Together with the grizzly bear, the polar bear is the largest land-dwelling predatory animal on earth. Weighing in at more than 500 kg and measuring almost 3 m in length, this bear is twice as large as a Siberian tiger. In order to withstand the extreme Arctic cold, polar bears have a thick layer of fat. They also have an undercoat and a layer of transparent protective fur. This allows them to hunt and swim in very low temperatures. Polar bears are very good swimmers and have been sighted as far as 300 km from the coast. They need a highly sensitive sense of smell when hunting for food and can smell things located 1.5 metres away or buried under a layer of ice one metre thick! Their hearing and vision are comparable with those of a human being. Polar bears are solitary animals but do not have defined territories and enjoy playing with each other. Mating takes place in May and during gestation, the female polar bear nearly triples in weight.