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.