When winter winds chill us to the bone, we bundle up in sweaters, down vests and fleece parkas. Wild animals, on the other hand, must endure the cold.
A mammal’s fur and its thick layers of fat provide insulation that conserves body heat. Fur is made of two kinds of hair: guard hairs and underfur. Guard hairs are long and glossy and lay over the shorter, duller, downier underfur. Guard hairs waterproof the animal’s coat by blocking moisture and keeping the underfur dry. They also protect the underfur from wear. Underfur traps air warmed by the animal’s body heat and insulates the animal from the frigid air outside.
In North America, the length and thickness of an animal’s fur is greatest sometime between November and March. This winter coat is referred to as “prime,” when the animal’s fur is prime. Its skin turns blue or creamy white. This occurs because the blood supply to the hair decreases and production of hair pigments stop.
In spring, mammals begin to shed their fur. Some species shed twice a year, in spring and fall, while others shed continuously from early summer through fall.
For more on how animals survive the cold, visit the National Snow and Ice Data Center’s website.