Cougars in OC mountains reach dangerous levels of inbreeding

Cougars in the Santa Ana mountains between Orange and Riverside counties are seeing the lowest genetic diversity ever reported for a puma population since the Florida Panther, which almost went extinct because of it.

That’s according to new research overseen by UC Davis and involving scientists from the University of Wyoming and the University of Massachusetts-Amherst. 

The research collaboration - divided into two studies - found that lions in the Santa Ana mountains are extremely isolated due to the busy 1-15 freeway. There is a genetically distinct population of lions to the east, but the freeway makes it virtually impossible to cross over to the isolated population to the west.

“I thought they would find a way, but they’re just not finding a way enough,” said Winston Vickers, a researcher and veterinarian at the UC Davis Wildlife Health Center.

Mountain lion populations are extremely isolated in Southern California due to highways like the 1-15, which cut off genetically distinct populations from each other.

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UC Davis

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Vickers said that many lions are struck and killed on the highway as they attempt to cross into the mountain range. This adds to their high mortality rate. 

A UC Davis study released in 2015 found that that humans were the primary cause of mountain lion deaths.

The plight of mountain lions in the region around the Santa Monica mountains is well-documented through a study by the National Park Service and the popularity of one lion - P22 - with his own Twitter account. 

But lead author Kyle Gustafson, a postdoctoral conservation geneticist with the University of Wyoming, told KPCC that mountain lions in the Santa Anas are faring worse. 

"It's somewhat of a joke, but we like to say we're competing for the worst mountain lion population," Gustafson said. 

But the research also showed the positive effect of even just one mountain lion defying the odds. 

Gustafson told KPCC that the Santa Ana population significantly increased their genetic diversity as a result of one male lion producing 11 offspring. 

The lion - called M86 - was the only one of seven male lions in the past 20 years who crossed into the Santa Ana mountains to successfully reproduce. 

"In general, scientists don't think individuals make big contributions to populations," Gustafson said. "But our study clearly shows that an individual can make a major impact on a population, especially when times get tough."

The biggest struggle in the region is simply keeping those genes alive, Gustafson said. M86 was struck and killed by a car between 2014 and 2015. And only a handful of his offspring remain alive in the wild. 

“He had a positive genetic impact - but that’s over 15, 16 years, that’s definitely not enough," Vickers said. 

Researchers with the UC Davis collaboration say a wildlife corridor to areas east of the 15 would help restore the cougar population in the Santa Anas.

But Gustafson said there's no current funding source identified for these structures.

A temporary solution might be to physically transport lions from one population to the other, but "there's no guarantee" that they would mate, he said. 

Senior author Holly Ernest, a wildlife population geneticist at the University of Wyoming, says the outlook is bleak unless the lions are able to move more freely. 

"Without some kind of continued migration, we expect the genetic diversity to decrease as fast as it did before," she said.