They usually dig a den which they may use for several consecutive years. Natural caves or rock fissures sometimes also serve as retreats. Before the winter sets in, the bears cushion their dens nicely with grass, leaves, ferns, moss and lichen.
This cosy hole is ideal for dozing, because brown bears are not 'true' hibernators like, for example, hedgehogs. Although the frequency of their heartbeat and breathing slows down, the bears are easily woken and are able to defend themselves in the case of attack.
Before their winter rest, bears must eat enough to form a decent layer of fat since they lose around a third of their body weight during this sleeping phase.
Incidentally, the scientific community is divided about how to describe the bears' resting condition: as winter sleep, winter rest, torpor, hibernation — all these terms are in circulation. But it is always about saving energy during a time of scarce food.
It is often falsely assumed that bears are driven into their dens by the cold. But contrary to us humans, the bear is relatively insensitive to minus degrees, snow and frost. Bears use the rich autumn time when fruits containing plenty of fat and sugar such as nuts, beechnuts, seeds, berries, etc.
This layer of fat enables their survival in winter, under the condition of reduced energy consumption. Hibernation and torpor significantly differ because, during torpor, the animal is inactive during cold periods but in case of disturbance such as loud noise, they wake up quickly.
On the other hand, during hibernation, the animal does not wake up under any condition. Whether they are touched, disturbed by a loud noise, or moved, they will remain in a deep sleep. Bears are, therefore, not true hibernators. However, it is during winter that their body conditions change to adapt to the harsh conditions of the winter environment. Winter is characterized by low temperatures and to ensure that they are not affected by these conditions, bears remain inactive.
They dig caves and holes to sleep in until the harsh winter subsides. Bears use fats stored in their bodies during the winter. Before winter, bears are heavy but after the winter they are thin and lean because the body uses up the stored fats to maintain their body processes and to keep them warm. When the substance responsible for this phenomenon is discovered it may help people who suffer from weak bones. Beecham, J. Reynolds, and M.
Black bear denning activities and den characteristics in west-central Idaho. Bear Res. Brown, G. The Great bear almanac. Lyons and Burford, publishers. New York, N. Craighead, F. Grizzly bear prehibernation and denning activities as determined by radiotracking. Haroldson, M. Ternent, K. Gunther, and C. Grizzly bear denning chronology and movements in the Greater Yellowstone Ecosystem. Ursus Jonkel, C. Black, brown grizzly , and polar bears. Stackpole Books, Harrisburg, PA. Judd, S. Knight, and B.
Denning of grizzly bears in the Yellowstone National Park area. Kolenosky, G. Winter denning of black bears in east-central Ontario. Lindzey, F. Winter dormancy in black bears in southwestern Washington. Linnell, J. Swenson, R. Anderson, and B. How vulnerable are denning bears to disturbance? Wildlife Society Bulletin During this fall feeding frenzy, grizzlies can eat up to 20, calories —and put on up to three pounds of weight—each day. This helps Mama Bear to conserve energy until hibernation, and may be a way to control the population if food is scarce.
If she has not accumulated enough fat by the time she settles into her den, the egg will spontaneously abort. Yellowstone bears typically dig their dens on slopes at high elevation. The den entrance is just large enough for the bear to squeeze through so it will cover quickly with insulating snow.
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