Species Profile: Red-legged Frog

(Rana aurora)

by Ken Steffenson

Observations in the Hylebos Wetlands

The most common and easiest place to view red-legged frogs in the Hylebos Wetlands is at the Deep Sink. I have also witnessed both adults and tadpoles in several other pools along the sides of the boardwalk. Adults are rarely witnessed in the winter, but I have seen them often in the spring, summer and fall. Tadpoles seem to be most active and easily seen in the summer months.

The adults are usually seen sitting in the mud very near the edge of the water, and because they blend in very well, careful observation is necessary to spot them. They are fairly easily frightened, and will dive into the water and hide well submerged if disturbed. Care should be taken to avoid disturbing them, so as not to interfere with their normal lifestyle.
Appearance

Red-legged frogs are up to 10 cm long, and have recognizable, well-developed dorsolateral folds (raised ridges of skin) starting behind the eye and running along the edge of the back for about two-thirds of the length of the trunk. The body is reddish-brown to olive on the back, usually with a considerable flecking of small, black spots or blotches. The underside of the belly and inner surfaces of the legs are a pretty shade of reddish-pink (from which comes the common name and the species name, aurora, meaning dawn). Red-legged frogs usually have a light lip-line that runs eye to shoulder, bordered above by a darker mask.

Tadpoles are dark brown above, with scattered small clumps of metallic-looking flecks. The abdomen is an iridescent brassy to pinkish color. Tadpole length before metamorphosis ranges from 50 mm up to 75 mm, depending on the permanency of the waters they inhabit.

Taxonomy and Close Relatives

Kingdom: Animalia. Phylum: Chordata. Class: Amphibia. Order: Anura (frogs and toads). Family: Ranidae. Genus: Rana (true frogs). Species: Aurora.

Order Anura, the frogs and toads, evolved during the time of the dinosaurs, and now number more than 3500 species. Family Ranidae is possibly the most widespread family of frogs. The family has about 45 genera and 590 species. The genus Rana has a large range, and is the only genus in the family that is found in the United States. Rana is composed of 250 species, eight of which (including two introduced species) are found in the Northwest.

Rana aurora consists of two subspecies, the northern red-legged frog (Rana aurora aurora), and the California red-legged frog (Rana aurora draytonii). The California red-legged frog, a Federal Threatened species and a California Species of Special Concern, does not occur in the Pacific Northwest. The northern red-legged frog, also a California Species of Special Concern, is the subspecies that does occur in the Northwest.    The related Cascades frog (Rana cascadae) is found in the Northwest, usually at higher elevations than the red-legged species.

Another close relative found locally is a subspecies of Rana pretiosa, the Oregon spotted frog. It appears much similar to the red-legged frog, but is less common here.

Geographical Distribution and Habitat

The northern red-legged frog occurs from southwestern British Columbia south to northern California, between the Pacific coast and the Cascade ridge.
Red-legged frogs prefer streams, ponds and marshes in wooded areas, so the Hylebos Wetlands area is fairly good habitat for them. For breeding waters, they need areas with little or no flow, and waters that remain long enough for metamorphosis to take place. The waters must contain sturdy, underwater stems, roots, or branches for egg attachment.

Ecological Lifestyle

Red-legged frogs in our area have a fairly early reproductive season, and require cold waters in deep pools. Eggs are usually deposited as early as late January, and usually in February or early March. Males are quiet as frogs go, and will usually congregate at pond edges as early as mid-December. It is not known if males of the species are territorial. The males can be monogamous, but in some years they mate with more than one female.

The eggs are deposited in a rounded mass of 50

Friends' member Ken Steffenson is the Publications and Website Director for the Washington Toxics Coalition.