Hibernation is often described as when bears sleep during the winter, but that isn’t physiologically accurate. Black bears and grizzly bears slow their bodies way down — more than during mere sleep — for hibernation to survive about five months in their dens. Here are the main differences for bears:
Bears aren’t out cold in the winter. They will wake up to defend themselves and their young if disturbed by predators or unsuspecting recreationalists. Bears begin to emerge from their dens as early as March, groggily in search of spring’s early green grasses and winter-killed ungulates to eat. So it’s important to remember that spring is also a time to be bear aware when recreating in Wyoming’s bear country.
- They work to get fat. In preparation for hibernation, bears work to pack on the pounds and grow a winter coat. A female bear must have at least 20 percent body fat to carry a pregnancy and 35 to 40 percent is typical
- Their bodies change. When a bear slips into a hibernation state, its body temperature drops from about 98 degrees to the low 90s, and its heart rate slows from 40-50 beats per minute to the teens. During hibernation, bears don’t emit waste nor consume food or water. A bear’s body changes physiologically so their kidneys can process nitrogen waste and not poison themselves
- They have cubs. Pregnant bears give birth during hibernation in their den, rousing only slightly. When the youngsters are born in February, their job is to nurse and nestle closely to their mother for warmth. The cubs won’t hibernate until next year when they enter the den with their mother. Black bear cubs will hibernate once with their mother. Grizzly bear cubs will hibernate with her twice.
- They lose weight but stay strong. During the five months bears remain in the den, they lose about 15 to 30 percent of their body weight. But unlike humans, who would lose muscle mass if they lingered in bed for months, bears maintain their physique with micro-movements to prevent atrophy.
Bears aren’t out cold in the winter. They will wake up to defend themselves and their young if disturbed by predators or unsuspecting recreationalists. Bears begin to emerge from their dens as early as March, groggily in search of spring’s early green grasses and winter-killed ungulates to eat. So it’s important to remember that spring is also a time to be bear aware when recreating in Wyoming’s bear country.
Publish Date
Answered By
Dan Bjornlie
Job Title
Large Carnivore Biologist
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Ask Game ID
227
Node order
77
Parent Node
1135