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LA lions to roam over freeway

Larry Buhl
January 17, 2017

Planning has started on the largest wildlife crossing in the world. The privately-funded bridge would allow the endangered Santa Monica mountain lion and other species to dodge safely the insanity of LA traffic.

A female mountain lion roams above the crowded Los Angeles basin
Image: National Wildlife Federation

The Ventura Freeway, known to locals as the 101, is a relentlessly busy east-west road that carries up to 175,000 vehicles through Los Angeles' San Fernando Valley every day. Though a veritable artery for traffic, the 101 has created a roaming blockage for mountain lions, bobcats and other wild animals.

A few animals have managed to escape the triangle formed by the 101, the 405 - another major freeway - and the Pacific Ocean to find mates in other areas of southern California. 

Indeed, it has been speculated that LA's prosaically named mountain lion P22 crossed two freeways to famously end up in the rugged hills of the city's Griffith Park, a municipal expanse of green at the eastern end of the Santa Monica Mountains - and only a few miles from dense urban development.

Most cougars are neither that ambitious, nor that lucky. The majority of those who take on the daunting challenge of crossing eight lanes of fast-moving traffic are killed. 

But now, the California Department of Transportation (Caltrans) is working with conservation groups to build a wildlife corridor and freeway overpass that connect the Santa Monica Mountains with the nearby Simi Hills and Santa Susana Mountains. 
If all goes to schedule, it will be open by 2021 - and will, biologists say, come just in time to save the mountain lion from extinction in the region.

Saving lions from inbreeding and extinction

Just over a dozen mountain lions, which are also known as cougars or pumas, live in the Santa Monica Mountains. There, for the time being at least, the large felines are able to find enough prey to keep the population alive.

But it's not enough space to prevent inbreeding. The freeway bottleneck means adults frequently kill younger rivals, even if they’re related. Such behavior, unusual in the species, is indicative of unusually fierce competition for mates. 

A young male mountain lion
P22 is a young male mountain lion who crossed two Los Angeles freeways to take up residence in the city's Griffith ParkImage: National Wildlife Federation

A research paper published in PLOS ONE in 2016 concluded that unless their range is increased, the region’s mountain lions will face "inbreeding depression" - a term used to describe the genetic result of confinement that means the animals would have to mate with close relatives. 

The upshot is a decrease in genetic diversity, which in turn makes the species more vulnerable to health problems and disease. Researchers say that without intervention, there is a 99 percent chance that the LA region's mountain lions will disappear within the next 50 years.

Learning from the past

John Benson, an assistant professor of vertebrate ecology at the University of Nebraska and lead author of the study, saw a similar situation among the panther population in Florida. He says there are lessons to be drawn from history.

"When their genetic diversity reached very low levels in the 1990s, panthers nearly went extinct," Benson said. He attributed it to factors associated with inbreeding depression.

Introducing new genes into the population can restore genetic variability, thereby improving survival and reproduction and preventing extinction.  

"In Florida, this was done by translocating mountain lions and their novel genes from Texas into south Florida after panthers had begun experiencing inbreeding depression."

The scientist says there's still a chance to restore "landscape connectivity and gene flow" in southern California before things get so dire.

"Our model suggests that if one new mountain lion enters the population every two to four years, this would be enough to largely maintain genetic diversity and greatly reduce the probability of extinction," he said. But for that to happen, the cougars need to be able to move around more.

Bridge for biodiversity

This could be the route wild animals take to expand their range
A rendering of the proposed wildlife overpass above the 101 freeway in Agoura Hills, CaliforniaImage: Resource Conservation District

Enter highway crossings. 

The proposed wildlife bridge, which carries an estimated price tag of $56 million (54 million euros) would create a 200-foot long by 165-foot wide (61 by 50 meter) span over the 101 freeway in the suburban city of Agoura Hills.

It would be also extended over an adjacent road in that city, and natural vegetation would be added to block out noise and light from the freeway.

Highway crossings similar to the land bridge proposed over the 101 have been used in Alberta, Canada, and the Netherlands to maintain or restore landscape connectivity for wildlife in areas fragmented by roads.

But so far, none have been developed in dense urban areas like Los Angeles. 

If built, the 101 freeway bridge would be the largest such crossing in the world, and a model for urban wildlife conservation, proponents say.

All animals free to roam

According to Paul Edelman, Director of National Resources and Planning at the Mountain Recreation and Conservation Authority, other species as well facing the threat of inbreeding, and would benefit from the project.

"The grey fox and the bobcat will be able to use the bridge - and even birds will change their flight plans to be over green space," Edelman said.

Funding for the proposed crossing will come largely from private donations and nonprofit sources, with any public money coming from funds earmarked for conservation, according to Caltrans. 

But if the project is to meet the completion date of 2021, advocates say they’ll need to raise $10 million by early 2017 to start the engineering design phase.

 A big-eyed bobcat kitten
A bobcat kitten named B327, one of the dozens of species that will benefit from the LA wildlife bridgeImage: Santa Monica Mountains National Recreation Area

Beth Pratt-Bergstrom, State Director of the National Wildlife Federation (NWF), says the local community and the city of Agoura Hills are squarely behind the project, but that money remains a worry.

"The only thing that could possibly hold it back is the fundraising," she said, adding that if built, the construction would set an example for other future wildlife crossings in similar urban areas.

"When the region’s freeways were built, wildlife wasn't a consideration," Platt-Bergstrom said. "I think from now on, wildlife corridors - when appropriate - will be integral to freeway design."