Rana draytonii ranges in size from 1.5 to 5 inches in length, making it the largest native frog in the Western United States (Wright and Wright 1949). Adult females are significantly longer than males, with an average snout- urostyle length of 138 mm versus 116 mm for adult males (Hayes and Miyamoto 1984).
Dorsolateral folds are prominent. Tadpoles range in length from 14 to 80 mm, and are a dark brown or olive, marked with darker spots (Storer 1925).
The hind legs and lower abdomen of adult frogs are often characterized by a reddish or salmon pink color, and the back is brown, gray, olive, or reddish brown, marked with small black flecks and larger irregular dark blotches (Recovery Plan for the California Red-legged Frog 2002; Stebbins 1985).
Dorsal spots often have light centers, and in some individuals form a network of black lines (Stebbins 1985).
Rana draytonii differs from its close relative R. aurora , the Northern red-legged frog, in several ways. Adult R. draytonii are 35 to 40 millimeters longer than adult R. aurora (Hayes and Miyamoto 1984). The dorsal spots of R. draytonii are more numerous, and usually have light centers (Stebbins 1985).
R. draytonii also has rougher skin, shorter limbs and smaller eyes than R. aurora (Stebbins 1985).
R. draytonii has paired vocal sacs and typically calls from the air, while R. aurora lacks vocal sacs and may call underwater (Hayes and Krempels 1986; Licht 1969).
Egg masses in R. draytonii are deposited such that the mass floats at the surface (Hayes and Miyamoto 1984), whereas R. aurora submerge the mass in deeper water (Licht 1969; Storm 1960).
R. draytonii breed from November to April (Storer 1925), while R. aurora breeds from January to March (Nussbaum et al 1983).
Distribution and Habitat
Country distribution from AmphibiaWeb's database: United States
U.S. state distribution from AmphibiaWeb's database: California
Before the settlement of Europeans on the west coast, R. draytonii was probably common throughout the Coast Range from Point Arena (Mendocino County) south to Baja California, in the Sierra Nevada foothills, and around the northern part of the Central Valley. Records of this frog on the floor of the Central Valley probably represented short-term populations that did not survive the seasonal flooding of the valley floor (Zeiner et al. 1988; Jennings and Hayes 1985; Hayes and Krempels 1986).
Today the species is still common in the San Francisco Bay area (primarily Marin, Contra Costa, and Alameda Counties). Moderately large populations are also found in some parts of the Coast Range from San Mateo County south to San Luis Obispo ). Isolated populations exist in the Sierra Nevada foothills, northern Transverse Ranges, and Baja California (Natural Diversity Data Base 2001; Jennings in litt. 1998; Fellers unpubl.).
R. draytonii live in areas subject to temporal and spatial changes, and therefore make use of a variety of habits, consisting of both aquatic, upland and riparian (Recovery Plan for the California Red-legged Frog 2002).
Adults breed in ponds or deep pools in slow-moving creeks. Where ponds are seasonal in nature, thickets and log jams along riparian corridors provide important non-breeding habitat. Populations are most likely to persist in areas with multiple breeding sites surrounded by suitable non-breeding habitat(N. Scott and G. Rathbun in litt. 1998).
Life History, Abundance, Activity, and Special Behaviors
R. draytonii breeds during a 1-2 week period between November and April, depending on locality (Stebbins 1985; Storer 1925).
Egg masses consist of between 300 and 5,000 eggs (Recovery Plan for the California Red-legged Frog 2002; Storer 1925; Fellers unpubl.).
Egg masses are nearly always attached to emergent vegetation. Eggs hatch after 6 to 14 days depending on water temperature ( Jennings 1988).
Larvae typically metamorphose in 3.5 to 7 months, usually between July and September ( Storer 1925; Wright and Wright 1949),
but some overwinter and transform after more than 12 months in the larval stage (Fellers et al. in press). Males may attain sexual maturity at 2 years, females at 3 (Jennings and Hayes 1985),
and adult frogs may live 8 to 10 years. (Jennings et al in lit 1992).
