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Warm Weather Drives Bears Out of Hibernation

Utah animals left dens early but found little food.

Warm weather in southeastern Utah drew hibernating bears out of their dens too early.

In Utah, female black bears with young cubs typically emerge from their hibernation dens at the end of March. But when state biologists entered two dens in mid-February to count cubs, both were already empty.

A third den concealed an awake adult female bear “that almost attacked the biologists,” says Tonya Keiffer of the Utah Department of Natural Resources.

The bears were likely roused by unseasonably warm temperatures and may have wandered out looking for food, says Dale Liechty, a state bear biologist.

The bears have had their work cut out for them this spring, since plants didn’t start growing in much of Utah until weeks after the bears started stirring. (See pictures of bears.)

Bear Behavior

It’s unclear if climate change is responsible for this year’s warmer weather in Utah, but state scientists are concerned about future impacts on bears and other wildlife if the warming continues.

Lone bears and females with yearlings typically emerge from hibernation first. That’s usually in early March in Utah. Females with young cubs typically follow by the end of March. Both groups of bears emerged about a month early this year.

It’s hard to tell if the early awakenings will have a long-term effect on the health of the region’s bears, says Leslie McFarlane, Utah's mammals program coordinator. In addition to a wide range of plants, bears also eat insects, which are in short supply in the winter and early spring.

They can catch larger animals or find acorns, but overall the availability of food has been low, says McFarlane.

Bears carry fat reserves for lean times, but drawing on them too much can make them weaker and more susceptible to illness. And bears that have been out looking for food earlier are probably more likely to come into contact with people. (Learn about efforts to save the world’s largest bear.)

Counting Bears

Another people problem: the warming has disrupted scientists’ ability to count and measure Utah’s bears. Researchers typically enter bear dens in late February and early March, when the animals tend to be lethargic. They tranquilize the animals, count cubs, and take measurements such as weights and blood samples.

Utah’s bears have made a steady recovery from a low point in the 1980s and 1990s, when there were an estimated 2,000 to 3,000 black bears in the state. Since then the number has increased to around 4,000 bears, with a recent annual growth rate of five to six percent.

But McFarlane is worried that a warming climate may stall that recovery. (Learn about the 1,000-year drought predicted for the U.S. West.)

Follow Brian Clark Howard on Twitter and Google+.