,

Why do bears hibernate? Bears in Winter Part 1

,

During the deep cold of winter I think about our wildlife. How do they cope? 

I often think of bears, in particular. I think of bears out there, in their dens - quiet and still. Waiting out winter. 

The way the sun hits the snow this time of year, the sound of the snowpack crunching under my weight, the steely smell and the sensation of the icy air as I breathe it in - it all reminds me of my days visiting bear dens. 

For several winters in the 90s and 2000s, I worked with other bear biologists doing "den work" to collect reproductive and survival data for state wildlife agencies and research institutions (here in Maine, as well as in New Mexico and Tennessee).

A female black bear at her den in northern Maine (photo: Iain Stenhouse). My family and I were visiting this den as guests of the field crew of the Maine Black Bear Study in 2016. I had handled this bear as a 2 year-old in 1999, and again as a 4 year-old in 2001 when I was on the den crew. Seeing “Spunky” again at 19 years old — with her three healthy cubs — with my husband and young daughter in tow, was the joy of a lifetime!

Book my Bear Talk

Over the course of my years working on various bear studies I learned a lot about why and how bears go into a dormant state during the winter. Here are just a few fascinating facts to ponder.

Bears don't hibernate* because it's cold and dark. Bears hibernate* because food is lacking. A bear's diet is about 85-90% plant-based, and their grocery store shelves are pretty empty right now.

“A bear’s diet is about 85-90% plant-based, and their grocery store shelves are pretty empty right now.”

Bears spend most of the year preparing for winter. They build up fat reserves when food is abundant, and then den up. They make their fat reserves last by dramatically reducing their metabolic activity.

For example, a denning bear’s heart rate slows down to just 8 beats per minute (!!), as compared to a regular heart rate of 45-50 bpm. 

Here's the fact that truly takes my breath away. Bears reduce their respiration down to one breath every 45 seconds. Hold your breath for 45 seconds...and keep doing that for five months straight!

Bear physiology during hibernation* is so fascinating, that I can't possibly do it justice in just one Phenology Note - so stay tuned for Part 2. 

*Are bears "true hibernators"? I decided to not go into the technical aspect of "true hibernation" in this post because it's a complicated answer. For many years bears were not considered true hibernators because they do not lower their body temperature as drastically as deep hibernators. Many scientists now believe bears to be “super hibernators”. Or you can call it torpor, but the physiological state of bears in winter is totally unique to bears and bears alone.

Hear a podcast with me about bears

I hope you enjoyed this Phenology Note!

Join me in witnessing the seasons of our wild world.

Posted regularly here, and on Facebook and Instagram:

Follow #ThePersonalEcologist & #PhenologyNotes

SIGN UP TO RECEIVE EVENT NOTICES & FREE HABITAT TIPS, TOOLS, AND TRICKS.

#ThePersonalEcologistI partner with eco-minded landowners to create thriving wildlife habitats in their backyards, gardens, fields and farms, woods or campuses - at any scale.I have 25 years of experience in my field, and a lifelong commitment to wi…

#ThePersonalEcologist

I co-create biodiverse habitats with eco-minded stewards throughout the Northeast - at any scale.

I have 30 years of experience and a lifelong commitment to wildlife conservation.

Read My Story.

Deborah Perkins