(Map may reflect historical as well as recent sightings)
In 1993, the U.S. Fish and Wildlife Service determined that the Oregon spotted frog warranted listing under the Endangered Species Act, but doing so was precluded by higher priority listing actions. The frog then became a candidate for listing in the future. On August 29, 2013, the USFWS proposed to list the frog as a threatened species and to designate critical habitat.
Historical Status and
The Oregon spotted frog has been lost from at least 78 percent of its former range. Precise historic data is lacking, but this species has been documented in British Columbia, Washington, Oregon, and California. It is believed to have been extirpated (locally extinct but exists elsewhere) from California. It is currently known to occur from extreme southwestern British Columbia, south through the eastern side of the Puget/Willamette Valley Trough and the Columbia River Gorge in south-central Washington, to the central Cascades Range and Klamath Valley in Oregon.
In Oregon, Oregon spotted frogs historically were found in Multnomah, Clackamas, Marion, Linn, Benton, Jackson, Lane, Wasco, Deschutes and Klamath counties. Currently, this species is only known to occur in Wasco, Deschutes, Klamath, Jackson and Lane counties.
This species is the most aquatic native frog in the Pacific Northwest.
It is almost always found in or near a perennial body of water
that includes zones of shallow water and abundant emergent or
floating aquatic plants, which the frogs use for basking and escape
cover (Leonard et al. 1993, Corkran and Thoms 1996, McAllister
and Leonard 1997, Pearl 1997, Pearl 1999). Oregon spotted frogs
seem to prefer fairly large, warm marshes (approximate minimum
size of 4 hectares (9 acres)) that can support a large enough population
to persist despite high predation rates (Hayes 1994) and sporadic
reproductive failures. Large concentrations of Oregon spotted
frogs have been found in areas with the following characteristics:
(1) the presence of good breeding and overwintering sites connected
by year-round water; (2) reliable water levels that maintain depth
throughout the period between oviposition and metamorphosis; and
(3) the absence of introduced predators, especially warm-water
game fish and bullfrogs.
In Oregon, the Oregon spotted frog occurs on federal lands managed
by USDA Forest Service (Mt. Hood, Deschutes, Willamette and Winema National
Forests), Bureau of Land Management (Wood River Ranch), U.S. Fish
and Wildlife Service (Klamath National Wildlife Refuge), and on
The Oregon spotted frog is named for the black spots that cover
the head, back, sides, and legs. The dark spots have ragged edges
and light centers, which are usually associated with tubercles
or raised areas of skin; these spots become larger and darker
and the edges become more ragged with age. Body color also varies
with age. Juveniles are usually brown or, occasionally, olive
green on the back and white or cream with reddish pigments on
the underlegs and abdomen. Adults range from brown to reddish
brown, but tend to become more red with age; large, presumably
older individuals may be brick red over most of the back. Red
increases on the abdomen with age, and the underlegs become a
vivid orange-red. This red coloration can be used to distinguish
the spotted frogs from other native frogs.
The Oregon spotted frog is a medium-sized frog, ranging from
44 to 100 millimeters (1.74 to 4 inches) in body length (McAllister
and Leonard 1997). Females are typically larger than males and can
reach up to 100 millimeters (4 inches) (Leonard et al. 1993).
This species typically begins to breed at three years of age. Breeding
occurs in February or March at lower elevations and in late May
or early June at higher elevations. Females may deposit egg masses
at the same location in successive years in shallow, often temporary,
pools no more than six inches deep. Eggs usually hatch within three
weeks after oviposition. Tadpoles are grazers, having rough tooth
rows for scraping plant surfaces and ingesting plant tissue and
bacteria. They also consume algae, detritus, and probably carrion
(Licht 1974, McAllister and Leonard 1997). Tadpoles then metamorphose
into froglets during their first summer (Leonard et al. 1993).
Post-metamorphic Oregon spotted frogs feed on live animals, primarily
Reasons for Decline
Many factors are believed to have caused Oregon spotted frogs
to decline and continue to threaten this species, including loss
of habitat, non-native plant invasions, and the introduction of
exotic predators such as bullfrogs. Over 95 percent of historic
marsh habitat, and consequently Oregon spotted frog habitat, has
been lost in the Willamette and Klamath basins. Changes in hydrology
(due to construction of ditches and dams) and water quality, development,
and livestock overgrazing continue to result in habitat loss,
alteration, and/or fragmentation. Non-native plant invasions
by such aggressive species as reed canarygrass (Phalaris
and succession of plant communities from marsh to meadow also
threaten this species' existence. Introductions of bullfrogs and
non-native fishes have affected this species both directly, by
eating them, and indirectly, by outcompeting or displacing them
from their habitat.
The majority of Oregon spotted frog populations are small and
isolated. These factors make the Oregon spotted frog more vulnerable
than large connected populations to random, naturally occurring
events, such as drought, disease, and predation.
Efforts are being made to eliminate and to prevent
future introductions of bullfrogs and warm-water game fish from
spotted frog habitat. Active management is also required to control
non-native plant species like reed canarygrass. Protecting Oregon
spotted frog populations through maintaining healthy aquatic habitats
will continue to be the key objective of land managers.
References and Links
Corkran, C.C. and C.R. Thoms. 1996. Amphibians of Oregon, Washington,
and British Columbia: A field identification guide. Lone Pine
Publishing, Edmonton, Alberta. 175 pp.
Hayes, M.P. 1994. The spotted frog (Rana pretiosa) in western
Oregon. Part I. Background. Part II. Current status. Oregon Department
of Fish and Wildlife Tech. Rept. #94101. Unpublished
Leonard, W.P., H.A. Brown, L.L.C. Jones, K.R. McAllister, and
R.M. Storm. 1993. Amphibians of Washington and Oregon.