The endemic river-dwelling Foothill Yellow-legged Frog (Rana boylii) of California and Oregon (U.S.A.) has disappeared from over 50% of historically occupied localities, with absences more common in close proximity to large dams. Persisting populations are small relative to those in rivers without reservoirs and are harmed by poorly timed flow releases and habitat fragmentation. A general population model developed for this species indicates that many R. boylii populations are at risk of extirpation by virtue of low abundance, even before hydrologic stressors and non-native predators (such as bull frogs or bass) are considered. (Kupferberg et al. 2009 (see report here); Sarah Kupferberg, in litt. August 2010)
Recent radiotelemetry and genetic research shows that these frogs use entire watersheds, sometimes migrating many kilometers to mate and lay eggs at breeding sites that are used year after year. To be successful, their unique survival strategy requires use of all habitats from small creeks to big rivers within a basin. Tadpoles cannot mature into frogs without access to sunlit channels with abundant algal foods in the summer, while juveniles and adults cannot survive winter floods without access to refugia such as small tributaries. During the past 150 years, humans have permanently and drastically transformed riverscapes in the Sierran foothills and the Pacific coast-ranges. This human appropriation of rivers is likely to intensify as we search for carbon-neutral methods to produce electricity (e.g., harnessing hydropower), provide drinking water to urban centers, and deliver irrigation to agricultural users. Current listing status as a California Species of Special Concern does not provide adequate protection for these frogs. (Sarah Kupferberg, in litt. August 2010)
No one has provided updates yet.