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Bears Go Down for Winter Naps

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Bears Go Down for Winter Naps
November 19, 2020

The black bears at Northwest Trek are slowing down and getting ready for their winter naps, also known as torpor. During torpor, a bear’s body temperature, respiratory rate and metabolic rates all decrease to conserve energy. The bears can maintain this low-energy sleeping state for days, weeks or even months without having much activity outside of their den, including eating and going to the bathroom.

Northwest Trek’s black bears, Benton and Fern, typically go into torpor from November until February or March. They do have periods of activity during the winter months, where they will eat, defecate/urinate and remake their winter “beds.”

Can you keep them awake?

Scientists describe torpor as an involuntary state, meaning naturally, the bears will experience some level of sleepiness. At zoos in warmer climates, where seasons don’t drastically change, bears will often have a shorter amount of time in torpor.

“We have four very different seasons at Northwest Trek,” said keeper Haley Withers. “We want to support the bears in what comes naturally to them. We make sure the bears have exceptionally quiet surroundings this time of year so they can sleep as long as they like.”

Withers said she and other keepers also feed the bears a seasonally appropriate diet leading up to torpor, in order for them to acclimate to the change in seasons as they would in the wild.

Can you spot them?

Benton and Fern have two options for sleeping at Northwest Trek. They each have man-made dens behind-the-scenes, where they are offered food daily (although, they don’t always wake up for it). The dens have heated floors and giant straw beds for them to get cozy in.

The bears also have a hibernation den near the center of the public exhibit. Try to see if you can spot either bear napping there! Benton and Fern put a lot of work into preparing that den for winter each year, using ferns, fir boughs and grasses as bedding.

black bear hibernation den
Can you spot the bears? Their hibernation den is near the center of the public exhibit

“The den is a hole, five-feet in diameter, with an opening just large enough to accommodate the bears’ body size,” said Withers.  “The den is meant to be pretty snug, in order for them to keep heat inside.”

Black bear hibernation den
Black bear hibernation den

Once comfortably inside, the bears will pull down even more vegetation toward the opening to keep it warm and dry. The den only fits one bear, and Benton and Fern will only trade places a few times throughout the four or five months of torpor.

What about the grizzlies?

Grizzly bears Huckleberry and Hawthorne, now three years old, have not gone into torpor since they arrived at Northwest Trek as cubs.

“We think that’s because of their age,” said Withers. “They are still growing and learning how and where to create successful denning sites in their habitat.”

Withers said she does expect them to slow down significantly this winter, but doesn’t expect them to go into torpor like the black bears. Huckleberry and Hawthorne will have access to both their man-made dens complete with heated floors and fluffy bedding as well as the exhibit.