Its den may be found under the border of a rockslide or on open hilly ground under some huge boulder or in the loose shale talus under a cliff. Large boulders provide protection against the grizzly bear's efforts to dig out this creature. Its nest, hidden deep in the crevice, is composed of grasses. In the spring the winter nest is frequently thrown out of the burrow and replaced by a new one of fresh grasses. Well-beaten trails extend from the burrow entrance to feeding locations.
Hoary marmots live in loose colonies, taking advantage of their neighbors' watchfulness.
If danger approaches, they pass the warning whistle along the valley and those feeding or sunning on a rock will gallop for home. They also take note of the alarm calls of some of their lesser neighbors such as pikas and ground squirrels. Their predators include grizzly and black bears, wolves and wolverines, and golden eagles which are likely their main predator. Diurnal in activity, hoary mnarrnots spend about eight months of each year in a kind of hibernation. It is not actual hibernation but a lethargic, torpid state, during which breathing, pulse rate and body temperature are only slightly depressed.