WEST GLACIER - The old grizzly sow was rumbling straight toward a campground full of hikers, chubby cubs laboring along behind, when two rangers simultaneously pulled their triggers.

It wasn't the way they'd planned to kill the bear, but there she was, heading for camp, a big wild bear as unpredictable as the campers she was about to surprise. No one could say what might happen if she were allowed to barrel between the tents unannounced.

They shot her at dinnertime Monday, and by dark only one cub was still alive, trapped and sedated and headed for a zoo in the Bronx. The other succumbed to the tranquilizer.

"This was it," Jack Potter said of the bears' final beeline for the Old Man Lake campground. "This was exactly the type of situation we've been worried about, the type of situation we've been warning about. It had to end."

And so it did.

The 17-year-old bear was called the Old Man Lake female because she often haunted the backcountry camp of that name, high on Glacier National Park's eastern flanks.

She startled people there for years, nosing around camp and rustling tent flaps during the night, pushing hikers off the trails. She wasn't necessarily aggressive, but she was friendly to a fault. Dangerously friendly, Potter said.

He is chief of science and natural resources at Glacier, and has been following the grizzly for years. She first was caught and fitted with a radio collar in 2004, and a year later rangers spent two weeks hazing her away from people places. They hazed her again in 2006, and then for two summers she melted into the wilderness.

But in 2009, the Old Man Lake female returned, with a couple of yearling cubs tagging along. This time, though, she didn't seem attracted only to campgrounds. This time, she appeared to be attracted to people.

She'd spot hikers and seek them out, circling around the backcountry lake to greet people, or shadowing them on the trail. She crossed a line, Potter said, and park policy is clear about that line: When a grizzly bear begins approaching people on purpose, that bear must go.

The risks, he said, were too great to ignore. And as the hazing lessons hadn't stuck, she would have to be removed. Alternatives were few. No other public land agencies wanted her; they had enough problem bears of their own. And although the Bronx Zoo finally agreed to take the cubs, no zoos wanted a 17-year-old adult.

And so three rangers camped themselves north of Morning Star Lake, armed with rifles and tranquilizer guns. They set a family trap at the lake, and planned to catch all three at once.

But the Old Man Lake female disappeared. Rangers worked the valley for days, but couldn't get a lock on her radio collar signal.

On Monday, Potter said, the team climbed Pitamakan Pass, a high rocky saddle that separates Morning Star from Old Man. The receiver squeaked its telltale ping almost immediately - she was down below, in Old Man, on the hillside above camp. Mount Morgan was beginning to throw shadows over the lake as the afternoon sun dipped westward.

"They weren't expecting to find her there," Potter said. "They didn't have the tranquilizing equipment with them, and the trap was back up at Morning Star."

And so the crew dialed up their satellite phone and called for backup. Fly in a trap, they said, and bring the dart guns. Clear the campground. We'll move on her tomorrow.

No sooner had they hung up, however, and the old bear headed for camp.

The grizzly, Potter said, posed a very real and immediate threat not only because she was so familiar with people, but also because of those cubs. Cubs make mama bears protective, which can be decidedly unhealthy for people. And cubs learn habits - both good and bad - from their mothers.

So the rangers canceled that call for backup and headed downhill, fast. The bears were perhaps 300 yards from the campground when two shots, overlapping into one, cracked Glacier's stillness. She dropped straightaway.

Rangers know from experience that cubs will stay with an incapacitated mother for only about 12 hours, and night was coming fast. They recalled that helicopter, which arrived with tranquilizer guns. One hour later, two darts - easy shots - and the cubs conked out.

But the male cub didn't look so good. It's tough to gauge dosage when you don't know an animal's weight, temperature, vital signs, underlying health condition.

"There's a lot of factors you can't control," Potter said.

First one ranger tried CPR, then another, going mouth to snout while coaxing the 100-pound yearling back to life. It did not work, "and that is very sad," Potter said. "But what's really sad is losing three bears from this ecosystem. The reality is, that bear was already lost to the population, but that doesn't make it any easier."

Rangers have for years recognized the dangers of tranquilizing wildlife, especially youngsters - "because it can never be a 100 percent controlled situation," Potter said - and so they have increasingly turned to noninvasive DNA techniques for research purposes. But this wasn't research, and collecting hair just wouldn't do. For this, they had to risk the dart.

The surviving cub was loaded into a culvert trap and ferried by helicopter to the front country, where she'll be transferred to the zoo. Her sibling's body has been taken to a wildlife laboratory for necropsy, to determine why he didn't make it.

The outcome, while arguably unavoidable, was tragic, Potter admitted, particularly for those wildlife lovers who had rallied around the three bears. In the days prior to the shooting, park e-mail folders had been barraged by messages pleading clemency.

At least some of those letters came from Donald Witulski, a retired forester from Idaho, who heard the news of the bears' deaths with both sadness and hope.

"We need to make a positive out of a negative," Witulski said. "We need to tell the story better, so the public pays more attention."

Already, backcountry hikers at Glacier must watch a brief "bear-aware" video before hitting the trail. Perhaps, Witulski said, the story of the Old Man Lake female could be added to that primer, to illustrate exactly what's at stake for bears that become conditioned to humans.

Or perhaps all those who followed the story with such interest can donate to grizzly bear habitat protection, or to the park's bear management team, which even as the shots rang out were working two other grizzly family groups up near the park's backcountry chalets.

They're hazing those bears, Potter said, driving them from human habitations hopefully before they become too comfortable there.

"I'd like to help the bear team any way I can," Witulski said, "so we don't have to watch another bear killed."

"They're doing a good job," he said. "Don't get me wrong. But maybe there's more we can do, if we can get the message out there. It's the people who are the problem, not the bears, and so we need to get through to the people."

Reporter Michael Jamison can be reached at (406) 862-0324 or at mjamison@missoulian.com.