Billings, Mont. ? Yellowstone’s grizzlies are going to be particularly hungry this fall, and that means more dangerous meetings with humans in a year that is already the area’s deadliest on record.

Kevin Kammer, 48, of Grand Rapids, Mich., was killed and two people were hospitalized in a grizzly attack in Montana, and another death occurred in Wyoming.

Scientists report that a favorite food of many bears, nuts from whitebark pine cones, is scarce. So as grizzlies look to put on some major pounds in preparation for the long winter ahead, scientists say, they will be looking for another source of protein — meat — and running into trouble along the way.

Wildlife managers already report bears coming down off the mountains and into areas frequented by hunters, berry pickers and hikers.

“Pack your bear spray: there’s going to be run-ins,” said grizzly researcher Chuck Schwartz with the U.S. Geological Survey.

Experts said the deaths are the most in one year in at least a century for the Yellowstone region, which also includes parts of Idaho.

The bears in both instances were later killed.

Full-grown Yellowstone bears can stand 6 feet tall and top 600 pounds. They have been known to peel off a man’s face with a single swipe of their massive, clawed paws.

In the latest attack, Kammer and the two others were injured when an undernourished bear and her three cubs marauded through a crowded campground near Cooke City, Mont., on July 28. A month earlier, a botanist from Cody, Wyo., was killed by a bear shortly after the animal woke up from being tranquilized by researchers.

And it’s not just humans at risk.

Yellowstone’s grizzlies were recently ordered back onto the threatened species list by a federal judge who cited in part a decline in whitebark pine.