The Bridge to Coexistence

Former State Senator Fran Pavley is hiking in the blazing sun through a section of the dry-grass canyon along Highway 101 in Agoura Hills, talking about this radical moment. The last remnants of the mustard bloom spread over the low mountains, a gorgeous stretch of uninterrupted open space that would connect the Santa Susana Mountains to the north of Simi Valley all the way through this spot at the Liberty Canyon exit and southward into Malibu Creek State Park. Would, that is, if not for the 10-shrieking-lane barrier that is the 101 Freeway. 

That barrier, though, is about to be bridged. 

Only a few days earlier, on April 22, Pavley helped break ground for the Wallis Annenberg Wildlife Crossing, which will vault over the deadly highway and allow deer, coyotes, roadrunners and mountain lions to cross the freeway unharmed by vehicles.  

The Wildlife Crossing is an ordinary, human-built thing: a bridge. But this bridge marks the humbling moment when we, Americans, took a significant step toward a new phase of co-existence with the more-than-human world — a phase in which we finally go all-out to do what is right for what Aldo Leopold called “the land community.” And because this effort is all-out, it will be the largest and most biologically complex wildlife crossing in the world.

Former State Senator Pavley hiking along Ventura Freeway at the site she has worked for decades to protect. Photo by Dean Kuipers

“I have had mountain lions in my backyard,” says Pavley, who was Agoura Hills’ first mayor and has lived in the Hills since before the town was incorporated. “Bobcats, foxes, coyotes, deer, raccoons, possum [and] quail.” 

For more than 40 years, she has worked tirelessly to preserve the huge tracts of parkland along the spine of the Santa Monica Mountains that are home to a rare urban population of pumas that — thanks to their superstar, Griffith Park’s mountain lion P-22 — are a global symbol of human-wildlife coexistence.

And when it became obvious, more than 10 years ago, that those pumas were suffering the effects of inbreeding as a result of the highway-made barrier from genetic diversity, Pavley worked toward a solution in her neighborhood: this bridge.

“Biologists figured all this out,” she says. “I don’t remember the concept of crossings and corridors and connectivity being normal words people use. Now, they’re understanding you can’t just have an island of open space.”

History is made along the Ventura Freeway this year as the Wildlife Crossing is built. Photo by Dean Kuipers

Indeed, the groundbreaking for this bridge marked the arrival of a more complex understanding of how wildlife and people share urban space. There was an almost giddy outpouring of joy and relief among the more than 40 dignitaries wrestling for the mic at the groundbreaking, including Governor Gavin Newsom, Wallis Annenberg and several U.S Congresspersons, though only Congressman Ted Lieu has the overpass in his district. After all, it took a ten-year campaign to get to this day. Many of us want to do something to stop species loss, curb climate change and give the foot-draggers a shove, but rarely do projects on this scale see completion.

We begin to reconnect the land and its wildlife, which never should have been fractured in the first place.

Corridors and connectivity are gaining champions. Rep. Adam Schiff, whose district is just to the east, has sponsored the Rim of the Valley Corridor Preservation Act (reference “The Most Amazing Park Expansion You’ve Never Heard About”), which would add a massive, 191,000-acre ring of urban-adjacent — and thickly connected — mountain and river spaces around the San Fernando Valley to the Santa Monica Mountains National Recreation Area. The Act passed the House last year. Senators Dianne Feinstein and Alex Padilla (both D-Calif.) subsequently introduced a companion bill to the Senate. If enacted, the expansion would join the wildlife overpass as critical pieces for reestablishing some of the region’s ecological integrity. 

“Today we begin to reconnect the land and its wildlife, which never should have been fractured in the first place,” said Annenberg, who put up the $25 million challenge grant that anchored the $87 million project, at the Wildlife Crossing groundbreaking.

Do you see the radical nature of what’s being said? This is not the save-the-untrammeled-wilderness ethos of Muir and Roosevelt, in which we all take pride—this is a little more down-and-dirty. This bridge, like Schiff’s Rim of the Valley addition, is about granting a kind of equality to wildlife that lives amongst the Los Angeles metro area’s 13 million people. This is about building pumas and other creatures right into our dense city infrastructure — right into our lives.

