Together with the grizzly, the polar bear is the largest land predator on earth. With a weight of more than 500 kilos and a length of almost three meters, this bear is twice the size of a Siberian tiger. In order to withstand the extreme Arctic cold, polar bears are equipped with a thick layer of fat. They also have a layer of underfur and a layer of transparent protective hair. This enables them to swim and hunt at very low temperatures. Polar bears are very good swimmers and have been seen as far as 300 kilometers from the coast. A highly sensitive sense of smell is useful to polar bears in their search for food. They can detect a scent one and a half kilometers away or buried under a one meter thick layer of snow! Their hearing and eyesight are comparable to those of humans. Although polar bears live as loners, they do not have fixed territories and like to play with each other. Mating takes place in May, and during the gestation period the female polar bear almost triples her weight.