Bridge to Coexistence

By: Carla Rohde Robinson, Education Coordinator at Wildlife Waystation

Southern California is a highly developed area with a large human population, countless freeways, cars, and sprawl. There are over 13 million people living in just Orange and Los Angeles counties alone. Biologists believe Los Angeles is one of the last remaining mega-cities in the world, if not the only one, that a large carnivore calls home - the Mountain lion.

credit: Valerie/Flickr

Mountain lions have the greatest geographic range (distribution) of any carnivore in the Western Hemisphere and they are the largest wild cat found in North America. Widely distributed across California wherever deer are present, it is estimated there are only between 3,000 to 6,000 cats left statewide, typically found in the foothill and more mountainous regions of the state. In addition to being found in the United States, they are also native and thriving in many Central and South American countries.  Their former range was once all of what is now the continental United States, but mountain lion populations were drastically reduced during the great expansion westward beginning in the 1800’s. The main threats facing the mountain lion today are habitat loss and fragmentation, depredation (hunting) permits, wildfires, urban sprawl, highway development and cars.

credit: National Park Service

Their populations in southern California are facing more pressure now than ever, and biologists are concerned that these great predators could quickly disappear from the Southern California landscape all together if we do not act fast. Since researchers began studying the mountain lion populations in 2002 to observe how they survive in an urban metropolis environment, there have been 12 mountain lions killed while attempting to cross busy streets and freeways.

Most recent was on August 10, 2015, when P-32, known to many as a wanderer, was struck and killed by a motorist as he tried to cross Interstate 5 near Castaic, following a near 150 mile journey to find new territory and mates. Kate Kuykendall, a spokesperson for the Santa Monica Mountains National Recreation Area, said P-32 was the “only known male to venture out of the Santa Monica Mountains and wander north into other habitat areas.” (Curwen 2015)


Adult mountain lions require around 200 square miles of territory, and will kill other lions found roaming in their space. In southern California, however, these big cats have limited space, mainly due to habitat fragmentation and development. The end result is that many cubs and juvenile lions never make it to adulthood. If they do survive to breeding age, then they are at high risk of being hit by a car or accidentally poisoned by second-generation rodenticides. There have also been cases of sub-adult to adult mountain lions wandering into neighborhoods and backyards looking to expand their territory, but instead being viewed as an aggressive animal and a threat to public safety threat, often resulting in the animal being euthanized.

credit: Tambako the Jaguar

Roadways are not just physical barriers that can affect wildlife, but they also fragment habitat and result in highly decreased genetic diversity for the species. Mountain lion’s movements are restricted due to lack of proper habitat, so it is not uncommon for inbreeding to occur within the Southern California cats. A study published in 2014 by the University Of California Davis School Of Veterinary Medicine looked at 354 mountain lions statewide, including 97 from Southern California. It found a correlation between low genetic diversity (implicating inbreeding) and lions living in isolated areas where they were unable to freely roam and establish new territories or mates.  During their study, they observed just one lion known to cross the 101 freeway, P-12, and it was found he “significantly increased the genetic diversity of that population.” (US Davis)

Habitat Linkages and Wildlife Bridges

The first mile of the 101 Freeway opened in 1940 between Hollywood and the San Fernando Valley, making it one of the oldest freeways in California. In the decades to follow, the freeway was expanded to accommodate an increasing number of automobiles on the road, and the once continuous stretches of natural habitat traversing numerous mountain ranges soon became fragmented and divided territory.  Presently, the 101 Freeway is an expansive, 8-lane freeway that is quite dangerous for any wildlife to cross safely. Home Range Map PDF.

In 2012, biologists began to study how large carnivores like coyotes, bobcats and mountain lions in the area were travelling, mating, and interacting with other groups through the use of radio collars. The results of the on-going study revealed that the severely fragmented habitat between mountain ranges was, in fact, leading to increased inbreeding and lowered genetic diversity, isolation between groups, and increased competition for resources. Through these studies, we have learned this type of access can be provided to wildlife by working to connect existing natural habitat and create continuous habitat linkages wherever possible. Wildlife bridges, tunnels and underpasses used to connect natural areas are also a big part of this puzzle. Many of the large mammals inhabiting the state, particularly mountain lions and bobcats, need large swaths of undisturbed, continuous territories in order to survive and thrive as a species.


