Elephants don't have floppy sun hats, battery-powered misting fans, or ice-cold popsicles to help keep them cool on a hot day. The animals have a lot of mass compared with their skin's surface area and can't get rid of much heat through the skin. Instead, they store that heat in their bodies. So how hot is too hot for a 4-tonne pachyderm? Biologist Michael Rowe (shown, in green, with elephants and keepers at the Indianapolis Zoo) kept a close eye on the temperatures of two Asian elephants, named Panya and Jean, while they exercised. Keepers at the Audubon Zoo in New Orleans walked the elephants around a half-mile track in weather ranging from 13°C to 31°C, while Rowe monitored their internal and external temperatures. On hot days, the elephants' sun-drenched skin was above their body temperature, preventing any heat from radiating away. The gigantic animals held on to about 100% of the heat generated by exercise, Rowe reports today in The Journal of Experimental Biology. All experiments were conducted safely, but Rowe projected that a mere 4 hours of walking in the heat of a summer day could be fatal to elephants. The animals avoid overheating by resting during the day, cooling off in water, or shifting their activity to nighttime. Rowe's work may explain how dinosaurs like Edmontosaurus, about the same size as an elephant, dealt with heat—an element of dinosaur behavior that can't be deduced from fossils.
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