A grizzly bear attacked a group of animal-rights activists hiking near West Yelowstone, mauling a 38-year-old man.
The victim, who was not identified, was hospitalized in fair condition in Idaho Falls, Idaho. Gallatin National Forest officials closed the area to hiking and tent camping.
The victim and the three others are members of Buffalo Field Campaign, an activist group that protests the killing of bison from nearby Yellowstone National Park to prevent the spread of disease in Montana.
The four surprised a grizzly sow and two cubs. One hiker said the lead hiker dropped to the ground, but another ran and the bear attacked him.
Biologists are worried that attacks on humans will rise as a key source of food for bears--nuts from whitebark pines--dries up.