While they’re sleeping, their bodies break down their own body fat to use as energy and keep them alive. Essentially, they stock up on extra calories when food is plentiful and then go into a den and sleep for a majority of the winter.

Over eons of time, most bears have developed physiological adaptations that enable them to live with these conditions. To complicate things more, if the snow piles too deeply, even mobility becomes difficult. During this time, not only is it cold, but their food supply becomes very limited. A large percentage of bear habitat in North America, Europe, and Asia goes through extremely cold conditions in the winter. Bears sometimes become active during short, warm periods and dig for roots in the frost-free forest floor, then disappear back into the den with the new onset of winter.Yes, most bears do hibernate. In the same way, there are no fixed times for the start and end of the winter resting period. Or because they have learnt to access alternative sources of food such as deer feeding stations, winter fields or waste produced by humans. In isolated cases, bears do not enter torpor at all – sometimes because they are good hunters and have specialised in capturing old, weak or injured prey in the winter forest. Like with all biological phenomena, a high degree of flexibility is involved. And that is vital because in changing environmental conditions, inflexibility has often led to the extinction of animal species. The only reliable thing that can be said here is: bears are extraordinary individualists! This means that no one bear behaves like another, just as each winter is different. Questions often crop up concerning the basic parameters of the winter resting phase, for example: how long do bears sleep? How much do they cool down? How much weight do they put on beforehand, and so on. And while kidney patients often need life-long dialysis, the bear can seemingly switch its kidney function 'on and off' when necessary. Taking into account that bears lie around for weeks without suffering a breakdown of bone or muscle mass, nor does the skin develop sores, a link can be made to one of the biggest challenges faced by geriatric medicine. These questions are of great interest to human medicine. The exact manner in which it manages its energy balance, the shape of its temperature curves and its restricted kidney function – this all largely remains a mystery. If it were to reduce the temperature of its heavy body, which weighs several hundred kilogrammes, to three degrees Celsius, it would be unable to 'get into gear' without an external energy source.

The bear, on the other hand, reduces its circulation, breathing and heartbeat only to a level at which it is able to defend its den at any time. Its body temperature drops to only three degrees Celcius. During hibernation, the marmot reduces its metabolic rate to a tenth of its normal level: it breathes only once or twice per minute and its heart beats a maximum five times. For the latter, rest is an important precondition.īears go into torpor, which should not be confused with the deep hibernation of smaller mammals such as hedgehogs and marmots. This layer of fat enables their survival in winter, under the condition of reduced energy consumption. Bears use the rich autumn time when fruits containing plenty of fat and sugar such as nuts, beechnuts, seeds, berries, etc. can be harvested in order to gorge themselves fat. But contrary to us humans, the bear is relatively insensitive to minus degrees, snow and frost. It is often falsely assumed that bears are driven into their dens by the cold. But it is always about saving energy during a time of scarce food. 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. 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.īefore 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. This cosy hole is ideal for dozing, because brown bears are not 'true' hibernators like, for example, hedgehogs. Before the winter sets in, the bears cushion their dens nicely with grass, leaves, ferns, moss and lichen. Natural caves or rock fissures sometimes also serve as retreats. They usually dig a den which they may use for several consecutive years. Brown bears enter a winter resting period between October and December.

Do grizzly bears hibernate in a cave