In winter, bats, ground squirrels, marmots, jumping mice, bears and other true hibernators become inactive. By entering a state of deep dormancy they lower their body temperature to just above freezing and reduce their activity for several weeks. Fat accumulated throughout the summer provides vital energy during hibernation.

Most mammals do not hibernate. They remain active throughout the winter and have various strategies to conserve heat. A thick coat of winter fur increases insulation by up to 20 per cent. Shrews and small rodents like mice and voles stay under the snow, finding food in an environment of constant temperature and humidity. Temperatures below the snow can be up to 25°C warmer than on the exposed surface. Winter nests constructed of dried plants and fur provide additional insulation. Many small animals live communally in winter, huddling together in their winter nest or den to reduce heat loss.

Snowshoe Hares and Lynx move easily on top of snow. Dense fur on the soles of their feet acts as snowshoes. Caribou don't sink in deep snow — large semicircular hooves and prominent dew claws located behind the main hooves prevent this.

Snowshoe Hares and Ermines depend on concealment to escape predators. In winter, they acquire a white coat that provides effective camouflage against a snowy background.

Many mammals place large food stores in their burrow or near their winter nest to avoid winter shortages and foraging in extreme weather. The Red Squirrel's large food middens can contain thousands of cut conifer cones.