Long winter’s rest: WSU bears begin hibernation

The grizzly bears at Washington State University’s Bear Research, Education, and Conservation Center are now hibernating, completing a process that started in August. They won’t eat anything and will drink very little for the next four months.

The hibernation cycle starts when natural cues, such as the amount of daylight and types of food available, tell bears to start eating more. Once that process, called hyperphagia, starts, bears are ravenous. They can add up to 20% of their entire body weight in less than two months.

“Hibernation is a very complicated process,” said Chelsea Davis, WSU Bear Center manager. “The extra weight is what they use for energy during hibernation to maintain things like body temperature and other core functions.”

By October, the decrease in food availability and shorter days signal to bears that it’s time to hibernate. At the Bear Center, the grizzlies have already gained their hibernation weight and don’t need to add more. As October wanes, Davis and WSU experts, as well as student volunteers, start reducing the size of the bears’ meals. By the end of the month, feedings stop until spring.

Side-by-side overhead shots the same bear. On the left, the bear is skinnier than the bear on the right.
John, one of our male bears at the WSU Bear Center, seen in spring after waking up (left) and in the fall after adding his hibernation weight (right). In November 2022, John weighed 572 pounds entering hibernation. He weighed 482 pounds 134 days later, a loss of 90 pounds, or 16% of his body weight.

“We mimic the natural cycle of what bears in the region do, as far as timing,” Davis said. “Bears don’t need to hibernate; many zoos keep feeding their bears so they don’t. But since one of our top priorities is helping and understanding bears in the wild, we follow their natural patterns as much as possible.”

Even though they don’t get fed for months, the bears aren’t starving.

“When we’ve offered food during hibernation, they either completely refuse it or eat very little,” Davis said.

After feedings stop for the year, the humans at the Bear Center wait a day as each bear cleans out its gastrointestinal tract and bladder. Afterward, staff clean the dens and give each bear a bale of fresh straw to make its own bed.

Bears don’t sleep nonstop for four straight months, though they do snooze more than 20 hours a day. They get up, move around, and re-arrange their bedding almost every day.

During hibernation, the bears are remotely monitored by cameras in each den. The ability to watch remotely means fewer people are coming and going, reducing potential interruptions for sleeping bears while ensuring they remain healthy.

“This allows us to monitor their health and make sure they are appropriately progressing through hibernation,” Davis said. “In spring, as the days start getting longer and temperatures increase, they naturally start waking up and walking around again. The whole process starts over.”