California Red-Legged Frog (Rana aurora draytonii)
Photograph (C) Gary Nafis
General Distribution
Red-legged frogs historically occurred on all four National Forests in southern California, but now appear to be extirpated from the Cleveland and San Bernardino National Forests. Most California red-legged frog locations on National Forest System lands are on the Los Padres National Forest. The California red-legged frog is known to occur in multiple locations on Branch, La Brea, Sespe, Piru, Ventana, and Morro Creeks, and the Santa Ynez, Sisquoc, and Carmel Rivers. The largest known populations occur on the upper Carmel River, Mono Creek upstream of Mono Campground, and near Juncal Campground on the Santa Ynez River (Stephenson and Calcarone 1999, U.S. Fish and Wildlife Service 2000b). The only known red-legged frog occurrence on the Angeles National Forest was located in 1999 in San Francisquito Canyon. Red-legged frogs occurred historically in several locations on the San Bernardino National Forest, but were last observed there more than 25 years ago. There were several historic locations on the Cleveland National Forest, and suitable habitat still occurs there, but California red-legged frogs have not been observed on this Forest since the 1980s (Stephenson and Calcarone 1999).
Systematics
The California red-legged frog is one of two subspecies of red-legged frog (R. aurora). Northern red-legged frog (R. a. aurora) occurs from northern Humboldt County to British Columbia (Jennings and Hayes 1994). The two subspecies, and intergrades of the subspecies, may occur together in the vicinity of Pt. Reyes National Seashore in Marin County and in portions of Sonoma County (U.S. Fish and Wildlife Service 2000a).
Habitat Requirements
The California red-legged frog has been found at elevations that range from sea level to about 5,000 feet (1,500 meters). They use a variety of habitat types, including aquatic, riparian, and upland habitats. The habitat descriptions below are meant to describe the range of habitat types utilized by California red-legged frog. However, there is much variation in how the taxon uses the environment. In many cases California red-legged frogs may complete their entire life cycle in a particular area without using other components (e.g., a pond is suitable for each life stage and use of upland habitat or a riparian corridor is not necessary). Populations appear to persist where a mosaic of habitat elements exists, embedded within a matrix of dispersal habitat. Under such conditions, local extinctions may be counterbalanced by recolonizations of new or unoccupied areas of suitable habitat (U.S. Fish and Wildlife Service 2000b). Breeding sites of California red-legged frog are always in aquatic habitats. An important factor influencing the suitability of aquatic breeding sites is the general lack of introduced aquatic predators.?Larvae, juveniles, and adult frogs have been collected from streams, creeks, ponds, marshes, sag ponds, deep pools and backwaters within streams and creeks, dune ponds, lagoons, and estuaries. Breeding adults are often associated with dense, shrubby riparian or emergent vegetation and areas with deep ( > 27 inches [0.7 meter]) still or slow-moving water (Hayes and Jennings 1988). However, frogs often successfully breed in artificial ponds with little or no emergent vegetation and have been observed in stream reaches that are not cloaked in riparian vegetation (U.S. Fish and Wildlife Service 2000a). The importance of riparian vegetation for this species is not well understood. While frogs successfully breed in streams and riparian systems, high spring flows and cold temperatures in streams often make these sites risky environments for eggs and tadpoles. When riparian vegetation is present, frogs spend considerable time resting and feeding in it; the moisture and camouflage provided by the riparian plant community may provide good foraging habitat and may facilitate dispersal in addition to providing pools and backwater aquatic areas for breeding. Radio telemetry studies showed that individual California red-legged frogs move within the riparian zone from vegetated areas to pools (U.S. Fish and Wildlife Service 2000b).
Reproduction
The California red-legged frog breeds from November–March, although earlier breeding has been recorded in southern localities (Storer 1925). Males have paired vocal sacs and call in air (Hayes and Krempels 1986). Males appear at breeding sites 2-4 weeks before females (Storer 1925). Females individually move toward individual males or male calling groups. Females deposit egg masses on emergent vegetation so that the masses float on the surface of the water (Hayes and Miyamoto 1984). Egg masses contain about 2,000-5,000 moderate-sized (0.08-0.11 inches [2.0- 2.8 millimeters] in diameter), dark reddish brown eggs (Jennings and Hayes 1985, Storer 1925). Eggs hatch in 6–14 days (Storer 1925). Larvae undergo metamorphosis 3.5–7 months after hatching (Jennings and Hayes 1990, Storer 1925, Wright and Wright 1949). Males attain sexual maturity by 2 years of age; females are sexually mature by 3 years (Jennings and Hayes 1985).
Daily/Seasonal Activity
Hayes and Tennant (1985) found juvenile frogs to be active both diurnally and nocturnally, whereas adult frogs were largely active at night. The season of activity for red-legged frog seems to vary with the local climate (Storer 1925); individuals from coastal populations with more constant temperatures are rarely inactive. Individuals from inland sites, where temperatures are lower, may become inactive for long intervals (Jennings and others 1992).During periods of wet weather, starting with the first rains of fall, some individuals may make overland excursions through upland habitats. Most of these overland movements occur at night. Evidence from marked frogs on the San Simeon coast of California suggests that frog movements of about 1 mile (1.6 kilometers) via upland habitats are possible over the course of a wet season. In addition, red-legged frogs have been observed to make long-distance migrations following straight-line, point-to-point routes rather than corridors between habitats. Red-legged frogs in northern Santa Cruz County traveled distances from 0.25 mile (0.4 kilometer) to more than 2 miles (3.2 kilometers) without apparent regard to topography, vegetation type, or riparian corridors (U.S. Fish and Wildlife Service 2000b). The manner in which California red-legged frog uses upland habitats is not well understood. Studies are being conducted to determine how much time California red-legged frogs spend in upland habitats; patterns of use; and whether there is differential use of uplands by juveniles, subadults, and adults.