And even though it took more ten years to make this crossing a reality, it’s only the beginning. 

***

“P-22 is really the reason I got involved,” says Regional Executive Director of the National Wildlife Federation’s (NWF) California Regional Center, Beth Pratt, who spearheaded the overpass project. 

We talked via Zoom from her home near Yosemite, where wild creatures can roam with fewer human-made barriers or hazards. When she first heard about the big cat in Griffith Park in 2012, she thought he should not be in this human-populated urban landscape. But then she realized that wasn’t what the cat wanted. 

“I think he did for me what he has done for a lot of people around the globe: get us to get over ourselves and to really check our biases about where nature should be, what is worthy of conservation work, and where we should invest our time,” she says.

She asked National Park Service biologist Jeff Sikich how she and the NWF could help. 

“He just kind of turns to me and says, ‘Well, there’s this little wildlife corridor we’ve been trying to get built,’” she recalls, smiling. “And I’m like, ‘Sure, how hard can it be?’ Not knowing it would be ten years of my life and $87 million.”

P-22 photographed in February, 2021. Courtesy of Santa Monica Mountains National Recreation Area

Pavley, then a state senator for the district, already had a few meetings on the project, and the work that had been done over the previous decades meant that no land had to be purchased; the Mountains Recreation and Conservation Authority (MRCA), a government land-management agency which comprises a partnership of a number of local parks, had already acquired the land on both sides of the highway at the Liberty Canyon exit as part of open-space preservation efforts. In fact, the north end of the overpass will land next to the MRCA’s Fran Pavley Meadow.

Sikich has been studying the impacts of urbanization and habitat fragmentation on pumas in the Santa Monica Mountains since the early 2000s. Mumbai, India, is the only place that has a similarly urbanized population of big cats. Disease, rodenticide poisoning, wildfires and territorial battles kill a lot of Santa Monica’s lions. Sometimes they even wander into the city, such as when a female was shot in the courtyard of an office building in Santa Monica. 

But biologists warn that the biggest risk to their continued success may be their extremely low genetic diversity. Having a mate is part of it; P-22, for instance, is now approaching a ripe old age for a wild mountain lion, but he has produced no offspring. Having a mate from outside the population’s gene pool is the other part of the battle. The genes begin to fail when mating is restricted to within an isolated population. These mountain lions are currently isolated on their habitat island and need new genetic input. Scientists estimate that this isolated population now faces a 16- 28 percent chance of extinction in the next 50 years, primarily due to inbreeding.

Artist rendering depicting the Wildlife Crossing that aims to bridge the genetic diversity gap for Santa Monica’s mountain lions. Courtesy of Living Habitats

Though there have been loads of mountain lions in the Santa Monica Mountains, with over 100 collared cats studied since 2002, the available habitat can only accommodate about a dozen breeding adults at any one time. Mountain lions are mostly solitary in adulthood and require a lot of hunting space. Male territories average about 100 square miles but can measure over 350 square miles. 

When Sikich and Pratt met, there were already serious concerns about the isolation of the Santa Monica Mountain population. Now, a study from January 2022 has found hard evidence that Southern California cats are suffering a genetic decline known as “inbreeding depression.” 

Published in the journal Theriogenology and led by Audra Huffmeyer, a postdoctoral researcher at the University of California, Los Angeles and co-authored by Sikich and others, the study found nine pumas in the LA area with either an L-shaped kink in their tails or testicle abnormalities and all the male animals tested had malformed sperm levels of 93 percent — all of which are signs of inbreeding that could mean low reproduction. The lions were from geographically isolated populations in the Santa Monica Mountains, the Santa Susana range, the Santa Ana range southeast of Los Angeles and the Eastern Peninsular range in San Diego County.

In the mid-1990s, Florida’s panthers, a sub-species of mountain lion that had diminished to only 20 or so individuals, showed similar signs of inbreeding. Trapped in the Everglades with no corridor to genetic diversity, they were doomed until eight female cougars from Texas were introduced in 1995. Today, they number around 125 across the whole state of Florida (in comparison to the 4000-6000 in California) and still face challenges coexisting with human suburbs and finding ways to disperse to new areas.

