Many small animals, especially amphibian populations that must migrate between aquatic and terrestrial habitats, are susceptible to negative impacts from roads within their habitat. Yosemite toads have been tracked moving away from breeding meadows over 0.78 miles through dry upland habitats where they spend most of their lives. Toads move during the day or night, especially during summer rain events making them susceptible to mortality. Over a 4-month period in the summer of 2017, Sierra National Forest staff recorded 88 Federally threatened Yosemite toad (Anaxyrus canorus) confirmed mortalities spanning about 2 miles along a single forest service road (9S09) that crossed through occupied terrestrial habitat.
Narrow tunnels (<1m) under roads with directional barriers are a standard mitigation solution to reduce amphibian road mortality along roadways. However, there is recent evidence that these tunnel mitigation systems may act to filter migratory movements of species that disperse over large areas and unintentionally cause population decline. For these situations, larger movement corridors across roads are warranted. In 2018 we tested a new and novel passage prototype, an 8" high elevated road segment using road mats designed for use by heavy equipment at construction sites. The prototype was installed on top of the road along a 9S09 Yosemite toad mortality "hotspot" providing a safe crossing nearly 100' wide while allowing both light and rain to pass through. We monitored toad activity along attached directional fencing and under the passage using specialized cameras and conducted regular road mortality surveys. In 2018, we recorded many toads using the passage and no mortality within the project footprint.
This concept is currently being adapted to improved roads and highways and can be made to any length to better preserve connectivity of sensitive small animals in roaded areas. This study supports a broader research program to inform best management practices for barrier and crossing systems for sensitive amphibians and reptiles in California.