The California Department of Fish & Wildlife further explains “a functional network of connected habitats is essential to the continued existence of California's diverse species and natural communities in the face of both human land use and climate change. Habitat is [the] key to the conservation of fish and wildlife. Terrestrial species must navigate a habitat landscape that meets their needs for breeding, feeding and shelter. Natural and semi-natural components of the landscape must be large enough and connected enough to meet the needs of all species that use them. As habitat conditions change in the face of climate change, some species ranges are already shifting and wildlife must be provided greater opportunities for movement, migration, and changes in distribution.” (CDFW 2015) Regional Wildlife Linkage Map - Credit: LA County Department of Regional Planning.

Current Liberty Canyon area of the 101 Freeway

With this in mind, a number of groups and influential individuals are pushing forward to raise support and the $30 million needed for construction of a wildlife bridge across the 101 Freeway near Liberty Canyon Road in Agoura Hills in an effort to protect the genetic diversity of wildlife populations across various mountain ranges. In addition, the City of Agoura has agreed to help build a bridge over Agoura Road in an effort to further connect this important corridor. The Mountains Recreation and Conservation Authority (MRCA) owns the land to the right and left of the road.

In an interview with the Wildlife Waystation on September 24, 2015, Clark Stevens, lead architect of the bridge and Executive Officer for the Resource Conversation District of the Santa Monica Mountains (RCDSMM), the organization handling the design and engineering of the project, noted the need for a secondary bridge. He explained that because the area to the south drops off very steeply, it “would be a shame for an animal to make it across the main land bridge, only to get hit by a car on Agoura Road.”  Currently, animals that cross Agoura lose site of the creek bed quickly and are more likely to stop when they cannot see their destination, but with the addition of a secondary bridge, they will be funneled right across the road until safely in new habitat.

The planned structures will “allow animals to roam between Simi Hills to the north and the Santa Monica Mountains to the south,” and once complete, the main bridge may be the largest structure of its kind in the world – nearing roughly 200 feet in length and 165 feet in width. (Loesing, 2015) In early September 2015, the California Department of Transportation (Caltrans) released findings from the Project Study Report (PSR), which was meant to evaluate “feasibility and cost” of the proposed wildlife passage. This was the first step towards the structure being built. Stevens, the bridge’s architect, explained that now RCDSMM is in the second phase of a three step process – waiting for a full environmental impact study to be completed. After that is accomplished and additional funds are raised, the construction process will begin. Once ground is broken, he estimated that it could take up to five years before the project is finished. RCDSMM is also working with other organizations to create a new trail that would take outdoor enthusiasts from Malibu across the Wildlife Bridge and north into the Sierra Madre Mountain range, thereby expanding outdoor recreational opportunities in the state and allowing residents and visitors to Southern California to experience the benefits of the bridge firsthand.

Here is a time lapse of Liberty Canyon Wildlife Crossing!
credit: Resource Conservation District of the Santa Monica Mountains

The new bridge will be covered with drought-tolerant, native plants to provide natural cover and encourage animals to use the crossing by creating a natural funnel, and it will have barriers installed to reduce noise and light from traffic to make it more appealing for wildlife. Stevens also stated that at least one third to one half of the dirt being used to build the land bridge is coming from an existing “fill dirt” dump site just to the north, which will help cut down on the overall cost since the dirt is locally sourced, as well as decrease the number of trucks present on the freeway during construction. “A lot of animals come down from the north and through that dump area. So, we are doing riparian restoration and habitat creation there so that there is a secondary zone that will help funnel animals up to the land bridge. After they come through the restored site, the animals will already be on the land bridge before they really know it,” Stevens went on to say. Other native wildlife like bobcats, coyotes, skunks, badgers, foxes, and mule deer will likely use the crossing as well to travel in between mountain ranges while searching for food, water and mates.

