These declines are linked to earlier breakup of pack ice in the bay, caused by warmer spring temperatures. Polar bears feed mainly on ringed and bearded seals, hunting on the ice throughout the winter. The best hunting occurs when baby seals are abundant and relatively easy to catch from early April until the ice breaks up. Bears reach their lowest weight in March, so the spring ice season is critical for storing fat reserves that will see them through their summer on land, when they eat very little. Ian Stirling, Nicholas Lunn, and John Iacozza of the Canadian Wildlife Service have been monitoring polar bears in Hudson Bay since 1981.
Lighter females have lower fat reserves and tend to have fewer cubs.
Inc. Polar Bear Swimming with Cubs. Meanwhile, the endangered Peary caribou inhabiting a few islands in the High Arctic are on even thinner ice. Canadian biologist Anne Gunn blames the decline on increasing temperatures in the region. Not only is snowfall higher, but the snow is wetter and denser making it more difficult for the caribou to dig through the snow to reach the food below. According to Gunn, no population surveys have been conducted since 1997 because of the great expense involved.