World’s Largest Wildlife Bridge Could Save Mountain Lions

Biologist Jeff Sikich has worked at the Santa Monica Mountains National Recreation Area since 2002. He has dealt with a lot of odd things, including, on one memorable occasion, a call to bring his dart gun to tranquilize what turned…

Biologist Jeff Sikich has worked at the Santa Monica Mountains National Recreation Area since 2002. He has dealt with a lot of odd things, including, on one memorable occasion, a call to bring his dart gun to tranquilize what turned out to be a three-foot-tall statue of a mountain lion rather than an actual mountain lion. But what he was seeing one March day in 2020 was unusual and ominous. It was also not that surprising. “It had always been in the back of my mind” that this might happen, he says, although he had hoped it never would.

Sikich had set out a cage trap with a roadkilled deer inside, hoping to catch a young male mountain lion. When it worked, he used a tranquilizer dart to knock the cat out. But upon examining the animal closely, “something looked funky with his tail,” Sikich recalls. The tail, he realized, ended with a 90-degree turn—a distinctive kink with an angle as precise as that of a drawing in a geometry text. In addition, the young male had only one testicle. The second one had not descended as it should have. Sikich placed a radio-tracking collar around the cat’s neck and named him P-81 because he was the 81st puma in that region to be captured and collared. P-81 wouldn’t be the last mountain lion to show such genetic defects. After P-81’s capture, as Sikich was doing routine reviews of footage from several different trail cams, two more cats with kinked tails turned up. He couldn’t tell about their testicles, but the kinked tail was bad enough. It is a troubling omen for this small colony of apex predators that belong to a subspecies of Puma concolor, commonly known as the puma, panther, cougar or mountain lion. More than 30 years have passed since the last time scientists discovered genetic defects like these in pumas. Back then they happened across the country to a different puma subspecies, the Florida panther. Despite the gap in time and space, the mountain lions are reproducing two of the exact defects that the panthers manifested—defects that were forecast to doom them to extinction. “It’s certainly a bad sign,” says Stephen J. O’Brien, a genetic epidemiologist at Nova Southeastern University, who worked with Florida officials to save the panthers. “It’s a wake-up call.” Rescuing the Florida panther required an extraordinary intervention by humans. Rescuing the Santa Monica mountain lions will require another extraordinary human effort—but a different kind. Fortunately, there’s a cat up in Hollywood who’s helping, prowling around near the iconic sign overlooking the Hollywood Hills. As recently as the 1700s, pumas roamed all across North and South America. Today their distribution is patchy, but their population still stretches from Canada to Argentina. P. concolor is not exactly the same cat wherever it is found—there are slight genetic differences—but all its members are silent hunters, swift assassins and tenacious fighters, with long, lean bodies built for speed. The males measure six to eight feet from the nose to the tip of their long, heavy tail; females stretch five to seven feet. In a sprint, they can reach 50 miles an hour. Mountain lions are solitary animals. They hunt alone, sleeping by day and emerging at dusk to search for prey. In the wild, they can live for around a dozen years, assuming they don’t get run over or killed by another mountain lion. Santa Monica mountain lion P-81 has genetic defects associated with inbreeding, including a kinked tail. Credit: National Park Service When mountain lions are born, they are adorable little balls of fluffy spotted fur. Once fully grown, though, everything about them screams “predator.” A mountain lion’s body is adapted to hunting, with a light but strong skeleton that anchors heavy muscles. Mountain lions have longer rear legs than other large cats, which makes them capable of vertical leaps of up to 15 feet and horizontal leaps of up to 45 feet. This phenomenal jumping ability enables them to surprise their prey by flying in from above, seemingly out of nowhere. The mountain lion’s heavy tail enables it to keep its balance during such long jumps. If the hunted animal tries to run, the cat’s large paws—nearly five inches wide—provide good traction for turns, a definite advantage during a pursuit. When the cat is ready to kill, its retracted claws pop out to grab onto whatever it has caught. It chomps down hard with its powerful jaws, which are lined with 16 teeth on the top and 14 on the bottom. Pumas play a crucial role in the health of their ecosystems. They keep prey populations in check. And because they seldom devour a kill in one sitting, preferring to eat their fill and hide the rest for later, their leftovers become ready-made meals for more than 200 species of birds and mammals. Then the insects move in, some spending their entire lives in those left-behind carcasses. The insects break down what remains, releasing nutrients into the soil. To make this elaborate chain work, though, the cats need a lot of room to roam. Male mountain lions have a range of around 150 square miles; females, 65 square miles. And that is where the mountain lions of the Santa Monica Mountains have run into trouble. Because it borders sprawling Los Angeles, the 153,000-acre Santa Monica Mountains National Recreation Area is considered the largest urban national park in the U.S. Its valleys have been covered in concrete to create some of the busiest highways in the nation, which serve a still-growing mishmash of