Molecular and Metabolic Aspects of Mammalian Hibernation

Abstract

As winter approaches and snow fills the air, mammals that hibernate avoid the energetic demands of maintaining high body temperatures by seeking shelter, falling asleep, and becoming deeply hypothermic. Hibernation is best viewed as an adaptation to anticipated famine and not to winter or cold per se. For example, near the beaches of Santa Cruz, adult California ground squirrels hibernate from late May until November, avoiding the hot summer months when grasses are dried and seeds long blown away. Even in northern climes, hibernators often overlap in distribution with species of similar body size that feed and remain active throughout the winter. Throughout montane and boreal forests, red tree squirrels and flying squirrels continue to move about during winter, high above buried hibernating ground squirrels, in their search for treeborne seeds and dormant insects. These animals also make use of cached cones, fungi, and berries. During winter on the tundra, small voles and lemmings live in the subnivian space between the ground and depth hoar layers of snow. All winter long they continue to clip and feed from grasses and sedges. In contrast, most hibernating species do not climb trees or eat seeds from cones and are too large to use the subnivian space; for these animals, winter can be a long season without foraging opportunities, and they have therefore evolved the ability to pass winter by while in a torpid state of lethargy.