Polar Bear (Ursus maritimus)

By Jennifer Kennedy, About.com Guide

Polar Bear with Cub

Scott Schliebe/USFWS

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The polar bear (Ursus maritimus) is the largest bear species, and lives only in Arctic regions.

Description:

Polar bears are 8-11 feet tall and about 8 feet long. Bears may weigh 500-1,700 pounds, or possibly even more (the largest polar bear, according to Discovery.com, weighed 2,200 pounds). Male polar bears are about twice as large as females.

Polar bears appear white, but their fur is made up of clear, hollow hairs that reflect light. They have a thick undercoat that is covered with longer guard hairs that protect the bear from moisture. They also have black, rather than light, skin.

Classification:

Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Superclass: Gnathostomata
Superclass: Tetrapoda
Class: Mammalia
Subclass: Theria
Order: Carnivora
Suborder: Caniformia
Infraorder: Pinnipedia
Family: Ursidae
Genus: Ursus
Species: maritimus

Feeding:

Polar bears feed primarily on seals (particularly ringed and bearded seals). They will stalk their prey, waiting patiently at the edge of the ice or at a seal breathing hole, sometimes for hours, for a seal to pop up. If seals are not available, polar bears may eat other marine mammals such as walruses and whales, and sometimes feed on carcasses or in garbage dumps.

Reproduction:

Female polar bears become sexually mature when they are 4-8 years old, and males are sexually mature around age 6, although they don't usually mate successfully until they are at least a couple years older. Males may track females for miles, and will also compete with each other for access to females. A male may mate with several females in one breeding season. Mating occurs in the spring.

Favoring Survival Over Reproduction

Since the polar bear reproduction cycle is long, polar bears reproduce slowly overall, and as a species, the best strategy for success is to reproduce only when they are health enough to do so. After mating, females experience delayed implantation, in which the fertilized egg may take several months to implant in the uterus and start growing, so that the egg or fetus may be aborted or the female may fail to nurse her young if she is not healthy/nourished enough to do so.

In a successful pregancy, the female's gestation period lasts about 8 months (including the time the implantation off the egg is delayed). Then, the female digs a den in the snow, and gives birth to 1-4 cubs that are about 12" long and 1 pound in weight. She gives birth during the winter. The cubs are blind at birth, and stay with their mother in the den until spring, nursing her rich milk and growing quickly. Cubs stay with their mothers for 2-2.5 years. Females mate every third year, and may reproduce only 5 times in their lives.

Polar bears are thought to live 25-30 years.

Habitat and Distribution:

Polar bears live in cold, Arctic regions. They are found in areas around the North Pole, but not the South Pole. They are found in northern parts of Canada, Greenland/Denmark, Norway, Russia, western and northern Alaska and occasionally Iceland. Click here for a range map.

Status and Conservation:

The polar bear is listed as "vulnerable" on the IUCN Red List. Threats to polar bears include global climate change/loss of sea ice, pollution, shipping, recreational viewing, oil and gas exploration and overharvesting/unregulated harvesting and poaching. In some areas, sea ice decreases during the summer to such a point that polar bears are forced onto land, and need to survive on fat reserves.

References and Further Information:

ARKive. Polar Bear Fact File. Accessed December 31, 2012.
Armstrup, S.C. 2003. The Polar Bear - Ursinus maritimus, Biology, Management and Conservation. In Wild Mammals of North America. 2nd. edition. Accessed online December 31, 2012.
Berta, A.; Churchill, M. 2012. Ursus maritimus Phipps, 1774. Accessed through: World Register of Marine Species on December 31, 2012.
Defenders of Wildlife. Basic Facts About Polar Bears. Accessed December 31, 2012.
Polar Bears International. About Polar Bears. Accessed December 31, 2012.
San Diego Zoo. Mammals: Polar Bear. Accessed December 31,2012.
Schliebe, S., Wiig, Ø., Derocher, A. & Lunn, N. (IUCN SSC Polar Bear Specialist Group) 2008. Ursus maritimus. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2. . Accessed December 31, 2012.
SeaWorld. Polar Bears InfoBook. Accessed December 31, 2012.
U.S. Fish and Wildlife Service. Polar Bear, Ursus maritimus. Accessed December 31, 2012.