Ensuring habitat connectivity for transportation projects - Examining the feasibility of wildlife crossings along State Route 101 in northern Sonoma County, California

Christopher Pincetich, Caltrans
Matthew Rechs, Caltrans
Heather Fountain, Caltrans
Andrew Amacher, Caltrans

Habitat connectivity across the Russian River valley is affected in some areas by the 4-lane State highway 101, which runs north and south across the valley and Santa Rosa plains in northern Sonoma County, California, USA. A total of nineteen monitoring cameras were deployed within the project area of a planned rehabilitation of this route to examine the role of existing culverts to serve as wildlife crossing structures for large and small mammals. Additionally, landscape-scale analyses were conducted to evaluate areas where connectivity of natural landscapes on opposite sides of the highway would benefit from improved crossing structures. The Browning Dark Ops 940 was the camera model used in this project, which uses an infrared sensor and flash to capture images of animals day or night. Placement of cameras was prioritized to occur only within the project limits that funded the camera purchases, at the largest existing structures with potential to be used by wildlife to cross under the highway, and in locations not visible to the traveling public on the highway as to avoid distraction of drivers and theft or vandalism of cameras. Paired cameras were installed at the entry and exit of potential crossing sites within the highway right of way lands, but many cameras were installed at either a culvert exit or entry point only as the other end of the culvert was on private lands. The results document the seasonal use of some culverts by small mammals to cross under the highway, the refusal of small and large mammals to enter most culverts, and the documented presence of small and large mammals occurring near the roadway. Large mammals observed included mule deer, coyote, bobcat, and mountain lion. Small mammals observed include grey fox, racoon, opossum, squirrels, and woodrats. The landscape analysis revealed that the highway separated areas of mixed hardwood forest with good habitat value from privately developed housing and commercial agricultural lands with limited habitat value. Regional, landscape-scale analysis of large ecological networks showed potential wildlife migration corridors that were outside the area of this study. The results of the camera observations and the landscape level analysis show some potential for improved connectivity between areas on either side of the highway to improve wildlife habitat. The project did serve to improve the culture of the local transportation agency District to more readily embrace planning for wildlife crossings in projects and resulted in the purchase of monitoring cameras that are now being deployed to study additional areas for potential wildlife crossing structures within the District.

Abstract Keywords
Terrestrial Wildlife and Ecosystem Interactions with Transportation