CODY, Wyoming A female grizzly bear attacked and killed a man who encountered the bruin and her cubs while he was hiking with his wife on Wednesday in Yellowstone National Park, park officials said.
The fatal mauling occurred about a mile and a half from the start of the Wapiti Lake trail, and another group of hikers nearby heard the victim's wife crying out for help and used a cell phone to call park rangers for assistance.
A National Park Service statement said the couple had inadvertently surprised the mother grizzly and her cubs, and in "an attempt to defend a perceived threat to her cubs, the bear attacked and fatally wounded the man."
The victim's identity and hometown have been withheld pending notification of other family members.
The bears involved in Wednesday's encounter have not been captured, and park officials said they did not immediately have enough information to determine what measures, if any, they might take in the aftermath of the attack.
Initial information indicated the mother bear behaved normally in defending her cubs and would not be killed as a result of her actions, park spokeswoman Linda Miller said.
However, bears found to have had repeated run-ins with park visitors are sometimes relocated.
"If we have an aggressive bear that continually poses a threat to human safety, then we work to remove it from the ecosystem," Yellowstone spokesman Al Nash said, adding he did not know if this grizzly had any previous human encounters.
Attacks by bears are extremely rare. No visitors were injured by bears in Yellowstone during all of last year, and Wednesday's incident marked the first bear-caused human death in the park since 1986, the Park Service said.
But a mother grizzly killed one man and injured two other people in an unusual night-time attack on sleeping campers just outside Yellowstone in Montana last July. The bruin involved in that incident was later trapped and destroyed because the attacks were considered to be unprovoked and predatory.
Park officials have focused their initial response to Wednesday's mauling on closing the Wapiti Lake trailhead and removing any remaining hikers from the area.
A bear warning sign is posted at the trailhead because it is an access point to the Pelican Valley area known for significant bear activity. No bear encounters had been reported along or near that trail this season, the Park Service said.