Surviving the winter: what we can learn from hibernating bears

February 28, 2019

Many of us have known since we were children that bears go into hibernation for the winter. This doesn’t seem like a miracle: it is simply a part of nature. But have you ever considered what REALLY goes into a bear’s long winter sleep?

Contrary to popular belief, grizzlies don’t truly hibernate - they enter a state of torpor,  which is a mild form of hibernation. Their body temperature dips to about 30-35°C, and their heart rate slows to around 8-19 beats per minute. While this may seem drastic to us, it’s not nearly the rate of ‘deep freeze’ that many other small mammals enter during the winter months. In their torpor, they still sometimes wake, move around, stretch, and even walk. (This is why the recent sighting of a grizzly bear at its den site in Kannanaskis is not surprising to us - it may have been awake in its den already and popped up when it smelled or heard the skiers above).

Grizzly bears are actually doing amazing things while in torpor - their bodies are undergoing incredible processes that scientists are only beginning to understand. Nephrologists, who study kidneys, are particularly curious as to how bears’ bodies have adapted to hibernation. Grizzlies don’t urinate or defecate when in torpor. They form a fecal plug that lasts until spring, and amazingly, they are capable of recycling urea into protein - a critical piece of their ability to hibernate. If this wasn’t possible, the body would continue to create the waste product until it got to the point of toxicity.

Unsurprisingly, nephrologists want to understand this process better, as it could help treat humans with kidney disease. Converting urea into protein explains how grizzly bears retain their muscle mass even after such as long period of little activity.

Another amazing thing happens during a bears’ hibernation - birth! Cubs are born while females are still in their state of torpor - generally from late January - late February. Blind and about the size of a squirrel, the cubs figure out how to nurse on their own and spend the last few weeks doing so until their mother wakes up.

It’s clear that grizzlies are doing far more than we give them credit for during the winter months  - while it seems like an adorable long winter’s nap, in reality it’s an incredible process in which to  survive the harsh winter conditions and low food availability. When they enter their dens each year we’re in awe of this natural process, and are renewed with a sense of wonder about our natural world.

If you’re interested, you can watch the two rescued grizzlies at Grouse Mountain throughout the winter via the Bear Den webcam. Hint - click on the top right of the video to access a 24 hr timelapse of each day’s footage.

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