Do polar bears hibernate?

No, most polar bears do not hibernate. Males and females without cubs stay active all winter, hunting seals on the sea ice. Only pregnant females spend the winter in a snow den, where they give birth and go without food for up to eight months, says San Diego Zoo Wildlife Alliance. Even that is not quite true hibernation.

Do polar bears hibernate in winter?

Not the way you might expect. The Alaska Department of Fish and Game states that polar bears do not undergo true hibernation. For most bears, winter is hunting time. The sea ice is frozen and wide, so seals are easier to reach.

The table shows what each kind of polar bear does in winter, with two hibernating relatives for comparison.

What polar bears do in winter, compared with other bears

Bear	Winter behaviour	How long	Source
Adult male polar bear	Active, hunting on sea ice	All winter	San Diego Zoo Wildlife Alliance
Female polar bear without cubs	Active, hunting on sea ice	All winter	San Diego Zoo Wildlife Alliance
Pregnant female polar bear	Digs a maternity den, gives birth, fasts	October–November to March–April; up to 8 months without food	ADFG; San Diego Zoo
Newborn polar bear cubs	Born in the den, drink milk	Born December–January; leave the den in spring	ADFG; PBI
American black bear	Hibernates; body temperature drops only 5–6 °C	5–7 months without eating, drinking or urinating	Tøien and others, 2011
Brown bear in northern Alaska	Dens through winter	Up to 8 months; some Kodiak males stay active	ADFG

Why don’t most polar bears hibernate?

Because their food does not disappear in winter. Black and brown bears den because berries, roots and insects vanish under the snow. Polar bears eat seals, and seals live under the sea ice all year. Our page on what polar bears eat explains how bears hunt at breathing holes.

Winter is often the time bears most need the ice. The hard season for polar bears is summer, when the ice melts and many must wait on land with little to eat. A bear fattens up on seals in spring, lives off that fat in summer and hunts again once the ice returns. That is why melting sea ice worries scientists, as our page on polar bear status explains.

What happens inside a polar bear den?

In October or November, a pregnant female digs a den, usually into a snowdrift, says the Alaska Department of Fish and Game. Most dens are on land near the coast, though some are on sea ice. The den is a small chamber, and the snow keeps it much warmer than the air outside.

The cubs, usually twins, are born in December or January. Each weighs only about 500 g (1 lb), roughly 1/400th of its mother’s weight, says Polar Bears International. That is lighter than a loaf of bread. Over the next three months they drink rich milk and gain about 10 to 15 kg (22 to 33 lb).

All that time, the mother eats nothing. She lives on the fat she stored the spring and summer before. San Diego Zoo says a pregnant female can top 450 kg (1,000 lb) before denning, and that she may stay in the den without leaving for as long as eight months if you count the time before the birth.

How long do polar bears stay in their dens?

Most families come out in March or April, after about three months with the cubs inside, says PBI. ADFG says cubs weigh around 9 to 11 kg (20 to 25 lb) when they leave. The family often stays near the den for a while so the cubs can get used to the cold before walking to the sea ice.

The timing matters. Mothers come out just as seals are giving birth on the ice, which gives a hungry bear plenty of easy meals. Follow the cubs’ first years in our polar bear life cycle guide.

Is a denning polar bear hibernating?

Scientists use the word carefully. In hibernating bears, the body slows but stays fairly warm. A 2011 study of black bears in Alaska found their body temperature fell by only 5 to 6 °C, while their metabolism dropped by about 75%, reports EurekAlert. Small hibernators such as ground squirrels cool to near freezing.

A denning mother polar bear also goes months without food and slows down, but she has to stay warm enough for newborn cubs. ADFG says polar bears do not undergo true hibernation, while other sources call it a hibernation-like state. The safest summary is that only pregnant females den, and they do something close to a bear’s winter sleep.

What is “walking hibernation”?

It was an idea, now largely rejected. Some scientists thought polar bears stuck on land in summer might slow their bodies down while still walking about. A 2015 study in Science tested this by fitting bears in the Beaufort Sea with collars and body-temperature loggers.

The summer bears cooled only slightly, far less than in true hibernation, reports EurekAlert. The authors concluded polar bears cannot use a lower metabolism to stretch their fat much further. That is bad news for bears facing longer ice-free summers. For more on bear biology, see polar bear adaptations and how long polar bears live.

Frequently asked questions

Sources

1. San Diego Zoo Wildlife Alliance. Polar bear.
2. Alaska Department of Fish and Game. Polar bear species profile.
3. Polar Bears International. The basics of polar bear denning.
4. EurekAlert! (AAAS) (2015). Polar bear metabolism less resilient to summer ice melt than expected (on Whiteman et al. 2015, Science).
5. EurekAlert! (University of Alaska Fairbanks) (2011). Bears uncouple temperature and metabolism for hibernation (on Tøien et al. 2011, Science, doi:10.1126/science.1199435).
6. Alaska Department of Fish and Game. Brown bear species profile.
7. Polar Bears International. Polar bear facts.

Sources checked 15 September 2026.