In Glacier National Park, Montana, a black bear has emerged from hibernation, but hasn’t left his tree cavity den.

According to the park website, this bear was first seen on March 23. Since then, the black bear, who is male, has mostly rested in the tree cavity. After a long winter of hibernation, you might assume a bear would be eager to get moving and find something to eat, but bears often don’t leave their denning site for days, sometimes weeks, after they emerge in the spring.

A bear fresh out of the den isn’t the same bear it will be in May. Immediately after emerging from their dens, bears are active but neither hungry nor particularly thirsty. In one of the first studies on the physiology of hibernating bears, researchers found captive bears ignored food and water for up to two weeks and some bears didn’t begin to eat and drink normally for three weeks after they emerged from their dens. One grizzly bear didn’t even urinate for two days after it emerged. (In contrast, during another study a black bear in the fall urinated copiously, producing eight to sixteen liters of urine per day.)

This annual life stage of springtime bears has been described as “walking hibernation.” Compared to summer and, especially, early fall, bears in walking hibernation are hypophagic. They actively ignore food and drink little water while still surviving on body fat. During walking hibernation, bears experience an internal transition from full hibernation to a more active physiology. Research on brown bears in Sweden, which I wrote about previously, has found the body temperature and metabolic rate of brown bears doesn’t stabilize until 10 and 15 days, respectively, after den emergence and their heart rate doesn’t stabilize for another month.

These graphs chart the relationship between physiological parameters of brown bears in Sweden. Den entry (left column) and exit (right column) are indicated by time zero (the green vertical line) to determine the sequence of physiological events. SDANN is the standard deviation of heart rate variability over five minute intervals. It was used a proxy measure of metabolic activity. A red line denotes when a variable was decreasing, while a blue line indicates when a variable was increasing, with the number of days from the entry/exit indicated. From Drivers of Hibernation in the Brown Bear and reposted under the Creative Commons Attribution 4.0
International License.

The transition from hibernation to fully active includes lots of resting. Screen shots from the Glacier National Park bear den live stream.

Possibly because their metabolism and heart rate remain somewhat low, many bears seem to loathe leave their dens, at least right away. So, it’s not uncommon for bears to remain near their denning site while their bodies transition back to more active levels.

The bear at Glacier will leave its tree cavity den relatively soon. His hunger will grow as his metabolism returns to active levels. His libido will increase too, and he’ll begin to prowl the land for females in estrous (the mating season for black and grizzly bears peaks in late spring). Compared to other stages in their annual cycle, less is known about the first few weeks of life for bears after they emergence from hibernation. It is rare for us to witness a bear’s life at this time. With webcams and other digital tools like GPS collars, we’re gaining a greater depth of knowledge about many wild animals. Glacier’s webcam provides a rare opportunity to observe a bear shortly after it has emerged from hibernation. Like most bears right now, it remains in a bit of a hibernative hangover.