How Many Mountain Lions Crossed the 101 Before a Cat Bridge Was Finally Built? Too Many

It hasn’t happened yet

The Santa Monica Mountains cover a wide expanse of land. They stretch 40 miles—from the Hollywood Hills in the east to Point Mugu in the west— and contain some 500 miles of hiking trails punctuated by curving canyon roads and splayed across a mosaic of federal, state, county, and city parks.

Despite all that space, the Santa Monicas aren’t big enough for the mountain lions that inhabit them. Don’t let P-22 fool you; he is surviving in the eight square miles of Griffith Park, but most male mountain lions need something closer to 200 square miles to thrive.

That’s why a 17-month-old male mountain lion dubbed P-32 ventured north out of the Santa Monicas on April 3. Most mountain lions that dare to cross the 101 freeway in search of more personal space and resources don’t make it to the other side. Big cats have not evolved to understand cars; our big fat primate brains are barely better at navigating L.A. traffic than theirs are, after all. Amazingly, P-32 survived.

It’s only the third time wildlife biologists with the National Park Service (NPS), who have been monitoring the mountain lions of the Santa Monica Mountains National Recreation Area for nearly 15 years, have been able to record evidence of a lion successfully crossing the 101.

The first time was in 2009, when a male called P-12 crossed the freeway from north to south, adding a bit of much-needed genetic diversity to the population in the Santa Monicas. His genes proved to be of limited utility, however. P-12 has since gone on to mate and produce kittens with one of his own daughters; P-12 is both father and grandfather to P-32.

The second successful crossing happened last month, when P-32’s sister, P-33, made it across the 101 alive. Because the cats are outfitted with radio collars, NPS researchers were able to work out that P-32 and P-33 crossed the 101 within a mile of each other, traveling north along highway 23 towards the Simi Hills. P-32 made his way into the undeveloped landscapes of Simi Valley, where history tells us he will attempt to establish a territory and find a mate. His sister meanwhile wound up wandering back towards the 101 where she first crossed.

P-32 and P-33 got incredibly lucky—and could grab some much-needed attention. That’s because their movements further underscore the need for a wildlife crossing, a car-free route that provides animals safe passage over the busy Hollywood Freeway. Creating one would be an admittedly difficult task in a landscape dominated by roads, but it’s the mountain lions of L.A.’s best chance at survival.

Wildlife advocates are currently working to raise $4 million dollars to fund the planning of such a crossing through the #SaveLACougars campaign. Using scientific research, the campaign’s leaders have determined that Liberty Canyon is the best place to put one, and they’ve raised some $1.1 million already.

Of course, mountain lions aren’t the only critters that stand to benefit from an animal crossing. Data from the California Roadkill Observation System show that mammals, birds, amphibians, and reptiles would also gain from a car-free passage. Coyotes, deer, raccoons, squirrels, opossums, rabbits, snakes, lizards, and frogs would all be much happier. Even butterflies seem hemmed in by our highways.

The smaller of our native felines, bobcats, also suffer from a lack of connectivity caused by the L.A. freeways. In an article published this month in the journal Evolutionary Applications, urban carnivore researcher Laurel E. K. Serieys reported that the 101 and 405 separate our bobcat population into three genetically distinct groups: one east of the 405, one west of the 405 and south of the 101, and a third north of the 101. Because they’re isolated, each of the groups has a lower chance of surviving a disease outbreak. That’s exactly what happened between 2002 and 2005, when the group north of the 101 experienced a severe decline due to mange brought on by overexposure to rat poison. The same illness briefly afflicted P-22 last year, too.

Like mountain lions, our bobcats risk suffering from the effects of inbreeding unless they can find ways to cross those busy highways. The wildlife bridge under consideration for Liberty Canyon may not sound as exciting as a park over the 101, but it’s a matter of life and death for the frisky cats looking to meet up, hang out, and swap DNA on both sides of the freeway.