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Road Ecology Center Shines Light on Roadkill Hotspots

June 9, 2015

Andrea Sargis, University of California, Davis

CA Road with CloudsFraser Shilling of UC Davis’ Department of Environmental Science and Policy and Road Ecology Center is stirring up awareness of California's roadkill hotspots. Many of us have seen roadkills, but where and how often do they occur? What species are most involved?  How can we minimize roadkill incidents? All of these questions require long-term investment in large-scale monitoring and analysis. As Co-Director of the Road Ecology Center, Shilling is the first to focus attention on roadkills and develop a state-wide volunteer system of documenting and quantifying them--the California Roadkill Observation System (CROS).

CROS, which currently stands as the largest volunteer based roadkill observation system in the world, has attracted consistent media attention and discussion (e.g., VoxHuffington Post, KQED, The Press Democrat, NBC Bay Area).  According to Shilling’s Special Report on Roadkill Hotspots along California Highways (2009-2014), this project represents one of the largest wildlife monitoring programs in California, with over 1100 contributors and 30,000 observations in the last six years.

Road Ecology is “the study of the effects of roads and road systems on natural and human communities,” states Shilling. According to Shilling, there are about half a million kilometers of dirt and paved roads in California, state highways and interstates being the most travelled. Therefore, he works primarily with state agencies such as Caltrans to advocate for changes in the way wildlife is treated within the road system.

In addition to CROS, Shilling conducts research and observation through a system of motion-triggered infrared cameras set up along California’s major highways. He is observing, “whether, where and how wildlife are interacting with underpasses built under highways.”

According to Shilling, only a few mammal species will tolerate the human structure and go through these underpass tunnels, deer and raccoons are two examples. By examining these kinds of behavioral impacts, it becomes apparent that roadkills are only part of the problem. “If you think about the distribution of highways around California you are cutting up all of these populations of wildlife species into smaller units, with big consequences for the genetics within a species and the likelihood of [that species] continuing.”

Anyone can check out CROS ( and consider both contributing observations and requesting specific data to help with your own studies. Ultimately, the goal is to reduce roadkills by understanding where wildlife-vehicle collisions occur, what animals are involved, and on what kinds of roads these collisions are frequent. This information will help inform policy, management, and encourage financial investment in reducing roadkills across the state.

CROS is already having positive impacts. Just recently the Sonoma Land Trust (SLT) and US Fish and Wildlife Service (USFWS) announced plans to restore vegetation for wildlife passage under Highway 37, which bisects the coastal tidal marshes of the North Bay—this is one of three roadkill hotspots along that highway identified by CROS.

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