What is the typical hibernation duration of a grizzly bear in Yellowstone?

A grizzly bear in Yellowstone typically hibernates for about 5 to 6 months. In the Greater Yellowstone Ecosystem, bears usually enter dens in autumn and emerge in spring, though the exact schedule varies with sex, pregnancy, cubs, weather, and food availability.

The long denning period is powered by hyperphagia, the intense fall feeding season when grizzlies build substantial fat reserves. During hibernation, they generally do not eat, drink, urinate, or defecate. Their heart and breathing rates fall sharply, while their body temperature decreases only modestly compared with that of small hibernating mammals.

Females with newborn cubs often remain in dens longer than males or females without cubs. Cubs are born during the winter denning period, usually in January or February, and nurse while their mother remains largely inactive.

A common mix-up is treating 5 to 6 months as a universal figure for every grizzly population. Denning can last four to six months in the contiguous United States and five to seven months across the species’ broader range. Yellowstone’s typical estimate is therefore best understood as a regional average, not a strict calendar rule.