Benjamin Hess is collections manager of mammals for the N.C. Museum of Natural Sciences. Here he explains how mammals big and small combat the cold. Questions and answers have been edited.
A seasonal color change from brown to white occurs in a number of mammals, like collared lemmings and snowshoe hares. Black or dark-colored animals lose heat faster by radiation than white-colored animals.
A large mammal has a smaller surface area to volume ratio than small mammals, which enhances their heat conservation. Curling the body into a ball, like a pet dog tightly curled up on a cold day, can decrease the exposed surface area and reduce the amount of heat lost. According to a scientific postulate known as Bergmann’s rule, the body size of most mammals tends to increase with increased latitude.
Other adaptations such as voluntary muscle contractions will produce heat, and involuntary muscle contractions, such as shivering, help an animal’s core temperature for short-term survival. Adding a layer of fat or blubber will also insulate and provide a site for storing energy.
Bears are not true hibernators. They do experience a lethargic period over the winter characterized by a slight decrease in body temperature. For a bear to reduce its body temperature close to the ambient temperature, the energy required to arouse the bear out of a true hibernation would be incredible.