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Work starting on world's largest wildlife crossing, but research set stage for Conejo Valley project

National Park Service
Mountain lion kittens P-46 and P-47.

Biologists have been studying the lives of carnivores in the Santa Monica Mountains for more than two decades.

It’s a project that’s been talked about for years.

Work will officially get underway Friday on what’s being called the world’s largest wildlife highway crossing, which is being built over Highway 101 in the Conejo Valley. The idea is of course to help wildlife from mountain lions down to lizards safely cross ten lanes of freeway. But, it’s about much more than preventing roadkill.

"It's probably not going to make much difference in how many animals get killed on 101," said Seth Riley is a Wildlife Ecologist with the National Park Service. He’s been studying carnivores in the Santa Monica Mountains, and especially mountain lions for the last two decades.

"Animals mostly just don't even try that," said Riley.

He says there’s an adult breeding population of about a dozen of the big cats in the region, when there should ideally be about 50. Riley says the 101 has served as a barrier separating two major mountain lion habitats — the Santa Monica Mountains, and the Simi Hills. The result is a major threat to their future — inbreeding.

"Because of the freeways and development, there's very little movement, or no movement essentially into or out of the Santa Monicas," said Riley. "We have close relatives breeding with each other," he said. "We've seen mating between fathers and daughters, fathers and granddaughters, and even fathers and great-granddaughters."

Riley says the reality is the mountain lions, and many other animals don’t even try to cross the freeway, impacting the genetic diversity of the species.

The researcher says the hope is the wildlife overcrossing at Liberty Canyon in the Agoura Hills area will not only help with that movement, but also serve as a model for other crossings.

Riley and other researchers are busy with the concept. Caltrans just funded a $300,000 effort to look at the wildlife situation, and the potential for a 101 over or undercrossing in the Conejo Grade area.

And, there are projects to look at the issue along Highways 118 and 126 in the region.

Riley looks at the Liberty Canyon project as a start, one which will open the door to similar projects to ease the some of the conflict between urbanization and wildlife habitats.

Work symbolically kicks off Friday, which is Earth Day, on the more than 200-foot-long, 165 foot wide Liberty Canyon overcrossing. When it’s finished, it will be landscaped with native plants and trees to give wildlife a natural feeling crossing. The $90 million project is expected to be completed in 2025.