Why isn't anyone hibernating at the Zoo?

During our first animal science class we were taught that bears hibernate. So, it’s only natural that our Rocky Mountain Wild grizzly bear keepers keep getting asked, “Why are Digger and Emmett still awake?”

It’s a great question!

The purpose of hibernation is for an animal to conserve energy when food sources are limited, thus it is associated with winter months. Before going into hibernation, grizzly bears go through a period called hyperphagia, meaning they eat in excess. Some bears will gain up to 400 pounds in preparation for hibernation – Digger and Emmitt naturally gain between 100-150 pounds in the fall. After the first substantial snowstorm of the season, wild grizzlies will enter their dens and remain in hibernation until late winter or early spring, when food sources become more abundant. They’ll occasionally have periods of time in the winter when they will wake up, move around and even go outside. This type of hibernation is sometimes referred to as false hibernation. 

Grizzly bears that have a consistent food source in the winter, like Emmett and Digger, do not have to hibernate at all. Keepers report that they are hardwired to go through seasonal behavior changes, though. Right now, our grizzly boys are experiencing a phenomenon called “torpor.”

Torpor is a period of time when bears have lower body temperatures and lower metabolism. They are sleepier and have less of an appetite. In the summer, Digger and Emmitt eat 20-25 pounds of food everyday. Right now, they are eating 10 pounds of food daily. While they normally love eating meat, fish, romaine, celery, carrots and bear chow, keepers report that they will leave portions of food and naturally start to lose weight during the winter months.

Our grizzlies are a little more sluggish these days, but they still are fun to watch.

“Sometimes in the morning they want a few more hours of sleep,” said Rebecca Zwicker, Rocky Mountain Wild Keeper. “But, even in the winter, the problem is trying to get them to go back  into their den at night.”

Zwicker reports that another fun “gearing-up-for-winter” behavior to watch is Digger stepping up his den digging in the yard. “It’s always in a new place, and I think he feels like it’s never quite done. This year, it’s under a log near the trout pond. Every night he has to dig to just the right point before he’ll come into their building.”

During snow storms, it’s fun to watch our grizzly bears play in the powder. The unique experience often makes them hyper-active – the exact opposite of hibernating.