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Hibernation

Hibernation

Hibernation is a state of inactivity, in which an animal's heart rate, body temperature, and breathing rate are decreased in order to conserve energy through the cold months of winter. A similar state, known as estivation, occurs in some desert animals during the dry months of summer.

Hibernation is a technique that animals have developed in order to adapt to harsh climates. When food is scarce, an animal may use up more energy maintaining its body temperature and in searching for food than it would receive from consuming the food. Hibernating animals use 70 to 100 times less energy than when active, allowing them to survive until food is once again plentiful.

Many animals sleep more often when food is scarce, but only a few truly hibernate. Hibernation differs from sleep in that a hibernating animal shows a drastic reduction in metabolism, and then awakes relatively slowly. (Metabolism is the process by which cells in an organism break down compounds to produce energy.) By contrast, a sleeping animal decreases its metabolism only slightly, and can wake up almost instantly if disturbed. Also, hibernating animals do not show periods of rapid eye movement (REM), the stage of sleep associated with dreaming in humans.

Bears, which many people think of as the classic hibernating animals, are actually just deep sleepers. They do not significantly lower their metabolism and body temperature. True hibernation occurs only in small mammals, such as bats and woodchucks, and a few birds, such as poorwills and nighthawks. Some species of insects show periods of inactivity during which growth and development cease and metabolism is greatly reduced. This state is generally referred to as diapause, although when correlated with the winter months, it would also fit the definition of hibernation.

Preparing for hibernation

Animals prepare for hibernation in the fall by storing enough food to last them until spring. Chipmunks accomplish this task by filling their burrows with food, which they consume during periodic arousals from hibernation throughout the winter. Most animals, however, store energy internally, as fat. A woodchuck in early summer may have only about 5 percent body fat. However, as fall approaches, changes occur in the animal's brain chemistry that cause it to feel hungry and to eat constantly. As a result, the woodchuck's body fat increases to about 15 percent of its total weight. In other animals, such as the dormouse, fat may comprise as much as 50 percent of the animal's weight by the time hibernation begins. A short period of fasting usually follows the feeding frenzy, to ensure that the digestive tract is completely emptied before hibernation begins.

Entering hibernation

Going into hibernation is a gradual process. Over a period of days, an animal's heart rate and breathing rate drop slowly, eventually

reaching rates of just a few times per minute. Their body temperature also drops from levels of 37° to 38°C (99° to 100°F) to 10° to 20°C (50° to 70°F). The lowered body temperature makes fewer demands on metabolism and food stores.

Electrical activity in the brain almost completely ceases during hibernation, although some areas remain active. These areas are those that respond to external stimuli such as light, temperature, and noise. Thus, the hibernating animal can be aroused under extreme conditions.

Arousal

Periodically, perhaps every two weeks or so, the hibernating animal awakes and takes a few deep breaths to refresh its air supply, or in the case of the chipmunk, to grab a bite to eat. If the weather is particularly mild, some animals may venture above ground. These animals, including chipmunks, skunks, and raccoons, are sometimes called shallow hibernators.

Arousal begins with an increase in the heart rate. Blood vessels dilate, particularly around the heart, lungs and brain, leading to an increased breathing rate. Eventually, the increase in circulation and metabolic activity spreads throughout the body, reaching the hindquarters last. It usually takes several hours for the animal to become fully active.

[See also Metabolism ]

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hibernation

hibernation (hī´bərnā´shən) [Lat.,= wintering], practice, among certain animals, of spending part of the cold season in a more or less dormant state, apparently as protection from cold when normal body temperature cannot be maintained and food is scarce. Hibernating animals are able to store enough food in their bodies to carry them over until food is again obtainable. They do not grow during hibernation, and all body activities are reduced to a minimum: there may be as few as one or two heartbeats a minute. Cold-blooded animals (e.g., insects, reptiles, amphibians, and fish) must hibernate if they live in environments where the temperature—and hence their own body temperature—drops below freezing. Some insects pass their larval stage in a state of hibernation; in such cases hibernation is closely associated with the reproductive cycle (see larva; pupa). However, most warm-blooded animals, i.e., birds and mammals, can survive freezing environments because their metabolism controls their body temperatures. Many hibernating animals seek insulation from excessive cold; bears and bats retire to caves, and frogs and fish bury themselves in pond bottoms below the frost line. Analogous to hibernation is aestivation, a dormant period of escape from heat and drought. Other methods of avoiding excessively high or low temperatures and destructive increases or decreases in the water supply are encystment and ensuing dormancy, e.g., in plant seeds and bacteria, and migration. Some animals, such as rabbits, raccoons, and squirrels, store food against scarcity and spend cold periods asleep in their burrows, though they may emerge on warm days.

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hibernation

hibernation A sleeplike state in which some animals pass the winter months as a way of surviving food scarcity and cold weather. Various physiological changes occur, such as lowering of the body temperature and slowing of the pulse rate and other vital processes, and the animal lives on its reserve of body fat. Animals that hibernate include bats, hedgehogs, and many fish, amphibians, and reptiles. See also dormancy. Compare aestivation.

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hibernation

hibernation A strategy for surviving winter cold that is characteristic of some mammals. Metabolic rate is reduced to a minimum and the animal enters a deep sleep, surviving on food reserves stored in the body during the favourable summer period. Compare AESTIVATION. See also TORPOR.

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hibernation

hibernation Dormant (sleep-like) condition adopted by some animals, such as bears, bats and squirrels, to survive harsh winters. Adaptive mechanisms to avoid starvation and extreme temperatures include reduced body temperature, slower heartbeat, breathing rate, and metabolism.

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"hibernation." World Encyclopedia. . Encyclopedia.com. 17 Aug. 2017 <http://www.encyclopedia.com>.

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"hibernation." World Encyclopedia. . Retrieved August 17, 2017 from Encyclopedia.com: http://www.encyclopedia.com/environment/encyclopedias-almanacs-transcripts-and-maps/hibernation

hibernation

hibernation A strategy for surviving winter cold that is characteristic of some mammals. Metabolic rate is reduced to a minimum and the animal enters a deep sleep, surviving on food reserves stored in the body during the favourable summer period. Compare aestivation.

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"hibernation." A Dictionary of Ecology. . Encyclopedia.com. 17 Aug. 2017 <http://www.encyclopedia.com>.

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"hibernation." A Dictionary of Ecology. . Retrieved August 17, 2017 from Encyclopedia.com: http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/hibernation