Polar Bear
(Ursus maritimus) #62-250

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Coronal section through middle of brain
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Physical characteristics and distribution

Polar Bears are pure white following the spring molt, but their fur may become yellowish in the summer. The head and body length of polar bears range from 2,000-2,500 mm, tail from 76-127 mm. Females weigh 150-330 kg, while females weigh 300-800 kg. For a short distance, the Polar bear can outrun a reindeer on land. In water, they can reach a swimming speed of about 6.5 km/hr. The neck of a polar bear is longer than that of other bears and their heads are relatively smaller and flatter.

Polar Bears feed primarily on ringed seals, which they catch at or near their breathing holes in the pack ice. The bear either remains still near a breathing hole, or stealthily stalks its prey on the ice. In addition, they eat carcasses of stranded marine mammals, small land mammals, reindeer, fish, and vegetation. In the waters they may swim among sea birds and catch them as they sit on the water. Any individual bear may make a winter den for temporary shelter during severe weather, but only females, especially those that are pregnant, generally hibernate for lengthy periods.

Most pregnant females hibernate on land in excavated dens in the snow, usually on a steep slope. The sexes usually come together only briefly during the mating season, in March-June. Delayed implantation extends the period of pregnancy to 195-265 days. The young are born from November to January, while the mother is in her winter den. Females give birth every 2-4 years. Litter size ranges from 2-4 pups, weighing about 600 grms each. They weigh 10-15 kg when they leave the den with their mother; they leave the mother at 24- 28 months. Age of sexual maturity varies from 5-6 years.

Polar Bears (Ursus maritimus) are considered to be marine mammals, as they are adept swimmers. Their preferred habitat is on pack ice. It may swim as far as 65 km across open water to reach land or ice. There are populations in Canada, Greenland, USA (Alaska), Russia. Circumpolar in the Arctic, S limits determined by ice pack.

Description of the brain

Animal source and preparation

Our specimen was obtained from the Henry Vilas Park Zoo, in Madison, Wisconsin, and was an old adult male.

All specimens collected followed the same preparation and histological procedure.

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