At the Top of the Food ChainWith a thick covering of blubber, two layers of fur, small ears and a short tail, the polar bear is perfectly adapted for survival in the icy north. For the polar bear the problem is not the cold but overheating, which is why it prefers to move at a leisurely pace. The polar bear roams the Arctic Ocean and surrounding seas, including Canada’s Hudson Bay to the south. As the top of the food chain in the Arctic, the polar bear spends most of the year on the frozen sea, hunting for seals..... In Western Hudson Bay, the ice now breaks up three weeks earlier than it did in the early 1970s. Starvation has already reduced the survival rate of cubs and young bears, and made bears of all ages less healthy. Within the next 35 to 50 years, a decline in the overall polar bear population of more than 30% is expected, and within 100 years they may become extirpated from most of their geographic range.

Photograph: Norbert Rosing/guardian.co.uk