A critical stretch of the Orange County wildlife corridor connecting coastal preserves to the Santa Ana Mountains’ Cleveland National Forest – 2.5 miles on 178 acres of prime real estate traversing Irvine – has been under construction for 1 1/2 years, with huge swaths of a former Marine base being returned to nature.

But there’s a problem.

The animals whose long-term survival could depend on the passage can’t find their way there.

The culvert under the I-5 freeway where it merges with the I-405 is a key component of a wildlife corridor connecting coastal wilderness areas to the Santa Ana Mountains. But few animals from coastal preserves use the culvert. (Photo by Paul Bersebach, Orange County Register/SCNG)

Gray foxes, such as this one photographed in 2012 in the Laguna Coast Wilderness Park, are at risk of extinction in the area without the introduction of fresh genes. A wildlife corridor “pinch point” at Interstate 5 makes the culvert there unattractive for foxes and bobcats to cross under the freeway to a broaden the gene pool. (Photo courtesy of OC Parks and the Laguna Canyon Foundation.)

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John Leonard, project manager with FivePoint, talks about the Astor Road tunnel that is part of a wildlife corridor in Irvine, CA on Monday, October 7, 2019. The corridor will connect coastal wildlife preserves with the Santa Ana Mountains, with the Astor Road tunnel expected to successfully accommodate animals on the move. (Photo by Paul Bersebach, Orange County Register/SCNG)

The culvert under the I-5 freeway where it merges with the I-405 is a key component of a wildlife corridor connecting coastal wilderness areas to the Santa Ana Mountains. But few animals from coastal preserves use the culvert. (Photo courtesy of Laguna Greenbelt, Inc.)

A tunnel goes under Irvine Boulevard in Irvine, CA, on Monday, October 7, 2019. The tunnel is part of a wildlife corridor that will connect the Santa Ana Mountains, in background, and coastal preserves. (Photo by Paul Bersebach, Orange County Register/SCNG)



A 16-month wildlife study using 17 trail cameras just south of the I-5 captured only this one image of a bobcat approaching the culvert under the freeway. Bobcats’ long-term survival in the coastal wilderness area could depend on using the culvert under the freeway to access fresh genes in the Santa Ana Mountains. (Photo courtesy of Laguna Greenbelt, Inc.)

A wildlife corridor is being built that will connect the Santa Ana Mountains and coastal preserves. It is ranges from 300 feet to 1,100 feet, seen here, at its widest in Irvine, CA on Monday, October 7, 2019. (Photo by Paul Bersebach, Orange County Register/SCNG)

A tunnel goes under Irvine Boulevard in Irvine, CA, on Monday, October 7, 2019. The tunnel is part of a wildlife corridor that will connect the Santa Ana Mountains, in background, and coastal preserves. (Photo by Paul Bersebach, Orange County Register/SCNG)

Laguna Greenbelt board members John Foley and Norm Grossman talks with FivePoint wildlife corridor project manager John Leonard at the corridor in Irvine, CA on Monday, October 7, 2019. The tunnel is part of a wildlife corridor being built that will connect the Santa Ana Mountains, in background, and coastal wildlife preserves. (Photo by Paul Bersebach, Orange County Register/SCNG)

The bobcats and gray foxes of the Laguna Coast Wilderness Park and adjoining coastal reserves have to negotiate increasingly urbanized real estate as they approach the I-5 freeway from the south, traveling on a small maze of creek beds and culverts that snake around business parks and under roadways.

The final obstacle before getting to the Irvine portion of the corridor is the El Toro Y, where I-405 merges with I-5. The intended wildlife crossing beneath the freeway is 1,100 feet of mostly pitch-black culvert, passing under 17 lanes of traffic, filling with water during heavy rains and frequented by taggers and the homeless.

Environmentalists call it “The Scary Tunnel.”

A 2008 study found that even back then – and likely for more than a decade before – it was rare for animals to use the culvert. A study completed last month shows that still fewer animals even approach the area these days, likely deterred by subsequent development and increased human activity.

“It’s a pinch point. If you don’t solve the problem there, the corridor doesn’t function the way it needs to,” said Lance Vallery of the non-profit Laguna Greenbelt, Inc., which commissioned the new study and has been the lead advocate for what it dubs the Coast to Cleveland Wildlife Corridor.

While the 22,000 acres of coastal preserves is a relatively large wildlife habitat for Southern California, biologists say it’s probably not enough to prevent the eventual extinction of some species in that area, including bobcats and gray foxes.

The genetic diversity of the estimated 30 bobcats there is limited, according to a 2012 study, with several decades of isolation from other bobcat populations. The same is likely for the area’s gray foxes.

That’s expected to lead to inbred depression, which can greatly reduce the fertility of the animals and lead to the disappearance of animals in a given range. Historical inhabitants already gone from the coastal area include mountain lions, badgers and black-tailed jackrabbits.

“I don’t think it’s long before we start seeing signs of inbred depression among other animals,” said Kevin Clark, lead author of the new study and director of biological services at the San Diego Natural History Museum.

