PLANET EARTH Deserts

Any kangaroo out in the open is in serious danger of overheating. In the full sun the temperature on the ground soars（飞升到） to 70 degrees. By midday the radiation is so intense they must take shelter. In the shade they're shielded from much of the sun's energy but their body temperature can still rise. So they lick saliva on to their forearms where there is a network of blood vessels close to the surface of the skin and, as the saliva evaporates, their blood is cooled.



This thermal image shows just how effective the process is. The blue areas on the body are the cooler parts. As the saliva dries it has to be replaced and this is a real drain on the kangaroo's body fluids. Even in the shade the earth is baking hot so the kangaroos dig away the warmed topsoil to get at the cooler ground beneath. By staying in the shade and licking to control their body temperature kangaroos manage to get through the hottest part of the day without heat stroke（中暑）.



But for the majority of desert animals this strategy would not be enough for survival. The extraordinary ears of the fennec（大耳小狐，主要产地为非洲） foxes of Africa radiate heat but the animals have another way of keeping cool. They spend their days underground and only emerge at sunset. Darkness brings huge changes. In the Sahara the temperature can drop as much as 30 degrees during the night, so it's cool enough to allow these desert fox cubs to play.