Opossum at one-way gate used along the 101 Freeway to keep wildlife from turning back onto the road after crossing

RCDSMM did explore other options for the project prior to completing the schematic design, including two tunnel options. However, after discussing with the National Park Service at a wildlife crossing workshop that included experts from all over the country, they determined the most effective way to get wildlife to use a new structure was by creating a land bridge. Stevens explained that the experts “studied other sites along the 101 Freeway, as well as in Temecula and San Diego. If the highway has a lot of barriers, then the animals are less likely to use it…and animals have shown they do not want to use tunnels, we think because they cannot see to the end. That’s where they pushed for the bridge including the integration of Agoura Road.” He went on to add that land bridges, tunnels, and underpasses should all be integrated into use for wildlife and to help create more habitat linkages. “The idea is that there really should be all of them. For example, Conejo grade has some underpasses, and there are some other places where we are hoping to build and connect underpasses and tunnels for use by wildlife in the future,” said Stevens.

The Conejo Grade, a 7% grade stretch of the 101 Freeway that links Thousand Oaks and cities in the Conejo Valley, was the area wildlife biologists believe a female lion, known as P-33, crossed the 101 Freeway in March 2015. As far as they know, P-33 was only the second mountain lion in the area to have successfully crossed the 8-lane freeway, and the only lion out of 35 studied to have dispersed out of the Santa Monica Mountains, something very important to the overall genetic health of mountain lions in the area. In a March 20, 2015 interview with KTLA5, Seth Riley, a wildlife ecologist for the Santa Monica Mountains National Recreation Area studying the big cats in Southern California, explained that “the GPS points show that the lions we’re tracking frequently come right up to the edges of the freeway and then turn around. After more than 10 years of seeing the same pattern in our data, it is very cool to see a lion figure out how to cross the freeway and reach other natural areas to the north.” (Soley-Cerro, 2015) It was unclear whether lion P-33 used the only underpass in the Conejo Grade area near Camarillo Springs Road to safely traverse the freeway but it is likely.

credit: LTMayers/Flickr

The long-term goal of the RCDSMM and many other agencies involved is to find ways to enhance and link these existing tunnels and underpasses with new wildlife bridges and passages to create as many habitat linkages as possible. A major backer of the Liberty Canyon crossing is the National Wildlife Federation, who has been working hard to raise money for the project. “According to urban wildlife experts, creating a safe passage for wildlife in one of the last undeveloped areas [along] the 101 will give us a chance to ensure the future of cougars in the Santa Monica Mountains and Los Angeles area. NWF and our partners are proud to work with Californians and Americans everywhere to find ways for people to successfully coexist with and help wildlife prosper in an increasingly urbanized landscape.” (National Wildlife Federation)

For more information on the Liberty Canyon Wildlife Bridge and what you can do to help support the project, visit the National Wildlife Federation.

Caltrans and CA Department of Fish & Wildlife - Download their Watch Out for Wildlife Week PDF and learn about additional wildlife bridges and tunnels being considered in the state, as well as tips to avoid collisions with wildlife on the road.

For more information on the natural history of mountain lions, please visit the Natural History Museum of Los Angeles.

The Wildlife Waystation is currently home to seven unreleasable mountain lions and other native, unreleasable wildlife! Please visit for more information on getting involved or supporting our animals.

Organizations and individuals currently working on the project include: the Mountains Recreation and Conservation Authority (MRCA), the Santa Monica Mountains Conservancy (SMMC), the California Department of Transportation (Caltrans), National Wildlife Federation, the Santa Monica Mountains National Recreations Area, the Resource Conservation District of the Santa Monica Mountains, the City of Agoura Hills, CA State Senator Fran Pavley, CA State Assembly member Richard Bloom, US Congressman Ted Lieu, LA County Supervisor Sheila Kuehl, and Ventura County Supervisor Linda Parks.

credit: Dan Hutcheson/Flickr


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