Caltrans’ Efforts Improve Wildlife Movement, Decrease Deaths

A recently released report from the National Park Service concludes that Caltrans’ efforts to mitigate the impact of the widening of State Route 23 (SR-23) on local wildlife are 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 SR 23 in Ventura County over a seven-year period, from 2004 to 2011. Biologists from Santa Monica Mountains National Recreation Area (SMMNRA), 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 adding a broader range of design elements to encourage use by smaller mammals. Rabbit roadkills actually increased four-fold, suggesting that smaller animals found ways through or around the fence. See full report: nps.gov/samo/parknews/upload/SR23-Final-Report.pdf.

“We are pleased with the results of our mitigation efforts and are working to further improve wildlife-freeway crossings in the region,” said Caltrans Sr. Environmental Planner Barbara Marquez.

The study is one of 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.