The researchers, from the University of Wyoming report that hibernating bears preserve as much as 80 per cent of their muscle strength during winter. Their findings are the result of five years of probing hundreds of mountain caves to determine why bears are still so strong and active when they emerge from their winter dens. Bed-ridden patients lose 0.7 per cent of their strength per day, resulting in problems such as severe atrophy. This just doesn't happen in bears, and we've been working on finding out why. Contrary to popular belief, for the black bear, hibernation is more to avoid the lack of food than the cold.
Most dens are nearly as chilly as the surrounding countryside.
Dens may be burrows, caves, hollow trees, or simply nests on the ground. Bears bedding down Hibernation can last up to seven months and undisturbed black bears remain nearly inactive during hibernation, unlike smaller hibernators that raise their body temperatures to summer levels every few days so they can eat stored food and pass wastes. To survive long winters without eating, drinking, exercising, or passing wastes, hibernating bears cut their metabolic rates in half. Sleeping heart rate drops from a summer rate of between 60 and 90 beats per minute to a hibernating rate between 8 and 40 beats per minute. Bears can maintain this high body temperature despite their slower metabolism in winter because they develop highly insulative fur and reduce blood supplies to their limbs.