Invites like this are rare, almost as rare as the cats themselves. That’s because tracking, trapping, darting and swapping out radio collar batteries and taking tissue samples is stressful on the animals — and researchers. But it’s an essential stage of a 13-year study that’s building a case for the construction of a wildlife bridge over a 10-lane freeway, a $55 million project that looks like the last hope for L.A.’s lions.

“Without increasing connectivity and basically building wildlife crossings like a tunnel or an overpass, I think the mountain lions here are definitely going to be lost,” Park Service wildlife ecologist Seth Riley said.

The lions in the Santa Monica mountains, the range bisecting the nation’s second-largest megacity, are living on borrowed time. Hemmed in on all sides by freeways, the Park Service says the only option is to link these cats with their neighbors to the north and east in the Santa Susanas and Angeles National Forest.

Isolation means increased competition for territory and mates. An adult male’s home range can extend over 200 square miles, and the Santa Monicas total a mere 275 square miles. About 12 to 15 lions live here, and there’s enough prey to keep the population healthy. But this bottleneck has anomalous side-effects — for cats. Inbreeding is rampant. Adult males frequently kill younger rivals, even sons or brothers.

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Human-lion encounters in L.A, on the other hand, are rare. A cat was found in a crawl space under a Los Feliz home last year before leaving without incident. In 2012, a juvenile male wandered into downtown Santa Monica and was killed by police officers before the Park Service could arrive and dart him.

“I wasn’t able to get there in time, and they shot the cat,” said Jeff Sikich, the Park Service field biologist who since 2002 has trapped 47 lions in more than 100 captures, without injury to man or beast.

They’re called ghost cats for a reason — mountain lions avoid humans whenever possible. But young lions are so desperate to establish new territory and procreate, 12 have been killed attempting to traverse freeways since 2002. Some have died from eating prey laced with rodent poison.

Only once, in 2009, has a lion born outside the Santa Monicas made it across Highway 101. Genetic diversity among these cats is the lowest of any population in the Western United States, a trend that would likely lead to infertility and this group’s extinction.

Hence the proposed crossing at Liberty Canyon, a stretch of the 101 near the suburb of Agoura Hills. GPS tracking has shown lions frequent the area. So do bobcats, deer and coyotes, all of which could use the crossing to travel back and forth, establish new territory and escape the metropolitan sprawl. Humans could hike it as well.

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Wildlife bridges have been built before, but never in such an urban environment, and never over a freeway that sees nearly 175,000 vehicles a day. This crossing would be vegetated to mimic the surrounding landscape and elevated over the freeway and an adjacent road.

Despite the price tag, the project is widely supported. Unlike in more rural environs such as Montana or Canada, where modest crossings exist, there are no ranchers or farmers to contend with here, nor are large numbers of domestic livestock at risk. The Park Service has also forged an ally in Caltrans, the state transportation agency that’s already funded a $200,000 environmental design study and vegetated the area.

The Park Service’s work has created a cause célèbre whose poster child is a lion dubbed P-22. The 125-pound, five-year-old male somehow navigated the width of the city and several freeways before landing in Griffith Park, where he was photographed in an iconic National Geographic image in front of the Hollywood sign. But P-22 is now the only lion in an eight-square-mile oasis.

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Next Steps

Fundraising for the crossing is being led by a National Wildlife Federation veteran so dedicated that she inked a six-inch effigy of a lion on her left bicep and plans to donate the proceeds of her new book on lions to the project.

Beth Pratt-Bergstrom, the federation’s California director, said she’s targeting private backers and state and federal conservation funds in a grass-roots campaign that’s even tapped actor Rainn Wilson for support. So far, only about $1.1 million has been raised.

“We have a goal of $10 million by 2017, and then the remainder by the summer of 2019, with shovel ready, ready to begin construction early 2020,” said Pratt-Bergstrom. “I know it’s going to happen.”

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To those worried that the crossing will trigger a lion population boom, Sikich replies that the land’s lion-carrying capacity has already been reached. In fact, he believes this will create fewer human-feline run-ins, because it allows lions to spread out and spread their genes. Now the question is: Can the cats hold out while the project raises funds?

On Track

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When I get to the pin drop location, a shopping mall parking lot on the western edge of the Santa Monicas, the waiting biologists are anxious, like a sports team before a big game.

The night before, a female lion had taken down a coyote. Hoping she would return to finish the carcass, Sikich had placed the canid’s remains in a box trap connected to a GPS transmitter that sends an SMS when the trap’s door closes. Sikich uses GPS points from collars to track movement. Collars are fitted with VHF, allowing researchers to listen through receivers and antennas. The plan: Wait and see if she returns and springs the trap.

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“These cats are crepuscular, and if P-33 is going to return to that kill, she’s probably coming back at sunset,” he said.

We waited two hours, but the lioness never did return. So I got back in my car, back on the freeway, back through the urban-wild purgatory.

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The next morning, Sikich hiked to the kill and removed the trap. P-33 is still slated for recapture; the question is when. It’s been nearly a month and I’m still on standby. The wait is tedious, but the prize will be great. How many Angelenos have been face-to-face with the lions that live in their back yard?

Adam Popescu is a Los Angeles-based freelance writer. Find him on Twitter at @adampopescu.