Thousands of people streamed into the park Thursday, a day after a 57-year-old California man was attacked and killed by a female bear on a backcountry trail. Officials said the sow was only defending its cubs, had not threatened humans before, and would be left to wander the wilderness.
"This is bear country," said Elizabeth Hoffman, a tourist from California who agreed with park officials' decision not to hunt the bear. "It's got babies. If someone came after a human mother, I don't think that we'd take her from her children."
Cars jammed Yellowstone's roadways for wildlife spottings, including a 20-minute delay while motorists gawked at two black bear cubs romping in a field while their mother rooted around in the grass nearby.
By late Thursday, most tourists seemed to know about the attack. Desk clerks at hotels inside the park told arrivals that there had been a bear incident. Worried relatives called or texted other visitors. And some were surprised that rangers didn't let them know when they entered the park that one popular destination - access to iconic Artist Point - had been temporarily closed.
"They didn't say one word about it at the gate," said Leslie Finch, who was visiting with her husband and two children from Missoula, Mont. "I would have thought they'd say this area is closed. But they didn't say anything."
The attack highlighted the potential dangers, however rare, that face tourists who come in record numbers each year to a park known for its burgeoning bear population and the Old Faithful geyser.
Whenever there is a run-in or attack involving bears, park officials must decide whether the attack was defensive or an act of aggression. In Wednesday's mauling, they based their conclusion on the account of the hiker's wife, who survived, as well as their knowledge of bear behavior.
Brian and Marylyn Matayoshi, of Torrance, Calif., were hiking in a backcountry meadow along a trail a mile and a half from the trailhead when they spotted the bear foraging about 100 yards away. The couple immediately turned and began walking away, officials said.
The grizzly charged and attacked Brian Matayoshi, then went for his wife, who ran for cover behind a tree. The grizzly lifted her off the ground by the day pack she was wearing and then dropped her.
She tried to call 911 on her cell phone, but couldn't get a signal. Other hikers in the area responded to her cries for help and managed to get through to emergency officials.
Marylyn Matayoshi told rescuers that the couple surprised the sow, its cubs nearby - one of the most dangerous situations possible for humans encountering grizzlies. Park officials believe the grizzly had two six-month-old cubs, based on previous sightings in the area and cub tracks where the attack occurred.
"It was not predatory and so we see no reason to take action against the bear," said Kerry Gunther, bear management biologist for Yellowstone.
The bear had never been documented before, never been tagged, and there was no reason to believe it had interacted with humans before, said park spokesman Al Nash.
Marylyn Matayoshi escaped injury and was no longer at the park, and officials declined to reveal her whereabouts.
In Torrance, neighbor Kathy Hester said Matayoshi and his wife kept their house immaculate and recently had put in a new lawn. "They are the sweetest people you'd ever want to meet," Hester said.
Park officials called the mauling a "1-in-3-million" encounter that shouldn't condition the sow to attack again. They collected DNA samples from fur at the attack site, so they can determine if the bear is involved in another attack, Gunther said.
Decades of research has established that grizzlies, while dangerous, rarely get aggressive with people except under very predictable circumstances, said Mark Bruscino, a Wyoming state bear biologist who has investigated some 40 attacks.
Grizzlies become aggressive when they are harassed, taken by surprise up close, are defending a food source or are defending their cubs, Bruscino said.
"You can almost explain every incident that occurs with a grizzly bear around those four," he said.
A bear that fatally attacked a man and seriously injured two people at a campground east of Yellowstone last July was killed in part because the circumstances didn't neatly fit into predictable bear behavior, he said.
Hunger and internal parasites afflicted that grizzly, but investigators said they could not explain its late-night rampage through the crowded campground near Cooke City, Mont. That grizzly was captured and euthanized. Its three cubs are now in a Billings, Mont., zoo.
Wednesday's mauling was the park's first fatal grizzly attack since 1986, but the third in the region in just over a year amid ever-growing numbers of grizzlies and tourists roaming the same wild landscape. In June 2010, a grizzly just released after being tranquilized for study killed an Illinois hiker outside the park.
Brett Clark, who was visiting Yellowstone from Steamboat Springs, Colo., and Jenny Alm of Wakefield, R.I., said they wouldn't change their plans because of the attacks. Clark appeared to grow concerned when he heard the Mayatoshis were hiking in the region he had planned to visit on Friday.
"It's interesting that they were doing what we would have done," Clark said. "It doesn't worry me. I feel like those things are bound to happen in areas with high density of animals."