The southernmost home of the northern flying squirrel is high in the mountains of western North Carolina. They do not fly, but glide, using a flap of skin that runs down their sides. Because they only come out at night, they are difficult to observe and study. Flying squirrels are the only gliding mammal found in the western hemisphere. The northern flying squirrel is distributed throughout the northern United States and Canada. Its smaller relative in the southern Appalachians is confined to the higher elevations. Scientists speculate that this species was marooned on the mountains by a warming climate and the retreat of the glaciers during the last Ice Age.