California red-legged frog (Rana draytonii) is Federally-listed as Threatened (May 23, 1996) under the Federal Endangered Species Act and is designated as a “California Species of Special Concern” by the California Department of Fish and Game. This species historically ranged from Marin County southward to northern Baja California. The current range has been greatly reduced, with most remaining populations occurring in portions of the San Francisco Bay area, including Marin County, and along the central coast. Only isolated populations of this species have been documented along the western slopes of the Sierra Nevada and in the foothills region. Ongoing threats to remaining populations of California red-legged frog include loss and disturbance of suitable aquatic habitat, and the presence of introduced predators, such as bullfrog.
California red-legged frog is the largest native frog in the western United States. Adults range in size from 1.5 to 5 inches in length. Coloring of adult frogs is reddish-brown or brown, gray, or olive overall, with small, black irregular flecks and spots on the back and sides, and dark banding on the legs. The hind legs are red underneath and on older frogs the red coloring extends onto the belly and sides. The chest and throat are creamy and marbled with dark gray. The legs of adult frogs are relatively long and their toes are not completely webbed. Two distinct folds extend from just behind the eyes down the length of the back. Tadpoles range from 0.6 to 3 inches in length, are brown marked with dark spots and have eyes set in from the margin of the head.
California red-legged frog occurs in quiet pools of streams, marshes, and occasionally ponds. This species prefers aquatic habitats with little or no flow, the presence of surface water to at least early June, surface water depths of at least two to three feet, and the presence of fairly sturdy underwater supports such as cattails. The largest densities of this species occur in areas with dense stands of overhanging willows and an intermixed fringe of sturdy emergent vegetation. Breeding sites for California red-legged frog includes coastal lagoons, marshes, springs, permanent and semi-permanent natural ponds, and slow-moving sections of streams. Breeding has also been known to occur in stock ponds and irrigation ponds where there are few aquatic predators, such as bullfrog. They typically breed from November to April, after heavy rainfall. Females lay 750 to 4,000 eggs in clusters that are attached to vegetation beneath the water’s surface. Hatched tadpoles require 11 to 20 weeks to metamorphose (transform).
Adult California red-legged frogs are mainly active at night while juvenile frogs are active both during the day and at night. Feeding activity usually occurs along the shoreline and on the surface of the water. Adult and juvenile frogs eat a variety of invertebrates including aquatic and terrestrial insects, crustaceans, snails, and worms. Larger frogs are also known to eat fish, other tadpoles, smaller frogs, and occasionally small mice. Tadpoles mainly eat algae.
California red-legged frogs occur at several WHF preserves in the Bay Area, including Gale Ranch, Intervening Properties, Montenara, and Wendt Ranch.