California Red-Legged Frog

Rana draytonii

Red-legged frog, photo © californiaherps.com

The California red-legged frog (RLF) is the largest native frog in the western United States. The Los Padres National Forest supports more California red-legged frogs than any other public lands in California. These threatened frogs have been eliminated from over 70 percent of their historic habitat, and today can be found primarily in the coastal streams and wetlands of Monterey, San Luis Obispo, and Santa Barbara counties.

In the southern Los Padres, RLF were common throughout the Piru and Sespe Creek and Ventura River drainages until about 1970, but are all gone now except for small parts of the Ventura River drainage. They have entirely disappeared south of Ventura County, and their numbers are now declining along the south coast of Santa Barbara County. The largest known populations currently occur on the upper Carmel River, Mono Creek above Mono Campground, and on the Santa Ynez River between Jameson and Gibraltar reservoirs in the Santa Barbara backcountry. Look for the tell-tale pink to red belly and hind legs if you come across a large frog on one of your adventures on the Los Padres!

Habitat and Life Cycle

The habitat of the red-legged frog.

These frogs have been found at elevations ranging from sea level to about 5,000 feet. They utilize a variety of habitat types, including aquatic, riparian, and upland habitats – RLFs are sometimes found up to 300 feet from water! They need water during the breeding season (generally November – April) for laying their eggs, with the males arriving at breeding sites 2-4 weeks before the females to ‘set up camp’ and practice their singing voices. It takes seven long and dangerous months for the fertilized eggs to make it to metamorphosis—survival from hatching to metamorphosis has been estimated to range as low as less than 1 percent!

Survival often hinges on the presence of bullfrog tadpoles, which eat RLF larvae and tadpoles (in one study, survival was estimated at less than 5 percent for red-legged frog larvae occurring with bullfrog tadpoles, contrasted with 30–40 percent for red-legged frog larvae occurring without bullfrog tadpoles). The amount of rain also affects RLF egg survival, as eggs are susceptible to being washed away by high stream flows.

California red-legged frog tadpole. Photo © californiaherps.com

Once they’ve grown their legs, frog juveniles and adults may disperse from breeding sites at any time of the year. Dispersal sites typically include boulders or rocks and organic debris such as downed trees or logs, which provide shelter and feeding areas. The RLF have been recorded traveling more than two miles in search of new dispersal sites. Frogs will remain out and about throughout the year until water disappears, when they take refuge in burrows.

Juvenile frogs are busy hunting both diurnally and nocturnally, whereas adult frogs are largely active at night. Their diet is highly variable—tadpoles probably eat algae, insects appear to be the most common food item for adults, and larger animals such as Pacific tree frogs and mice represent over half of the prey mass eaten by larger California red-legged frogs.

Threats

Several factors combined are contributing to the extreme decline of RLF. Predatory nonnative fish and amphibians (like introduced bullfrogs) are particularly serious threats to red-legged frogs. With few exceptions, the red-legged frog has disappeared from virtually all areas where nonnative bullfrogs have become established. Bullfrogs are larger, have more generalized food habits, and have an extended breeding season; moreover, bullfrog larvae are unpalatable to predatory fish—all characteristics giving them a competitive advantage over RLF.

Other threats include impacts from campgrounds and roads in frog habitat (including potential crushing of frogs and egg masses from foot and vehicle traffic); livestock grazing that degrades riparian, wetland, or upland habitat; water diversions like groundwater extraction and stock pond and small reservoir developments; and chytrid fungus (a lethal skin disease).

Finally, one cannot forget the general threat of past and continued destruction of suitable habitat for the frogs to live and breed in. Historically the RLF extended from Point Reyes National Seashore (just across the Golden Gate bridge from San Francisco), as far east as the Sierra foothills, and down into Baja California, Mexico. However as the Central Valley became the agricultural powerhouse it is today, more than 90 percent of historical wetlands were lost and by 1960 the frogs were gone from most of the valley and their old coastal stronghold of Monterey County. In Southern California in the 1960s urbanization was having the same effect and today the frogs are gone south of Ventura County.

Conservation & Protection

The U.S. Fish & Wildlife Service prepared a Recovery Plan for the RLF in 2002, recommending the development of management plans and surveys in key habitat areas and taking other steps to reduce or eliminate threats to RLF. In 2010, the Service also designated critical habitat for RLF, identifying key areas for the survival and recovery for RLF. Critical habitat in the Los Padres National Forest includes the following watersheds:

  • Monterey County: Carmel River & Big Sur Coast
  • San Luis Obispo County: several streams in the Santa Lucia Range, and the Upper Salinas River
  • Santa Barbara County: La Brea Creek, several streams along the Gaviota Coast (SB County), and Upper Santa Ynez River
  • Ventura County: Matilija Creek & Piru Creek

The Los Padres National Forest continues to provide a population stronghold for California red-legged frogs, and ForestWatch will continue to monitor projects on the forest with the protection of the California red-legged frog in mind.

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