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State of greatly slowed metabolism and low body temperature in winter in certain animals.

True hibernators include many cold-blooded animals and a few mammals (e.g., bats, hedgehogs) that go into a near-dead state with a near-freezing body temperature and very slow breathing and heart rate. Mammals such as bears that sleep in dens with only slightly lowered body temperature wake easily and are not considered true hibernators. Most hibernators build up a reserve of body fat or store food ahead of time. They may wake and eat several times during the winter. Cold-blooded animals must hibernate where the weather drops below freezing. Hibernation's warm-weather equivalent is estivation.

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 a state of greatly reduced metabolic activity (metabolism) and lowered body temperature adopted by certain mammals as an adaptation to adverse winter conditions. A brief treatment of hibernation follows. For full treatment, see dormancy.

      The term hibernation is commonly applied to all types of winter dormancy in vertebrate animals. Thus defined, hibernators include many fishes, amphibians, and reptiles that overwinter with body temperatures near freezing, as well as bears and a few other mammals that spend most of the winter sleeping in dens. The latter, however, do not undergo much lowering of body temperature and are rather easily awakened; they are not considered true hibernators.

      The true hibernator spends most of the winter in a state close to death; in fact, the animal may appear to be dead. The body temperature is close to 0° C (32° F); the respiration is only a few breaths per minute; and the heartbeat is so slow and gradual as to be barely perceptible. Exposed to moderate warmth, the animal slowly awakens, requiring an hour or more to reach an alert state.

      Among mammals, true hibernators are found only in the orders Chiroptera (bats), Insectivora (hedgehogs and allies), and Rodentia (ground squirrels, marmots, etc.). Typically, the hibernator relies on a combination of reserve body fat, stored food supplies (in rodents only), and a protected den to enable it to survive the winter. At intervals of several weeks the animal elevates its body temperature, awakens, moves about, feeds, and then returns to its state of torpor.

      In some desert regions, certain animals escape the rigours of summer drought by entering a torpid state, estivation, that is similar in many ways to hibernation.

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Universalium. 2010.

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