Most bears will hibernate in winter, entering a long low-energy state, rather than migrating to look for food like other animals. However, polar bears are different from most bears as they have evolved to cope with the extreme Arctic temperatures, So, do polar bears hibernate or migrate?
Unlike other bears, polar bears do not hibernate. Instead, they migrate, spending winter on the sea ice where they have plentiful access to seals and marine mammals before migrating to the mainland or islands in the Arctic during summer. Only female polar bears enter a hibernation-like state during pregnancy.
Keep reading to find out more about the migration habits of polar bears and to learn other ways they have adapted to life in the Arctic.
How Do Polar Bears Migrate?
Migration is when animals travel long distances from one habitat to another, usually because the resources they need to survive change with the seasons
People are most familiar with bird migration because this is the most visible, however, many other animals migrate too. Polar bears are an excellent example of mammals that migrate.
During winter, polar bears spend their time on the sea ice that accumulates in the Arctic. From here, there is access to an abundant supply of seals and other marine mammals that make up the majority of a polar bear’s carnivorous diet.
However, during summer, most of this sea ice melts so polar bears migrate to the mainland or archipelagos (small groups of islands) in the Arctic.
Doing this is no mean feat and usually involves long journeys. Polar bears are not fast with a typical pace of 5.5 km/h (3.4 mph)1 (source: Seaworld), so these journeys can take many days of walking and swimming.
Do Polar Bears Hibernate?
Hibernation is when animals enter a low-energy state by reducing their heart rate and metabolic rate. This is to get them through periods where food is scarce which is typically the winter months.
Although many bears do hibernate such as the grizzly bear, polar bears do not hibernate.
They spend winter out on the sea ice hunting for seals which is the primary diet for a polar bear. In summer, they move to the mainland or small groups of islands in the Arctic when the sea ice melts.
As they do not have access to seals year-round, they must build up their fat reserves during the winter which they can then convert to energy during the summer.
They may add up to 50% to their body weight as extra fat around the base of their back and butt2 (source: Polar Bears: A Complete Guide to Their Biology and Behavior, A. E. Derocher, 2012). The excess winter weight also keeps them warm in the freezing arctic conditions.
Where Do Polar Bears Live in Summer?
During summer, when the sea ice melts, polar bears move to the mainland or archipelagos in the Arctic.
Although they do not hibernate during the summer when food is more scarce, they do change their behavior by slowing their heart rate, reducing body temperature, and stopping urinating and defecating to conserve energy. This is sometimes called ‘walking hibernation’.
They continue to hunt for food in summer, opting for terrestrial mammals, such as caribou and muskox, and birds which are more abundant.
Despite being widely considered to be carnivores, during summer they are known to eat marine algae, grass, berries, and eggs4 (source: Ecology and Evolution, L. J. Gormezano & R. F. Rockwell, Vol 3, No. 10, 2013), so describing polar bears as hypercarnivores (a diet of more than 70% meat) would be more accurate.
Females and Maternity Dens
However, female polar bears do enter a hibernation-like state during pregnancy. During these 8 months, they remain in their maternity dens in a reduced metabolic state to conserve energy. They do not eat, drink, urinate, or defecate 5 (source: Polar Bears: A Complete Guide to Their Biology and Behavior, A. E. Derocher, 2012).
The female will remain in the maternity den for the first few months of their lives until they weigh around 10kg and have learned to walk. They will leave the den around April7 (source: Arctic Animals and Their Adaptations to Life on the Edge, A. S. Blix, 2005).
Polar bear dens are usually dug into thick snowbanks of hills or valleys. They will typically have one or more rooms inside8 (source: Denning habits of the polar bear, C. R. Harington, 1968).
Do Polar Bears Live on Land or Water?
Polar bears live on land because they are terrestrial mammals, much like other bear species that they have evolved from. However, their diet consists of marine mammals such as seals, walrus, and whales, so they have evolved an excellent swimming ability.
They are great at diving and holding their breath underwater which allows them to sneak up on their prey from beneath the surface of the water.
Polar bears are able to swim for several days at a time. This is because they must get from the melting sea ice to stable land during the summer which involves long distances.
The longest known swim by a polar bear lasted over 9 days and totaled 687km in distance10 (source: Canadian Journal of Zoology, A.M. Pagano, et al, Vol 90, No. 5, 2012).
How Do Polar Bears Survive?
Their migratory behavior and incredible swimming ability are not the only ways polar bears have adapted to survive in the arctic.
Some other adaptations of polar bears include:
- Two layers of fur and excess fat to survive the cold arctic.
- Their paws and their gait (the way they walk) are well adapted for the snowy conditions to spread their weight evenly and maintain traction on the ice.
- A small tail and ears help minimize heat loss through a smaller surface area.
- Their long neck and head allow them to catch seals through holes in the ice.
- They have an excellent sense of smell, this allows them to smell animals, including humans, up to up to 32km (20 miles) away (don’t worry, polar bears don’t eat humans and will usually avoid them).
Read our full article to find out more about how polar bears survive in the cold.