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Mammals - Polar Bear

Region: Americas

Class: Mammalia

Order: Carnivora

Family: Ursidae

Genus: Ursus

Scientific Name: Ursus maritimus

Description: In comparison to other bears, the polar bear are equipped with longer legs and neck, the ears are relatively short, the nose is more “roman”, the cheek teeth are sharper and more edged and the canine teeth are more prominent. The rhinarium (nose-pad) and tongue are black, the eyes brown. The soles of the feet are bordered with dense fur and the claws are shorter but sharper. Polar bears differ in size throughout their range. Males are approximately one third larger than females.

Distribution: The polar bear is circumpolar in distribution, inhabiting all Arctic seas and coastlines. It is found on the pack-ice off the Alaskan coast north of Bering Strait, off the coasts of Greenland and along the Eurasian Arctic coast from Spitsbergen to Wrangell Island. Rare stragglers reach Iceland. Individual bears have been seen on the frozen Arctic Ocean as far as latitude 88 degrees north, only 2 degrees from the North Pole. In Canada they are found along the arctic coasts from Alaska to Labrador and from the tip of James Bay to northern Ellesmere Island. Polar bears do roam as far as 150 kilometres inland into the coniferous forests, where they live very differently from the polar bears which belong to the high Arctic.

Habitat: Frequent the southern broken edge of the arctic ice pack. They avoid solidly frozen sea ice and the open seas. Some live inland in coniferous forest areas in summer months.

Food: The ringed seal is by far the most important prey. Polar bears also eat the bearded seal, harp seal and hooded seal. Young walrus are sometimes taken. During the summer months it feeds upon the shoreline carrion, fish, mussels, crabs, starfish and the eggs and nestling young of waterfowl and cliff-dwelling birds. It also grazes on kelp, grasses and eats mushrooms, crowberries and lemmings.

Skin/Color/Coat: Polar bears are considered the largest land carnivores in the world, matched perhaps only by the kodiak brown bear. Their pelage is thick, coarse and long. The guard hairs are shiny, almost glossy, oily and waterproof, and have hollow shafts. Polar bears are pure white in winter; in summer and autumn, the coat is thinner and has yellow wash or is almost a golden colour. Polar bears moult annually between the end of May and August.

Reproduction and Development: Normally solitary animals outside the breeding season, polar bears mate in midsummer. Females breed between the ages of 3 and 7 at two to four year intervals. The gestation period is 195 - 265 days, including a period of delayed implantation. Females retreat to their winter dens to give birth to 1-4 cubs, which takes place between late November and early January. The newborns are small (30 cm long), blind and almost naked and weigh less than 1 kg. Growth is very quick. At 2 months they weigh about 5 kg and move about the den. Their eyes open at 6 weeks. By mid-March to early April, when the den is opened, the cubs weigh about 10 kg and are surprisingly strong. The cubs suckle for 9 months, occasionally one year. They are very dependent on their mother and stay with her for 2 years. At that time they weigh 90 - 180 kg and are half grown. Female polar bears are polyandrous. The males fight among themselves for the female’s attention and a couple will pair off for a period of a few days to two weeks

Adaptations: On land a shuffling walk may be increased to a rolling gallop of 40 km/h. the polar bears can outrun caribou over a short distance. They are often seen standing high on their hind legs, stretching their neck in order to scan the landscape. On thin ice, the polar bear will spread its legs to distribute its mass. Its thickly padded and furred soles allow the bear to move quietly as well as providing good traction. The claws are used to dig into icy slopes and to grip its prey. The polar bear is a strong swimmer, paddling with its forefeet only and trailing its hind feet. It can stay submerged for 2 minutes and swim at a speed of approximately 6.4 km/h, often covering long distances.Insulation: The polar bear has a thick layer of sub-cutaneous fat, very dense underfur with several layers of glossy guard hair on the outside. Their pelt is much thicker in winter and provides excellent insulation. The fat layers also add to buoyancy in the water. Water is shed easily from the oily waterproof fur. The ears are small and furry with a heavy network of blood vessels to keep them warm and conserve heat. The tail is short and rounded. Colouration: The creamy white coat allows the bear to be inconspicuous when hunting seal. The colourless hair is hollow and picks up the colour of its surroundings. Polar bears are the only Arctic species in which all individuals stay white year round. Skin and tongue are black . Hunting: Polar bears will stand or lie by the seal’s blowhole in the ice for hours; they may swim towards seals resting on the ice flows with only their nose showing above the water. They will dive quietly, then swim up to the ice edge and jump out on the seal, and will also crawl towards a sunbathing seal using every piece of raised ice to conceal the approach. Senses: Polar bears have good eyesight. Their eyes have inner eyelids that keep the glare of the sun on snow and ice from blinding them. They keep their eyes open under water. They also have a keen sense of smell, however, their sense of hearing is dull. Denning: Polar bears of both sexes occupy dens for shelter. There appear to be 3 main types of winter refuges: maternity dens, temporary dens and winter shelters. Temporary dens are generally excavated by single bears and are occupied for periods of a single day or two, to up to three to four months. The bears use them to escape the bad weather and as resting places. Maternity dens are occupied by pregnant females not only as a safe place to give birth to her cubs, but as well as a place of protection for the cubs during their first few months. Topographic factors influence the den sites. In Canadian core areas, dens frequently occur on south-facing slopes where northerly prevailing winds create the best drifts, where the wind-chill is least and insulation (received solar radiation) is greatest. Polar bears do not always, or even ordinarily hibernate in winter – especially the males – though the degree of inactivity may depend on the weather, the state of the ice pack, and the fat reserves of the bear. The lethargy displayed by bears while in the den enables them to rest and conserve their vital fat reserves. During this time, the body temperature of the polar bear decreases by a few degrees from normal and the respiration rates are markedly reduced.

Threats: Extensive hunting, started in 17th century. Protective measures were taken in 1960 through an international agreement (Canada, former USSR and Norway) to protect the bears in part of their range. Exploitation of minerals and fossil fuels in the Arctic pose a continuous threat. Research to identify the effects of Arctic development on the bear population continues. Native people may legally hunt them. Follow up on tagged polar bears throughout the Arctic confirm the theory that they occur in separate populations with limited exchange between them. Polar bears may be one of the animals most threatened by global warming. They depend entirely on sea ice as a platform from which to hunt seals. If the ice does not form or forms too late in the season many polar bears could starve.

Status: Conservation Dependent

References: Banfield, A.W.; Mammals of Canada, 2nd edition, 1981 Forsyth, Adrian. Mammals of the Canadian Wild, 1985. Larsen; The World of the Polar Bear Canadian Wildlife Service Report; Denning Habits of the Polar Bear, Smithonian, February, 1978 Stirling, Ian. Polar Bears. Ann Arbor: The University of Michigan Press, 1988. Whitfield, Dr. Philip,The Simon & Schuster Encyclopedia of Animals , 1998.