The National Park Service says researchers have documented a rare case of a cougar from the Santa Monica Mountains successfully crossing U.S. Highway 101.

The service said Tuesday it's only the second time in more than 15 years of study that a mountain lion from outside the Santa Monica Mountains crossed the freeway to enter the isolated mountain range.

There are only about 15 mountain lions living in the Santa Monica Mountains, and researchers say the small population is rapidly becoming inbred. Within 50 years, the lions could be locally extinct due to inbreeding, according to a 2016 study.

That’s why Seth Riley, a wildlife ecologist with the National Park Service, was so excited when he saw blurry, black-and-white photos taken by a motion-detecting camera of a young male mountain lion emerging from a culvert beneath the 101 freeway near Liberty Canyon Road, about 35 miles west of downtown Los Angeles. Many lions approach the freeway and then turn around, Riley said, but this animal found a way through the culvert.

“That was pretty amazing!” he said. “We were just surprised that he was using that structure. It just shows you how good these animals are at figuring this stuff out.”

Previous studies of the culvert by California State University, Northridge master’s student Sandy Ng had showed zero mountain lions using the tunnel to cross the freeway in a 12-month period between 1999 and 2000. Instead, her motion-detecting cameras captured skunks, raccoons and opossums – nocturnal animals that Riley said are less dissuaded by long, dark tunnels.

Since the cougar was first sighted exiting the culvert earlier this year, National Park Service researchers captured what they believe to be the same mountain lion on the Boeing property in the Santa Susana Mountains and put a collar with a GPS tracker on him. And since then, P-64 has crossed the 101 three additional times and has passed beneath the 118 freeway using an equestrian tunnel.

"That's five freeway crossings in 14 days of GPS monitoring!” said Kate Kuykendall, a spokeswoman for the National Park Service.

Of course, P-64 will only contribute to the genetic diversity of the Santa Monica Mountains population if he stays put and reproduces — or if he isn't killed, either by another male mountain lion in a fight or in a vehicle collision. Eighteen mountain lions have been hit and killed by vehicles since 2002, when the National Park Service began tracking them.

Riley said even though one mountain lion seems to have figured out how to use the culvert, it doesn’t necessarily mean other cougars will do the same. In fact, he says they may be put off by the frequent presence of a large, male lion.

“They’re the biggest, scariest thing out there,” Riley said. “Adult males fight with and kill young males on a regular basis. That’s the source of mortality that we’ve seen most commonly in our study.”

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A planned landscaped wildlife overpass would be more amenable to mountain lions and other animals like bobcats and deer that are currently hemmed in by the 10-lane 101 freeway.

Caltrans will design and build the bridge, but the state agency won’t fund it. Instead, environmental activists are trying to raise $60 million by 2020 to pay for construction. As of early February, they had raised just under $4 million.