Polar bears evolved from brown bears and are the largest member of the bear family. Male polar bears measure 2.4- 2.6 m (8-9 ft) from nose to tail and generally weigh up to 600 kg (1,320 lbs), but may reach up to 800 kg (1,760 lbs). Females measure around 2 m (6-7 ft) and are typically about half the weight of males.
Nineteen populations of polar bears are distributed in Alaska, Canada, Greenland, Norway, and Russia. The world wide population is estimated to be 22,000-25,000 bears. Two populations occur in Alaska: the southern Beaufort Sea stock, shared with Canada; and the Bering Chukchi/Seas stock, shared with the Russian Federation.
Map of the 19 polar bear subpopulations (source: Polar Bear Specialist Group. The subpopulations include: Southern Beaufort Sea (SB), Chukchi Sea, Laptev Sea, Kara Sea, Barents Sea, East Greenland, Northern Beaufort (NB), Kane Basin (KB), Norwegian Bay (NW), Lancaster Sound (LS), Gulf of Boothia (GB), M’Clintock Channel (MC), Viscount Melville Sound (VM), Baffin Bay, Davis Strait, Foxe Basin, Western Hudson Bay (WH), Southern Hudson Bay and the Arctic Basin (AB).
Polar bears are specially adapted to the polar marine environment in which they live. Adaptations include: white coloration for camouflage; water repellent guard hairs, dense underfur, and black skin for absorbing warmth; small “suction cups” on the soles of their feet for traction on slippery ice; teeth specialized for a carnivorous rather than omnivorous diet; and the ability to store large amounts of fat when food is available and then use it later when food is unavailable. Polar bears’ primary food source are ringed seals but they also hunt bearded seals, walrus, and beluga whales, and will scavenge on beached carrion such as whale, walrus and seal carcasses found along the coast.
Polar bears generally live alone except when concentrating along the coast during the open water period, or when mating or rearing cubs. Pregnant females will enter maternity dens in October/November; most dens in the circumpolar Arctic are located on land in areas where snow accumulates, such as along coastal bluffs or river banks. In Alaska, dens are excavated on either sea ice or on land. One to three cubs are born in December/January; cubs remain with their mother for about 2 1/4 years.
Worldwide, polar bear populations remain relatively stable; however, climate change, contamination of the Arctic environment, potential over-harvest, and increasing human development in polar bear habitat pose conservation challenges for polar bears.
Additional species information can be found on the IUCN Red List polar bear page