Mountain Lion Movement Across a Fragmented Landscape

Highways and housing developments straddle the hills and valleys of Southern California, cutting across the landscape from Los Angeles all the way down to San Diego and into Mexico. Southern California came to prominence with the rise of the automobile, making it a signature example of how urban sprawl can encroach on the natural territory of wildlife.

If we keep building without attention to these issues, we’re going to keep creating more pockets of isolation where animals can no longer connect with each other.
— Winston Vickers, Southern California Mountain Lion Project

One species feeling the effect is the mountain lion, whose survival is dependent entirely on its ability to range widely across the landscape to hunt and establish territory. Predator-prey dynamics have evolved so that the prey knows when the predator is near; therefore the predator must be constantly on the move in order to catch the prey by surprise.

Because mountain lions are not hunted by humans in California, many people have no idea that they are under significant stress in some parts of the state. But their struggle is complex. Mountain lions and other wide-ranging animals in Southern California have essentially become boxed in by the human world that surrounds them.

 Interstate 15 splits the mountain lion territory in two. 

Interstate 15 splits the mountain lion territory in two. 

They are threatened by vehicle strikes as they cross roads. They are killed through depredation permits by landowners who have lost livestock to them. The inability to cross large highways has resulted in a loss of genetic diversity, leaving them exposed to birth defects and diseases caused by inbreeding.

The three mountain lions featured below were tracked with GPS collars by researchers with the Karen C. Drayer Wildlife Health Center and collaborative partners. Strategically placed motion-sensing trail cameras photographed and videotaped them as they moved through undercrossings. Animals were sampled so that their genes could be analyzed to measure genetic diversity.

Each mountain lion tells a different slice of the story, which is the ongoing struggle of the species in Southern California. 


Retrace the steps of a mountain lion who traveled more than 100 miles and crossed several major highways before meeting his end.

Young male mountain lions are the most likely to carry genes from one territory to another because they range so widely. Such travel is key to increasing genetic diversity in populations. 

During a three-and-a-half week period, M56 (Male #56) crossed many large highways, including Interstate 5 multiple times. Through his travels, he managed to avoid succumbing to the top cause of death for mountain lions in the Santa Ana Range: vehicle strikes.

He traversed more than 100 miles across highly fragmented landscapes from Orange County all the way to the Mexican border across all kinds of terrain, both urban and natural.

But his story ended abruptly: He killed several inadequately protected sheep on private land and was promptly killed when a local person obtained a depredation permit. His GPS collar stopped moving, and just like that, his story was over.

“M56 was killed doing what we expect any predator to do if encountering a ‘free meal’ like inadequately protected small livestock," said Winston Vickers, who co-leads the Southern California Mountain Lion Project for the Karen C. Drayer Wildlife Health Center. "Livestock owners, especially those with small livestock like goats and sheep, need to have their animals in a fully enclosed pen with a solid roof from dusk to dawn. As veterinarians, we have just as much concern about the domestic animals as we do the mountain lions; it's a matter of protecting them from a natural threat.”

Even after surviving his long journey across dangerous highways and interstates, he was killed by the number one cause of death in the Peninsular Range: depredation permits.

Such is the challenge for a young male mountain lion looking to establish territory.


Cut off by freeways and human development, mountain lions in Southern California are facing a severe loss of genetic diversity.

A recent study published in PLOS ONE and conducted by the Karen C. Drayer Wildlife Health Center at UC Davis in partnership with The Nature Conservancy, raises concerns about the long-term outlook for mountain lions in the Santa Ana Mountains and across Southern California.

The Santa Ana range is surrounded by urbanization and a growing population. A small habitat linkage to the southeast connects mountain lions to the Peninsular Range, but it is bisected by the bustling Interstate 15 and other associated human development. There is very little connectivity remaining for the mountain lions in the Santa Anas, which is where F89’s story takes place. 

F89 is a female mountain lion who mothered the children of M86 – the only mountain lion that the team has confirmed migrated west across the 10 lane highway, Interstate 15 – an extremely rare occurrence. M86 had not yet been collared when he crossed the Interstate; researchers learned of his origin after they trapped him and analyzed his genes.

