It is early morning in the Great Smoky Mountains. Kevin Burrell is half asleep and wrapped tightly in his sleeping bag. Before surrendering his warm cocoon to the chilly morning air, he hears the call of a hermit thrush just above his tent, coaxing him to stay in bed for just a few seconds longer. The flutelike tune stops but is promptly followed by the quick chirps of a northern cardinal and the cheerful song of a tufted titmouse.