Rana muscosa (mountain yellow-legged frog) is one of a number of amphibians around the world that reportedly have declined in numbers in recent years in seemingly well-protected environments. In Sequoia and Kings Canyon National Parks, California, two study areas comprising the headwaters of seven creek systems were surveyed for R. muscosa and Pseudacris regilla (Pacific chorus frog) in 1978-1979 and again in 1989. R. muscosa was found at 27 sites greater than 200 m apart in 1978-1979, but at only one site in 1989, and the population at this site disappeared by 1991. In contrast, P. regilla was found at 15 to 17 sites both times. A comparison of 21 historical (1955-1979) and recent (1989-1990) records scattered throughout the parks showed that R. muscosa remained at only 11 of these sites in 1989-1990. A similar comparison of 24 historical and recent records elsewhere in the Sierra Nevada showed that R. muscosa remained at only three sites. We conclude that R. muscosa has disappeared from about half of its historical localities in Sequoia and Kings Canyon National Parks during the past three decades, and has been extirpated in some drainages. The magnitude of decline appears to be even more pronounced outside the parks. The causes for these declines are not clear.
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