Tatum McConnell from vitalground said that Making your bed can be a pain, and nobody knows that better than the grizzly bear. Each fall a grizzly moves an incredible one ton of material to make its den. By January, bears in the Northern Rockies are taking full advantage of their cozy winter homes, settled into a long slumber until spring. This is commonly referred to as hibernation—but is that really the right description for their winter retreat?
Do Grizzly Bears Hibernate?
Experts say that hibernation isn’t quite the accurate term for a bear’s long winter rest. True hibernators include squirrels, mice, and bats, who experience long periods of deep sleep, heart rate decreases, and a drop in body temperature. That last component is where bears miss the hibernation benchmark, with body temperatures dropping only slightly from their summer averages. The technical term for their winter sleep is instead “torpor” which refers to a long period of rest without a completely dormant state. (We’ll stick to hibernation here, since it’s commonly used and a pretty close description.)
Despite not truly hibernating, grizzlies undergo some pretty incredible changes during their winter rest. Their heart rate drops from a typical 40-50 beat per minute to 8-19 bpm. For comparison, a human’s sleeping heart rate ranges from 40-100 bpm. Grizzlies are well adapted to hibernation, losing 15-30 percent of body weight but experiencing little muscle and bone loss despite remaining inactive for many months. Research to understand their incredible anatomy is ongoing, with many scientists hoping to apply the findings to medicine.
Climate Change and Hibernation
Bismark Meadows in northern Idaho provides key habitat for grizzly bears emerging from their dens in spring. (Photo: Linda Lantzy)
Like so many things in nature, a bear’s hibernation is finely tuned to seasonal variation and long-standing natural patterns. Unfortunately, human-driven climate change affects grizzly hibernation for the worse.