YELLOWSTONE NATIONAL PARK, Wyo. - Officials at Yellowstone National Park say grizzly bears are emerging from their dens.

Park officials say that as grizzlies come out of hibernation, hikers, skiers and people on snowshoes should stay in groups of three of more, make noise on the trail and carry bear spray.

Bears look for food as soon as they emerge from their dens. Park officials say bears are attracted to elk and bison that have died during the winter. The bears can react aggressively if they're surprised while feeding on the carcasses.

Yellowstone imposes seasonal closures in areas where there are many elk and bison carcasses to try to reduce conflicts between bears and people. Visitors to the park must stay at least 100 yards from black and grizzly bears at all times.