L.A.’s Cougars Were Driven to Extremes by Wildfire

When the Woolsey Fire ripped through neighborhoods west of Los Angeles in 2018, plenty of celebrities were evacuated, and some, including Miley Cyrus, Gerard Butler and Neil Young, lost their homes to the flames. Four years later, many wealthy and famous Malibu residents are back on their feet. But out of the limelight, some of the area’s most reclusive inhabitants are still facing dangers in the burn’s aftermath.

Scientists tracking the mountain lions around L.A. have found that the big cats, already squeezed for space and forced to run a gauntlet of roadways, began taking a lot more risks after the Woolsey Fire. Using GPS collars to compare movements of mountain lions before and after the Santa Monica Mountains blaze reveals that the animals avoided about half of their previous habitat, which was turned into a “moonscape” by the flames. This led the cats to attempt more dangerous behaviors, like crossing highways and moving about in broad daylight, which make them vulnerable to injury or death by cars and trucks. L.A. residents won’t much notice the new behaviors, however, because the big cats’ aversion to humans remains intact. Even with far less wild space to roam, the animals showed no inclination to venture more often into neighborhoods or heavily populated areas, according to the study published today in Current Biology.

“I love that they were able to fill in some of those gaps about what’s happening in this immediate post-fire landscape, when everything looks really different,” says Megan Jennings, an ecologist at San Diego State University who wasn’t involved in the research but has studied the effects of fire and urbanization on California cougars. “It’s a look at how these animals are adapting, and what that means for how they bounce up against things like roads and development.”

Among the world’s megacities, only L.A. and Mumbai have big cats living within the city limits. The National Park Service and its collaborators have studied this incredible California population for two decades, in its stomping grounds around the Santa Monica Mountains, the Santa Susanas and the Santa Anas.

Living in proximity to some 18 million people poses serious challenges for mountain lions—also known as cougars, panthers and pumas—who prefer wild environs. Urban development has crowded the solitary, territorial animals into smaller spaces than they’d normally roam. One study area of the Santa Monica Mountains south of U.S. Highway 101 is home to at least eight male mountain lions, though it would only be home to one or two if their ranges were of typical size. Conflicts between territorial mountain lions in these close quarters are the top cause of mortality among subadult mountain lions, and full-grown males there have killed adult females and kittens—including their own offspring.

Big cat habitat is fragmented by the city’s famously trafficked roadways, which pose mortal dangers to mountain lions. Mountain lion P-90, killed in August while crossing Highway 33 in Ventura County, was the seventh radio-collared cat that was part of the research study to lose its life on the roads this year. His brother, P-89, was killed on Highway 101 in Woodland Hills just a month earlier.

Perhaps most troubling of all, mountain lion isolation is making it difficult for the animals to mate, and some studies suggest that trend, if not reversed, could lead the local population to extinction. Earlier this year, a study of mountain lions in the Santa Monica and Santa Ana Mountains revealed the first troubling signs of inbreeding, with a few cats sporting deformed tails, abnormal testicles and defective sperm that signify reduced fertility. These genetic findings echo those that appeared among inbred and endangered Florida panthers during the 1990s, before those tiny populations were diversified with transplanted Texas mountain lions.

Unfortunately, the new research suggests that wildfires like the 2018 Woolsey Fire have stacked the deck further against the already imperiled population and led the cats to adopt more desperate and dangerous behaviors.

The study used tracking data from GPS collars, part of the larger data set co-authors Seth Riley and Jeff Sikich have compiled in two decades of researching the cats with the National Park Service. The authors mapped the recorded movements of 17 mountain lions and compared their behavior during the 15 months prior to the fire with that of the first 15 months after the fire—showing the changes caused by the disastrous event that burned 96,000 acres.

“Most of these animals are able to get out of the way, and they don’t die in the fire,” says Riley, a wildlife ecologist with the National Park Service at the Santa Monica Mountains National Recreation Area. “So, the effects that we were interested in were what happens afterward. We knew that it would have a big effect on what these animals do.”

They found that L.A. cougars upped their monthly traveling from about 155 miles before the fire to 250 miles afterward, looking for mule deer to ambush or, in the case of young males, new territories. In urban landscapes, that means putting their lives at risk. The cats crossed roads an average of five times per month after the fire, compared to three times per month before—a 67 percent increase. When it comes to the massive 10-lane U.S. Highway 101, the cats attempted to cross it about once every four months. Before the fire, they would go an average of two years between crossings.

Though they live around one of the world’s largest urban areas, L.A.’s mountain lions aren’t seen very often, because they take pains to avoid humans. Last year, the National Park Service published a study analyzing 15 years of tracking data showing L.A.-area cougars avoid neighborhoods, golf courses, cemeteries and other human habitat—spending only about 1 percent of their time in what would be considered urban areas.

“I think that a lot of people had the idea that after the Woolsey Fire mountain lions would just start pouring out into the urban landscape,” says co-author Rachel Blakey, a biologist with the University of California, Los Angeles. But after the fire, the new study shows, the cats continued to avoid human environments just as they had before.

“It just goes to show to what lengths they go to avoid encountering humans,” Blakey says. “They’d rather run across a 10-lane freeway than hang out with you.”

One reason cougars likely avoid areas scorched by the Woolsey Fire has to do with their hunting technique. New vegetation that sprouts in recently burned areas is a food source that can attract mule deer, which make up as much as 90 percent of the local mountain lion diet. However, the ambush predators rely on cover and concealment to surprise their victims, making the barren post-fire landscape an unproductive hunting ground.

How this shrubland bounces back from the fire will likely impact mountain lions’ survival. Blakey and colleagues are studying plant regeneration by using laser mapping technology known as LiDAR to quantify 3-D vegetational structure, and pairing that information with cougar tracking data to learn how the animals do—and don’t—use the post-fire landscape.

The local environment is dependent on a natural fire regime, regenerating after periodic burns, Jennings, the San Diego State University ecologist, says. But fires are now occurring more frequently, which makes it difficult for shrubs to seed and regenerate. That raises the possibility that the area could convert to grasslands or other environments. “Where the Woolsey Fire was, that area around Malibu has burned, and burned, and burned,” Jennings says. “What’s the long-term outlook for that segment of habitat that’s been left for these mountain lions? Is it going to be unsuitable at some point? I think it’s important that we start looking at that.”

Though threats from future fires may loom, the worst impacts of the Woolsey Fire appear to be diminishing. “So far, they have weathered the storm of that giant fire,” Riley says. “We’re now a couple years further on than those first 15 months post-fire, and they have started to use some those burned areas more than they did in those early months.”

Some help is also on the way, giving mountain lions a chance to do what many animals prefer when faced with a fire landscape—move. Earlier this year, workers broke ground on the Wallis Annenberg Wildlife Crossing, which will be the world’s largest such bridge, allowing mountain lions and other animals to safely move out of the Santa Monica Mountains and north over Los Angeles’s 101 into the Simi Hills and beyond. The project will reconnect an ecosystem that has been split since the construction of the highway. While not a panacea, Blakey believes the crossing may bring some relief to several issues facing the area’s mountain lions—including their ability to survive and adapt to fire.

“In the event of these big disasters that happen frequently in California, it will be able to help these animals move in and out of areas safely,” she says.

Brian Handwerk | READ MORE

Brian Handwerk is a science correspondent based in Amherst, New Hampshire.