LA’s young mountain lions are forced to make perilous journeys out of their isolated mountains to look for new territory and mates. Over the past two decades, 26 of those within the Santa Monica Mountains study area have ended up as roadkill on LA’s freeways. A lion was killed crossing the Pacific Coast Highway on March 23 and, adding a grim note of urgency to construction of the new crossing, another one was killed crossing the 405 the day before the groundbreaking.

Another dozen or so mountain lions live in the Santa Susana Mountains, and lions regularly attempt to find mates by traveling to the other range, only rarely making it across the roaring 101 Freeway. That’s about to get easier. 

***

“You put aside a Yosemite. You put a little wildlife refuge here [and] check, you saved wildlife. [It] doesn’t work,” says Pratt. “I mean, we need to keep Yosemite, but nature needs connection for resiliency.”

She points out that this is not just true for big charismatic predators like pumas. National Park Service research is now showing that Western fence lizards, California quail and a bunch of other species are starting to demonstrate genetic fragmentation. This scenario is playing out across the ecosystem, including in plants. As climate change increasingly affects habitat, plants need to disperse to new areas. On the 85-degree day in May when I visited the site, the creek that runs under the highway at Liberty Canyon was dry; Pavley noted that it used to flow reliably through June.

A sample of the expected wildlife that will inhabit the Wildlife Crossing. Courtesy of Living Habitats

The Wallis Annenberg Wildlife Crossing is a global experiment in what an urban intervention, such as an overpass, can achieve. First, it will be the largest bridge of this nature, measuring 210 feet long and 165 feet wide that spans the highway, Agoura Road, the creek and existing powerlines. More important, landscape architects Living Habitats in Chicago have designed it to seamlessly replace the environment lost to the highway below, with planted sound walls blocking out the traffic noise and light, and very specific plants and animals living on it. All manner of specialists are consulting; a soil scientist is helping to grow local trees, a herpetologist, and a mycologist collecting the appropriate fungi. Fencing will funnel animals into the crossing and discourage them from approaching the highway — which usually turns them back — or from using the existing underpass and risking the cars there.

CalTrans is looking to complete construction in 2025. But, Pratt already has her sights set on opening more connections.

“Nature needs connection for resiliency.”

“If you look at that larger [Santa Monica Mountains] corridor, you see we need interventions,” she says, growing excited. “[Highways] 118, the 126, the 5, the 405. The National Park Service put together some of their next priorities, at least in the Santa Monica mountains roughly, to make the rest of the corridor.”

The team putting together the Annenberg crossing invited veterinarian Dr. Winston Vickers, who has studied the Santa Ana Mountains’ population of about 20 mountain lions, to speak at the groundbreaking about the need for underpasses and overpasses in that area to get the cats past the I-15 so they can disperse into the Peninsular Ranges. 

This is going on all over the state, and not just with pumas. Pratt is currently advising on a potential crossing for mule deer migrations that cross Highway 395 near the Mammoth Airport in the Eastern Sierra — an area where black bears are also often hit.

The freeway that facilitates drivers’ daily commute is a deadly barrier for mountain lions. Photo by Steven Gute

The one she’s really eyeing, personally, is the spot near Lebec, in Kern County, where the long-traveling wolf named OR-93 was killed while crossing the I-5. His story has captured Pratt’s imagination, and she figures building a crossing there would not be nearly as technically challenging as the Annenberg.

“People call me up, hot, ‘Can you help us?’ [I’m] happy to. I want more of these,” Pratt says.

In a recent profile on Pratt in the Los Angeles Times, Louis Sahagun wrote that there is so much energy around these projects that “future historians may look back on the second decade or so of 21st century American architecture as the Age of Wildlife Crossings.” 

Pratt is doing everything in her power to make that happen.

“Let’s turn this into the battle,” she says, nodding emphatically. “We say this is the world’s largest crossing. But somebody’s going to knock us off and I want to be, bring it on, New York City, or whatever. Let’s do this and I’m with you. Let’s turn it into a really, really wonderful competition for nature. But LA was first.”