Читать книгу Polar Exploration. A practical handbook for North and South Pole expeditions онлайн

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Mammals have hair, fur or blubber, and birds have feathers to help keep them warm. Mammals with thick coats of fur which keep them warm in winter shed much of this in summer to help them cool off and maintain body temperature. Warm-blooded animals can also shiver to generate more heat when they get too cold. Some warm-blooded animals, especially birds, migrate from colder to warmer regions in the winter.

Thus warm-blooded creatures try to keep their body temperature constant by generating their own heat when in a cooler environment, and by cooling themselves when in a hotter environment. To generate heat, warm-blooded animals convert food into energy; compared to cold-blooded species they have to eat a lot of food to maintain a constant body temperature. Only a small amount of food is converted into body mass; the rest is used to fuel a constant body temperature.

Cold-blooded creatures take on the temperature of their surroundings: they are hot when their environment is hot, and cold when it is cold. In hot environments, the blood of cold-blooded animals can be much warmer than warm-blooded animals. Cold-blooded animals are much more active in warm environments, and very sluggish in cold environments: their muscle activity depends on chemical reactions which work quickly when it is hot and slowly when it is cold. A cold-blooded animal can convert much more of its food into body mass.