Hoary marmots are one of seven mammals in Alaska that curl up in dens or burrows and sleep through Alaska's cold, dark season. The other mammalian hibernators are Alaska marmots, woodchucks, black bears, brown bears, arctic ground squirrels and little brown bats.
Hibernation is not the same for all animals. Arctic ground squirrels are the deepest sleepers and drop their core body temperatures to 27 degrees Fahrenheit, the lowest known body temperature for a hibernating mammal in the world.
Arctic ground squirrels hibernate alone, but Alaska's marmots hibernate in family groups or small colonies in burrows under rock piles or boulder fields. They insulate their rocky burrows with dry foliage and plug the entrance before they settle in for a six or seven month sleep.
The little brown bat, which is just about half the size of a chickadee, is the tiniest hibernating mammal in Alaska. Bats hibernate in groups, in protected roosts called hibernaculum, in rock crevices, inside tree cavities and root wads, and even in buildings. It is believed that bats in Interior Alaska migrate to moister, warmer parts of the state to hibernate.
Bears are the lightest sleepers, and will wake up occasionally and move around inside the den, shifting their sleeping position. Bears also shift positions to better conserve heat and to prevent pressure sores from developing. Waking a hibernating arctic ground squirrel can take hours or days. Bears, on the other hand, can rouse quickly when disturbed.