Diurnal Versus Nocturnal Surveys for California Red-Legged Frogs

The United States Fish and Wildlife Service (USFWS) federally listed the California red-legged frog (Rana draytonii; Shaffer et al. 2004) as a threatened species in June 1996 (USFWS 1996). The listing justification stated that a variety of human activities, including urban encroachment, construction of reservoirs and water diversions, introduction of exotic predators and competitors, livestock grazing, and habitat fragmentation, had extirpated redlegged frogs from 70% of their former range and continue to be a threat (see also Fellers 2005). Because the Endangered Species Act of 1973 now protects this frog, biologists must conduct surveys prior to any federally permitted habitat modifications or any activity on federal lands that has the potential to affect this species.