Those at highest risk are our warm-blooded (or endothermic) animals: birds and mammals. These animals can only tolerate a narrow range of internal temperature without serious damage to vital tissues and organs. Therefore, nights where temperatures approach or dip below zero can be lethal. Our mammals are fairly well protected as many have heavy fur coats and a layer of fat to help insulate them. Noses, feet, and other poorly protected body parts are usually tucked away into warmer parts of the body. Gray squirrels and red foxes will wrap themselves in their bushy tails, while white-tailed deer will fold their long legs under their warm bodies. Many of these animals will shiver the night away. Shivering keeps warm blood moving through their muscles and skin, lessening the chance of frostbite.
In general, the larger the animal, the easier it is to maintain a high core temperature and thus the easier it is to survive extreme temperatures. A healthy layer of snow (something that has been notably absent this winter) helps insulate our smaller mammals. Many small rodents such as the meadow vole and the white-footed mouse will use the subnivean zone (the area where snow meets frozen ground) to avoid predation and stay warm. Studies have shown that temperatures in the subnivean zone rarely drop below the freezing mark.