NATURAL HISTORY

CALIFORNIA RED-LEGGED FROG } Rana draytonii;
formerly Rana aurora draytonii
FAMILY: Osmeridae

The California red-legged frog and northern red-legged frog were once both classified as subspecies — Rana a. draytonii and Rana a. aurora, respectively — of the red-legged frog (Rana aurora). But a 2004 genetics study recognized them as separate species, Rana draytonii and Rana aurora. A main distinction: the California red-legged frog has paired vocal sacs, while its northern cousin lacks vocal sacs altogether.

DESCRIPTION: The largest native frog in the American West, the red-legged frog can be five inches long. In adults, the bellies and undersides of the hind legs are red or salmon pink; backs are brownish and flecked with spots. Juveniles, with more pronounced dorsal spotting, may have yellow, not red, on the underside of the legs.

HABITAT: This frog prefers aquatic habitat such as ponds, marshes and creeks with still water for breeding. It needs riparian and upland areas with dense vegetation and open areas for cover, aestivation (summertime hibernation), food and basking. Frogs in cooler areas may hibernate in burrows for the winter.

RANGE: California red-legged frogs were once common throughout California’s Central Valley, from Point Reyes National Seashore down to northwestern Baja California. Today they occupy Sonoma and Butte counties in the north to Riverside County in the south, mostly in the western counties. They reside in about 238 streams or drainages in 23 counties, with Monterey, San Luis Obispo, and Santa Barbara counties supporting the most frogs. They now exist in about 30 percent of their historic range.

MIGRATION: Frogs may make overland excursions of up to one mile through upland habitats in wet weather and can disperse up to two miles from breeding ponds.

BREEDING: California red-legged frogs breed from November through April, during or after rainfall. Males appear at breeding sites before females and usually call in small groups. A frog pair clasped in the breeding position with the male riding piggyback on the female, called amplexus, moves to a site where eggs are laid.

LIFE CYCLE: Tadpoles hatch within two weeks, then take up to half a year to develop into frogs. Young frogs become sexually mature in the third year after metamorphosis.

FEEDING: Hunting largely at night, adult frogs use their sticky tongues to draw prey into their mouths. They commonly chow on insects, but about half their food consists of Pacific tree frogs and California mice. Tadpoles and young frogs hunt invertebrates both day and night, adding to their vulnerability to predators.

THREATS: Habitat loss to urban development, agriculture, logging and wetland draining, impacts of dams and water diversions, competition and predation by introduced species, pesticides, cattle grazing, and global warming are driving frog populations down.

POPULATION TREND: Population has declined by at least 90 percent; the frog is gone from 70 percent of its former range. The only large breeding populations left are on the coast from San Mateo to San Luis Obispo counties. The species is extinct in the Central Valley and almost completely extirpated from the Sierra Nevada.

 

Photo: public domain