If you found yourself instantly transported to thefreezing arctic, your first concern would be keepingwarm. But what about the animals that make theirhomes on these vast fields of ice and snow? Do polarbears need to worry about freezing to death?

如果你发现自己突然置身于天寒地冻的北极，你首先考虑的事情是保暖。但是在这片白茫茫的冰天雪地上兴建家园的动物们会怎么办呢?北极熊会担心被冻死吗?

Actually, a polar bear's biggest problem is keepingcool, not keeping warm. Thanks to its thick coat offur, 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 withinfra-red film—a kind of film which can measure the amount of heat escaping from a body–thepolar bear won't even show up at all. That doesn't mean polar bears are as cold as thesurrounding ice; their normal body temperature is about the same as ours.It simply meansthat polar bears retain their body heat very well. In fact, a polar bear can rest in a pit of icysnow, at temperatures as low as minus thirty-four degrees Fahrenheit, without needing to burnany extra fat for warmth!

实际上，北极熊面对的最大问题不是保暖，而是保持冷静。在厚厚的毛发，坚硬的熊皮和厚约四英寸的脂肪层的保护下，北极熊能够极好地防止热量流失。事实上，如果用红外感热胶片(一种可以测量从体内流失的热量的胶片)拍摄一只休息中的北极熊，可能根本看不到它的存在。这并不说明北极熊像周围的冰雪一样冰冷，它们的正常体温跟人类一样。这只能说明北极熊可以很好地保存身体里的热量。北极熊可以躺在温度低到零下34度的雪坑里休息，而且不需要燃烧额外的脂肪来取暖。

While this insulation is great for keeping warm, it can lead to some serious overheating. As aresult, polar bears don't like to run after their prey. Chasing a seal at only four and a half milesan hour, a polar bear's temperature climbs to a feverish hundred degrees. It may have to lieon its back with its feet in the air to cool down. Polar bears prefer to hunt by waiting near a holein the ice, and letting dinner come to them. It's the best way to conserve energy, and keepcool, in the Arctic north.

虽然与外界绝缘能保持体温，但也会导致体温严重升高。因此北极熊不喜欢追逐猎物。北极熊在追逐一只时速4.5英里的猎海豹时，身体会变得炙热，体温升高到100度。它不得不四脚朝天仰躺着使身体冷却下来。北极熊更喜欢守株待兔，它们在冰窟附近等着猎物上钩。在北极，这就是即能保持体力又能冷静下来的最佳方法。