During the past century, the mountain yellow-legged frog has gone from being one of the most common vertebrates throughout its range to one of the rarest. These declines were first noted as long ago as the early 1900s (Grinnell and Storer 1924), but their severity was unrecognized until recently. Surveys conducted during the last 12 years at more than 15,000 sites throughout the range of the mountain yellow-legged frog by researchers and the California Department of Fish and Game (Knapp et al. 2003; Knapp 2005; California Department of Fish and Game, unpublished data) has allowed analyses that paint a grim picture.
Results from recent studies
A recent comparison of historical versus current occupancy for all verified localities (based on museum specimens) indicated that Rana sierrae and Rana muscosa are now absent from more than 92% of historic localities in the Sierra Nevada, and R. muscosa is absent from 98% of historic localities in the Transverse Ranges (Vredenburg et al. 2007). In the Sierra Nevada, mountain yellow-legged frogs have disappeared from nearly all known low-elevation sites on the west slope (4,500-9,000 feet; 1,370-2,740 m), are extremely rare east of the Sierra crest, and are increasingly uncommon even in the most remote alpine habitats along the west side of the Sierra crest (10,000-12,000 feet; 3,050-3,660 m). In addition, most remaining mountain yellow-legged frog populations are located in Sequoia, Kings Canyon, and Yosemite National Parks, and are very rare in national forest wilderness areas (e.g., John Muir Wilderness, Ansel Adams Wilderness, Desolation Wilderness; Knapp and Matthews 2000a). In southern California, R. muscosa is now restricted to fewer than 10 sites in the San Gabriel and San Jacinto Mountains that collectively harbor fewer than 100 adult frogs (Jennings and Hayes 1994).
Listing under the Endangered Species Act
Based on the severity of the mountain yellow-legged frog's decline, in 1995 the Biodiversity Legal Foundation petitioned the U.S. Fish and Wildlife Service (USFWS) to list the mountain yellow-legged frog in southern California as "endangered". In December 1999, the USFWS issued a proposed rule supporting this listing. In February 2000, the Center for Biological Diversity and Pacific Rivers Council petitioned the USFWS to list the Sierra Nevada populations of the mountain yellow-legged frog as endangered. The USFWS released its "12-month finding" regarding the listing petition in January 2003, specifying that the listing of the Sierra Nevada populations of the mountain yellow-legged frog as "endangered" was "warranted" but precluded by other higher priority listing actions. Despite a successful lawsuit by the original petitioners challenging this finding, the Sierra Nevada populations remain unlisted. For additional details, check out In The News > ESA listing.