Mountain Yellow-Legged Frog Rana muscosa
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When Dr. David Wake, a herpetologist with the U.C. Berkeley Museum of Vertebrate Zoology, hiked through Yosemite National Park in 1959, he noted that the mountain yellow-legged frogs were so numerous near Tioga Pass that "it was difficult to walk without stepping on them". When he returned to Tioga Pass in the late 1980's, he saw none.
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©
Deanna Spooner 2001
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Historic
Background
The mountain yellow-legged frog (Rana
muscosa) has been a resident of the Sierra
Nevada for over a million years. With populations
stretching throughout the region, many historical
accounts note the abundance of frogs throughout
the area, describing the populations as "thriving"
and some of the "densest aggregations of frogs ever
noted". Current estimates show that there has been
a 50% to 90% decline in population levels over the
last century.
Physical Description
Though the mountain yellow-legged frog is highly variable in color, the species is generally gray or reddish brown, with variably sized black or brown spots. The underside of the legs are yellow, sometimes stretching to its underbelly. Males are usually smaller than females, and have a larger, darkened thumb. Interestingly, the frogs smell like garlic when handled.
Habitat
High elevation lakes, ponds, springs and streams. Tadpoles overwinter one or more years and thus require aquatic habitat deep enough that it does not dry up in the summer or freeze through the winter. Riparian vegetation is important to provide shelter; banks and rocks are used for basking.
Historic Range & Current Distribution
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R. muscosa populations were
abundant in the upper elevations of the Sierra
Nevada from Plumas to Tulare County. Currently,
there are scattered and reduced populations across
the historic range of the species. Of 86 population
sites surveyed between 1915 and 1959, only 16
of these sites contained frogs in surveys conducted
between 1989 and 1995. Most of the populations
which still exist are found in the Sequoia, Kings
Canyon, and Yosemite National Parks. However,
these populations are drastically smaller than
those observed in the past.
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Rana
Lake, Murphy's Basin, John Muir Wilderness(Mountain yellow-legged
frog habitat in the High Sierra) © Deanna Spooner 2001
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Status
Forest Service Sensitive Species; candidate for listing under the Endangered Species Act
Primary Threats
- Introduction of predatory trout;
- Population fragmentation; and
- Habitat degradation from pack stock use, recreation, and pesticide/herbicide use.
Conservation Needs
Rana muscosa does not enjoy any formal protections, although it is a candidate for listing under the Endangered Species Act. Currently, the Forest Service and the California Department of Fish and Game are conducting surveys of for the mountain yellow-legged frog which theoretically will provide the basis of conservation strategy. However, past efforts to draft such a strategy have fallen apart, partly because they lacked binding provisions with regard to fish stocking. To better protect the species, a network of refugia lakes should be established to ensure continued survival of breeding populations and aid in the recolonization of formerly occupied habitat. Moreover, aerial fish stocking should be ceased permanently in all currently occupied and potential future habitat. Federal and state agencies should further adjust management practices regarding fish stocking, pack stock use and access, recreation, and application of pesticides/herbicides to benefit the species.
Sources
Cory, L.R. Memorandum to National Park Serivce dated February 28, 1989, as cited in Center for Biological Diversity and Pacific Rivers Council. 2000b. Petition to List the Sierra Nevada Mountian Yellow-Legged Frog (Rana Muscosa) as an Endangered Species under the Endangered Species Act.
Knapp, R.A., and Matthews, K.R. 2000. Non-Native Fish Introductions and the Decline of the Mountain Yellow-Legged Frog from within Protected Areas. Conservation Biology, vol. 14 2:428-438.
Mountain Yellow-legged Frog website, http://www.mylfrog.info
Mullally, D.P. and J.D. Cunningham 1956. Ecological relations of Rana muscosa at high elevations in the Sierra Nevade. Herpetologica 12 (3):189-198, as cited in Center for Biological Diversity and Pacific Rivers Council. 2000b. Petition to List the Sierra Nevada Mountian Yellow-Legged Frog (Rana Muscosa) as an Endangered Species under the Endangered Species Act.
Parker, D. 1994. Inyo National Forest amphibian status report. U.S. Forest Service, Bishop California Office, as cited in Center for Biological Diversity and Pacific Rivers Council. 2000b. Petition to List the Sierra Nevada Mountian Yellow-Legged Frog (Rana Muscosa) as an Endangered Species under the Endangered Species Act.
Stebbins, R.C. 1985. Western Reptiles and Amphibians.New York: Houghton Mifflin Company.
USFS. 1998. Region 5 Sensitive Species List (dated June 10, 1998). USDA Forest Service, San Francisco.
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