Larvae are thought to be algal grazers ( Jennings et al in lit 1992),
and the adult diet consists mostly of invertebrates. Pacific Tree Fogs (Hyla regilla) and California mice (Peromyscus californicus are occasionally consumed by adult frogs ( Hayes and Tennant 1985).
Juvenile frogs may be active both nocturnally and diurnally, whereas adult frogs are primarily active nocturnally ( Hayes and Tennant 1985).
The primary predators on R. draytonii include garter snakes (Thamnophis spp.), raccoons (Procyon lotor), and great blue herons (Ardea herodias). Less frequently, red-legged frogs are eaten by American bitterns (Botaurus lentiginosus), black-crowned night herons(Nycticorax nycticorax), and rarely by red-shouldered hawks (Buteo lineatus)(Jennings and Hayes 1990; Rathbun and Murphy 1996). Other introduced species such as the bullfrog (Rana catesbeiana) and non-native fish also prey on the frog.
Trends and Threats
Many factors are contributing to the decline of R. draytonii populations, the main being habitat destruction and degradation. Introduced predators and perhaps disease have also contributed to the decline of this species.
This species has been extirpated from 99% of its Sierra Nevada range and is believed to be extinct in the Central Valley. Breeding populations remain along the coast, from San Mateo County to San Luis Obispo County. In 1996, it was declared a threatened species and over 4 million acres of habitat were designated as critical. However, in 2006 developers sued and 90% of that habitat designation was lost.
Now that has been partially remedied, thanks to legal action by the Center for Biological Diversity. As of March 16, 2010, the U. S. Fish and Wildlife Service has designated 1.6 million acres of habitat as critical, and the agency has acknowledged that the earlier reduction was flawed because of political interference from the Bush Administration.
The US Fish and Wildlife Service has published A Recovery Plan (2002, pdf) for the California Red-legged Frog, which remains a guideline for conservation of this iconic species. Delisting of the species may be possible by 2025 if recovery goals are met according to this report.
Relation to Humans
The primary impact from humans has been from direct habitat loss, especially the construction of houses, shopping centers, and roads. Much of the range of Rana draytonii has been historically grazed, both by dairy and by beef cattle. Cattle grazing in riparian zones causes serious damage to the vegetation, stream channel, and water quality. Rana draytonii may have benefited from beef cattle grazing due to the increased number of stock ponds that are maintained for the cattle.
Rana draytonii are also threatened by a number of introduced (non-native) species, some of which are regularly introduced by humans. These include sunfish, bass, trout, mosquitofish, and bullfrogs.
Possible reasons for amphibian decline
General habitat alteration and loss
Habitat modification from deforestation, or logging related activities
Intensified agriculture or grazing
Predators (natural or introduced)
Rana draytonii is widely believed to have inspired Mark Twain's fabled story, "The Celebrated Jumping Frog of Calaveras County."
The California red-legged frog was Federally listed on June 24, 1996.
This species was featured as News of the Week:
May 13, 2019: The California Red-legged Frog, Rana draytonii, has not been seen in Yosemite National Park for at least 50 years. Yet, thanks to the cooperative efforts of the National Park Service, Yosemite Conservancy, San Francisco Zoo & Gardens, U. S. Fish & Wildlife Service, California Department of Fish & Wildlife, and NatureBridge, once again Red-legged frogs are back in Yosemite. In a program that began in 2016, an estimated 4,000 frog eggs and 500 adult frogs have been reintroduced from a captive breeding program at the zoo. But with another 200 adult frogs released in April and another 275 to be released in June, the reintroduction program is now fully operational. The captive population was founded with frogs collected in El Dorado County, in the foothills of the Sierra Nevada north of Yosemite. The frogs were released in Cook’s Meadow, in view of Yosemite Falls in Yosemite Valley. Transponders attached to 75 frogs will enable researchers to follow the frogs in the future. This trial reestablishment might set the stage for future attempts in other parts of the Sierra Nevada where the frogs once thrived. (David B. Wake)
Hayes, M. P. and 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. and Miyamoto, M. M. (1984). ''Biochemical, behavioral and body size difference between Rana aurora aurora and R. a. draytonii.'' Copeia, 1984(4), 1018-1022.
