This robust frog may be brown, reddish-brown or red above with a variable number of large, black spots and blotches on the back, sides, and legs. The spots are usually irregular-shaped, with indistinct edges and light centers. The skin on back and sides is often covered with small bumps and tubercles. The eyes are upturned. The lower abdomen and the undersides of the hind legs are usually colored by a reddish-orange or salmon-colored pigment that appears as though it has been painted on (Leonard et al. 1993; Nussbaum 1984; Stebbins 1985). Oregon spotted frogs have relatively short hind legs and extensive webbing between the toes of the hind feet. Sexually mature females range between 60 and 100 mm snout-vent length and males range between 45 and 75 mm (Licht 1975).
Distribution and Habitat
Country distribution from AmphibiaWeb's database: Canada, United States
U.S. state distribution from AmphibiaWeb's database: California, Oregon, Washington
Canadian province distribution from AmphibiaWeb's database: British Columbia
The Oregon spotted frog once occurred from southwest British Columbia through western Washington and Oregon into northeastern California. Today the species is known from three localities in British Columbia, four localities in Washington and approximately twenty-four localities in Oregon (Marc Hayes pers. comm.) (McAllister and Leonard 1997; Green et al. 1997). In Washington, it occurs at elevations ranging from 40 to 620 meters (McAllister and Leonard 1997) .
Oregon spotted frog populations occur in association with relatively large wetland complexes. Breeding occurs in shallow, relatively unshaded emergent wetlands. The breeding ponds, which are typically dry by mid- to late summer, range in depth from 2 to 14 inches during the breeding season, and are vegetated by low-growing emergent species such as grasses, sedges (Carex spp.), and rushes (Juncus spp.). After breeding adults disperse into adjacent wetland and riparian habitats. Adults remain active year-around near sea-level, but freezing temperatures apparently cause adults and juveniles to hibernate in streams, oxbows and springs at higher elevations.
Life History, Abundance, Activity, and Special Behaviors
Breeding occurs sometime in February or March at lower elevations, but does not occur until March or April at the two Washington sites in the Cascade Range (McAllister and Leonard 1997). The Oregon Spotted Frog exhibits strong fidelity to breeding sites and eggs are often deposited the same locations in successive years.
Males arrive first, gathering in "lek-like" groups and float in the shallows, calling while awaiting the arrival of a female. Male advertisement calls, consisting of a rapid series of 5 to 50 faint "tapping" notes notes, are given throughout the breeding season (particularly on sunny days) and again in fall (Davidson 1995; Leonard et al. 1997). Most breeding takes place within a two-to-three-week "window" when most of eggs are deposited. However, breeding may be interrupted for up to several weeks by the onset of cold weather; in such cases a second bout of breeding may occur. Upon release, the ova are tightly packed in a mass roughly the size of a ping-pong ball, but within a few hours the mass swells to the size of an average-size human fist. Females usually lay their eggs atop or adjacent to other egg masses (some of the larger aggregations may contain more than 100 individual egg masses). The egg masses are not attached to vegetation, but are deposited in still, shallow waters atop submergent herbaceous vegetation or freely floating amongst clumps of emergent wetland plants such as sedges (Carex spp.) and rushes (Juncus spp). Often-times, the the upper portions of the egg masses protrude above the water surface resulting in severe egg mortality from freeze-thaw damage or desiccation.
After a few weeks of embryonic development, thousands of small tadpoles emerge and cling to the remnants of the gelatinous egg masses, their densely packed, dark bodies acting as solar collectors and warming the water adjacent to the mass. After several days, the hatchlings become free-swimming tadpoles, using their minute brush-like mouthparts to feed upon algae, detritus, and, in some cases, bacteria (but see McDiarmid and Altig 1999). Tadpoles may grow to 90 mm total length before metamorphosing in their first summer or fall (Licht 1975) .
Mortality of eggs, tadpoles, and newly metamorphosed frogs is high, and it is likely that only about 1% of an annual cohort survive to the first winter (Licht 1974) . Near sea-level sexual maturity is attained at age two, while at higher elevations one or two additional years is required (Licht 1975).
Adults feed upon arthropods (e.g., spiders, insects), earthworms and other invertebrate prey. In turn, Oregon Spotted Frogs may be preyed upon by mink, river otter, raccoon, herons, bitterns, corvids and garter snakes (Licht 1974) , while larvae may be consumed by larvae of dragonflies, predacious diving beetles, fish, garter snakes and wading birds.
Trends and Threats
This species is rare and has undergone significant declines in range over the past half century. It is now presumed to be extirpated in California and is in serious jeopardy in southwestern British Columbia, Canada. The most probable cause for this frog's precipitous decline is the hydrological modification and destruction (draining, flooding, and filling) of specialized shallow-water, emergent wetlands used for breeding. However, introduced predators including bullfrogs and sport fishes pose serious threats from predation and from competition for critical habitats.
Possible reasons for amphibian decline
General habitat alteration and loss
Drainage of habitat
Subtle changes to necessary specialized habitat
Predators (natural or introduced)
Since nearly the time of its original description in 1853, the systematics of the "Western Spotted Frog" group has been a source of both confusion and debate. In 1996, however, a team led by David M. Green published the results of a study on the genetics of Spotted Frogs and concluded that the group actually contained two "sibling" species-the Oregon Spotted Frog and the Columbia Spotted Frog (Green et al. 1996 1997) . The decision to "split" the species was based upon the results of laboratory studies that indicated significant genetic differences, despite a lack of reliable morphological differences. Because the two species have allopatric ranges, they may be reliably identified based upon the location where a frog is encountered.
See another account at californiaherps.com.
Davidson, C. (1995). Frog and Toad Calls of the Pacific Coast: Vanishing Voices (recording). Library of Natural Sounds, Cornell Laboratory of Ornithology, Ithaca.
Green, D. M., Kaiser, H., Sharbel, T. F., Kearsley, J. and McAllister, K. R. (1997). ''Cryptic species of spotted frogs, Rana pretiosa complex, in western North America.'' Copeia, 1997, 1-8.
Green, D. M., Sharbel, T. F., Kearsley, J. and Kaiser, H. (1996). ''Postglacial range fluctuation, genetic subdivision and speciation in the western North American Spotted Frog complex, Rana pretiosa.'' Evolution, 50, 374-390.
Leonard, W.P., Leonard, N. P., Storm, R.M., and Petzel, P.E. (1996). ''Rana pretiosa (Spotted Frog). Behavior and reproduction.'' Herpetological Review, 27(4), 195.
Licht, L. E. (1974). "Survival of embryos, tadpoles, and adults of the frogs Rana aurora aurora and Rana pretiosa pretiosa sympatric in southwestern British Columbia." Canadian Journal of Zoology, 52(5), 613-627.
Licht, L.E. (1975). ''Comparative life history features of the Western Spotted Frog, Rana pretiosa, from lowland and high-elevation populations.'' Canadian Journal of Zoology, 53(9), 1254-1257.
McAllister, K.R. and Leonard, W.P. (1997). Washington State Status Report for the Oregon Spotted Frog. Washington Department of Fish and Wildlife, Olympia, WA.
McDiarmid, R.W. and Altig, R. (1999). ''Research materials and techniques.'' Tadpoles: The Biology of Anuran Larvae. University of Chicago Press, Chicago, IL, 2–22.
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.
Stebbins, R. C. (1985). A Field Guide to Western Reptiles and Amphibians. Houghton Mifflin, Boston.
Written by William P. Leonard (Mollusca1 AT home.com), WSDOT, Environmental Affairs Office
First submitted 2000-07-09
Edited by M. J. Mahoney (2004-04-05)
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