residential and commercial buildings. Every new housing development or shopping center whittles away five or 10 acres here, maybe 15 there, fragmenting the landscape and the population of pumas. At its worst, this fragmentation separates males from reproductively available females. As a result, the mountain lion dating pool has become perilously small—something like what happened with the Florida panther. Most Florida panthers live in a low-lying, soggy landscape adjacent to the Everglades known as Big Cypress National Preserve. They are the last remnant of the pumas that Spanish explorers and early settlers called “lions” or “catamounts.” They once roamed the whole Southeast, but by the 1980s Florida panthers were the only pumas east of the Mississippi. As the panthers lost habitat and their preferred prey fled, their numbers dwindled until there were no more than 30. Some estimates put the number in single digits. With such a small population, inbreeding was inevitable. Fathers mated with daughters, brothers with sisters, and mothers with sons. Soon they were producing offspring with kinked tails and undescended testicles. Some even had atrial septal defects—holes in their hearts. It was as if they had hit a biological brick wall. Genetic diversity ensures that a species can survive and adapt to changing conditions. Without it, an infectious disease can easily wipe out the entire group. The genetic defects among panthers were the visible marks of an invisible degradation. Male panther sperm had a ratio of 6 percent normal to 94 percent developmentally malformed, according to O’Brien. Some experts proposed a captive-breeding program to fortify the panther population. The idea was to capture wild panther kittens to raise in a special facility, where they could be selectively bred to create a genetically diverse source population that could be reintroduced to the wild. But the plan never got off the ground, because all the kittens that were supposed to be used for breeding turned out to suffer from the defects. Ultimately state officials persuaded the U.S. Fish and Wildlife Service to approve an unprecedented experiment. In 1995 they dispatched an expert tracker named Roy McBride to capture eight female cougars from Texas and bring them back to Florida, releasing them into the wild to breed with the male panthers. They believed this plan might work because the two subspecies probably interbred in the past, back when their ranges overlapped. Sure enough, five of the eight females produced hybrid offspring that were free of defects. The healthy offspring sparked a baby boom among the panthers. Now an estimated 130 to 200 adults prowl what is left of Florida’s wilderness. Credit: Mapping Specialists; Sources: “Genetic Source–Sink Dynamics among Naturally Structured and Anthropogenically Fragmented Puma Populations,” by Kyle D. Gustafson et al., in Conservation Genetics, Vol. 20; December 2018 (California map reference); “Survival and Competing Mortality Risks of Mountain Lions in a Major Metropolitan Area,” by John F. Benson, Jeff A. Sikich and Seth P. D. Riley, in Biological Conservation, Vol. 241; January 2020 (mountain lion range reference) One reason no experiment like this had ever been attempted before was a fear it would end the legal protection provided by the Endangered Species Act. Critics worried that offspring arising from interbreeding between Florida panthers and Texas cougars might not be considered Florida panthers and thus would not qualify for protection. The Fish and Wildlife Service issued a provisional rule so the experiment could proceed. The other fear: The cougars’ distinctive genes would swamp the panthers’ genetic material. Although they are from the same species of cat, scientists say they have genetic markers that show they are subspecies distinct from each other. Afterward, though, two different studies determined that genetic swamping did not occur. One study examined genetic samples taken from nearly 600 individual Florida panthers that had been collected since 1981 and traced the bloodlines of all the panthers then alive, comparing them with panthers born after the Texas cats were brought in. The study found that the panther population increased threefold, genetic diversity doubled, survival and fitness measures improved, and correlates of inbreeding declined. In the future, the panthers will need to have five Texas cougars introduced every 20 years to prevent inbreeding and reduce the risk of extinction, assuming there is room for them as people rapidly develop the landscape. But as successful as the Florida panther’s “genetic rescue” program has been, California’s mountain lions require a wholly different intervention because they are that much more restricted by habitat fragmentation. The solution to their genetic defect problem, experts say, lies much closer to home. And it involves more concrete, not less. John Benson was thinking about what happened to the Florida panthers while writing up a study on the future of two populations of Santa Monica mountain lions that humans have cut off from the larger group in nearby natural areas. Specifically, the study was trying to forecast the possibility of their extinction within 50 years. Benson, then a wildlife ecologist with the La Kretz Center for California Conservation Science at the University of California, Los Angeles, had previously studied panthers while working for the Florida Fish and Wildlife Conservation Commission, so he knew the story. He viewed what happened with the panthers as a cautionary tale for the mountain lions. Researchers who work with various types of pumas know they’re dealing with charismatic megafauna that laypeople often view as overgrown house cats. In fact, they