It was believed for generations that bears hibernated for the winter months. Thanks to many studies, including tracking Boo the Grizzly at Kicking Horse Mountain Resort’s Bear Refuge, we now know that bears don’t actually reach that true state of hibernation.

True hibernators experience a very deep sleep with a slowed heart rate and a significantly lowered body temperature. Bats, squirrels and mice are examples of true hibernators. What makes a bear’s winter slumber different is their body temperature, which only drops slightly from the summer months spent awake and feeding.

Instead, bears enter a slightly lighter form of sleep known as torpor. A bear in torpor still experiences slowed heart rate and metabolism, which allows them to survive the winter months in their dens. They don’t need to eat during this period, and they transform their urine into protein, which helps keep them alive. They don’t suffer muscle atrophy despite long periods of inactivity. Bears also do amazing things while asleep, like give birth to cubs who know to nurse until their mother wakes up.

A bear can wake from torpor relatively quickly if they need to defend their den or deal with needy little ones. True hibernators need more time for their body temperature to rise and their bodily functions to resume.

For more information on bears in torpor, check out this great article from the Grizzly Bear Foundation.

To find out when Boo wakes up from his winter torpor, follow him on Instagram @boogrizzly.

Kate Barker