DURANGO, Colo. (CBS4) – An autopsy is planned for Wednesday on the 39-year-old woman found dead in Trimble north of Durango, where signs point to a bear attack. The woman was out walking her dogs Friday and did not return. She was later discovered by her boyfriend.

Wildlife officers found evidence of bear scat and hair along with indications bears had consumed some of the remains. A necropsy showed two the bears, a 10-year-old sow and one of two female yearling cubs, had human remains in their digestive tracts says Colorado Parks and Wildlife.  There was no indication of trash.

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The bears were all euthanized.

Unprovoked attacks by black bears that populate Colorado are very rare, but can happen.

“Bears are smart animals that exploit the food sources around them. And a lot of times they’ll just take advantage of what’s on the landscape. And so you’ll get a bear that just behaves differently than the other bears,” said Colorado Parks and Wildlife’s Kristin Cannon, a deputy regional director.

Cannon has investigated bear attacks as a wildlife officer. Among the incidents, an attack on a 19 year old in Ward in July of 2017.

“We felt based on the behavior that it was a predatory attack. This bear attacked that young man in order to kill and eat him,” she said.

The victim survived after the bear bit him on the head at night and attempted to drag him away by the head. It took nine staples to close the wound.

“It’s horrible when somebody loses their life from an encounter with a bear or any other animal. But, risk is relative,” said David Neils, a wildlife conservationist who has shared hundreds of videos of animals in Colorado online.

Neils is a keen observer of bears, mountain lions and other wildlife in the state and has recorded them extensively in Colorado’s forests engaging in natural behavior, away from human interaction, on his Wild Nature Media website. He does not consider black bears apex predators like grizzly bears (also known as brown bears, no grizzly bears have been sighted in Colorado since the last one was killed when it attacked a hunting guide in southern Colorado in 1979). Neils grew up among both types of bears in Montana and was pursued by a black bear at the age of 15 as he was out photographing ducks.

“Two cubs came running up the hill and I didn’t see them until they were about 15 yards away coming at me and I looked and I made eye contact with the sow at the same time and then she barked and the two cubs ran up the tree and she charged me. And I went up a tree … and she pushed on the tree for several minutes to try to get me out of the tree but I hung on tight.”

He scrambled down after the bears left.

Cannon says grizzly bears are more likely to be aggressive around their cubs.

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“In everything I’ve seen, sow black bears aren’t typically aggressive around their cubs … black bears when they feel threatened, they’re more likely to run away or go up a tree. If they have young cubs, they’re more likely to send those cubs up a tree.”

Now it’s not to say that if you don’t surprise a sow and she doesn’t expect you and you’re too close to her cubs that she won’t act defensively.

“Bears can have vastly different behaviors,” notes Cannon. “So you’ll have bears that are more shy and retiring than other bears, you’ll have aggressive bears that are more territorial. When bears lose their fear of people sometimes they can be more assertive and aggressive.”

That sort of habituation can come from humans treating bears as entertainment, says Neils. Feeding or leaving food or trash within the reach of bears can lead to bear problems.

“All animals will do what they can to minimize calorie loss while maximizing calorie gain” — says Neils, even hummingbirds. They will choose a feeder over going to 150 different flowers.

Black bears are not terribly efficient hunters.

“They do prey on livestock. They do prey on deer fawns and other mammals or other prey sources,” said Cannon.

But once fawns and elk calves get up to speed, black bears are not quick enough to catch them very often.

“Very, very rarely they will prey on people,” said Cannon. If the cause of death is the bear attack, it will be only the fourth in known Colorado history. The last was in Ouray in 2009, when a woman who regularly fed bears in her yard was killed.

The best way to stop a black bear attack is to fight back.

“You can convince those bears, even if they’re behaving in a predatory way that you’re a danger to them still, that you’re a threat and that you can injure them and you can convince them to give up,” said Cannon. “Fight back with everything you have.”

“I just started hitting the bear as hard as I could. And I found its eye, and I started poking its eye with my fingers,” said the 19 year old attacked in 2017.

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Other people at the camp helped scare that bear off as well.

Alan Gionet