Oregon Spotted Frog

Name: Oregon Spotted Frog

(Rana pretiosa)

Status: Federal Candidate, State Endangered (WA), Sensitive Species (OR)

Description: A medium sized frog that can be reddish-brown, tan, or olive-green, with irregular-shaped black spots on back, sides and legs. Adults have a narrow, pointed snout, upturned eyes, and a light colored stripe on the upper lip. Webbing on feet extends to the end of toes. Ventral side is pink or yellow. Tadpoles are brownish-green with visible intestines. Adult size: females: 6-10 cm, males: 4-7 cm. The call of the Oregon Spotted Frog is a weak series of 6 – 9 clucking noises, and is usually only heard during breeding season.

Threats: Wetland loss and degradation, introduction of new predators such as Bullfrogs (Rana catesbeiana).

Note:

Oregon Spotted Frogs have recently been classified as a species separate from the Columbia Spotted Frog, now Rana luteiventris. Researchers at McGill University in Canada split the species into Rana luteiventris and Rana pretiosa in 1996 (Green el al., 1996, Leonard). The researchers found that while the two species are nearly identical morphologically, they differ genetically and occupy different ranges.

Ecology:

Oregon Spotted Frogs are highly aquatic and live in or near permanent bodies of water, including lakes, ponds, slow streams and marshes. They prefer areas with thick algae and vegetation for cover, but may also hide under decaying vegetation. They are most often found in non-woody wetland plant communities (species such as sedges, rushes and grasses). Most Oregon Spotted Frogs hibernate and aestivate. Oregon Spotted Frogs distribute through a wide range of altitudes and in Washington have been found from 40 to 620 meters above sea level (McAllister and Leonard, 1997). Adults eat insects, mollusks, crustaceans and arachnids. Larvae eat algae and organic debris. Bullfrogs are a major predator of adult Oregon Spotted Frogs. Other predators include river otter, raccoons, herons, and garter snakes. Larvae are preyed upon by the larvae of dragonflies, predacious diving beetles, fish and garter snakes. The timing of breeding is related to ice melt on lakes, ponds and marshes. Breeding occurs from February to March in the lower elevations, and from March to April in the higher elevations in the Cascade Range. Oregon Spotted Frogs lay their eggs in the shallows of a permanent water source. The eggs are deposited in spherical clusters of up to 1,300 eggs and are allowed to float freely. Often, the egg masses protrude above the water surface, which results in egg mortality due to freezing and dessication.

Oregon Spotted Frog tadpoles

Population Trends and Possible Threats:
According to a report done for the Committee on the Status of Endangered Wildlife in Canada, the range of the Oregon Spotted Frog has dramatically declined in the last 50 years. It is presumed extirpated in its former range in California, and is near extinction in British Columbia (Leonard). Although Oregon Spotted Frogs have only been found in six sites in British Columbia, they have not been detected in three of those sites in recent years. The causes of decline are not fully understood, but like most amphibians, a major threat is the destruction and degradation of wetlands. The introduction of non-native predators such as Bullfrogs, bass and other predatory fresh-water fish species are believed to contribute to their decline.

Click here to read: Focus on Amphibian Decline and Environmental Change

Distribution:
Rana pretiosa exists in isolated populations in British Columbia, Washington, Oregon and northern California. It has only been found in six sites in British Columbia, and has not been detected on 3 of those sites in recent years. It has not been detected on over 80 to 90% of known sites in the rest of its range. There are four known localities in Washington State and 24 in Oregon.

Click on map to enlarge

Further information on Rana pretiosa:

A good list of identification characteristics: http://splash.metrokc.gov/wlr/waterres/amphibian/spottedfrog.htm

Information on Canada's listing of Rana pretiosa as endangered: http://www.ec.gc.ca/press/bcfrog_n_e.htm

References:

Environment Canada News Release. Online: http://www/ec/gc/ca/press/bcfrog_n_e.htm November 11, 2000.

Green, D.M., T.F. Sharbel, Kearsley, J., and H. Kaiser (1996). Postglacial range fluctuation, genetic subdivision and the speciation in the western North American spotted frog complex, Rana pretiosa. Evolution.

Leonard, William. AmphibiaWeb page – Rana pretiosa. Online: http://elib.cs.berkeley.edu/aw (Accessed 7/26/00).

Leonard, William P., Herbert A. Brown, Lawrence L.C. Jones, Kelly R. McAllister, and Robert M. Storm. (1993) Amphibians of Washington and Oregon. Seattle Audubon Society. Seattle, Washington.

McAllister, K.R., Leonard, W.P. (1997). “Washington State Status Report for the Oregon Spotted Frog.” Washington Dept. of Fish and Wildlife, Wildlife Management Program. Olympia, WA.

Nussbaum, R.A., Brodie, E.D., and R.M. Storm. (1983). Amphibians and Reptiles of the Pacific Northwest. University of Idaho Press. Moscow, Idaho.

Peterson, Charles R. Atlas of Idaho’s Wildlife in PDF. Digital Atlas of Idaho: Preliminary Beta Version.

Last updated October 24, 2001

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