Some mammals, like bears, conserve energy by hibernating. In hibernation, animals such as bears have a lowered body temperature and a lowered metabolic rate. Some species, like the collared lemming, the arctic fox and the weasel, grow white coats in winter. These coats serve as camouflage against the white backdrop of snow and ice. Some mammals, like the arctic fox, curl up together in a den for shared body warmth.
Beavers have a unique winter survival strategy among Alaskan mammals.
They build themselves a well-insulated lodge, where air temperatures remain quite comfortable no matter how cold it is outside. Unless they hibernate, they also have to find food. This is not easy when the ground is covered by snow most of the year. Some animals, like the musk-ox, build up a thick layer of fat to see them through times of fasting or food scarcity. Pregnant polar bears enter maternity dens in late summer or early autumn.