are attempting to manage large apex predators, each one with its own distinct personality and specific needs. Pumas tend to be elusive and averse to being around humans, further complicating efforts to understand them. Because of the animals’ size, they are sometimes feared by the public, which contributes to political pressure on biologists to minimize risks of a confrontation that might arise from conservation efforts that increase the population. When Benson, Sikich, Sikich’s National Park Service colleague Seth Riley and their colleagues published their paper, they described a couple of different scenarios. According to the computer model, “their reproduction was pretty good … and the population would remain stable,” Benson says. The study found only a 16 to 21 percent probability of extinction, mitigated by their scrubland habitat and the availability of prey. “Although there is lots of development and roads all around, within the Santa Monicas themselves about 90 percent of the area is still natural, or relatively so, and half of it is actually publicly owned,” Riley says. The problem, Riley notes, is that “the Santa Monicas are not big enough by themselves for a viable population genetically or demographically and that they are also not well enough connected to the other nearby natural areas.” When the authors factored in the lack of genetic diversity among the mountain lions, the modeling outcome changed dramatically because of what scientists refer to as “inbreeding depression.” The Santa Monica Mountains population and the one in the Santa Ana Mountains in Orange County already had the lowest genetic diversity documented for mountain lions—aside from that of the 1995 Florida panthers. After accounting for the lack of genetic diversity, Benson says, every run of the model found that once the inbreeding depression began, the cats would probably go extinct in 50 years. Benson and his co-authors had no idea when the paper came out that the first signs of genetic defects would crop up so soon. But they knew it was likely to happen eventually because the biggest obstacle to improving the mountain lions’ genetic diversity had been blocking their path since 1950. Los Angeles is a city of highways, and the biggest one of all is U.S. 101, a major north-south route linking L.A. to San Francisco and the Pacific Northwest. The road varies between eight and 10 lanes of traffic and sees around 300,000 vehicles a day. That highway prevents the Santa Monica mountain lions from getting across to mate with the larger population of mountain lions in the 2,970-square-mile Los Padres National Forest. Once biologists began putting radio collars on the dozen or so mountain lions that they were monitoring in the Santa Monica Mountains, Riley says, they would track the males as they traveled to the 101, saw the river of traffic and then turned back. “The habitat we have there for them seems good,” Riley says of the cats in the Santa Monica Mountains. “They find plenty of deer.” But because of the 101, their only potential mates are close relatives, which leads to inbreeding. A wildlife bridge to be built across Highway 101, shown in an artist’s rendition, would be the world’s largest. Credit: Living Habitats LLC and National Wildlife Federation Then, in 2009, a miracle happened. The 12th puma they had captured and collared, P-12, found a way to cross the road, in an area called Liberty Canyon where there is natural habitat on both sides of the highway. “That was a pretty big deal,” Riley recalls, “because he not only crossed and survived, but he also reproduced.” A handful of other mountain lions have since followed P-12’s lead, mostly at night when traffic is lighter. One figured out how to cross using a six-foot-wide culvert under the 101 and made 42 crossings in less than a year, Riley says. But then that cat died from injuries suffered in a forest fire, and no other cats have set foot in that long, dark culvert since. To California biologists, attempting to help the Santa Monica mountain lions by trucking them to a place with a more diverse puma population or hauling individuals from a more diverse population to breed with the Santa Monica cats like the Florida officials did seemed like too much human intervention, with too much risk for trauma to the wild creatures. Still, the repeated crossings gave the scientists an idea for how to help the Santa Monica mountain lions: Build them a safe place to cross the 101. That way the cats would be reconnected to the larger population of pumas in the Sierra Madre range to the north, which would allow them to find mates capable of boosting the smaller group’s genetic diversity. The Fish and Wildlife Service and transportation officials considered the idea of a tunnel but rejected it. It would cost too much and be too disruptive to the drivers using the highway, and there was no guarantee the animals would use it. That left only one option: An overpass that would soar above the 101 and allow the mountain lions on both sides of the highway to come and go as they please. Fencing built on either end would funnel the lions toward the overpass so they would not wander into traffic. That way there would be no need for humans to capture the cats and move them. “Ideally, if we get them this vegetated overpass built, they’ll do it on their own,” Sikich says. National Park Service officials, after consulting with wildlife-crossing experts and the California Department of Transportation, nicknamed Caltrans, came up with plans for a 165-foot-wide overpass positioned 16 feet above the pavement of the 101. The north end connects to a hillside, and as the overpass reaches the south side it slopes down a bit, Sikich says. If built, it will be the world’s largest