A loss of bobcats and gray foxes in the area would likely mean an increase in their natural prey, which includes raccoons, possums and skunks. That, in turn, would have a trickle-down effect on smaller animals, vegetation and even birds.

“Raccoons eat the eggs of quail and other birds,” Clark said. “If you have top carnivores drop out of the population, you see a degradation of the area very quickly.”

As envisioned, a functioning wildlife corridor would provide a usable route from coastal wilderness to 150,000-acres of Cleveland National Forest in the Santa Ana Mountains, allowing fresh genes to be introduced into the inbred populations. It would also improve habitat for the endangered Least Bell’s vireo and California gnatcatcher, according to Laguna Greenbelt documents.

But nobody’s quite sure how such a fully functioning corridor will come about.

Decades in the making

Plans for the corridor have been developing since the early 1990s. The closure of the Marine Corps Air Station El Toro in 1999 increased the possibility of establishing the 2.5-mile central link of 6-mile corridor.

FivePoint, the primary developer of the former airbase, fully embraced creation of that central segment, agreeing to the route preferred by ecologists and to a minimum width of 300 feet.

“That was a huge gift toward making this corridor sustainable,” said Mary Fegraus, a veteran advocate for wildlife in the coastal wilderness area.

Besides agreeing to the preferred route and donating the land, FivePoint is spending $13 million to return the stretch – which once included a golf course and a jet runway – to its natural state. It’s about two-thirds graded with planting to begin later this year. Completion is expected in two to three years, depending on the rate of surrounding development, according to FivePoint CEO Emile Haddad.

But while the central stretch of the corridor appears secure, there are concerns at both ends.

To the north, at the gateway to the Santa Ana Mountains near the intersection of Irvine Boulevard and Alton Parkway, there’s an 803-home residential subdivision proposed on 32 acres on either side of the corridor. Environmentalists worry that the project, on what is known as the West Alton Parcel, will deter animals from using that part of the passage.

Development is currently on hold because of lawsuits alleging a host of issues, including the claim that the county inadequately examined the proposal’s impact on the corridor. The plaintiffs are the cities of Irvine and Laguna Beach, and Heritage Fields, which is a FivePoint development venture in the area.

But the bigger obstacle is the I-5 crossing at the southern segment of the corridor.

A 2008 study of the area by the U.S. Geographical Survey found bobcats from the coastal area approached the I-5 area with some frequency, with one GPS-tagged feline regularly approaching the area near the culvert and possibly even venturing into it.

But the latest study provides evidence that bobcats are far less likely to visit the area these days. Clark and his team placed 17 trail cameras in the wildlife corridor in the mile before the south entrance to the culvert, with filming taking place from May 2017 to November 2018. They tallied each day that a camera captured a given species.

There was just one bobcat sighting and no gray foxes. The coyote tally was 581, followed by humans (529), raccoons (39), California ground squirrels (53), great blue herons (32) and desert cottontails (20). The study also found that the areas where humans were most often found had fewer animal sightings.

Possible solutions

Two large-scale wildlife freeway crossings have been proposed elsewhere in Southern California.

Money is being raised for a $88 million overpass from the Santa Monica Mountains across the 101 Freeway in Agoura Hills. Less far along are tentative plans for an I-15 Freeway crossing near Temecula. For that area, Cal Poly Pomona faculty and staff have drawn up blueprints for an overpass ($17.6 million), culvert upgrades ($9 million to $10 million) and an underpass upgrade ($570,000), but nothing has been finalized.

Among suggestions for the I-15 culvert upgrade is putting a skylight at the freeway median and sound baffles to quiet noise from the freeway. Recommendations for the underpass upgrade include measures to keep people out of the area.

In both cases, a driving force is the desire to expand habitat for mountain lions threatened by limited gene pools and inbred depression. These cougars have a higher public profile, are rarer and are more at risk than the bobcats and other animals in Orange County’s coastal preserves.

“The Santa Monica mountain lions have had a lot of great studies and cute pictures,” Clark said. “The public has really rallied to their cause.”

In his report, Clark recommends a number of low-budget suggestions for the I-5 culvert area, including covering rip-rap near arterial underpasses with dirt to make them more inviting to animals, fences to funnel animals toward crossing areas and discourage humans from approaching, and constructing elevated “critter shelves” for animals to traverse the main culvert.

Environmentalist Fegraus has limited expectations for the results of such small-scale efforts.

“They could help but they’re not going to solve the problem,” she said.

At a Tuesday meeting of some 40 wildlife experts and advocates, other suggestions included a stop-gap measure of importing bobcats to the area to introduce fresh genes and building a wildlife bridge over the freeway. The Nature Conservancy’s Trish Smith, who’s been working toward a wildlife crossing at the I-15 for years, urged patience and perseverance.

“These projects take decades,” she said. “We’ve got to think long term.”

Study author Clark stopped short of proposing a wildlife overpass, but he doesn’t rule out such grand solutions.

“Our effort here is maybe a first step down that road,” he said.