Environment & Science

Inbred mountain lion crosses the 101 Freeway

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In an encouraging sign to biologists trying to preserve genetic diversity among a population of mountain lions splintered into small groups by manmade obstacles, the first monitored mountain lion in more than a decade has crossed the 101-Freeway from its normal range into new territory.

It's the first documented case of a puma dispersing out of the Santa Monica Mountains; only one other mountain lion has ever been shown to have made it across the 101. “It’s only the second time in 13 years now since we’ve been doing the lion study,” said Seth Riley, a wildlife ecologist with the National Park Service. “We’ve had one crossing, one time before this.”

An effort is currently underway to raise funds for a wildlife crossing at Liberty Canyon, further east in the Santa Monica Mountains. It's hoped such a crossing would increase the flow of genetic material in and out of the range.

“When you have reduced genetic diversity, you definitely can create issues with more susceptibility to disease,” Riley said.

The female mountain lion known as P-33 had recently been photographed by a wildlife camera, feeding on a deer carcass with her mother and sibling.

Now, about a month later, the puma has left her home range and crossed the 101 in the Camarillo area at the far western end of the Santa Monica Mountains. 

Map of P-33's crossing point

Inbreeding is a problem

Crossing the 101 seems to be in P-33’s lineage. Her father and grandfather also successfully crossed the deadly stretch. The fact that her father and grandfather are the same mountain lion highlights one of the biggest problems facing this population: inbreeding.

The male mountain lion P-12 most likely crossed into the Santa Monica Mountains near Liberty Canyon in early 2009. He brought much-needed fresh genetic material to the population when he began mating with females. However, that benefit has waned, as he has mated with his own daughter.

Cougar P-33 was part of an inbred litter sired by P-12 onto his daughter P-19. The litter was discovered in November 2013 and was the third known to be the result of inbreeding. 

The population of pumas has among the most restricted genetic pools west of the Rocky Mountains. If inbreeding becomes too common, it can eventually result in sterility, birth defects and lowered immunity.

The road ahead

Now that she has crossed, it’s unclear in which direction P-33 will continue to move. Currently, she’s in a portion of the Simi Hills, an area Riley said is possibly large enough to support her. The patch, however, is less likely to contain a male with which she can mate.

Larger open space is in the Santa Susana Mountains between the 118 and 126 freeways. However, that would necessitate traversing developed portions of land and crossing yet another highway.

If she does make it to the Santa Susana Mountains, she will be closer to the Los Padres National Forest to the north. The forest encompasses a giant swath of habitat Riley said is believed to contain multiple populations of mountain lions.

He said increased opportunities to come across unrelated males would benefit her lineage, though it still doesn’t address the issue of isolation for her kin.

“From the perspective of the population in the Santa Monicas, movement in the other direction is much more important,” he added. “But it’s still a good thing. We prefer that lions in the Santa Monicas have a chance to emigrate out as well.”

“Now, she’s not going to mate with her father, if she stays up there,” he added.