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The crossing, set to open in 2025, is intended to help mountain lions and other wildlife travel amid Southern California’s mosaic of developments, highways and open space
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The world’s largest wildlife crossing broke ground on Friday outside of Los Angeles, creating a lifeline for threatened species among southern California’s fragmented and highly-developed landscape.
“We’re uplifting a model for urban wildlife crossings, not just in the region, not just throughout the state, but worldwide,” California Senator Alex Padilla said at the opening ceremony on Earth Day. “This project does represent the future of sustainable infrastructure.”
The 165ft-wide vegetated bridge, which is expected to cost around $90million, aims to help wildlife cross over LA County’s busy, ten-lane Highway 101.
The crossing will create a path for wildlife to travel unimpeded from the Santa Monica Mountains in Los Angeles County to the forests and mountains north of the metro area.
The Wallis Annenberg Wildlife Crossing — named for philanthropist Wallis Annenberg, who donated $26m to the project through her foundation — could benefit species as diverse as mule deer, lizards, snakes, and toads. But the campaign to build the bridge has centred around the Santa Monica Mountains’ iconic mountain lion population.
Wildlife crossing structures both protect animals from becoming roadkill and reconnect habitats where they have been divided by roads or development. They exist worldwide including underpasses for endangered elephants in Kenya and bridges used by elk and bears in Alberta, Canada.
The Santa Monica mountain lion population is at risk of inbreeding, and possible extinction, due to their isolation caused primarily by the highway and sprawling urban development.
It’s hoped that the new crossing will allow mountain lions from other areas reach the Santa Monica range, bringing much-needed new blood to the local population.
In addition, organizers hope the bridge will be an example of how to build wildlife crossings in a highly urbanized landscape.
A rendering of the under-construction Wallis Annenberg Wildlife Crossing, which organizers hope will be a lifeline for the Santa Monica mountain lion population.
“The chance to see how a wildlife crossing can help in, again, such an urbanized area, is really going to be a great scientific question and model for the world,” Beth Pratt, California regional executive director for the National Wildlife Federation, told The Independent.
Residents of Southern California have always been in close quarters with mountain lions — also known as cougars, panthers, pumas or catamounts, depending on who you ask — and not just when they go hiking.
While the mountain lions live in expansive wilderness areas like the Los Padres National Forest, north of Santa Barbara, the cats also inhabit smaller plots of undeveloped land surrounded by urban areas, like the Santa Monica Mountains, which rise between Malibu, Los Angeles and the valleys to the north.
“I’m just so relieved these mountain lions have a shot.”
In fact, the most famous of the region’s lions — a male named P-22, or “the Brad Pitt of the cougar world”, as Ms Pratt calls him — lives between downtown LA and the San Fernando Valley in Griffith Park, home to the famous “Hollywood” sign.
Biologists estimate that there’s around 10-15 adult cats in total at any one point in the Santa Monica range, which stretches from Griffith Park in the East to Oxnard in the West.
That small population size — coupled with the nearly impenetrable barrier of Highway 101 — is where the Santa Monica mountain lions’ trouble begins. With so few individuals and little fresh blood, the lions are at risk of losing necessary genetic diversity.
The population is at risk of falling into what biologists call an “inbreeding depression,” where generations of inbreeding leads to birth defects and potentially local extinction.
Inbreeding depression has already threatened another mountain lion population in the US. The Florida panthers, who live in the marshy southern end of the state near the Everglades, are the last remaining panther population on the US East Coast.
By the early 1990s, Florida’s population of around 20 -30 cats — restricted to a small remnant of habitat and hundreds of miles from any other populations — was starting to show potential signs of inbreeding, such as tails with kinks and reproductive difficulties.
The Santa Monica mountain lions haven’t yet experienced a serious threat to their survival from inbreeding depression, says John Benson, an ecologist at the University of Nebraska who’s studied mountain lions in both California and Florida told The Independent.
Yet some worrying signs are starting to show up, he said, such as documented instances of mating between close relatives and a couple of cats with kinked tails. A 2020 study Dr Benson co-authored found that if inbreeding depression were to set in, the Santa Monica mountain lions would be at serious risk of extinction.