wildlife bridge, with an estimated price tag of $87 million. The crossing would be constructed and landscaped to resemble the surrounding countryside, with sound-blocking barriers to quiet the noisy traffic below. The best spot for the overpass, the biologists concluded, would be the place where P-12 first crossed, the spot in Liberty Canyon with natural underbrush on both sides of the road. The lions could use it any time of the day or night without fear of becoming roadkill. The land on both sides of this segment of the highway had already been protected. Even better, it is contiguous with large swaths of protected habitat to the north and south of this connection, thus making it a viable solution for connectivity within the Santa Monica Mountains. Ideally the cats wouldn’t even realize they were on a human-made structure. Conservationists first tried such wildlife overpasses in France in the 1950s, and they have grown in popularity in Europe. They are beginning to catch on in the U.S., too. For instance, in 2018 Utah opened a 320-by-50-foot bridge to allow moose, elk, deer and other wildlife to cross over the six-lane Interstate 80 near Salt Lake City. There is just one problem with the Liberty Canyon bridge: Caltrans had no money set aside for building a highway in the skies whose primary users would be feline predators. That’s where the cardboard cat comes in. Beth Pratt of the National Wildlife Federation had worked in Yosemite and Yellowstone, so she was used to lonesome wilderness areas and their wildlife. Learning that the mountains adjacent to sprawling Los Angeles contained mountain lions was “mind-blowing,” she recalls. “It changed the way I looked at wildlife.” After Pratt became the regional executive director of the environmental group’s California Regional Center, she got in touch with the biologists at the Santa Monica Mountains National Recreation Area and asked if there was anything that her organization could do to help: “And they said, ‘Well, there’s this little corridor we’re trying to build.’” She met with Caltrans officials to talk about it. “Caltrans has been phenomenally supportive,” she says. “They told me, ‘We don’t have the money, but if you get us the money, we’ll build it.’” They worked out a deal in which 80 percent of the money—more than $69 million—would come from private donors and the other 20 percent from public funds for conservation projects. They do not need to raise all the money before starting work. The National Wildlife Federation launched a fundraising drive for the 80 percent, calling it “Save LA Cougars,” and it picked a mascot sure to attract public sympathy: A male mountain lion, P-22, that in 2012, against all odds, took up residence in Griffith Park near the famous Hollywood sign. Genetic tests determined that the cat came from the Santa Monica Mountains population, which means it crossed both the 101 and another major highway, I-405, to reach its current home. Despite the urban setting, Griffith Park offers P-22 plenty to eat and places to hide during the day. But it is the only mountain lion in the six-square-mile urban park, which makes P-22 ideal for the campaign. “We’re talking about a lonely bachelor doomed to never have a girlfriend,” Pratt says. “He has been embraced by the public. We have the perfect relatable victim.” Pratt had a life-size cardboard cutout of P-22 made, which she carries around to fundraising events all over Los Angeles and elsewhere. She has persuaded well-known figures such as actor Sean Penn and Representative Adam Schiff of California to pose with it, drawing even more attention to the puma’s plight. Word of the project has gone viral, she says: “We’ve gotten donations from London, Florida. One Kansas couple who have never been to California have given us $500,000.” Los Angeles even celebrates a “P-22 Day” every October featuring lots of festivities to raise money and awareness of the mountain lions’ plight. Last fall the festival went virtual, as so many events have been forced to do. That required taking a more creative approach to the event, Pratt says. “We got some game developers to create a game interface.” One of the games features P-22 using a jet pack to get out of the park. Some people have questioned the worth of the overpass, though not many. During the environmental review “there were more than 8,000 comments for the project and only 15 against,” Pratt recalls. People have rallied to the cause from all sides of the political spectrum because people love animals, and “this is a tangible problem to solve,” she says. As of May, the fundraising had hit the $44-million mark, more than enough to get the project to the final design and engineering phase. Then, in July, Governor Gavin Newsom approved a state budget that includes $7 million for the Liberty Canyon Wildlife Crossing. Caltrans expects to break ground as early as November. The goal is to have the overpass open for the mountain lions to use by 2024. Pratt says they have no plan B for the cats and don’t believe they will need one. Not hitting their funding targets “would only delay groundbreaking, not cancel the project, but we’re not even anticipating any delays at this point,” she says. But now that P-81 and the other two cats with kinked tails have shown up, the fundraising campaign has become a race to rescue the Santa Monica mountain lions before they are too far gone. “Their genetic diversity is likely to continue to erode,” Benson says. “What no one can say is when it’s likely to lead to extinction. You don’t want to wait until it’s too late.” On the other hand, he reflects, “if we can conserve large carnivores near Los Angeles, I think that bodes well for us being able to do the same thing elsewhere in the country.”