California Red-Legged Frog

Rana draytonii

  • Threatened – Endangered Species Act (1996)
  • Species of Special Concern – California Department of Fish and Wildlife
  • Vulnerable – IUCN Red List (2008)

Red-legged frog. Photo © californiaherps.com

Range and Description

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

In the southern Los Padres, the CRLF was common throughout the Santa Clara River watershed (particularly along Piru Creek and Sespe Creek) and the Ventura River watershed until about 1970. Now, the species can only be found in small areas of the Ventura River watershed. They entirely disappeared south of Ventura County before reintroduction efforts in some watersheds. Their numbers are now declining along the south coast of Santa Barbara County. The largest known populations currently occur along the upper Carmel River, Mono Creek above Mono Campground, and the Santa Ynez River between Jameson and Gibraltar reservoirs in the Santa Barbara backcountry. Some specimens have also been located in the Manzana Creek watershed within the Los Padres National Forest.

A medium-sized frog, the CRLF can be identified by its relatively long legs and distinctive reddish coloring on its belly and beneath its hind legs.  Their legs also have prominent dark bands.

The habitat of the red-legged frog.

Habitat and Life Cycle

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. In fact, CRLFs 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 CRLF larvae and tadpoles. In one study, survival was estimated at less than 5 percent for CRLF larvae occurring with bullfrog tadpoles, contrasted with 30–40 percent for larvae occurring without bullfrog tadpoles. The amount of rain also affects CRLF 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 CRLF has 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 as tadpoles eat algae while insects appear to be the most common food item for adults. However, larger animals such as Pacific tree frogs and mice represent over half of the prey mass eaten by larger CRLFs.

Threats

Several factors are contributing to the extreme decline of the CRLF. Predatory nonnative fish and amphibians (such as introduced bullfrogs) are particularly serious threats to the species. With few exceptions, the CRLF 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 CRLF.

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).

A juvenile California red-legged frog in a creek within the San Rafael Wilderness. Photo by Bryant Baker.

Perhaps the most important factor contributing to the decline of the CRLF is habitat destruction. Historically the CRLF extended from Point Reyes National Seashore near San Francisco, as far east as the Sierra foothills, and south into Baja California, Mexico. However as the Central Valley was converted into primarily agricultural lands, more than 90 percent of historical wetlands were lost. By 1960 the frogs were gone from most of the Central Valley as well as their old coastal stronghold of Monterey County. In Southern California, urbanization in the 1960s had the same effect, all but eliminating them from south of Ventura County.

Conservation and Protection

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

  • Monterey County: Carmel River and 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, and Upper Santa Ynez River
  • Ventura County: Matilija Creek and Piru Creek

The Los Padres National Forest provides prime habitat for the CRLF. ForestWatch will continue to monitor projects in the forest to ensure that CRLF populations are not disturbed and habitat is conserved.

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