Diet and Foraging
The diet of California red-legged frogs is highly variable. Tadpoles probably eat algae (Jennings and others 1992). Hayes and Tennant (1985) found invertebrates to be the most common food item for adults. Vertebrates such as Pacific tree frogs (Pseudacris [Hyla] regilla) and California mice (Peromyscus californicus) represented over half of the prey mass eaten by larger California red-legged frogs (Hayes and Tennant 1985). Feeding activity probably occurs along the shoreline and on the surface of the water.
Predator-Prey Relations
Predatory nonnative fish and amphibians are particularly serious threats to red-legged frogs. With few exceptions, the red-legged frog has disappeared from virtually all sites where bullfrogs have become established (Hayes and Jennings 1988). The only areas where the two species have managed to coexist for prolonged periods are immediately adjacent to the coast, where cool "fogbelt" temperatures appear to offer red-legged frogs some competitive advantages (U.S. Fish and Wildlife Service 2000b). Red-legged frogs appear more capable of persisting in the presence of nonnative fish; however, there are still strong negative correlations between the abundance of such fish and red-legged frog presence. Results of a recent study in artificial ponds showed that mosquitofish and bluegill were significant predators of red-legged frog larvae (Stephenson and Calcarone 1999).
Literature Cited
Cook, D. 1997. Biology of the California red-legged frog: A synopsis. 1997 Transactions of the Western Section of the Wildlife Society. 33: 79-82.
Morrison, M., ed. Oakland, CA: Western Section of the Wildlife Society.
Hayes, M.P.; Jennings, M.R. 1988. Habitat correlates of distribution of the California red-legged frog (Rana aurora draytonii) and the foothill yellow-legged frog (Rana boylii): Implications for management. In: Proceedings of the symposium on the management of amphibians, reptiles, and small mammals in North America. USDA Forest Service General Technical Report RM-166.
Hayes, M.P.; Krempels, D.M. 1986. Vocal sac variation among frogs of the genus Rana from western North America. Copeia 1986(4): 927-936.
Hayes, M.P.; Miyamoto, M.M. 1984. Biochemical, behavioral and body size differences between Rana aurora aurora and R. a. draytonii. Copeia 1984(4): 1018-1022.
Hayes, M.P.; Tennant, M.R. 1985. Diet and feeding behavior of the California red-legged frog, Rana aurora draytonii (Ranidae). Southwestern Naturalist 30(4): 601-605.
Jennings, M.R.; Hayes, M.P. 1985. Pre-1900 overharvest of California red-legged frogs (Rana aurora draytonii): The inducement for bullfrog (Rana catesbeiana) introduction. Herpetologica 41(1): 94-103.
Jennings, M.R.; Hayes, M.P. 1990. Status of the California red-legged frog Rana aurora draytonii in the Pescadero Marsh Natural Preserve. Report prepared for the California Department of Parks and Recreation, Sacramento, CA.
Jennings, M.R.; Hayes, M.P. 1994. Amphibian and reptile species of special concern in California. Final report to the California Department of Fish and Game, Inland Fisheries Division, Rancho Cordova, California, under contract 8023.
Jennings, M.R.; Hayes, M.P.; Holland, D.C. 1992. Petition to the U.S. Fish and Wildlife Service to place the California red-legged frog (Rana aurora draytonii) and the western pond turtle (Clemmys marmorata) on the list of endangered and threatened wildlife and plants.
Lawler, S.P.; Dritz, D.; Strange, R.; Holyoak, M. 1999. Effects of introduced mosquitofish and bullfrogs on the threatened California red-legged frog. Conservation Biology 13(3): 613-22.
Rathbun, G.B.; Jennings, M.R.; Murphey, T.G.; Siepel, N.R. 1993. Status and ecology of sensitive aquatic vertebrates in lower San Simeon and Pico Creeks, San Luis Obispo County, California. Prepared for the California Department of Parks and Recreation. San Simeon, CA: U.S. Fish and Wildlife Service, National Ecology Research Center.
Stephenson, J.R.; Calcarone, G.M. 1999. Southern California mountains and foothills assessment: Habitat and species conservation issues. General Technical Report GTR-PSW-172. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture.
Storer, T.I. 1925. A synopsis of the amphibia of California. University of California Publications in Zoology 27: 1-342.
U.S. Fish and Wildlife Service. 2000a. Draft recovery plan for the California red-legged frog (Rana aurora draytonii). Portland, OR: U.S. Fish and Wildlife Service.
U.S. Fish and Wildlife Service. 2000b. Biological opinion on the effects of ongoing forest activities that may affect listed riparian species on the Cleveland National Forest, the Los Padres National Forest, the San Bernardino National Forest, and Angeles National Forest in Southern California (1-6-99-F-21).
Wright, A.H.; Wright, A.A. 1949. Handbook of frogs and toads of the United States and Canada. Ithaca, NY: Comstock Publishing Company, Inc.
Information gathered from California DFG - California Interagency Wildlife Task Group