Historical range extended from the Diamond Mountains northeast of the Sierra Nevada in Plumas County, and from just north of the Feather River in the extreme northwest region of the Sierra Nevada, California, south through the Sierra Nevada to Inyo County, California, and east to Mt. Rose, northeast of Lake Tahoe, in Washoe County, Nevada (Vredenburg et al. 2007). West of the Sierra Nevada crest, the southern part of the range is bordered by ridges that divide the Middle and South Fork of the Kings River, ranging from Mather Pass to the Monarch Divide; east of the Sierra Nevada crest, R. sierrae occurs in the Glass Mountains just south of Mono Lake (Mono County) and along the east slope of the Sierra Nevada south to the type locality at Matlock Lake (Inyo County) (Vredenburg et al. 2007). Rana sierrae is now extirpated from Nevada and from large portions of the historical range in the Sierra Nevada of California.
Habitat and Ecology
The habitat of frogs of the Rana muscosa/Rana sierrae complex includes sunny river margins, meadow streams, isolated pools, and lake borders in the Sierra Nevada. Sierran frogs are most abundant in high elevation lakes and slow-moving portions of streams. They seldom are found away from water but may cross upland areas in moving between summer and winter habitats (Matthews and Pope 1999). Wintering sites include areas near shore under ledges and in deep underwater crevices (Matthews and Pope 1999).
Extensive surveys between 1995 and 2005 yielded only 11 occupied sites (Vredenburg et al. 2007). Total adult population size is unknown but may not exceed a couple thousand (generously assuming 20 sites each with 100 adults).
A precipitous decline in Rana muscosa/Rana sierrae appears to have occurred over the past 3-4 decades (Bradford 1991, USFWS 1999). For the Rana muscosa/Rana sierrae complex as a whole, Jennings and Hayes (1994) mapped many more extirpated populations than extant populations. Rana sierrae has declined greatly in the Yosemite area of the Sierra Nevada, California (Drost and Fellers 1996). In the Sierra Nevada, recent surveys indicate that Rana muscosa/Rana sierrae has been reduced to a small number of widely scattered, mostly very small populations (fewer than 20 adults) (Knapp and Matthews 2000). Surveys in the 1990s indicated that the rangewide decline in distribution may be as much as 70-90 percent (USFWS 2000).
Of the 146 historical R. sierrae sites studied by Vredenburg et al. (2007), only 11 sites contained frogs when revisited between 1995 and 2005 (92 percent extirpation rate).
The current trend (past 10 years) is unknown, but probably the decline is ongoing.
A petition to list the Rana muscosa/Rana sierrae complex as endangered cited the following threats: non-native fish introductions, contaminant introductions, livestock grazing, acidification from atmospheric deposition, nitrate deposition, ultraviolet radiation, drought, disease, and other factors (see USFWS 2000).
Extensive surveys in the Sierra Nevada clearly demonstrate the strong detrimental impact of introduced trouts on R. muscosa/Rana sierrae populations (Bradford 1989, Knapp and Matthews 2000). Removal of non-native fishes (relatively easy in some Sierra Nevada lakes) might easily reverse the decline (Knapp and Matthews 2000).
See Bradford (1991) for information on mass mortality and extinction of a population due at least in part to red-leg disease and predation on metamorphics by Brewer's blackbird; reestablishment of the extirpated population probably will be prevented through predation by introduced fishes.
Frogs of the Rana muscosa/Rana sierrae complex are possibly but probably not threatened by sublethal effects of low pH and elevated levels of dissolved aluminum (Bradford et al. 1992).
Fellers et al. (2001) documented oral chytridiomycosis (often indicated by oral disc abnormalities) in larvae and recently metamorphosed individuals of the Rana muscosa/Rana sierrae complex in the Sierra Nevada, where recent declines have occurred. However, loss of pigmentation of larval mouthparts does not always indicate chytridiomycosis (Batrachochytrium infection) (Rachowicz 2002).
Davidson et al. (2002) found support for the hypothesis that airborne agrochemicals have played a significant role in the decline of frogs of the Rana muscosa/Rana sierrae complex.
Most occurrences are on lands administered by the U.S. Forest Service or U.S. National Park Service. However, occurrence in protected, pristine areas does not ensure population persistence.
Red List Status
Listed as Endangered in view of severe recent declines that likely are continuing (rate of decline over past 10 years unknown) and that has left only a small number of extant populations occupying a small fragmented area.
Yellow-legged frog populations now recognized as Rana sierrae formerly were included in Rana muscosa. Vredenburg et al. (2007) examined phylogeography of Rana muscosa as defined by Stebbins (2003) and determined that R. muscosa occurs in the southern Sierra Nevada and in mountains to the south and that populations in the Sierra Nevada north of this range comprise a distinct species (Rana sierrae).
Geoffrey Hammerson 2008. Rana sierrae. The IUCN Red List of Threatened Species 2008: e.T136114A4240654. http://dx.doi.org/10.2305/IUCN.UK.2008.RLTS.T136114A4240654.en .Downloaded on 23 February 2019