Los Angeles mountain lions are becoming inbred, a troubling sign

Cut off from each other by roads and development, the cats have a dangerous lack of genetic diversity—but there is hope on the horizon.

Los Angeles is the only major metropolitan area in the world with a bevy of mountain lions, hunting and breeding in the hills above gleaming houses and suburbs. Some of these intrepid cats have become famous, such as the bachelor P22, which inhabits Griffith Park, a hilly region home to the iconic Hollywood sign.

But these large cats—also called cougars—are in trouble. New research shows that they are seriously inbred due to habitat fragmentation, caused primarily by major roads and highways, especially Route 101, which restrict movement and gene flow. Unless connectivity is increased by creating what’s known as wildlife corridors, these L.A. lions are likely to become locally extinct in the coming decades, experts say.

In a study published recently in the journal Theriogenology, scientists found that nine mountain lions in the Los Angeles area have either very high levels of abnormal sperm or possess kinked tails, both signs of a serious lack of genetic diversity. Two cats also had testicular abnormalities, which are likewise known to be manifestations of inbreeding. With only several dozen lions in the L.A. region, this result represents a significant proportion of the overall population. 

Some of these indicators—observed between December 2019 and December 2020, both as part of standard research efforts and roadkill necropsies—appear in the lions throughout the metropolitan area and its outskirts. Prior to this study, only one cat had been observed in the region with a kinked tail, in 2019.

“We’ve just reached a tipping point genetically,” says Audra Huffmeyer, a postdoctoral researcher in conservation biology at the University of California, Los Angeles, and a National Geographic Explorer

To survive long-term, more mountain lions need to be free to move into and out of the two most isolated areas where the animals live—in the Santa Monica Mountains northwest of the city, and the Santa Anas, to the southeast. 

Luckily for the cougars, a large new wildlife overpass will soon be constructed over the 101 to allow the animals safe passage. The project’s ceremonial groundbreaking took place on April 22, 2022—Earth Day—and will open in 2025.

“I think this crossing can stave off extinction” for the Santa Monica population, says study co-author Seth Riley, a wildlife ecologist with the U.S. National Park Service who also teaches at UCLA. “We are very confident that it will be super helpful for everything [wildlife], including mountain lions… by increasing connectivity.” 

Wide-ranging felines

Mountain lions once roamed throughout the majority of what is now the continental U.S. Widespread hunting, often government-sponsored, greatly reduced the cats’ range, mostly to the western part of the country, by the mid-1900s. The felines, which live throughout much of Central and South America, are also known as cougars, pumas, catamounts, and their scientific name, Puma concolor.

Florida panthers, currently recognized by the government as a subspecies of mountain lion, managed to hang on in the wilds of South Florida. But they become seriously inbred, with no connection to any other population, developing high levels of malformed sperm, testicular deformities, and kinked tails. This population was rescued by the 1995 introduction of eight female Texas cougars, five of which bred with the Florida panthers, reversing the population’s decline and improving genetic diversity.  

In the 1980s, before their genetic rescue, three-quarters of Florida panthers observed had kinked tails and more than half had testicular abnormalities—a far greater proportion than is seen in Southern California today, says Dave Onorato, a researcher with the Florida Fish and Wildlife Conservation Commission who wasn’t involved in this study. 

But in Los Angeles, Onorato says, “they are starting to see the signs, and that probably warrants getting the alarm bells ringing.” (Learn more: How America’s most endangered cat could help save Florida.)

Concerning evidence

Riley and many collaborators have been researching mountain lions in the Los Angeles region for two decades.

To conduct the most recent study, Huffmeyer and colleagues collected observations of mountain lion sightings throughout the Los Angeles area. Around a dozen of the cats live in the Santa Monica Mountains, and up to 12 more reside to the north, in the Santa Susanas, a range separated by Highway 101. Around 20 live in the Santa Anas, southeast of the city, and considerably more live in the Eastern Peninsular Range, further inland, according to Winston Vickers and Justin Dellinger, biologists with the Wildlife Health Center at UC Davis School of Veterinary Medicine.

Between December 2019 and December 2020, the researchers observed three animals with kinked tails in the Santa Monica and Santa Susana populations using camera traps. A fourth, which researchers examined in person in the Santa Monica mountains, had only one descended testicle, and a kinked tail.  

Huffmeyer also tested sperm quality in five cats that died from being shot, killed by rat poison, or hit by a car—from the Santa Monica, Santa Ana, and Eastern Peninsular Range populations. On average, 93 percent of these cats’ sperm was malformed. That’s a high number—about the same percentage of deformed sperm seen in Florida panthers before they were genetically rescued, Onorato says.  

Helping the lions

To increase genetic diversity, more cats need to be able to travel in and out of these isolated populations. On April 22, a consortium of environmental groups broke ground on the Wallis Annenberg Wildlife Crossing. The $90-million bridge will cross over 10 lanes of traffic on the 101 Freeway and allow mountain lions, coyotes, deer, and many other creatures to pass between the Santa Monica and Santa Susana Mountains.

The passage was chosen to be located in the Agoura hills, a rugged region which wildlife are naturally funneled toward, and researchers have no doubt it will be used by wildlife, especially wide-ranging species such as lions. 

But more wildlife crossings will be needed to save cougars, for example across Interstate 15, which separates the Santa Anas from mountain lion populations to the east. Translocation, or physically bringing in cougars from elsewhere to supplement the population’s diversity, might be considered one day, Huffmeyer says. But it’s a last resort. 

For now, scientists look forward to the completion of the new crossing on the 101—and to the mountain lions that could pass over. 

“You don’t need a huge number to make a big difference genetically,” Riley says. 

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