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DNA From Dead Mountain Lion Proves Need for 101 Freeway Wildlife Crossing

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P-12, captured here with a remote camera trap, is the only lion documented to have successfully crossed the 101 Freeway during the course of the decade-long National Park Service study | Photo: NPS


DNA tests performed on a mountain lion that was struck and killed on Route 101 near Agoura Hills underscore the threat the highway poses to the survival of the big cats in the Santa Monica Mountains, according to wildlife biologists working with the National Park Service.

The mountain lion, which was struck and killed October 7 near the Liberty Canyon interchange, was a young male whose DNA showed he originated in the rugged country north of the highway. Had he been able to cross the 101 and head into the Santa Monica Mountains he would have brought a much-needed boost to the Santa Monicas' mountain lion gene pool, which biologists say is showing signs of inbreeding. Only one lion is known to have survived the highway crossing in the ten years in which biologists have been keeping track, according to NPS.

Highway 101 is flanked on either side by undeveloped land at Liberty Canyon, and is a natural wildlife migration corridor between the Upper Las Virgenes Canyon Open Space Preserve (formerly Ahmanson Ranch) and the Santa Monica Mountains National Recreation Area (NRA). Wildlife advocates have long sought a protected wildlife crossing near where the mountain lion died in October, but Caltrans has so far failed to raise the $10 million such a crossing is expected to cost.

"The fact that this young male chose to cross -- unsuccessfully -- at Liberty Canyon shows how critical this wildlife corridor is for maintaining genetic diversity in the Santa Monica Mountains," said Seth Riley, an expert on urban wildlife working with Santa Monica Mountains NRA.

The Santa Monica Mountains may as well be an island as far as its pumas are concerned. The range is nearly completely surrounded by cities, ocean and farmland from Glendale to Oxnard. The Liberty Canyon corridor is basically the only intact swath of reasonably wild land connecting the range with the outside world, and a puma-friendly way to cross the freeway there would provide at least a little bit of room for the big cats to enter and leave the range.

The mountain lion killed in October was very likely looking for new territory. Young male lions generally leave their mothers' ranges when they're about a year old, which allows them to avoid conflict with older resident males. Due to the Santa Monica Mountains puma's isolation from their kin on the north side of the highway, the lions' gene pool is getting stretched a little thin. Scientists have found strong evidence that a male puma may mate with several generations of his female offspring, which isn't good for the population's genetic diversity.

Had the Liberty Canyon male made it across the highway, he'd have brought his genes with him -- potentially making the Santa Monica Mountains puma population much more viable in the long term.

Map of the Liberty Canyon exit showing where the mountain lion attempted to cross, and obstacles to crossing | Map: National Park Service


Caltrans has so far failed to secure grant funding to build the $10 million wildlife crossing tunnel whose proposed location is shown on the map above, according to a National Park Service press release, but an application period for another round of that funding is expected in the next few months.

For the record: A previous version of this story implied that Caltrans might not be giving a high enough priority to getting the wildlife crossing funded and built. This error stemmed from my misinterpretation of a press release. An NPS spokesperson assures me that Caltrans has been an enthusiastic partner in getting the crossing put in. That's great to hear, and I regret my error.

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