Southern California Mountain Lions Face Local Extinction

Mountain lions in Southern California are isolated from each other due largely to urban sprawl and freeways that disconnect their populations. (Johanna Turner via UC Davis)

Lions once prevalent over two Southern California mountain ranges could disappear entirely within 50 years, risking local extinction because of conditions both environmental and genetic.

That’s the conclusion of a new study published in the journal Ecological Applications that uses 15 years of observational data, modeling and DNA analysis to analyze how cougar populations are changing in the Santa Monica and Santa Ana mountains.

The coastal Santa Monica range is home to about 15 mountain lions; 30 more survive in the Santa Anas, straddling Orange and Riverside counties. They’re penned in by a century of development, ranch and agricultural land, and freeways – U.S. 101 in the Santa Monicas, Interstate 15 in the Santa Anas – that are two of the busiest in the world.

Humans are often to blame for mountain lion deaths: cars and rat poison are two common killers.

“Our research has shown that the mountain lions in the coastal Santa Ana Mountain Range are primarily put at risk by restriction of their movement across I-15," says T. Winston Vickers, an associate veterinarian at UC Davis who co-authored the report, "and their high mortality rates from vehicle collisions and being killed after they have killed unprotected pets or livestock.”

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The study pegs the chance of local extinction for the two lion populations at between 16 and 21 percent on the basis of geographic factors alone. And authors say inbreeding caused by the tiny available genetic pool could itself cause rapid extinction. Seth Riley, a co-author on the study and a National Park Service wildlife ecologist, called that result “sobering.”

But the report's lead author says the group’s modeling offers reason for optimism, too, in that enabling lions to cross freeways could minimize risks.

“It wouldn’t actually take a whole lot more movement of mountain lions," said John Benson, an ecologist at the University of Nebraska. "Just one every couple of years maybe, where these populations could maintain their genetic diversity and decrease their extinction probability.”

Engineered wildlife crossings carry steep price tags. One proposed at Liberty Canyon, near the 101 freeway in Agoura Hills, could cost $60 million. If funded, it could break ground within three years.

Benson says it would offer permanent benefits and an example to other communities.

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“If we’re able to do it here in Los Angeles, we can probably do it anywhere,” he says.

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