Conserving the Nature of America

News Release

Southern California Population of Mountain Yellow-Legged Frog Determined to be Endangered

July 2, 2002


Division of Public Affairs
External Affairs
Telephone: 703-358-2220

One of many native amphibian species in decline

The U.S. Fish and Wildlife Service announced today it is listing the southern California distinct population segment of mountain yellow-legged frog (Rana muscosa) as endangered under the Endangered Species Act. Seven small, isolated populations totaling fewer than 100 adult individuals are believed to still exist within portions of the San Gabriel, San Bernardino, and San Jacinto Mountains.

Mountain yellow-legged frogs inhabit stream reaches in southern California north to high mountain lakes in the Sierra Nevada Mountains. Research indicates that mountain yellow-legged frogs in the Sierra Nevada Mountains are distinct from those in southern California based upon geographical separation and genetic differences. The Service has determined that the southern California population of mountain yellow-legged frog constitutes a distinct vertebrate population segment (DPS) of the species.

Historically, the southern California population of mountain yellow-legged frog was known from about 166 documented localities ranging from Palomar Mountain in northern San Diego County to the San Gabriel Mountains in Los Angeles County. Today, this population segment has disappeared from a significant portion of its former range.

"It will take the combined efforts of Federal and State agencies and the public to chart a course for the recovery of this species," said Steve Thompson, Manager of the California Nevada Operations Office.

Although the exact causes of the California population’s dramatic decline are not fully understood, possible causes include predation from bullfrogs and introduced trout, disease, contaminants and alteration of habitat.

Almost all of the remaining populations of mountain yellow-legged frogs in southern California are confined to a few stream reaches within the boundaries of the U.S. Forest Service’s Angeles National Forest and San Bernardino National Forest.

Mountain yellow-legged frogs typically measure 1.5 to 3 inches long from the snout to the base of the backbone. Skin coloration and patterning varies and can consist of a few dark, irregular spots to smaller, more numerous spots; body color is usually a mix of brown and yellow, but can include gray, red, or greenish-brown. The underside of the belly and hind limbs vary from pale lemon yellow to brilliant sun yellow.

Eighteen species of amphibians in the United States and Puerto Rico are already listed under the Act, including the threatened California red-legged frog (Rana aurora draytonii) and the endangered arroyo toad (Bufo microscaphus). The decline of native amphibians in the western United States has been attributed to the loss, alteration, or degradation of habitat from logging, mining, and water development projects; and the introduction of non-native competitors such as bullfrogs and trout.

Other less well understood environmental factors which may be contributing to these declines include diseases, pathogens, effects of pesticides, and increased exposure to ultraviolet-B radiation.

The Department of the Interior, in partnership with other research entities, initiated a nationwide study in 2000, to study amphibian declines in the United States and why many of these species are exhibiting high rates of physical deformities.

Amphibians, including the mountain yellow-legged frog, are highly sensitive to changes in their aquatic environments because they breathe at least partially through their skin. The decline of amphibians and increased rates of physical abnormalities may be an indication of significant changes in the environment

The Service originally proposed to list the southern California DPS in 1999, but was unable to make a final determination due to the need to use its limited resources to comply with other, higher-priority listing actions. In 2001, the Department of the Interior, Center for Biological Diversity, Southern Appalachian Biodiversity Project, and the California Native Plant Society formalized a settlement agreement that allowed the Service to free up funding to complete final listing determinations for 14 species, including the southern California DPS of mountain yellow-legged frog. Today’s announcement complies with that settlement agreement.

The final determination to list the southern California distinct population segment of mountain yellow-legged frog was published in today’s Federal Register. To learn more about the final determination to list the southern California population of mountain yellow-legged frog as endangered, visit the Carlsbad Fish and Wildlife Office’s website at

The U.S. Fish and Wildlife Service is the principal Federal agency responsible for conserving, protecting and enhancing fish, wildlife and plants and their habitats for the continuing benefit of the American people. The Service manages the 95-million-acre National Wildlife Refuge System which encompasses nearly 540 national wildlife refuges, thousands of small wetlands and other special management areas. It also operates 70 national fish hatcheries, 64 fishery resource offices and 78 ecological services field stations. The agency enforces Federal wildlife laws, administers the Endangered Species Act, manages migratory bird populations, restores nationally significant fisheries, conserves and restores wildlife habitat such as wetlands, and helps foreign governments with their conservation efforts. It also oversees the Federal Aid program that distributes hundreds of millions of dollars in excise taxes on fishing and hunting equipment to state fish and wildlife agencies.