Polar bears have caught the attention of conservationists because global warming affects their habitat, which ranges across Alaska, Canada, Greenland, Norway and Russia. Though they are prodigious swimmers (this cub in Germany’s Nuremberg Zoo is practicing), the melting ice in the Arctic prevents bears from traveling long distances in search of food, making the species vulnerable. Fortunately, polar bears have noses so sensitive they can smell a seal on the ice 20 miles away.