Yellow Bellied Marmot Facts | Yosemite Wildlife Guide
They are “true hibernators,” which means they slow their metabolism significantly during the winter. Their active heart rate of 180 – 200 beats per minute slows to 30 beats per minute, and their body temperature drops to 41 degrees Fahrenheit. They dig underground burrows that can be over 20 feet long and fill them with hay to protect themselves from the severe cold of the high-country winters.
This long and deep hibernation means they have to fit a lot of living into the remaining 4 months of the year, which explains the almost manic activity you might observe after they emerge. They are frequently seen scrambling across rocks-strewn hillsides, gathering plants and emitting sharp whistles (they are sometimes called “whistle pigs”) to defend their territory.
They are the largest rodent in Yosemite, weighing up to 11 pounds right before hibernation. Bulking up for winter requires eating a lot of plants, insects and bird eggs, so they spend much of their day feeding.
They mate a mere two weeks after coming out of hibernation, followed by a 30-day gestation period. The young exit the burrow three weeks later and appear to be fairly independent at this stage, although family bonds remain strong in colonial populations.