively garrulous. An individual porpoise has a large 

 "vocabulary" of squeals, whistles, grunts, and rasping, 

 clicking sounds. While fishermen and whalers had heard 

 some of these sounds from time to time, it was only 

 during the last war that underwater listening became re- 

 fined enough and common enough to reveal the immense 

 variety of sounds used by the marine mammals. Many 

 of these sounds may be calls for signaling back and forth 

 from one porpoise to another, but some are clearly used 

 for echolocation. 



In recent experiments individual porpoises have been 

 isolated in small ponds or experimental tanks, such as 

 those at the larger marine aquaria of Florida and Cali- 

 fornia. When obstacles are set up in such a tank, the 

 porpoises are able to dodge them at high speed, even 

 when the obstacles are put into place on the darkest 

 nights. While doing this, porpoises make sounds of vari- 

 ous sorts, usually faint clicking sounds that were over- 

 looked at first because they were masked by incidental 

 noises in the ponds. Most porpoises spend their fives in 

 the open ocean, but there are a few smaller kinds which 

 live in the larger and often very muddy rivers, such as 

 the Amazon in South America and the Ganges in India. 

 These animals must often thread their way among un- 

 derwater obstructions, such as logs and fallen trees. 

 Even the species that five in open waters continue their 

 activities at night. All porpoises feed on fish, which they 

 must catch by active pursuit, much of the time in poor 

 fight where it is impossible to see clearly more than a 

 few centimeters. Therefore, it is not surprising that the 

 most impressive feats of underwater echolocation have 

 been exhibited in the capture of fish by hungry porpoises. 



Captive porpoises are usuaUy fed by tossing dead fish 



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