Polar bears

The polar bear is the largest living bear species and the largest carnivorous land animal of any kind. It is native to the Arctic region, where it is the apex predator of the marine environment, diving through sea ice to prey mainly on seals. Polar bears are popular and iconic in human culture, but face serious threats from climate change.

Quick Facts

• Classification:

• Kingdom: Animalia
• Subkingdom: Bilateria
• Phylum: Chordata
• Subphylum: Vertebrata
• Class: Mammalia
• Subclass: Theria
• Infraclass: Eutheria
• Order: Carnivora
• Suborder: Caniformia
• Family: Ursidae
• Genus and species: Ursus maritimus
• Geographical location: Northern marine areas of Alaska, Canada, Greenland, Norway’s Svalbard Archipelago, and Russia
• Habitat: The sea ice and adjacent land areas of the circumpolar Arctic
• Gestational period: About eight months
• Life span: Up to thirty-two years in the wild, over forty years in captivity
• Special anatomy: Fur, hide, and blubber providing effective insulation from the extreme arctic cold; white fur providing camouflage against the backdrop of ice and snow and greatly aiding in stalking seals; large paws used for paddling in water and that act like snowshoes on thin ice; pads of the feet covered with small, soft papillae that improve traction on ice; small ears and tail to reduce heat loss and a large body mass to conserve heat

Protected from cold by a thick fur coat and a layer of blubber, the polar bear hunts seals in open areas in the Arctic sea ice. A strong swimmer, the polar bear uses its large front paws as paddles. Its white fur blends in with the ice and snow as it stalks or still-hunts. Ringed seals are the polar bear’s primary food, but it also consumes bearded seals, and occasionally walruses, belugas, narwhals, musk oxen, and carrion (dead terrestrial and marine mammals). Although largely carnivorous, when on land the polar bear may eat grasses, kelp, berries, and lichens. Males and nonpregnant females do not make dens or hibernate, but spend the winter hunting on the sea ice.

The polar bear is believed to have evolved from the terrestrial brown bear about 100,000 to 200,000 years ago. In captivity, polar bears and brown bears have interbred and produced fertile offspring. This shows a high degree of genetic relatedness. In nature, however, these two species are geographically isolated from one another and would rarely meet.

Swimming in icy water among the ice floes of the Arctic, quietly stalking a resting seal, then killing it with a crushing blow of its forepaw, the polar bear is an impressive example of an animal’s ability to adapt to and live in one of the harshest environments on earth. Its distinctive, charismatic appearance and formidable reputation have also helped make it a popular symbol in many human cultures throughout history.

Physical Characteristics of Polar Bears

Male polar bears are up to five feet high at the shoulder while on all fours and up to ten feet long. When standing on its hind legs, a male can be eleven feet tall. Adult males are generally much bigger than females: 1,100 to 1,770 pounds for males, 330 to 770 pounds for females. Like other bears, polar bears are plantigrade.

Mating takes place in late March to late May. This is the only time that the male is with the female. Other than family groups of females with their cubs, polar bears are solitary. Pregnant females dig snow or earth dens in which they will give birth to one to three cubs in late November to early January. The mother’s milk is very rich, with an average fat content of 33 percent. The cubs, which weigh 1 to 1.5 pounds at birth, grow quickly and weigh 22 to 33 pounds when they emerge from the den with their mother in late February to early May. Polar bear cubs usually leave their mother at 2.5 years of age, at which time the mother is ready to breed again. Therefore, the female usually gives birth every third year.

Conservation

By the 1960s, polar bear populations were in serious decline due to sport hunting and public support for the conservation of polar bears increased. In 1967, the five “polar bear nations” (the United States, Canada, Denmark, Norway, and the Soviet Union) limited hunting to the Inuit people. By 2001, polar bears had recovered somewhat, and there were estimated to be twenty thousand to forty thousand living in the wild. However, in the twenty-first century it also became increasingly clear that polar bears were threatened by habitat loss due to climate change, as sea ice steadily took longer to form each fall and broke up earlier each spring. Indeed, imagery of polar bears struggling to survive became commonly used by environmental and conservation groups to raise awareness of global warming and its negative impact on biodiversity.

Scientists generally recognize eighteen or nineteen subpopulations of polar bear worldwide. A 2014 study found that three of these were declining, six were stable, one was increasing, and nine had insufficient data to draw conclusions. An update from the International Union for the Conservation of Nature (IUCN) Polar Bear Specialist Group in 2019 found that four subpopulations were declining, five were stable, two were growing, and eight had insufficient data. Researchers also warned that habitat loss was forcing polar bears to spend more time on land, increasing their chances of interacting with and posing danger to humans.

Principal Terms

blubber: thick layer of fat under the skin

carnivorous: eating meat

geographically isolated: living in different habitats

plantigrade: walking on the entire foot, not just the toes

terrestrial: living on land

Bibliography

Atwood, Todd C., et al. "Forecasting the Relative Influence of Environmental and Anthropogenic Stressors on Polar Bears." Ecosphere 7.6 (2016): 1–22. Web. 5 Oct. 2016.

Derocher, Andrew E. Polar Bears: A Complete Guide to Their Biology and Behavior. Baltimore: John Hopkins UP, 2012. Print.

Lynch, Wayne. Bears: Monarchs of the Northern Wilderness. Seattle: The Mountaineers, 1993. Print.

Matthews, Downs. Polar Bear. San Francisco: Chronicle, 1993. Print.

"Polar Bear." National Wildlife Federation, www.nwf.org/Educational-Resources/Wildlife-Guide/Mammals/Polar-Bear. Accessed 10 July 2024.

"Polar Bear." WWF, www.worldwildlife.org/species/polar-bear. Accessed 10 July 2024.

"Population Status." IUCN/SSC Polar Bear Specialist Group, www.iucn-pbsg.org/population-status/. Accessed 10 July 2024.

Stirling, Ian. Polar Bears. Ann Arbor: U of Michigan P, 1988. Print.

Stirling, Ian, Nicholas J. Lunn, and John Iacozza. “Long Term Trends in Population Ecology of Polar Bears in Western Hudson Bay in Relation to Climate Change.” Arctic 52.3 (1999): 294–306. Print.