Polar bears have an unusual hunting period. Most animals stock up on food in the warm months, building fat reserves to get through the long, cold winters. But polar bears in Canada's Hudson Bay area do the opposite: their best food source is the arctic seal, which they can only hunt in the coldest winter months. In the winter and spring, the polar bears head on out into the bay, frozen over with ice, and begin hunting delicious, fatty seals. In the summertime, the ice melts, and the bears retreat off the ice onto land, where they are less efficient hunters and, besides, there's less food on the land of the tundra than under the water.