Map reveals roadkill hot spots in Sonoma County

An opossum, a coyote, a gray fox, a raccoon, a crow and several squirrels - all dead - were just a few of the sightings Marlene Radigue reported in recent weeks from a stretch of Highway 12 through the Sonoma Valley, near her home.

A steadfast witness to the deadly encounters between vehicles and wildlife along the roadway, the Glen Ellen woman has spent several years somberly documenting the results, then respectfully moving animal remains to the edge of the road so scavengers can take over without the risk of being killed themselves.

It's sobering work. But it offers hope of change, as well.

Radigue, a textile designer, is part of an effort through UC Davis to identify California highway “hotspots” - areas where deadly collisions between motorists and animals are statistically high - in order to raise awareness about safety risks to both animals and motorists, and guide planning and design decisions toward increasing wildlife crossing opportunities in the state's complex highway system.

More than a thousand volunteer observers have contributed to the project since its inception in 2009, creating a growing database that's the basis of an updated report on “wildlife-vehicle conflict zones” released by the UC Davis Road Ecology Center last week.

The study, the third of its kind since 2013, includes more than 50,000 carcass observations reported by volunteers, including several hundred academic, agency and nongovernmental biologists and natural historians, said Fraser Shilling, co-director of the Road Ecology Center. It also takes into account preliminary reporting from crashes and other incidents where a motorist struck an animal or may have swerved to avoid one. The combined data represent only a fraction of the collisions that occur, Shilling said.

Not surprisingly, the greater Bay Area has a large number of high-volume highways, many of which bisect open spaces where animals make their homes.

Interstate 280, south of San Francisco through the Peninsula, is the state's No. 1 zone for wildlife collisions and encounters, particularly deer, the report states.

In the North Bay, trouble spots include:

• The whole of Highway 101 between Petaluma and the Golden Gate Bridge, and particularly south of the Highway 580 junction, including several stretches where wooded hills rise on either side of the road;

• Highway 12 through the Sonoma Valley, which is near a wildlife corridor; and

• Three segments of Highway 37 roughly along the shoreline of San Pablo Bay ­- at the mouth of the Petaluma River, near Highway 121 and Tolay Creek, and near Mare Island, west of the Napa River.

Shilling said the value of such information lies, in part, in raising driver awareness to the possibility of animal-related hazards and, perhaps, reducing speed.

The study cites Caltrans and California Highway Patrol figures indicating more than 4,000 accidents reported each year involve deer, other wildlife and livestock.

But it also can inform efforts toward creating avenues for wildlife to get over or under highways that impede their travel. High-profile examples include a project to build a land bridge across 10 lanes of Highway 101 in Agoura Hills, primarily to facilitate the movement of mountain lions between the Santa Monica Mountains and open space land on the north, and two undercrossings in the works for Highway 17, between Los Gatos and Santa Cruz, primarily for mountain lions and other large fauna.

Under a state law signed last year and authored by North Bay Assemblyman Marc Levine, D-San Rafael, construction of highways and other development in defined wildlife corridors must preserve the ability of animals to move freely.

Katerina Robinson, a policy associate with Environmental & Energy Consulting in Sacramento, said the need for wildlife crossings will only become more pressing as climate change disrupts habitats and migration patterns.

“As we're doing conservation and protecting high quality wildlife, we have to be cognizant of how that plays into our infrastructure planning,” she said.

In Sonoma County, portions of Highway 37 are already at risk of increased flooding due to sea level rise, Shilling said. If reconstruction is needed, it might make sense, he said, to incorporate wildlife undercrossings with fencing along the highway that could funnel animals toward safe passage.

The abundance of ground squirrels killed on Highway 12 as they move between tall trees on either side suggest the utility of rope bridges effective elsewhere for allowing squirrels and similar, small animals to move safely across the thoroughfare, he said.

Construction on the next phase of widening Highway 101, south of Petaluma, already will include a passageway for wildlife alongside San Antonio Creek, where the highway passes overhead, a Caltrans spokesman said.

Tony Nelson, a program manager with the Sonoma Land Trust, said tracks in and around the passage indicate it is heavily used.

But it also just a single undercrossing with few others nearby, he said. And as the highwaywidens, it will only become harder for wildlife to find a way across.

The Sonoma Land Trust, a leading conservation agency in the region, has long been attuned to a conflict between development along Highway 12 and a critical wildlife corridor that runs from the Mayacamas Mountains in the east, along the Sonoma Valley, up and over Sonoma Mountain on its way past Petaluma and west through Marin County to the coast.

A pinchpoint near the highway, where the corridor narrows to about 3/4 of a mile, has outreach efforts urging landowners to use only needed fencing, and that land acquisition decisions maintain a sufficiently wide corridor that animals can roam its full length.

Wildlife cameras posted at several creek culverts and undercrossings along Highway 12 and Arnold Drive have recorded bobcats, mountain lions, coyote, deer and even a beaver seeking safe passage beneath the road, the Sonoma Land Trust reported.

Tony Nelson, program manager with the land trust, said future work is expected to include tearing out blackberry patches and unnecessary fencing that may impede access to undercrossing, as well as increasing riparian plantings to provide screening for wildlife in the area.

Similar work is planned for two cattle crossings near Sears Point, an area of vast wetlands bordering San Pablo Bay, some recently restored, that draw large numbers of shorebirds and waterfowl, as well as small- and medium-sized mammals like otters and rabbits.

The cattle undercrossings, located west of Highway 121, have not proven useful to wildlife in general, in part because they become clogged with sediment during stormy years, said Don Brubaker, manager of nearby San Pablo Bay National Wildlife Refuge.

The Sonoma Land Trust, which partners with the refuge, hopes some upstream planting may limit erosion and make the area more appealing to wildlife, Julian Meisler, another agency programmer, said.

But “honestly, we didn't realize that (area) was such a death trap,” he said.

You can reach Staff Writer Mary Callahan at 521-5249 or On Twitter @MaryCallahanB. Staff researcher Janet Balicki contributed to this story.

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