Endangered Species in Santa Cruz County - Species Account


California Red-Legged Frog
(Rana aurora draytonii)


This information was excerpted from the following publication, which is available for reference use at the Central Branch Library:

  • U.S. Fish and Wildlife Service. "The California Red-Legged Frog," a fact sheet included with the "Draft Recovery Plan for the California Red-Legged Frog (Rana aurora draytonii)." Portland, Oregon. The Service, 2000.

It is used here with permission of the Sacramento Office of the U.S. Fish and Wildlife Service.


What is the California red-legged frog?

The California red-legged frog (Rana aurora draytonii) is the largest native frog in the western United States. It is one of two subspecies of the red-legged frog found on the Pacific coast. The California red-legged frog once ranged across much of California, including mining country, where it is believed to be the title character of Mark Twain's famed short story, "The Celebrated Jumping Frog of Calaveras County."

History

The historic range of the California red-legged frog extended coastally from the vicinity of Point Reyes National Seashore, Marin County, and inland from the vicinity of Redding, Shasta County, in California southward to northwestern Baja California, Mexico.

The California red-legged frog was harvested for food in the San Francisco Bay area and the Central Valley during the late 1800s and early 1900s with approximately 80,000 frogs harvested annually. As the frogs became more rare, the market for them declined. Bullfrogs were introduced in California around 1896, to help satisfy the demand for frog legs as the red-legged frog population dwindled. Ironically, the native red-legged frog soon became prey for the much larger bullfrog, a threat to the red-legged frog's existence that continues to today.

At about the same time the frog began its decline, Central Valley wetlands and riparian habitats were being converted to agricultural land. Streams were denuded of riparian vegetation and channelized. These changes resulted in a loss of over 90 percent of historic wetlands with the majority of that loss occurring before 1939. California red-legged frogs were eliminated from the Valley floor by 1960. Those populations that remained in the Sierra Nevada foothills were separated from other populations and nearly eliminated from this area as a result of reservoir construction, introduction of exotic species, and drought.

In Southern California, urbanization with its resulting infrastructure, including road construction, channeling of streams, and reservoir construction had a devastating impact on red-legged frogs. Of the 80 sites known to have harbored this species historically in Southern California, today only one population can be confirmed -- at a nature preserve in western Riverside County, which is managed by The Nature Conservancy.

Habitat

Red-legged frogs require habitat consisting of both aquatic and riparian components. Adults utilize dense, shrubby or emergent vegetation closely associated with deep-water pools with fringes of cattails and dense stands of overhanging vegetation such as willows.

Adult frogs that have access to permanent water will generally remain active throughout the summer. In cooler areas they may hibernate in burrows or other refuges. Red-legged frog adults may move both up and down stream of their breeding habitat to forage and find refuge.

Range and Current Distribution

California red-legged frogs have been eliminated from more than 70 percent of their historic habitat. Surveys indicate the frogs are present in about 10 percent of their historic locations.

The California red-legged frog is found primarily in wetlands and streams in coastal drainages of central California. Its historic range extended from Point Reyes National Seashore, coastally, and Redding, California, inland southward to northwestern Baja California. Today they are know to occur in about 238 streams or drainages in 23 counties. Monterey, San Luis Obispo, and Santa Barbara counties support the greatest amount of currently occupied habitat. Only four areas within the entire historic range of the subspecies may currently support more than 350 adults.

Life History

The California red-legged frog ranges from 1.5 to 5 inches in length. The belly and hind legs of adult frogs are often red or salmon pink; the back is characterized by small black flecks and larger dark blotches on a background of brown, gray, olive or reddish-brown.

California red-legged frogs are relatively prolific breeders, usually laying egg masses during or shortly following large rainfall events in late winter or early spring. Females can lay between 2,000 and 5,000 eggs in a single mass. The eggs are attached to vertical emergent vegetation such as bulrushes or cattails.

It takes between 6 to 14 day for the eggs to hatch and approximately 3.5 to 7 months for the tadpoles to develop into frogs. The highest rates of mortality for this species occur during the tadpole stage; less than 1% of eggs hatched reach adulthood.

Tadpoles and young frogs thrive on invertebrates, which they catch with their mouths. They hunt day and night. This constant activity makes them visible, and, therefore, more vulnerable to predators. More than half of the diet of adult frogs consists of Pacific tree frogs and California mice; the rest is insects. Adults feed and are active largely at night.

Why is the California red-legged frog threatened?

Over the last two decades, scientists have noted a widespread decline of frogs and other amphibian species, the causes of which are not fully understood. The decline of the California red-legged frog is attributed to the spread of exotic predators such as bullfrogs, and the widespread changes that have fragmented habitat, isolated populations, and degraded streams. Its decline signals a loss of diversity and environmental quality in wetlands and streams that are essential to clean water and to the survival of most fish and wildlife species.

What is being done to prevent extinction of the California red-legged frog?

Listing -- The California red-legged frog was federally listed as a threatened species in May 1996.

Recovery Plan -- The U.S. Fish and Wildlife Service's draft recovery plan for the California red-legged frog will be released for public review in the Spring of 2000. The strategy for recovery will involve protecting existing populations by reducing threats; restoring and creating habitat that will be protected and managed in perpetuity; surveying and monitoring populations and conducting research on the biology and threats of the species; and re-establishing populations of the species within the historic range.

Critical Habitat -- The Fish and Wildlife Service is under court order to propose critical habitat for the California red-legged frog by August 31, 2000. [Note: Critical Habitat was designated in 2006]