THOUSAND OAKS, Calif. - A recently released report from the National Park Service concludes that Caltrans' efforts to mitigate the impact of the widening of State Route 23 on local wildlife were effective. Installation of wildlife fencing and one-way gates, as well as clearance of three key underpasses, led to a six-fold increase in the number of successful wildlife crossings and an 88% decrease in coyote road mortalities.
"Roads fragment natural habitat and can have significant impacts on wildlife movement and survival," said Jeff Sikich, a biologist for the National Park Service. "These crossings can effectively reduce road mortalities and increase connectivity in fragmented landscapes."
Funded by Caltrans, the $90,000 study monitored wildlife movement and road mortality rates on State Route 23 (SR-23) in Ventura County over a seven-year period, from 2004 to 2011. Biologists from Santa Monica Mountains National Recreation Area, a unit of the National Park Service, conducted the road mortality surveys by driving a two-mile stretch of the highway three times per week and using remote cameras to monitor wildlife use of three underpasses. They found Caltrans mitigation efforts effective at increasing culvert use for many medium-sized mammals and reducing road mortality rates of coyotes, but recommended incorporating a broader range of design elements to also encourage use by smaller mammals. Rabbit roadkills actually increased four-fold, suggesting that smaller animals found ways through or around the fence.
"Caltrans is committed to the stewardship of our natural resources, including wildlife movement patterns," said Caltrans Senior Environmental Planner Barbara Marquez. "We are pleased with the results of our mitigation efforts for the SR-23 widening project and are working to further improve critical wildlife-freeway crossings in the region."
The study is one of the few to examine the impact of roads on wildlife both before and after mitigation efforts. In addition to the ecological importance of providing safe passage for animals to cross through Southern California's complex system of highways, successful wildlife crossings have important motorist safety implications in terms of reducing animal-vehicle collisions. The results and accompanying recommendations will inform Caltrans' future efforts to mitigate the impact of roads on local wildlife.
Santa Monica Mountains National Recreation Area (SMMNRA) is the largest urban national park in the country, encompassing more than 150,000 acres of mountains and coastline in Ventura and Los Angeles counties. It comprises a seamless network of local, state, and federal parks interwoven with private lands and communities. As one of only five Mediterranean ecosystems in the world, SMMNRA preserves the rich biological diversity of more than 450 animal species and 26 distinct plant communities.
The California Department of Transportation (Caltrans) is responsible for planning, design, construction, maintenance and operation of the state highway system. District 7, which includes Los Angeles and Ventura Counties, has 42 freeways and highways covering 1,188 miles. In keeping with its mission to improve mobility across California, District 7 also has the largest carpool lane system in the nation, stretching over 500 lane miles. On average motorists in District 7 travel 100 million vehicle miles every day.
