The World of Polar Bears

Habitat und Distribution

A. Distribution

1. Polar bears are found throughout the circumpolar Arctic.
2. Polar bears, or their tracks, have been reported almost as far north as the pole; however, scientists believe few bears frequent areas north of 82 north latitude. The northern Arctic Ocean has little food for them.
3. The polar bears’ southern range is limited by the amount of sea ice that forms in the winter. Polar bears prefer to travel on sea ice.
   a. In the south, polar bears are annual visitors to St. Lawrence Island, southern Labrador, and Svalbard.
   b. In heavy ice years, polar bears have travelled as far south as the Pribilof Islands, Kamchatka, Newfoundland, and Iceland.
   c. The most southerly dwelling polar bears live year-round in James Bay, Canada.
4. The majority of polar bears are found near land masses around the edge of the polar basin.
5. Scientists believe there are 15 relatively discrete polar bear subpopulations (Wiig, 1993-94). A subpopulation is a group of polar bears with a home range independent of but overlapping that of other polar bears. For example, two subpopulations live in the James/Hudson Bay area, one in western Hudson Bay and the other in north-western Ontario and James Bay (Stirling, 1988).

B. Habitat

1. Polar bears inhabit Arctic sea ice, water, islands, and continental coastlines.
2. Polar bears prefer sea ice habitat with leads, next to continental coastlines or islands(Stirling, 1993).
   a. Leads are water channels or cracks through ice which may remain open (ice free) for only a few minutes to several months, depending upon weather conditions and water currents.
   b. Polar bears hunt seals in the leads, using sea ice as a platform.
   c. The “Arctic ring of life” is a biologically rich system of leads and polynyas. It runs parallel to the polar basin coastline.
   (1) Polynyas are areas of water, surrounded by ice, that remain open throughout the year due to winds, upwellings, and tidal currents.
   (2) Polynyas are important breathing and feeding areas for wintering or migrating marine mammals and birds.
3. Some polar bears spend part of the year on land.
   a. Polar bears in warmer climates may become stranded on land. In summer, sea ice melts along the coastlines, and pack ice (floating sea ice, or floes, not connected to land) moves north.
   b. Most pregnant females spend the autumn and winter on land in maternity dens.
4. Air temperatures in the Arctic average -34C (-29F) in winter and 0C (32F) in summer. The coldest area in winter is north-eastern Siberia, where the temperature has been recorded as low as -69C (-92F). The warmest areas in summer are inland regions of Siberia, Alaska, and Canada where temperatures can reach as high as 32C (90F).
5. The ocean temperatures in the Arctic are about -1.5C (29F) in summer. In winter the ocean temperatures can drop to -2C (28F), at which point seawater freezes.

C. Migration

1. Polar bears travel throughout the year within individual home ranges.
   a. Home range size varies among individuals depending upon access to food, mates, and dens (Stirling, 1988).
   b. Home ranges tend to be larger than for other mammal species because sea ice habitat changes from season to season and year to year.
   (1) A small home range may be 50,000 to 60,000 square km (19,305/23,166 square mi.). Small home ranges can be found near Canadian Arctic islands.
   (2) A large home range may be in excess of 350,000 square km (135,135 square mi.). Large home ranges can be found in the Bering or Chukchi Seas.
   c. Polar bears don’t mark or defend their home ranges.
2. Polar bears show “seasonal fidelity”: they remain in the same area during the same season (Stirling, 1988).
3. Polar bears are capable of traveling 30 km (19 mi.) or more per day for several days (Stirling, 1988). One polar bear was tracked traveling 80 km (50 mi.) in 24 hours (Sage, 1986). Another polar bear travelled 1,119 km (695 mi.) in one year (Macdonald, 1987).

D. Population

1. The world polar bear population is estimated to be between 21,000 and 28,000 individuals (Wiig, 1993/94).
2. Due to governmental regulations on hunting, the population has increased from an estimated 10,000 polar bears in 1968 (Stirling, 1988).
3. The ratio of males to females is approximately one to one.