Oregon spotted frog (Rana pretiosa)

Physical description

The Oregon spotted frog is a medium to large aquatic frog (adults are 2 to 4 inches in length from snout to vent). The dorsal color is olive brown to brick red, with black spots that have ragged edges and light centers. The undersides of the legs and margin of the abdomen are orange-red to red (absent in newly metamorphosed frogs and small juveniles). The legs are relatively short, and the toes are nearly fully webbed. Breeding males develop large forelimbs and thumb bases and have a dark nuptial pad on each thumb. 

Image

Photo by Brome McCreary - US Geological Survey

Native True Frogs (Rana species) in Washington have dorsolateral folds (unlike other Washington anurans) and are similar in appearance. The Oregon spotted frog and Columbia spotted frog species have subtle color variations but are morphologically indistinct (they were distinguished as separate species by genetic analysis) and may be separated by geographic locality.

The following traits distinguish the Oregon spotted frog from the Cascades frog and northern red-legged frog: 1) the dorsal spots are black with ragged edges and light centers, 2) the eyes are oriented upward at roughly a 45-degree angle with the entire pupil of both eyes visible when the frog is viewed directly from above, 3) there is nearly full webbing between the toes with the webbing of the hind foot reaching almost to the tip of the longest toe and the webbing is almost straight when the toes are stretched apart, 4) the coloration in the groin area is similar to the coloration anteriorly on the side and posteriorly on the thighs with no obvious yellow and black mottled patch or patches, 5) when the hind leg is pressed forward against the body, the heel of the hind foot will seldom reach the nostril (similarly, the knee to heel measurement is typically less than half of the snout-vent length), 6) the dorsolateral folds are interrupted about two-thirds the distance down the back from the eye and often disappear entirely posteriorly, and 7) Cascade frogs have honey-colored and yellow undersides, not red. The above traits may be difficult to see or absent in small juvenile frogs.

American bullfrogs, a common non-native species, have a distinct fold from the posterior edge of the eye, around the top of the tympanum and ending at the arm and they lack dorsolateral folds.

Larvae

The tadpole (aquatic larval stage) has an oval body with dorsal eyes, a vent on the right side, a spiracle on the left side and a dorsal fin that originates on the body near the dorsal tail-body junction. The tip of the tail is pointed. At hatching, the tadpoles appear black, have long tails (greater than 1.5 times body length), obvious gills and remain associated with the egg mass for days. As the tadpoles grow, the ground color and belly lighten and silver flecks appear, eventually covering the gut. Tadpoles can grow to large sizes (4 inches total length) before metamorphosis.

In general, it is difficult to distinguish the tadpoles of the Oregon spotted frog from those of the Cascades frog and northern red-legged frog. Larger tadpoles (those greater than 2 inches total length) of the Oregon spotted frog have a tail length to body length ratio of 2.7 whereas Cascades frog and northern red-legged frog have a tail length to body length ratio 2.6 or smaller. This criterion can only be used if the tail is undamaged.

American bullfrog and American green frog tadpoles are also similar but larger tadpoles have distinct black spots over a typically khaki-colored body and tail and the abdomen is opaque and lacks pigments with a metallic quality.

Eggs

Image

Photo by Taylor Goforth - U.S. Fish and Wildlife Service Pacific Region

Individual egg masses are globular, loose to the touch, grapefruit-sized and not attached to a vegetation brace, although they may stick to the vegetation under the egg masses. The eggs and larvae appear black (but are actually dark brown). The frogs lay the egg masses at water body margins in water usually less than 6 inches deep. The top of the egg mass is often exposed at the water surface. Egg masses are typically communally laid, resulting in clustered egg mass groups of two to more than 100. Single egg masses in the vicinity of multi-mass clusters are common.

The communal egg masses of the Oregon spotted frog and Cascades frog cannot be easily distinguished. Northern red-legged frogs do not lay egg masses in communal overlapping clusters, although they may be closely spaced if the vegetation braces to which the egg masses are attached are close together; rather they attach egg masses to vegetation individually in water that is usually over 10 inches deep.

The northwestern salamander has a grapefruit-sized globular egg mass, but its jelly is solid to the touch, always attached to vegetation or woody debris and the eggs and larvae are brown not black. No other species that occur in the same range and habitat have large globular egg masses.

Voice

The call of the Oregon spotted frog is a series of six to nine low-pitched clucks similar to the sound made when the tongue is clicked against the roof of the mouth. One must typically be within 16 feet to hear this faint call.

For more details about the Oregon spotted frog, see the Washington Herp Atlas (PDF).

Ecology and life history

This species is highly aquatic and rarely found away from water.  Extant populations occur in large shallow wetland systems associated with a stream or stream network. Breeding habitat is in seasonally flooded margins of wetlands and areas of extensive shallows (approximately 6 to 8 inches deep). 

Waters that remain aerobic and do not freeze to the sediments are necessary for winter survival in areas subject to freezing. Beaver impounded systems appear to provide many of the habitat requirements of this species. Radio-telemetry and mark-recapture studies have revealed that Oregon spotted frogs are relatively sedentary during the summer (driest period) and remain active underwater during the winter.

Oregon spotted frogs eat mostly insects. Tadpoles eat algae and detritus (organic material) in the aquatic environment.  

These frogs are communal breeders that return to the same breeding areas each year. They require breeding sites in shallow water with short vegetation and full sun exposure. This habitat type is rapidly lost to invasive grasses without management such as grazing, haying, mowing or restoration to native flora.

Breeding occurs in February and March, and times can differ depending on location, elevation, and water temperatures. Egg masses are placed in areas where they receive little or no shading from vegetation. Embryos take approximately three weeks to develop to hatching. Tadpoles transform in mid-summer of their first year.

Oregon spotted frogs are preyed upon my many predators that live in wetlands, such as great blue herons and mink. Of particular concern are non-native predators such as American bullfrogs and warm-water game fish.  

Geographic range

The historical range for Oregon spotted frogs in Washington is the Puget Trough Ecoregion, in Whatcom, Skagit, and Thurston counties, and the southern extent of the Eastern Cascades Ecoregion, in Skamania and Klickitat counties.

Current occurrences are in the following watersheds: Sumas River, South Fork Nooksack River, Samish River, upper Black River, lower Trout Lake Creek and at Conboy Lake and Camas Prairie in the Outlet Creek drainage. Within a watershed, most breeding populations are small and many are isolated from other breeding populations. 

This map from the Washington Herp Atlas illustrates the distribution of Oregon spotted frog in Washington based on records in the WDFW database as of 2016. If you see this species in areas that are not indicated on the map or have more recent observations (less than 10 years), please share your observation using the WDFW wildlife reporting form. 

Image

For maps of range-wide distribution and conservation status of this species, check out NatureServe Explorer and the International Union for Conservation of Nature Red List.