The polar bear, along with the grizzly, is the largest land predator on Earth. Weighing over 500 kilograms and measuring nearly three meters in length, this bear is twice the size of a Siberian tiger. To withstand the extreme Arctic cold, polar bears are equipped with a thick layer of fat. They also have an undercoat and a layer of transparent guard hairs. This allows them to swim and hunt in very low temperatures. Polar bears are excellent swimmers and have been spotted 300 kilometers from the shore. In their search for food, polar bears benefit from a highly sensitive sense of smell. They can detect a scent from a kilometer and a half away or buried under a meter of snow. Their hearing and vision are comparable to that of humans. Although polar bears live as solitary animals, they do not have fixed territories and enjoy playing with one another. Mating occurs in May, and during their gestation period, a female polar bear nearly triples her weight.