- Polar Bears & Conservation
- Climate Change
- Pollution
- Drilling and Mining
- Hunting
- Other Human Interactions
- About the Polar Bear
- Polar Bear Cubs
- Polar Bear I.Q.
- Polar Bear Fur
- The Sea Bear
- More Facts
- Adaptions to Cold
- Communication
- Polar Bear Prey
- Home Range
- Bears in Motion
- Inuit & Polar Bears
- Bear Attacks
- Polar Bears in Zoos
- Myths & Misconceptions
- Hunting Seals
- Hibernation Facts
- Bathing Habits
- Sleepy Bears
- Name That Bear!
- Walking and Running
- Feasting Bears
- Polar Bear Evolution

Hibernation Facts

Hibernation in the true sense of the word does not apply to polar bears.

True hibernators experience a marked drop in heart rate and a body temperature that plunges to nearly O° C (32° F). It may take some time to wake them up.

Denning bears, including brown and black bears, are not true hibernators. Though their heart rate slows, their body temperature fails to undergo a dramatic decline, usually dropping to about 31° to 35° C (88° to 93° F). They may sleep deeply, but have no difficulty waking up.

Bears do not enter a state of deep hibernation because they need a higher body temperature in order to meet the demands of pregnancy, birth, and the nursing of young.

Though brown and black bears hibernate in winter, all polar bears do not. Only pregnant females hole up in a den. The rest of the population remains active throughout the year.

Pregnant female polar bears den up in the fall after feeding heavily in August and September. Most choose den sites in snowdrifts along mountain slopes or hills near the sea ice. Others den in banks of snow on the frozen sea.

To build her den, the female scrapes a tunnel into the snow and digs two chambers. She gives birth to her cubs in November or December.

When a female polar bear emerges from her den in March or April, she is in a physiological state similar to that of a hibernating black bear. Her body temperature, however, does not drop quite as low as that of a black bear. Instead it ranges from 35° to 37° C (95° to 98.6° F).

Those polar bears that spend the late summer and fall on the shores of Hudson Bay, beyond the reach of seals, also enter a state of hibernation due to the lack of food. Because they don't den, scientists have dubbed the condition "walking hibernation."

Interestingly, polar bears appear to have the ability to control their hibernation. A study done on a group of Hudson Bay polar bears that fed at a garbage dump during the fall "lean period" revealed that the animals were not in a state of hibernation. Those bears, however, that steered clear of the dump were.

Scientist Ian Stirling points out that a black bear deprived of food in summer would starve. A polar bear, however, appears to have the ability to turn on its hibernation mode when food is scarce and to turn it off when food becomes more abundant again.

Sources: Polar Bear by Downs Matthews (Chronicle Books, 1993); Polar Bears by Ian Stirling (University of Michigan Press, 1988).

Additional german informations can be found here.

Further informations and topics all around PBA:

How we started | Goals | The bear facts | Join us | Tours | Gallery | President's report