Gildart called for help, setting in motion an urgent medical mission. Hours later, as he slept in his apartment at park headquarters, a colleague knocked on his door.

“He said: ‘Bert, you’ve got to get up. There’s been a grizzly bear mauling,’ ” recalled Gildart, now 77. “I said, ‘I know.’ He said, ‘No: There’s been another one.’ ”

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The information, Gildart says today, was “mind-boggling,” and for good reason. The park, nearly 1,600 square miles of stunning peaks and valleys in northwest Montana, had recorded no grizzly-caused human fatalities since it was established in 1910. Then, on one night, two bears in spots several miles apart killed two campers. Both victims were 19-year-old women.

Those attacks, which took place 50 years ago this summer, set off an immediate quest at Glacier to understand how a tragedy of such infinitesimal odds could have happened. But they also marked a turning point in relations between North Americans and the continent’s largest predators, revolutionizing how public agencies deal with bears and inspiring new paths of research on grizzly behavior. The impact of the deaths still echoed in federal officials’ recent decision to remove Yellowstone-area grizzlies from the endangered species list.

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“We’ve certainly had our share of other types of fatalities, but none of them seemed to live like that particular event does,” said John Waller, Glacier’s bear biologist. “It was a watershed moment for bear management, not just in Glacier but the whole National Park Service. It fundamentally changed how we view our relationship with bears.”

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Theories about the attacks’ cause swirled in the aftermath. Perhaps lightning and dry conditions, which sparked wildfires that week, had possessed one bear to drag Julie Helgeson from the Granite Park campground where she slept and a second to mangle Michele Koons at the Trout Lake site where she camped with four friends. The women’s menstrual cycles and the possibility that someone had given the bears LSD were also suggested triggers.

But soon it became clear that the problem was far more mundane: human food and garbage.

Glacier, a park that had recorded just 110,000 visitors between 1910 and 1920, was in the late 1960s welcoming nearly 1 million people a year, and more of them were heading into the backcountry. Granite Park Chalet, a mountaintop site reachable by trail, had so many visitors in 1967 that its incinerator could not contain all their trash, and managers discarded the excess in a gully behind the facility. Soon the grizzly bears’ nightly foraging there became a tourist attraction.

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Many park staffers were uncomfortable with this situation, as recounted in Jack Olsen’s 1969 book, “Night of the Grizzlies.” Among them were Gildart and his friend, wildlife biologist Dave Shea. They had witnessed five bears dine on trash at the chalet days before, and both had expressed concern at park headquarters.

“It was basically an incident waiting to happen,” said Shea, 77, who worked at Glacier for 36 years.

In the Trout Lake area, meanwhile, one grizzly had spent that hot summer rummaging through garbage barrels near a collection of cabins, menacing hikers and raiding backcountry campsites. Although backpacking was becoming more popular, there “was no wilderness ethic,” Waller said: Campers would simply leave behind their trash, providing nourishment to bears smart enough to associate it with people.

Despite reports about the bear’s behavior, park officials took no action. It wasn’t that they didn’t know bears and human food were a dangerous mix, Waller said; enforcement just wasn’t a priority. Now we know that bear-caused injuries at national parks in the West were quite high at the time, but then, he said, “it all got swept under the carpet.”

The Glacier maulings also inspired a generation of scientists. Stephen Herrero had just finished his PhD in animal behavior in 1967 when he heard the news — and couldn’t stop thinking about it.

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“Here was an ideal and important topic to try to understand — what went on in the minds and bodies of bears,” said Herrero, who became a leading authority on bear attacks and behavior at the University of Calgary.

“The big problem with the bears at Glacier was too many of them had learned to tolerate people more and more, and ignore people more and more, and then finally go after people themselves,” Herrero said.