A rendering of the in-construction Wallis Annenberg Wildlife Crossing spanning Highway 101 in Los Angeles County
That’s in addition to the existing risks inherent to such a small population — with so few individuals, a particularly bad disaster could wipe out all the mountain lions in the range. And in a region facing the growing threat of wildfire from the climate crisis, that’s not necessarily a far-fetched idea.
To save the Florida panthers, biologists had to import some cats from Texas, one of the closest remaining populations, to add genetic diversity. But in the Santa Monica Mountains, the problem isn’t hundreds of miles of distance — it’s Highway 101.
The 101 spans the northern edge of the Santa Monica mountains, with almost two million people living nearby — plus the hundreds of thousands of cars that drive on the road every day.
That makes it virtually impossible for the big cats to cross.
“They literally come right up to the north side and turn around,” Ms Pratt says.
In addition, some mountain lions have been killed on local freeways — including a cat named P-97, who was killed on Highway 405 in Los Angeles just this week.
There is, certainly, an irony to the wider mountain lion population being so close by. “It’s kind of mind blowing when you’re like: “Wow, they’re, like — they’re right over there,” Dr Benson says.
But that relative proximity is also an opportunity.
“The good news is everywhere mountain lions should be in that area, they’re there. It’s just that this barrier separates them,” Ms Pratt says.
A mockup of a mountain lion, with cubs, crossing the Wallis Annenberg Wildlife Crossing in southern California
Santa Monica population may not need too many new faces to help, either. Dr Benson’s 2020 study found that just one new cat every year or two could make a sizeable difference to long-term population viability.
But with most of the corridor along the freeway covered in neighbourhoods, finding a place to build a habitat corridor for a large carnivore wasn’t necessarily going to be simple.
Luckily, near the border between Agoura Hills and Calabasas was a small strip of highway with undeveloped land on both sides.
“This is actually the last 1,600 feet, if you look, where you can even put a crossing,” says Ms Pratt.
Designing the crossing itself had its own challenges. To make sure the cats feel comfortable using the bridge, planners had to mitigate for light and noise, Ms Pratt says. They’ve made accommodations such as a sound wall to block highway noise and landscaping to reduce the glare of headlights/
When it’s finished, the bridge will join the landscapes on either side and hopefully connect the lion populations.
The push to build a crossing started about ten years ago, Ms Pratt says, and has transformed into a partnership between the National Parks Service, the National Wildlife Federation, the Santa Monica Mountains Conservancy, the Resource Conservation District of the Santa Monica Mountains and CalTrans, the state’s department of transportation.
California Governor Gavin Newsom speaks at the ground-breaking ceremony for the Wallis Annenberg Wildlife Crossing, April 22, 2022
The project has so far raised $77million from a combination of private and public funding, Ms Pratt says, though she is quick to point out that the project didn’t take any money from state transportation budgets.
She estimates that the total project costs, including final construction and additional costs like research on the local mountain lions and maintenance, will end up being a little over $100 million.
The project is scheduled for completion in 2025, Ms Pratt says. After it opens, the organizers are planning to put up camera traps to track how wildlife use the crossing.
This bridge is unlikely to be the last wildlife crossing in California. A new bill introduced in the California legislature this year would direct state agencies to study more potential locations for wildlife crossings. Nationally, the infrastructure law, signed by President Biden in November, includes a $350m allocation for wildlife crossings.
But for the Santa Monica mountain lions, this single bridge is a crucial step in securing their survival.
“I’m just so relieved these mountain lions have a shot,” Ms Pratt says.
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A rendering of the Wallis Annenberg Wildlife Crossing spanning Highway 101 in Los Angeles County
A rendering of the under-construction Wallis Annenberg Wildlife Crossing, which organizers hope will be a lifeline for the Santa Monica mountain lion population.
Living Habitats/National Wildlife Federation
A rendering of the in-construction Wallis Annenberg Wildlife Crossing spanning Highway 101 in Los Angeles County
Living Habitats/National Wildlife Federation
A mockup of a mountain lion, with cubs, crossing the Wallis Annenberg Wildlife Crossing in southern California
Living Habitats/National Wildlife Federation
California Governor Gavin Newsom speaks at the ground-breaking ceremony for the Wallis Annenberg Wildlife Crossing, April 22, 2022
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