美国科学60秒 SSS 2013-05-07（在线收听）

 　　When summer hits, I dread jogging outside. But a study finds that elephants can be in true danger in the heat. As creatures get bigger, they have smaller surface area to body volumn ratios. Fully-grown Asian eleplants thus pack a lot of mass into a body with a relatively small surface area. And surface area limits how much body heat you can dissipate. For the study, two female elephants in the Audubon zoo in New Orleans walked around a half mile track under various conditions. The outdoor temperature during the sessions ranged from a chilly 8 degree celsius to a scorching 35 degrees. Sunny hot day is where the worst. The already limited hide is now itself heated by the sun. With the equivlent of a busted radiator, the elephants retained 56% to 100% of their body heat internally, which could make a mere four hours of exercise, fatal. The research on the elephant exertion is in the journal of Experimenal Biology. Fortunately, elephants have ways to beat the heat: shift activity to after-dark and, of course, go for a dip.