About polar bears

 

Polar bears (Ursus maritimus) likely evolved from brown bears (Ursus arctos) and are the largest extant bears (Figure 1), estimated to reach 1,700 lbs (800 kg) in weight and 10 ft (285 cm) in length.

 

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Figure 1. This anesthetized adult male polar bear weighed 1,070 lbs.

Photograph by J. Whiteman.

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The extensive movements of polar bears and the harsh Arctic environment make it difficult to precisely assess population size. Current estimates for the total world population range from 21,500 to 25,000. This population is divided into 20 units (Figure 2).

Unlike other bears, polar bears are almost exclusively carnivorous. They travel on sea ice and use it as a platform to hunt ringed seals (Phoca hispida), bearded seals (Erignathus barbatus) and other prey.

Movements and activities of polar bears vary throughout the world, but a general pattern exists. Adult females and adult males mate in the spring. In the summer, some of the Arctic ice melts and polar bears must move to remaining ice or shore. In the fall, ice forms again and snow returns to most of the landscape. Pregnant adult females dig snow dens and hibernate in them for the winter, similar to black bears (Ursus americanus) and brown bears. Males and non-pregnant females remain active during the winter; in some areas they do use dens on occasion, possibly to conserve energy during times of food shortages or poor weather.

Young are born in mid-winter in the den and the mother begins nursing them. The family emerges from the den in spring, and remains together for 2-3 years. After 2-3 years the young become independent and the adult female is ready to mate again.

 

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Figure 2. Map showing the world’s polar bear population divided into 20 units.

Map reproduced from: Distribution of polar bear populations in the Arctic. 1998.

 UNEP/GRID-Arendal Maps and Graphics Library. Retrieved December 16, 2008 at

http://maps.grida.no/go/graphic/distribution_of_polar_bear_populations_in_the_arctic

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Conservation and management challenges facing polar bears include a decline in sea ice, increased human activity in the Arctic, and efforts to establish sustainable hunting rates. The United States recently listed the polar bear as a threatened species; click here for information on the listing from the the US Fish and Wildlife Service.

*Information on this page is taken from the book Wild Mammals of North America: Biology, Management, and Conservation, published in 2003 and edited by George A. Feldhamer, Bruce C. Thompson, and Joseph A. Chapman. Information is contained in Chapter 27, titled “Polar bear,” on pages 587–610, written by Steven C. Amstrup.

 

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