Polar bear Ursus maritimus (EEP)
Weight♂ 300–650kg, ♀ 150–250kg
Life-spanup to 40 years in zoos
carnivorous (90% ringed seals, walruses, beluga whales, fish, birds, occasional berries and plants)
coasts in summer, ice floes in winter
shores of the circumpolar Arctic Ocean
In most mammals, the egg is implanted into the uterus immediately after fertilisation. In polar bears, implantation is delayed. Indeed, shortly after their conception in spring (mating takes place between March and June), embryos begin a passive (‘dormant’) stage lasting several months, during which they stop developing. This waiting phase is called the embryonic diapause. The embryo starts developing again and is implanted in the uterus in autumn, so beginning true pregnancy.
Females, who take shelter in a den dug into the snow or peat, give birth to young (usually 2) in winter. These weigh less than 600g and remain in the den with the mother until spring, living on her fat-rich milk. They leave the shelter with their mother around April, when they weigh 10–12kg.
Polar bears are solitary creatures wholly adapted to their environment, especially the cold waters of the Arctic. They are the only bears considered marine mammals. Excellent swimmers and divers, they propel themselves through the water with their large front paws, using their back paws as a rudder. Small humps known as dermal papillae on the pads of their feet, together with hairs between their toes and over part of their arches, help them stick to the ice. The curved, sharp claws on their fingers help them catch their prey and get them out of the water. Polar bears have a very strong sense of smell: they can detect prey from a distance of several kilometres.
Polar bears have thick waterproof fur with hair that can be 12–15cm thick (‘guard hair’) and a layer of thick underfur. The guard hairs cover the entire body except for the snout and the pads of the feet. These translucent, hollow hairs capture air, thus ensuring good insulation and improving flotation. Finally, there is a thick layer of fat that increases protection against the cold. Polar bears’ ears and tails are tiny to avoid loss of heat. They moult between May and August, so their coat appears more white in winter.
Unlike other species of bear, polar bears are mainly carnivorous. Most of their preys are ringed seals, which they ambush either when they come to breathe through holes in the ice floe or in their dens (where the young live). They occasionally eat whale or walrus carcasses.
Today the main threat to their long-term survival is global warming, which is melting the ice floe more quickly and extensively, and delaying its formation each winter. Polar bears need the floes to hunt seals and thus build up enough fat reserves for winter. Fasting for too long causes them to lose weight, and lack of fat results in either a dwindling of the females’ milk supplies for her young or a lower birth weight and higher mortality rate in the young themselves.
Pollution is another threat to polar bears. Toxic products carried by air and water accumulate in the food chain and are found in large quantities in seals, the main source of food for polar bears, who are super-predators at the head of the food chain. Pollution can also have adverse effects on bears’ immune system or bring about hormonal imbalances affecting breeding.
Finally, the increase in petrol and gas prospecting is another significant threat to the species because of the risk of petrol spills in their environment and the increase in contact between humans and animals.
For centuries, hunters killed polar bears for their fur. Today only Inuits have hunting rights over the bears they call nanuks. Annual hunting quotas are set for each village. Bear skin is used to make clothes and their meat is eaten (it has to be well cooked because it may be infected by trichinella; polar bear livers, rich in vitamin A, can also be dangerous to eat). There are also some permits for hunting for sport, but if an animal is not caught, the permit cannot be reassigned.
Status in the wild (Source: IUCN)
- Not evaluatedNE
- Data deficientDD
- Least concernLC
- Near threatenedNT
- Critically endangeredCR
- Extinct in the wildEW