As you can see in the family tree above, F89 gave birth to three kittens. 

One of the males was killed on the 241 Toll Road, which was built in the late ‘90s to connect Interstate 5 to the heavily traveled 91 freeway. The 241 cuts directly through mountain lion territory and has been the scene of numerous vehicle strikes over the years. The Foothill/Eastern Transportation Corridor Agency, which oversees the toll road, is currently constructing a fence along a portion of the highway to attempt to reduce mortalities of mountain lions and other wildlife.

They sit there and they ponder crossing, but they do not cross the I-15 to make that connection.
— Trish Smith, The Nature Conservancy

The other male died of unknown causes in November of 2014. Foul play on the part of a landowner is suspected, but tests are still being run to confirm.   

The only surviving offspring of F89 is F92, who gave birth to three kittens, two of whom survived and appear to have dispersed from their mother. They represent a glimmer of genetic hope for the population, but the long-term problem is much larger:

Interstate 15 is a behemoth, and it, along with adjacent development, are absolutely blocking the movement of mountain lions.

“Improvements need to be made to I-15 to ensure safe passage under or over that roadway for mountain lions and a variety of other species,” said Trish Smith, a Regional Ecologist with The Nature Conservancy. “We know they stop and they sit there and they ponder crossing, but they do not cross the I-15 to make that connection.”

For a textbook example of why genetic diversity is important, look to the Florida panther. Loss of genetic diversity among the panthers had become so severe by the 1990s that panthers were having trouble reproducing. Several of those that did reproduce had babies with heart defects. Millions of dollars have since been spent on their slow recovery.

But researchers believe it’s not too late to protect the region’s mountain lions.

“I think there could be hope for this population,” said lead author of the PLOS ONE study, Holly Ernest, a former professor with the Karen C. Drayer Wildlife Health Center. “They’re at a point where they can be monitored and protected. They don’t have to end up like Florida panthers. With early interventions, we wouldn’t have to spend millions and millions of dollars later.”

F89, fitted with her tracking collar

F89, M91 and M93, all of whom are dead. 

F92 and her kittens. 


Click and slide the blue bar right and left to compare the mountain lion GPS points to the landscape. Interstate 15 cuts through the black space that divides the two population clusters. Note: This is not  precise map of the GPS coordinates; it's a representation of the divide.


If a highway has the ability to divide mountain lion territory, imagine what a nearly impenetrable border fence can do.  

The straight line that divides California and Mexico is a division that was drawn with humans in mind. It has zero regard for the natural landscape or the wildlife that inhabits it, which is why M53’s crossing back and forth from California to Mexico many times is noteworthy. He is an example of why preservation of connectivity is important not only in Southern California, but also beyond.

M53 recently dropped his collar and his status is currently unknown, but while he was being monitored he went from Anza Borrego Desert State Park in California to Parque Nacional Constitución in Mexico, 50 miles south of the border, several times. He did so despite the fencing that blocks much of the border. Where he crossed the border is a pinch point, but animals are still managing to cross in the mountains where the fence hasn’t been completed.

“The mountain lion habitat continues south of the border,” said Vickers. “We don’t have one geography in one country and a different geography across the border. It’s important that animals be able to cross.”

Meanwhile, north of the border, rapid development continues. The population in Orange, Riverside and San Diego Counties jumped from 2 million in 1960 to 9 million in 2010, and it’s not stopping. It’s projected to surpass 12 million by 2060.

The fragmented landscape will be an ongoing challenge for mountain lions, bobcats and other wide-ranging species in Southern California, even if a solution to the I-15 barrier emerges.

“It’s not just one isolated spot you can dismiss,” said Vickers. “It can happen anywhere. If we keep building without attention to these issues, we’re going to keep creating more pockets of isolation where animals can no longer connect with each other.”

And if the animals can’t connect with each other, the loss of genetic diversity will continue, and mountain lions will end up in the same boat as the Florida panther.

Contributors to this piece: Christopher Ancheta, Matthew Blake, Brian Cohen, Justin Cox, Doug Feremenga, Kat Kerlin, Valerie McFall, Trish Smith and Winston Vickers.


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