Hayes, M. P. and Tennant, M. R. (1985). ''Diet and feeding behavior of the California Red-legged Frog Rana aurora draytonii (Ranidae).'' The Southwestern Naturalist, 30(4), 601-605.
Jennings, M. (1988). ''Natural history and decline of native ranids in California.'' Proceedings of the Conference on California Herpetology. H.F. DeLise, P.R. Brown, B. Kaufman, and B.M. McGurty, eds., Southwestern Herpetologists Society Special Publication, 1-143.
Jennings, M. (1998). Electronic database of California red-legged frog occurrences.
Jennings, M.R. and Hayes, M.P. (1985). ''Pre-1900 overharvest of California Red-legged Frogs (Rana aurora draytonii):The inducement for bullfrog (Rana catesbeiana) introduction.'' Herpetological Review, 31(1), 94-103.
Jennings, M.R. and Hayes, M.P. (1990). ''Final report on the status of the California Red-Legged Frog in the Pescadero Marsh Natural Preserve. Prepared for the California Department of Parks and Recreation under contract no. 4-823-9081 with the California Academy of Sciences.''
Jennings, M.R., Hayes, M.P. and Holland, D.C. (1992). A 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.
Licht, L.E. (1969). ''Comparative breeding behavior of the Red-legged Frog (Rana aurora aurora) and the Western Spotted Frog (Rana pretiosa pretiosa) in southwestern British Columbia.'' Canadian Journal of Zoology, 47(6), 1287-1299.
Natural Diversity Data Base (2001). California Department of Fish and Game, Natural Heritage Division, Sacramento, California.
Nussbaum, R. A., Brodie, E. D., Jr., and Storm, R. M. (1983). Amphibians and Reptiles of the Pacific Northwest. University of Idaho Press, Moscow, Idaho.
Rathbun, G.B., and Murphy, T.G. (1996). ''Evaluation of a radio-belt for ranid frogs.'' Herpetological Review, 27(4), 197-199.
Scott, N. and Rathbun, G. (1998). ''Essays provided to Ina Pisani in response to a working draft of California red-legged frog recovery plan.''
Stebbins, R. C. (1985). A Field Guide to Western Reptiles and Amphibians. Houghton Mifflin, Boston.
Storer, T. I. (1925). "A synopsis of the amphibia of California." University of California Publications in Zoology, 27, 1-342.
Storm, R.M. (1960). ''Notes on the breeding biology of the Red-legged Frog (Rana aurora aurora).'' Herpetologica, 16, 251-259.
U.S. Fish and Wildlife Service (2002). Recovery Plan for the California Red-legged Frog (Rana aurora draytonii). U.S. Fish and Wildlife Service, Portland, Oregon.
Wright, A. H. and Wright, A. A. (1949). Handbook of Frogs and Toads of the United States and Canada. Comstock Publishing Company, Inc., Ithaca, New York.
Written by Tate Tunstall and Gary Fellers (gary_fellers AT usgs.gov), USGS
First submitted 1999-03-10
Edited by Michelle S. Koo, Kellie Whittaker, Vance Vredenburg (2019-08-02)
Species Account Citation: AmphibiaWeb 2019 Rana draytonii: California Red-legged Frog <http://amphibiaweb.org/species/5287> University of California, Berkeley, CA, USA. Accessed Nov 13, 2019.
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Citation: AmphibiaWeb. 2019. <http://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 13 Nov 2019.
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