【英语时差8,16】北极熊是怎样保持冷静的呢？（在线收听）

If you found yourself instantly transported to the freezing arctic, your first concern would be keeping warm. But what about the animals that make their homes on these vast fields of ice and snow? Do polar bears need to worry about freezing to death? Actually, a polar bear's biggest problem is keeping cool, not keeping warm. Thanks to its thick coat of fur, its tough hide, and a four inch layer of blubber, a polar bear is extremely well insulated. Indeed, if a resting polar bear is photographed with infra-red film–a kind of film which can measure the amount of heat escaping from a body–the polar bear won't even show up at all. That doesn't mean polar bears are as cold as the surrounding ice; their normal body temperature is about the same as ours. It simply means that polar bears retain their body heat very well. In fact, a polar bear can rest in a pit of icy snow, at temperatures as low as minus thirty-four degrees Fahrenheit, without needing to burn any extra fat for warmth! While this insulation is great for keeping warm, it can lead to some serious overheating. As a result, polar bears don't like to run after their prey. Chasing a seal at only four and a half miles an hour, a polar bear's temperature climbs to a feverish hundred degrees. It may have to lie on its back with its feet in the air to cool down. Polar bears prefer to hunt by waiting near a hole in the ice, and letting dinner come to them. It's the best way to conserve energy, and keep cool, in the Arctic north.