Adult R. aurora range from 4.4 to 8.4 cm in length, with females significantly larger than males (Stebbins 1985; Hayes and Miyamoto 1984).
The abdomen and underside of hind legs is characterized by a red or pinkish color, often set on a yellowish ground color (Stebbins 1985).
Back is a brown, gray, olive, or reddish color, often with may small black flecks and irregular dark splotches, in some individuals forming a network of black lines (Stebbins 1985).
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).
Distribution and Habitat
Country distribution from AmphibiaWeb's database: Canada, Mexico, United States
U.S. state distribution from AmphibiaWeb's database: Alaska, California, Nevada, Oregon, Washington
Canadian province distribution from AmphibiaWeb's database: British Columbia
R. aurora ranges from Vancouver Island, British Columbia, Canada, south along the Pacific coast, west of the Cascade Ranges to Northern California. R. aurora 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 (Draft Recovery Plan). Adults breed in ponds or deep pools in slow-moving creeks. Where ponds are seasonal in nature, thickets and logjams 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. aurora breed during a 1-2 week period between January and March, depending on locality (Stebbins 1985; Nussbaum et al. 1983). Nelson et al. (2017), using passive acoustic monitoring devices, have shed light on this cryptically breeding ranid dispelling previous notions of their natural history. They found that red-legged frogs actually breed over the course of at least 32 days instead of a brief two week window as previously thought. Most interestingly, they report that underwater chorus length lasted nearly 8 hours on average, with a maximum chorus length of 14 hours over the course of a single day! Their acoustic analyses also showed calling effort was affected by temperature specifically reduced by cold snaps.
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, submerged beneath the surface in the deepest water available (Hayes and Miyamoto 1984; Licht 1969; Storm 1960). Eggs hatch after 6 to 14 days depending on water temperature ( Jennings 1988).
Larvae typically metamorphose in 3.5 to 7 months ( 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. aurora 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. aurora populations, the main being habitat destruction and degradation. Introduced predators and perhaps disease have also contributed to the decline of this species (Fellers et al in press)
Rana aurora is of particular conservation concern in the Pacific Northwest, where their population has decreased in abundance and in site occupancy in recent years. Nelson et al. (2017), used passive acoustic monitoring devices to show that the species breeds longer than previously thought (see Life History) and demonstrated the importance of continued acoustic monitoring for this sensitive species, especially because conservation strategies often rely on occupancy and detection surveys.
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 R. aurora 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. R. aurora may have benefited from beef cattle grazing due to the increased number of stock ponds that are maintained for the cattle.
R. aurora 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 (Fellers et al in press).
Possible reasons for amphibian decline
General habitat alteration and loss
Intensified agriculture or grazing
Predators (natural or introduced)
R. aurora differs from its close relative, the California red legged frog, R. draytonii 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 sacks ( 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).
See other subspecies accounts at www.californiaherps.com: R. a. aurora and R. a. draytonii.
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.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.
Nelson, D.V., Garcia, T. S., Klinck, H. (2017). ''Seasonal and Diel Vocal Behavior of the Northern Red-Legged Frog, Rana aurora.'' Northwestern Naturalist, 98(1), 33-38.
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 1999-03-02
Edited by Vance Vredenburg, update by Ann T. Chang (2018-03-08)
Species Account Citation: AmphibiaWeb 2018 Rana aurora: Red-legged Frog <http://amphibiaweb.org/species/4987> University of California, Berkeley, CA, USA. Accessed Dec 6, 2019.
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Citation: AmphibiaWeb. 2019. <http://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 6 Dec 2019.
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