Getting A Mountain Lion To Safely Cross A Road Isn't Easy. What It Means For Planned $90M Land Bridge

It’s just past dusk and it’s getting dark as Travis Longcore and I tromp along a dirt trail in the hills above Agoura. It’s a struggle to see which animal’s passing through the nearby chaparral.

“It's still plenty bright for everything out here that's adapted to either nocturnal or crepuscular, meaning the period between day and night activity. But the birds are starting to go to bed,” says Longcore, an adjunct professor at the Institute of the Environment and Sustainability at UCLA.

The light expert is taking me on a path that mountain lions might traverse at night on their way to the Wallis Annenberg wildlife crossing, for which he’s consulted.

The yet-to-be-built bridge — estimated to cost about $90 million — is meant to help connect the Santa Monica Mountains to the world beyond the Transverse Ranges. Possibly, eventually, to vast wilderness like the Los Padres National Forest.

Scientists studying the mountain lions living in the Santa Monica Mountains have seen signs of low genetic diversity, including kinked tails.

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National Park Service

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Mountain lions in the Santa Monicas need this bridge, as they’ve been struggling for some time. There are only an estimated dozen or so adults and sub-adults left in the mountains above Malibu, and they’re showing signs of inbreeding. An indication that they’re rarely leaving and coming back into the area or that new genetic material is coming in, according to Seth Riley, Branch Chief for Wildlife at Santa Monica Mountains National Recreation Area.

Deadly river of light

As Longcore and I reach the top of the trail and turn around, there are beautifully dark hills off in the distance, ready for lions to go exploring.

But in between is one of the great man-made barriers preventing them from easily doing so: the 101 — a bright, deadly river of light made up of cars and trucks, bordered by street lights and homes.

The 101 — a deadly river of light — as seen from the hills above Liberty Canyon Road in Agoura.

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Jacob Margolis

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LAist

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“We believe … that seeing those cars going by and those streetlights, is going to give an animal navigating itself across the landscape some pause,” said Longcore, referencing recent research, to which he contributed.

The authors dug through 20 years of movement data for 102 different mountain lions in Southern California, which seemed to show that they try and avoid point sources of light at night.

Potentially because that light is associated with people, and at times, catastrophic consequences for the lions, according to Paul Beier, a former professor at Northern Arizona University.

“I think they do a lot of exploring and learning. They have very good memories. They might take a day or two or three to figure things out,” said Beier, who was one of the first people to write about how sensitive mountain lions can be to light and development.

Beier regularly tracked mountain lions, and was following one particular male through the Santa Anas. One night, around 1 a.m., the lion sat down on a bluff and looked out over a major road below.

“No doubt he was watching ribbons of light and he said, 'it's dark on the other side, but I don't know what's there. I'm not going to cross,'” said Beier.

The next morning he was able to look out over the landscape, and when the sun went down, he took a darkened underpass safely to the other side.

A mountain lion photographed with a motion sensor camera in the Verdugo Mountains overlooking the city lights of Los Angeles.

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Courtesy National Park Service

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“I had another one who went to the same area and instead of going through the underpass, he tried to cross that grade and he got hit by a vehicle. He wasn't killed. He stumbled his way back, but he never did make it across,” he said.

It’s clear that some lions do take the risk. Sometimes, having been kicked out of a territory ruled by a dominant male, or if they’re juveniles on the search for a mate. But any time they cross a road, there’s a risk they’ll be killed.

The design challenge

When it comes to the crossing, while roadway safety has taken precedence over every other design feature, there are considerations to be made to try and make mountain lions feel safe using it.

“It was a question of how do we do it while still maintaining Caltrans standards?” said Robert Rock, principle and COO of Living Habitats LLC, which is leading the design of the Wallis Annenberg project.

A rendering of what the Liberty Canyon Wildlife Corridor will look like upon completion. Also known as the Wallis Annenberg Wildlife Crossing (named for one of its largest donors), the project will provide safe passage over the 101 Freeway at a dangerous bottleneck for animals.

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Courtesy Living Habitats

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Rock explained that shields will be placed on street lights to focus light downward towards the travelway, instead of shining out into the wilderness. Also, large rock walls, vegetation and the crossing itself will help to cut down on light from the road.

It helps this area is one of the darkest and least developed along this stretch of 101 Freeway.

What comes after?

Later, Longcore and I walk right up next to the freeway to see what it’d be like for a curious mountain lion.

It was intimidating — so loud I can barely record our conversation, and bright enough to read your driver’s license, even though it's dark outside.

Every mountain lion expert I spoke with for this piece, including Longcore, said they think the crossing is going to work.

But as we're standing there, Longcore turns his attention to the areas around the future wildlife crossings that aren't going to be developed.

“My concerns are making sure that these lights along the freeway, and that the ones that may be off site, that we somehow can take care of those as well. So that it's just crystal clear to an animal that this is a safer route than anything else they might do,” he said.

The good news is that it could just take one juvenile male mountain lion moving into the Santa Monicas, to help with the inbreeding problem.

The Wallis Annenberg crossing will be built along this busy section of the 101 freeway in Agoura.

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Jacob Margolis

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LAist

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