Frog, California Red-legged

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Frog, California red-legged

Rana aurora draytonii

phylum: Chordata

class: Amphibia

order: Anura

family: Ranidae

status: Threatened, ESA

range: Mexico, USA (California)

Description and biology

The California red-legged frog was, until recent decades, abundant throughout much of the state of California. It is the largest native frog in the western United States, ranging from 2 to 5 inches (5 to 13 centimeters) in length. The frog's skin is rough and thick and mostly reddish-brown or gray in color. It has dark spots with light centers on its back. Its upper abdomen is yellow, and its lower abdomen and hind legs are red. The frog's toes are only partially webbed (joined by tissues or membranes). It has vocal sacs, with which it makes sharp, low grunts during the weeks when it breeds.

California red-legged frogs eat invertebrates (animals without a backbone), small mammals, and other amphibians. Tree frogs, mice, and insects are common food items. Adult frogs are nocturnal (active at night), while younger frogs are active both day and night. Among the animals that prey upon California red-legged frogs are wading birds, snakes, and raccoons. When the frogs sense an enemy is near, they swim far out into the water and hide themselves in its depths.

California red-legged frogs breed from late December to early April. Mating is through external fertilization. The male takes hold of the female, she lays her eggs, and then he fertilizes them. The female lays her eggs in a mass ranging from 2,000 to 5,000 eggs. The eggs, which are dark brown and about .07 to .1 inch (2.0 to 2.8 millimeters) wide, are attached to vegetation, such as cattails or bulrushes, at or near the surface of the water. In a week or two the eggs hatch, and dark brown tadpoles (immature or newly hatched frogs) emerge. At the tadpole stage, the young frog has external gills and a rounded body with a long tail bordered by fins. It will remain in this form for 3.5 to 7 months. The tail and gills disappear and legs develop by the end of this period and the tadpole becomes a young frog.

Habitat and current distribution

California red-legged frogs live in rivers, streams, ponds, lakes, and wetland areas near the water's edge. They are found in central and southern portions of California, west of the Sierra Nevada Mountains up to an altitude of 4,000 feet (1,220 meters). The species currently occurs in about 238 streams or drainages in 23 counties, with the largest populations in Monterey, San Luis Obispo, and Santa Barbara counties. The California red-legged frog has disappeared from about 70 percent of its original habitat.


Frogs have been around for millions of years; in fact, their immediate ancestors roamed the Earth with the dinosaurs. Over the years, frogs have evolved into many different species that have successfully adapted to almost every kind of climate and habitat. Although they have been around for a very long time—much longer than humans—frogs and other amphibians have been disappearing at a very fast rate worldwide since the 1980s. Although a variety of causes for the decline in frog populations have arisen, pollution is a major factor. Frogs take in much of the air they breathe through their skin. They have no filters, like human lungs, to protect them from pollution and disease. In the mid-1990s, an alarming number of malformed frogs began to appear—frogs with missing limbs, extra limbs, or oddly shaped limbs. A few years later studies showed that frogs exposed to very tiny amounts of the pesticide Atrazine were experiencing severe sexual abnormalities. Other studies suggest that air pollution and global warming may be contributing to the decline in the frog population. Scientists are particularly interested in frogs' plight, believing that if the world is too contaminated (full of poisons and harsh chemicals) to sustain the lives of frogs, it is probably not a healthy place for human beings either.

History and conservation measures

Before the nineteenth century, the California red-legged frog could be found throughout most of California, from north of the San Francisco bay area south to Baja California,

Mexico, and inland to Shasta County and the Sierra Nevada Mountains. The frog was common and familiar to most Californians, even making its way into Mark Twain's 1865 short story, "The Celebrated Jumping Frog of Calaveras County."

A large gold rush in the 1850s brought thousands of miners into California's Central Valley. The miners tore up the mountain streams in their search for gold, destroying large portions of the California red-legged frogs' habitat. Later in the century, frogs' legs became a very popular food item in San Francisco and the Central Valley. An estimated 80,000 frogs were killed for food each year. By the early 1900s, they had become harder and harder to find. To keep up with the demand for frogs' legs, bullfrogs were brought into California at the end of the century. Bullfrogs quickly became predators of the California red-legged frog, seriously reducing the population once again. Bullfrogs remain in the California red- legged frog's habitat and continue to prey upon the species.

After these early events seriously depleted the California red-legged frog population, loss of habitat and contamination brought the species to the risk of extinction. In fact, some of the worst damage to the species has occurred since 1985. Habitat loss due to the damming of waterways, livestock grazing, urbanization, loss of wetland environments, and agricultural development have led to the loss of 70 to 75 percent of the frogs' historical habitat. The introduction to California wetlands and streams of nonnative fish and bullfrogs, as well as alien plants, has further diminished the population. In the early 2000s, studies linked the losses in population to pesticides that were being used on nearby farms and were blown into the California red-legged frogs' habitat, contaminating it for the frogs.

The California red-legged frog was listed as threatened by the U.S. Fish and Wildlife Service (USFWS) in 1996. In March 2000, the USFWS designated 4.1 million acres as critical habitat for the California red-legged frog. Critical habitat is an area considered necessary to the conservation of the species. Critical habitat designation does not create a wildlife refuge and does not ban human activities in the area. Rather, it ensures that all federal agencies check with the USFWS about any activities they authorize in the area. A lawsuit was brought to the courts by a homebuilders association, which claimed that the USFWS had not adequately considered the economic impact of creating millions of acres of critical habitat. The courts agreed with the homebuilders association and revoked most of the critical habitat designation. This settlement, reached in July 2002, left as critical habitat 124,000 acres around Jordan Creek, a tributary to the Merced River in Tuolumne and Mariposa counties near the Sierra Nevada Mountains, and 75,000 acres in the Angeles National Forest near Los Angeles. The USFWS intends to propose a new critical habitat plan in 2004.