Most Yellow-bellied Marmots mate during May and June. The gestation period is for about 30 days, 3 to 8 pups in a litter. The young start to leave their nest at about 3 weeks of age and are weaned by 5 weeks old. The adult male will drive out his male offspring when they wake from hibernation. They’ll spend more than half of the year in hibernation, which can last from September to May depending on their home elevation.
These large rodents eat a large range of plant types, including grasses, flowers, and forbs. In late summer, large numbers of seeds are eaten. They are most likely not food limited, eating only 0.8 to 3.1% of available net primary production. Food might be limited in areas where snow cover remains into the spring. They are selective feeders and are known to reject parts of plants that are toxic.