Bears' near-skin hairs store heat and grow longer in cold weather. Bears hibernate in winter. Bears hibernate to conserve energy. They're asleep and don't require food, water, or the bathroom.
Warming up is easy for birds. Many birds have dinosaur-like scales to keep warm. Feathers, too. Water-resistant feathers are downy on the underside. In the cold, their feathers trap air. Shivering warms air and them.
Cold-climate deer are reindeer. Warmth from two fur layers. Fine, compact layer next to skin, longer, shaggier layer for insulation. They shed their winter coat in the summer. Reindeer noses warm lung air.
Leaves, grasses, and soft material make up opossum winter dens. They hibernate in their nest. Australian koalas don't sweat. Tree-climbing. Koalas cool off in trees since they're cooler than air.
Wintertime rodents nest indoors. Plant-lined burrows make comfortable dens. Nuts and seeds make them fat. Beavers store fat in their tails and spend the winter in their insulated lodge.
For heat relief, they can seek shelter and drink. Most species dwell in warm climates, however monkeys may snuggle together when it's cold. Japanese snow monkeys dunk in hot springs to remain warm in winter.
Big cats hunt in the morning and evening and cool themselves in the shade. Sweating from panting. Snow leopards live in snowy regions. Their thick fur traps heat. They can insulate their paws with fur.