The immediate response, however, was to find bears in the areas of the attacks and kill them. Within two days, rangers had fatally shot three at the chalet. Shea was among those who fired at the third, a sow with two cubs and a ripped paw pad that would have been painful, possibly increasing its aggression. Investigators concluded that this bear had likely killed Helgeson and seriously injured her boyfriend.

Gildart was deployed to track down the Trout Lake bear. He shot it two days after the attacks — an emaciated female that had glass from garbage embedded between its teeth and a mass of human hair in its stomach. Soon after, Gildart helped collect several giant burlap sacks of trash near the lake.

News of the maulings, splashed across newspapers nationwide, was a public relations crisis for the Interior Department. A few critics called on authorities to finish off the extirpation of grizzly bears that had begun as early settlers pushed West and left them in only a few patches of the United States, including Glacier.

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“Some people said, we ought to go in there and hunt them all out. And that first year, that’s kind of the way I felt,” Gildart said. But he changed his mind: “We learned all these bears being seen on a regular basis were conditioned to food — and had lost their fear of people.”

That understanding triggered major changes in Glacier and elsewhere. A strict “pack in, pack out” policy was established for backcountry sites, which were also given designated cooking areas that were separate from sleeping areas. Cables or hooks for hanging food out of bears’ reach were put in place. Campers were required to reserve spots, which limited their numbers.

In a controversial decision, Yellowstone National Park managers in 1968 abruptly closed several dumps where bears had long been eating — a move researchers (and brothers) Frank and John Craighead warned would cause the bears to seek food in campgrounds or populated areas outside the park, leading to more conflicts and bear deaths. Many researchers say they were right: Within a few years, dozens of Yellowstone-area grizzlies were killed or sent to zoos, contributing to a population drop that led to their inclusion in 1975 on the endangered species list. This spring, federal officials said Yellowstone grizzlies had finally recovered enough to be delisted.

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Strategies for what to do about “problem bears” — the kind that seek human food — have evolved. In the early 1980s, Glacier said it would shoot or move more of them. Later, trapping and relocating prevailed, until studies revealed that the animals usually returned to where they were caught. Now the preferred method is hazing, or using things like rubber bullets and loud cracker shells, “to teach that bear no,” Waller said.

But the big idea is conflict prevention, he said. These days, Glacier regularly closes trails so grizzlies can access berry patches or carcasses without running into people. And all those bear-proof garbage cans in national parks and elsewhere bears live? They’re produced by an industry that grew out of the Glacier attacks, Herrero said.

“Tremendous progress has been made to keep bears away from these attractants,” he said. “It’s really been quite successful — not only saving people’s lives, but also saving bears’ lives.”

There are no guarantees, of course, but park officials stress that the threat from bears is very low. Grizzlies have killed eight people in Glacier since 1967, most recently in 1998, and most were food-conditioned bears. Bears, both black and grizzly, have injured about 100 people in the park’s history, usually following a “surprise encounter,” Waller said.

In 1980, Gildart was assigned to patrol Glacier’s backcountry on horseback, making sure people and bears remained separated. He gave tickets to campers who left trash and posted warning signs when he spotted bear tracks or scat, and he often encountered bears. They did what bears that don’t eat human food typically do.

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“They’ve all run,” he said.

But neither he nor Shea go to Glacier anymore. It’s too crowded. The park expects to log 3 million visitors this year, many of whom act like they’re “walking in a zoo,” said Shea, who fears the potential for tragedy is rising. “The bears aren’t quite as wild as they used to be, because they’re hearing people and people noises all the time.”

The hordes inevitably mean that it is harder to keep bears and people apart, often because the people don’t heed park advice. Waller said rangers regularly find piles of blueberries and cans of cat food while on patrol — signs of attempts to lure predators that can weigh 700 pounds.

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“It astounds me to see grizzly bears along a trail and people approaching within 20 or 30 feet to get pictures,” Waller said. “Really, bears are very very good to us. They’re very tolerant, because despite our best efforts, people do amazingly stupid things every year.”