Yellow-bellied marmots (Marmota flaviventris) are the largest member of the squirrel family. Adults are about 26 inches long and weigh up to about 11 pounds. They are commonly called rockchucks in the West. Eastern marmots are called woodchucks or ground hogs (Marmota monax).
All marmots are burrowing animals and they rarely venture very far from their burrows. Marmots live in harems of one male, two or three females, and offspring. Most of the time, these family units live in neighborhoods of two or more families called colonies. Yellow-bellied marmots choose to dig burrows under rocks because predators are less likely to see their burrow. Burrows are usually three feet deep and can be over 50 feet long. For hibernating, marmots dig deeper burrows that may be 15-21 feet deep.
Yellow-bellied marmots are true hibernators. They hibernate from September to May, depending on elevation. During hibernation, their body temperature drops to a few degrees above freezing. They don't keep their body temperature down all winter, rather, they wake every week or so for a bit and then go back into deep hibernation. This cycle is repeated all winter.
When a marmot sees a predator it whistles to warn all other marmots in the area (giving it the common name the whistle pig). Most alarm calls are given by marmots who have already run back to their burrow before calling.