Investigators have been searching a swath of Yellowstone National Park by air and foot as they try to determine whether a man whose body was found on a backcountry trail was the victim of a grizzly bear attack.
Rangers and wildlife biologists hoping to find clues as to how the man died continued to comb a central portion of the park Saturday on foot. He was found a day earlier by two hikers on Mary Mountain Trail, which runs northeast of the iconic Old Faithful geyser.
Investigators found grizzly bear tracks and scat near the man, but were not immediately sure whether the grizzly caused the man's death or disturbed his body after he died.
"Bears are opportunistic when it comes to food sources," Yellowstone spokesman Al Nash said. "It's very clear that there was a bear around the victim's body. What we don't know is whether this was a bear attack, or whether the bear came upon this man's body after he died."
An aerial search of the area Saturday turned up no bear activity.
Authorities say the man likely died Wednesday or Thursday. Park officials did not plan to name the hiker _ a man in his 60s from the Upper Peninsula of Michigan _ until Sunday, pending family notification.
His death comes after a female bear attacked and killed a 57-year-old California man on the popular Wapiti Lake Trail, several miles away from where the Michigan man was discovered Friday.
The female bear that killed the California man was not killed because officials said the sow was only defending its cubs and had not threatened humans before.
An autopsy is planned for the Michigan man in Montana, outside the park.
Yellowstone Superintendent Dan Wenk said that the hiker was found with a snack bar in his closed backpack, but that it appears the grizzly did not try to get at the food.
The 21-mile Mary Mountain Trail is closed from March to June because park managers list it as "high-density grizzly bear habitat."
Mary Mountain was closed after the man was discovered, along with the Cygnet Lakes Trail and a section of the Hayden Valley west of the Grand Loop Road.
Nash said that the Michigan hiker was staying in the park, but not camping off the Mary Mountain Trail. He was not carrying bear pepper spray, which is advised for hikers in the area, Nash said.