Most drivers have had this experience: it’s late at night and out of nowhere an animal darts across the road. Thousands of animals are hit every year in California, taking a toll on both wildlife and drivers. Nationwide, wildlife collisions are estimated to cause $1 billion in damage.
Several western states have built infrastructure to help wildlife cross under highways safely—projects known as “wildlife corridors.” Some experts say that while California officials know about the extent of the problem, the state is way behind in solving it.
The dangers have recently become clear in the Santa Cruz Mountains, where mountain lions are crossing Highway 17, a winding, four-lane highway. The population is being studied by the Santa Cruz Puma Project, run out of the University of California-Santa Cruz.
On a sunny, late-spring afternoon, field biologist Paul Houghtaling meets up with Dan Tichenor, a volunteer from California Houndsmen for Conservation, and his hound dogs. They tracked the scent of a mountain lion, now in a tree to avoid the barking dogs.
“He’s looking at us,” Houghtaling says, looking up at the lion. “He’s interested in us but just a little while ago he had his head down on the branch. He’s gonna wait us out.”
Houghtaling intends to put a radio and GPS tracking collar on the lion. The data will feed into a five-year project to document mountain lion movements in the area and study how they live around people.
“We’ve had several lions that have crossed Highway 17 down near Santa Cruz many times,” he says. “One of them was hit and killed about a week before she was going to give birth to a single kitten.”
Four other lions have been killed on Highway 17 in the last few years. Houghtaling says the data show that most of them are trying to cross the highway at the same places, which makes those locations good candidates for wildlife corridor projects.
“Circle of Death”
“We know it’s a problem and we know how to fix it,” said Fraser Shilling, director of the Road Ecology Center at UC Davis. “Almost every place you have a highway near an open space area, we have hotspots. So it’s sort of a circle of death around the Bay Area.”
The Bay Area’s highway network fragments wildlife habitat, either forcing animals to cross freeways or isolating them in “islands” of habitat. Scientists say connecting habitat will be increasingly important with climate change, as animals and plants need to move with shifting conditions. A recent effort by conservation groups identified 14 places where preserving land would connect the Bay Area’s open spaces.
Citizen scientists have documented around 7,000 dead animals on Bay Area roads over the last four years, which Shilling says represents a fraction of the total number.
Another road-kill hotspot is Interstate 280, a commuter favorite heading south out of San Francisco. The multi-lane freeway opens to rolling, grassy hills on either side.
Shilling tracked deer behavior around the freeway for six months. “They’ll come right up to the edge of highway,” he says. “They’ll also try to cross the highway and because it’s so busy, they really can’t make it. They’ll get hit.”
Collisions at freeway speeds are often fatal for the deer, and sometimes for the driver. Every year, drivers hit about 40 deer along I-280, but Shilling found some deer are going under the freeway through culverts and underpasses.
In a report he’s drafting for Caltrans, Shilling recommends putting up wildlife fencing that would funnel deer to the underpasses, keeping them off the freeway. Those underpasses could be made more attractive to wildlife by creating separate pathways for people and animals to use. Animals tend to avoid areas that are heavily used by people.
Building fences can be expensive—up to $100,000 per mile—but Shilling compares that to cost of collisions from vehicle damage and injuries.
“On Interstate 280, there are places where the cost is about $10,000–40,000 per mile from collisions per year,” he says. “So when you add that up and say: what is that over ten years and would it be cost-effective to do something? Certainly, it would save society money.”
Other western states like Colorado and Montana have put in fences and built underpasses on major highways, and the projects have proven effective.
Shilling says California is lagging behind. “We build about one wildlife underpass per year and the scale of the problem here is huge,” he says. “Because this is framed as an environmental issue, Caltrans seems to ignore it.”
Waiting for Report
“It is a problem,” says Bob Haus, spokesman for Caltrans District 4, representing the Bay Area. “It’s very difficult for humans and wildlife to mix. If we can cut down on human injuries and wildlife injuries, then we’ll do anything we can to do that.”
Haus says Caltrans is building a culvert for wildlife near Napa as Highway 12 is widened. But that’s only one of five projects being built or designed specifically for wildlife in the Bay Area that Caltrans could name.
The agency also remains skeptical about using fencing as a guide path. “So, say if you have fencing that’s specifically designed for a deer, it might harm other species,” Haus says. “So if there’s anyway at all to avoid the fencing, we try to do that right now.”
Haus says his district has commissioned a report from UC Davis about Bay Area collision hotspots.
“It really depends on what they recommend. If it requires any changes to what our projects already are, we’ll go from there.”
Fraser Shilling wants to see legislation that requires Caltrans to make all highway projects more wildlife-safe. “The agency, Caltrans, has known about this problem for a long time,” he says. “They’ve heard about it from Fish and Game. They’ve heard about it from their peers. They’re not doing it.”
“I believe there’s a lot more that can be done in California to make habitats more connected for wildlife, particularly across roads and other kinds of barriers,” says David Wright, who works on the Resource Assessment Program at the California Department of Fish and Wildlife.
“I think that if we starting thinking about every project as it comes up and trying to make sure that we include something that improves connectivity for wildlife, then I think we’ll start seeing better habitat and more wildlife in our state,” Wright says.
Progress on Highway 17
Back in the Santa Cruz mountains, Paul Houghtaling loads his rifle with a dart to sedate the mountain lion in the tree above us. He takes aim and the dart hits square in the thigh. The mountain lion leaps down and runs by at full speed.
He catches up with her (turns out it’s a “she”) as she’s failing asleep under some bushes. Houghtaling takes her vitals and fits her with a radio collar, giving her the name “38F” as the 38th mountain lion in the study.
Things could be looking up for the Santa Cruz lion population. Local land trusts, including the Midpeninsula Regional Open Space District, the Land Trust of Santa Cruz County, and the Peninsula Open Space Trust, are working with another Caltrans district, District 5, to improve highway 17 by expanding culverts and putting up fencing in two locations. The group is using cameras to study animal movement in those corridors and is currently applying for state funding to complete the project.
See the mountain lion capture in KQED’s “Science on the SPOT: Chasing Pumas”: