How often have you been driving on a winding California highway and seen a deer dart across the road? Or caught a glimpse of a squirrel searching for an opening to dash to the other side. How about a mountain lion trying to cross with her young kittens?
While it may seem rare, UC Davis researchers estimate that over 70 mountain lions die every year due to collisions on California highways—and those are just the cats that have been reported to California Highway Patrol. Some scientists speculate that the number of puma deaths is much greater.
A recent collision on I-280 in San Mateo County—estimated to be the deadliest road in California for mountain lions—left a mother puma dead and her two cubs orphaned. The cubs were taken in by the Oakland Zoo and will remain in its care until they can find a permanent home. Mountain lion cubs typically stay with their mom for two years before they go out on their own. The orphaned cubs are six to ten weeks old and are too young to be rehabilitated and released back into the wild.
With roads and highways cutting further into wildlands, animals are increasingly left with two options: stay where they are—stuck in shrinking habitats with limited resources and dwindling mates—or run across busy streets, risking death.
This is why environmentalists across the state are calling for more wildlife crossings. And recently, the State of California has started to listen.
In the 2022-2023 legislative session, lawmakers approved almost $1 billion in funding for wildlife crossings and fencing across the state.
A wildlife crossing is any type of structure that is designed to help animals cross roads and other human-made structures safely. These crossings are usually constructed over, around or under large highways. They can be anything from large bridges covered in vegetation to small tunnels under the road.
As part of that funding, Alameda County has received a $7 million grant to begin planning for wildlife crossings that could be built along I-580, I-680, and State Route 84.
“Having protected lands and having wildlife crossings will help keep mountain lions safe,” said Marian Vernon, wildlife linkages program manager for Peninsula Open Space Trust.
While wildlife crossings may seem like a relatively new concept, wildlife overpasses, corridors, and culverts have been popular in other countries for some time. Originating in France in the 1950s, wildlife crossings were built en masse across the Netherlands with countries like Australia and Canada following suit.
California has comparatively few wildlife crossings on its highways and major roads
Often a leader in environmental work, California has been slow to catch up with others that have implemented substantial wildlife crossings. States like Colorado, Florida, Wyoming, and Montana have been constructing wildlife corridors and creating wildlife crossing legislation for years. Additionally, when it comes to wildlife death on roads, the Bay Area is notoriously bad.
According to the 2023 California Roadkill Hotspots Report by UC Davis’ Road Ecology Center, the California highways with the highest rates of wildlife-vehicle conflict in the last seven years “have included I-680 in Contra Costa and Alameda Counties and I-280 on the San Francisco Peninsula.”
“I don’t think there would be a mountain lion population on the San Francisco Peninsula if there wasn’t a source population somewhere else because they get killed so frequently,” said Fraser Shilling, director of the Road Ecology Center. Pumas from other areas occasionally migrate into the peninsula and replenish the area’s population.
These deaths not only take an environmental toll, they also have a financial toll. On I-680 and I-280 in the past seven years, collisions are estimated to have cost drivers and the public over $26 million.
The $1 billion recently approved for wildlife crossings is now being dispersed to local governments across the state. While this is a step in the right direction, experts emphasize the importance of implementing them correctly.
“Not all crossings are created equal,” said Tiffany Yap, an ecologist for the Center for Biological Diversity, a non-profit focused on protecting endangered species, and author of Tales of the Urban Wild: A Puma’s Journey.
Different animals require different types of crossings and corridors. Some animals like lots of vegetation, others like the quiet, and mountain lions, specifically, like it to be dark—but not so dark that they can’t see the other side of the road. These distinct differences require researchers to plan out their overpasses and underpasses carefully. They have to figure out what type of crossing will work best for the animals with the highest need. If the wildlife crossing doesn’t actually help the animals cross, then it is pointless.
The Alameda County Resource Conservation District is in the beginning stages of figuring out what kind of crossings will work best in this region, where they’ll need them, and how they’ll build them. Initially starting with collecting camera-trap data with the help of Shilling, the district has been studying animal mortality and isolation on Alameda’s most prominent roads. After a couple of attempts at applying for funding, the organization was awarded the $7 million grant from the Wildlife Conservation Board in August 2023. However, the ACRCD has a long way to go before they can begin building passages.
“I would not expect the crossings to be fully built for 10 or 12 years,” said Katherine Boxer, CEO of the conservation district.
Wildlife crossings require environmental reviews, engineering strategies, public outreach, and multiple other steps before they’re shovel-ready. Between now and 2027 the conservation district will focus on studying, planning, and designing potential wildlife corridors along I-580, I-680, and State Route 84.
The $7 million allows them to design up to three crossings on any combination of the roads listed. After this initial project is completed, the conservation district and its partners will apply for additional funding to begin construction.
Fencing, the less sexy part of the solution
Experts say that more than crossings are needed to protect wildlife from traffic. Adequate crossings mainly solve one portion of a two-part problem: road mortality and genetic isolation. While crossings can help animals that need to move more freely find additional habitat and mates, fencing can help them better stay off the roads.
“For the East Bay hills and the Diablo Range, it’s not just about thinking about wildlife crossings, it’s also thinking about how we are going to put wildlife fencing along these important roadway where wildlife are being killed,” said Shilling.
Shilling notes, however, that getting funding for fencing is more difficult. He says that fencing just isn’t “sexy” enough to gain the attention that wildlife corridors do. He stressed the importance of projects that prioritize both fencing and corridors.
“If you have a fence, you keep wildlife from getting on the road, they don’t get killed,” said Shilling, “If you have a crossing, animals may still be killed, but now they have a way to get from one side of the road to the other. So both are important. And conceptually, they both make sense, right? But right now, the ratio is 100 to one, where we’re going to spend a lot of money on crossing structures and not as much on fencing.”
While funding has not been historically equitable between crossings and fencing, Shilling is hopeful now that more non-profits and other environmental groups are advocating for it.
As the call for more—and more adequate—wildlife crossings and fencing continues, researchers like Vernon, want to remind California residents that the animals that these crossings protect are what help make California unique.
“We live in this really remarkable area where we do still have wildlife and large carnivores present,” said Vernon. “We do live in a biodiversity hotspot that has a lot of diverse species and also has a lot of habitat loss that’s occurring. So this is a really unique landscape to be doing this work. And I think we should be proud that we still have the amount of biodiversity that we have here and that the work we’re doing is to help protect that for future generations.”
