The California Red-legged Frog a local endangered species

by James Hale:

The California Red-legged Frog (Rana draytonii) is endemic to California, and ranges from extreme northern Baja California, Mexico through the northern half of the state. It is most common in the Coast Ranges and occurs in isolated, disjunct populations in the foothills of the Sierra Nevada Mountains. It is apparently absent from the Central Valley floor. It was formerly considered a subspecies of the Northern Red-legged Frog, however genetic studies have revealed it to be a distinct species. The California Red-legged Frog is estimated to have disappeared from over 75% of its historic range, and is now only found in about 256 streams or drainages in 28 counties of California. The frog is a federally listed threatened species of the United States and is protected by law throughout California. In March 2010, the US Fish and Wildlife Service announced 1,600,000 acres of protected land for the species throughout California.

The back or dorsal surface of the California Red-legged Frog is a brown, grey, olive or reddish color, with black flecks and dark, irregular, light-centered blotches, and is coarsely granulated. Above the upper jaw, a dark mask with a whitish border highlights the face. In adults, the undersides of the hind legs and abdomen are usually red, from which the frog gets its name. In young frogs the undersides may be yellow . Black, red and yellowish mottling accents the groin of mature frogs.  Another characteristic feature is the dorsolateral fold, which is visible on both sides of the frog, extending from the eye to the hip. The male can be recognized by its large forelimbs, swollen thumbs, and webbing. These features aid the male during amplexus, the courtship embrace to the female, during mating.

The California Red-legged Frog is chiefly a pond and riparian frog that inhabits streamsides, woodlands, grasslands and humid forests, especially where emergent vegetation such as cattails, rushes and other plants provide dense escape and protective cover. Permanent sources of water such as marshes, ponds, lakes, reservoirs and streams are preferred habitat. The frog is usually found in or near water, however after breeding and the first rains, it may disperse far from water. Overland movements of over two miles have been recorded in the Santa Cruz Mountains and elsewhere. It is both nocturnal and diurnal.

The breeding season for California Red-legged frogs is short, often lasting only one to three weeks. Depending upon locality, mating occurs from late November to May. The males call females with a stuttering, sometimes accelerating, series of guttural notes on one pitch. Usually from 4 to 7 notes, the call resembles a growl or groan. A continuous low clucking sound may be heard when frogs are in chorus. After fertilization, the female lays her 2,000 to 5,000 eggs in irregular grapelike clusters, 3 to 10 inches in diameter, attached to submergent vegetation in the shallows. Three jelly envelopes surround the individual eggs which are one third to one half inch in diameter. The tadpoles are yellowish brown above with an iridescent pink belly and about three inches long at transformation. The recent discovery that tadpoles may overwinter, taking up to 13 months to metamorphose, may have serious implications for this threatened species. Tadpoles feed on algae. Insects, beetles, caterpillars, isopods and other invertebrates are consumed by adults for food. Salamanders, smaller frogs and even small mammals are sometimes eaten. Males may live up to eight years while females may reach ten years of age.

Loss of habitat to developments, pesticides and other pollutants, and the introduction of the aggressive, nonnative Bullfrog and game fishes have all contributed to the decline of the California Red-legged Frog from its historic range. Agriculture, mining, overgrazing, recreation, timber-harvesting, non-native plants, impoundments, water diversions and degraded water quality are other factors leading to their decline. I used to encounter this species frequently along the lower tributaries throughout the Walnut Creek Watershed. Negative impacts have forced them to the upper reaches of the watershed. The California Red-legged Frog was heavily marketed in central California and elsewhere as a source of frog legs in the late 1800’s and early 1900’s which severely impacted local populations. It was the California Red-legged Frog that Mark Twain featured in “The Celebrated Jumping Frog of Calaveras County”¬Ě, an 1865 short story that brought him his first success as a writer, bringing him national attention.

James M. Hale

Wildlife Biologist

Vice Chair of the Contra Costa County Fish and Wildlife Committee