Black bears have the unique ability to hibernate for 5-7 months of the year. Their body temperatures drop by approximately 4 degrees celsius from their normal temperatures. During hibernation, bears rarely will eat, drink, urinate, or defecate.
During hibernation, bears lose less than 23% of their strength over 130 days. In comparison, under similar conditions of inactivity, it is predicted that humans would lose 90% of their strength over 130 days. Bears are capable of "turning over muscle;" their bodies use broken down muscle to rebuild muscle.
Black bears hibernate during the winter months because of a lack of food. The duration of hibernation greatly depends on location. Bears in warmer climates with abundent food sources may not hibernate at all.
Black bears in Minnesota use several different types of dens. The most common are nests, excavations, and tree roots. Bears have also been known to use draininge ditches and manmade culverts as their dens. Males hibernate by themselves, and females will hibernate with their cubs until they are yearlings. Bears typically do not re-use their dens from the previous year. It is also very uncommon for bears to use another bear's den.
Left: Mother and cub are utilizing an excavation. Right: This bear is hibernating in a nest made of reeds.