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Yellowstone's Grizzly Bears Are Already Emerging From Hibernation — And Warm Weather Could Be To Blame

In February, temperatures in the park can drop below zero, but this year they've been in the 40s — and even topped 50 degrees.

by Laura Dattaro
Feb 11 2015, 8:15pm

Image via Flickr

Humans are far from the only creatures who like to venture outside when the cold winter weather gives way to spring. In Yellowstone National Park, spring is arriving early this year, and so are the park's grizzly bears.

On Monday, park officials confirmed sightings of a grizzly in the center of the park, feeding on a bison carcass. The bears don't usually begin to emerge from hibernation until the beginning of March, making this bear's arrival about three weeks early.

"We have had bears observed in February before, in a few other years," Kerry Gunther, Yellowstone National Park's bear management biologist, told VICE News. "But this year, lately, it's been unseasonably warm. Certainly springlike temperatures, almost summerlike temperatures."

Several grizzlies have also been spotted beyond the park's boundaries in Montana and Wyoming.

Yellowstone is home to about 655 grizzlies, which hibernate in the winter months when food becomes scarce. Their thick fur and body fat makes them well equipped to handle cold temperatures, but the snow-packed winter months mean frozen ground and none of the roots, berries, and grasses the omnivores eat.

They generally emerge in early March and feed on carcasses of animals that died from the cold or were killed by wolves. This year, temperatures have been so warm that plants are starting to emerge in some areas of the park.

"I've worked here maybe 32 years, and a couple of times I've seen bears or bear tracks out in February," Gunther told VICE News. "But definitely in recent years we've had warmer winter temperatures."

There have been many days where temperatures reached into the 40s, and a few in the 50s, Gunther said. Historically, temperatures in the area this time of year could still be reaching 20 to 30 degrees below zero.

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Warm weather, melting snow, and a bear's individual health can all affect when it ends its hibernation and leaves the den.

"In a way, their body condition tells them whether they can afford to emerge and be active or not," Frank van Manen, an ecologist with the US Geological Survey and head of the Interagency Grizzly Bear Study Team, told VICE News. "It's very well possible this bear goes back into its den if the weather conditions substantially change."

Based on descriptions of the bear, Gunther said, it's likely an adult male, which usually emerges from a den earlier than adult females and cubs. It's not uncommon for males to venture out when temperatures warm, van Manen said. In the Yellowstone bear's case, the bear may have smelled the carcass, prompting it to leave.

While the first week of March is generally when most male bears begin to merge, some historical data indicates that it's not too uncommon, van Manen said. A study co-authored by Gunther co-authored found that about 5 percent of Yellowstone's male bears left their dens during the first week of February between 1975 and 1999.

While it's unusual for an individual bear to leave its den this early in the year, it's less uncommon statistically that a bear or two across the population will emerge early in any given season, van Maren said. 

"It always generates a lot of interest when we have these observations of bears already out of their den at this time of year," van Manen said. "But if you look at our data, it's really not that unusual."

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Grizzly bears have been listed for protections under the Endangered Species Act since 1975, and are listed as threatened in the contiguous United States, where about 1,500 of the bears live. There are about 30,000 grizzlies in Alaska.

Ending hibernation early doesn't cause any damage to the grizzlies if they can find enough to eat. Because plants are sprouting early as well, that shouldn't be a problem.

"As long as there's food, they'll do fine," Gunther told VICE News. 

Follow Laura Dattaro on Twitter: @ldattaro

Image via Flickr