In the high mountains of California, several breeding ponds exist within US Fish and Wildlife Service (USFWS) designated critical habitat for the Federally Threatened Yosemite toad (Anaxyrus canorus). Lower Sardine and Upper Sardine meadows are home to two of these breeding ponds, both of which are located directly adjacent to the roadway along State Route 108 in Mono County, California. Since 2016, Biologists for Humboldt-Toiyabe National Forest have been conducting breeding surveys within these meadows and, incidentally, have documented several vehicle-collision caused Yosemite toad mortalities along State Route 108 at the meadows, where the roadway crosses through critical habitat.
As a mitigation measure for a California Department of Transportation (Caltrans) Highway Maintenance Project constructed in 2020, Caltrans installed two experimental crossing structures in the roadbed at the “hotspot” with the highest recorded Yosemite toad roadkill – along State Route 108 at Upper Sardine meadow.
Decisions on location, design, and installation methods for the crossing structures have been a collaborative effort among stakeholder agencies. In the early stages of project development, Caltrans Environmental Staff reached out to agency personnel at the US Fish and Wildlife Service, US Forest Service, and US Geological Survey for input and comments. Several field visits that included Caltrans Design Engineers and Environmental Staff along with Federal agency personnel were conducted during the design phase of the project. The final crossing structure designs and locations were selected to target the Upper Sardine meadow hotspot, while at the same time implementing designs that could be constructed utilizing the allocated project budget. Two experimental designs were employed, a modified culvert system and a modified cattleguard structure.
With the two crossing structures in place, Caltrans Environmental Staff, along with staff from stakeholder agencies, are hoping to further our conservation efforts by installing barrier fencing and conducting a three-year research study (beginning in summer of 2021) on the use and effectiveness of the crossing structures. The study aims to draws conclusions from a real-world implementation of low-cost crossing structure designs by determining: (1) whether the crossing structure designs can be effective for reducing Yosemite toad road mortality and (2) if there is any preference for one or both crossing structure designs. Answers to these questions will add valuable data to the growing body of knowledge in road ecology and potentially help inform future road passage designs for amphibians and other small wildlife species.