The yellow-bellied marmot (Marmota flaviventris), also known as the rock chuck, is a ground squirrel in the marmot genus. They are heavy-set, brown grizzled animal with white areas on the chin and (as the name suggests) a yellowish belly. Marmots can be waddling fat in the fall, and their long fur makes them look even fatter. Adults are about 26 inches long and weigh up to about 11 pounds.
They live in the western United States and southwestern Canada, including the
Rocky Mountains and the Sierra Nevada and are abundant here in the Greater
Yellowstone Region. They inhabit steppes, meadows, talus fields and other open habitats, sometimes on the edge of deciduous or coniferous forests, and typically above 6,500 feet of elevation.
Their territory is about 4 to 7 acres around a number of summer burrows.
Marmots choose to dig burrows under rocks because predators are less likely to see their burrow. There are three types of burrows: home, flight and hibernating.
However, the same burrow can be used for all three. The yellow-bellied marmot spends approximately 80% of its life in a burrow. Marmots often switch burrows between seasons and females often move their young to a new burrow after birth. There is often a burrow plug during the hibernaculum that is composed of fecal matter and dry grass. This plug reduces circulation and keeps out small predators
Predators include wolves, foxes, coyotes, badgers, grizzly bears, coyotes, weasels, martens, and mountain lions and humans. When a marmot sees a predator, it whistles to warn all other marmots in the area, giving it the nickname
"whistle pig". Then it typically hides in a nearby rock pile. Predation is definitely a threat to the yellow-bellied marmot, but the threat of hibernation has been found to be greater in some cases.
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.
Marmots reproduce when about two years old, and may live up to an age of fifteen years. They reside in colonies of about ten to twenty individuals. Each male marmot digs a burrow soon after he wakes up from hibernation. He then starts looking for females, and by summer may have up to four female mates living with him. Litters usually average four to five offspring per female. Marmots have a "harem-polygynous" mating system in which the male defends up to four mates at the same time. Yellow-bellied marmots have a "harem-polygynous" social system whereby a male defends and mates with one or more females in a subalpine meadow. The severity of winter leads to greater mortality during hibernation. Winter also affects reproduction of the marmot. There are generally more young per female and more litters when winters are shorter

The marmot is an omnivore and a generalist herbivore eating grass, leaves, flowers, fruit, grasshoppers, and bird eggs. It feeds primarily on seeds, flowers, leaves, and stems of a wide variety of grasses, forbs, and shrubs. Diet choice and the amount of food that the marmot intake is very important because the marmot must acquire enough fat storage to last them throughout their hibernation period.