California Red-legged Frog (Rana Aurora Draytonii) are long-time Peninsula residents

California Red-legged Frog (Rana Aurora Draytonii)

California Red-legged Frog (Rana Aurora Draytonii)

Mark Twain first found fame for writing an account of a jumping frog contest in Calaveras County. While the story may be apocryphal, the “Celebrated Frogs” of Mark Twain’s article, the California red-legged frogs, as the largeset native frogs in the Gold Rush Country of California’s Western Sierras at that time, were likely the contestants in the event the gave birth to the tale.(1)

The California Red-Legged Frog (“CRLF”) became Federally listed as a Threatened species on May 23, 1996 (61 Federal Register 25813). Monterey County is roughly in the middle of the range of this species.

This native California frog is now gone from the Sierras, including Calaveras County, but it still hangs on in a very few places. One of those few places is at Rancho San Carlos in Carmel Valley. When these frogs were listed as an imperiled species, the federal experts made it clear that Rancho San Carlos is one of only three places left in the world where significant populations of Mark Twain’s frogs still live.

(From the Federal Register for Thursday, May 23, 1996) —

“Only three areas within the entire historic range of the California red-legged frog may currently support more than 350 adults, Pescardero Marsh Nature Preserve (San Mateo County), Point Reyes National Seashore (Marin County), and Rancho San Carlos (Monterey County). The San Francisco Airport drainage location, identified in the proposed rule as containing over 350 individuals, is now thought to be nearly extirpated. Threats, such as expansion of exotic predators, proposed residential development, and water storage projects, occur in the majority of drainages known to support California red-legged frogs.”

The CRLF US Fish & Wildlife Final Recovery Plan for the California Red-Legged Frog was signed May 28, 2002. The Plan designates all 255 square miles within the Carmel River Watershed as core area for recovery.

Independently, all 255 square miles of the Carmel River watershed was designated as “Critical Habitat” by federal ecologists at US-Fish & Wildlife Service in 2000. This designation has been temporarily suspended by a federal Judge because the FWS failed to prepare an adequate economic analysis. FWS’s ecological evaluation of the critical habitat areas will not change.

The frog can inhabit any aquatic area in its range. Unlike its main predator, the invasive Bullfrog, the red-legged frog can and does leave the river (up to 2 miles from their aquatic home) when storms arrive. The dim-witted Bullfrogs get washed downstream into the ocean and often drowned while the native red-legged frog sits high and well – maybe not exactly dry, but safely out of the swift flowing rivers and streams.

The US-Fish & Wildlife states —

“This species is the largest native frog in the western United States, ranging from 1.5 to 5.1 inches in length. The abdomen and hind legs of adults are largely red; the back is characterized by small black flecks and larger irregular dark blotches with indistinct outlines on a brown, gray, olive, or reddish background color. Dorsal spots usually have light centers, and dorsolateral folds are prominent on the back. Tadpoles range from 0.6 to 3.1 inches in length, and are dark brown and yellow with dark spots.

California red-legged frogs spend most of their lives in and near sheltered backwaters of ponds, Marshes, springs, streams, and reservoirs. Deep pools with dense stands of overhanging willows and an intermixed fringe of cattails are considered optimal habitat. California red-legged frog eggs, larvae, transformed juveniles, and adults also have been found in ephemeral creeks and drainages and in ponds that do not have riparian vegetation. Accessibility to sheltering habitat is essential for the survival of California red-legged frogs within a watershed, and can be a factor limiting population numbers and distribution.

Adventurous Traveling Frogs

Individual California red-legged frogs are known to move long distances over land (up to 2 miles) between water sources during winter rains.

Breeding

California red-legged frogs breed from November through March with earlier breeding records Occurring in southern localities. California red-legged frogs are often prolific breeders, typically laying their eggs during or shortly after large rainfall events in late winter and early spring. Embryos hatch 6 to 14 days after fertilization, and larvae require 3.5 to 7 months to attain metamorphosis.

Larvae probably experience the highest mortality rates of all life stages, with less than one percent of eggs laid reaching metamorphosis. Sexual maturity normally is reached at three to four years of age; California red-legged frogs may live eight to ten years. Juvenile frogs have been observed to be active Diurnally and nocturnally, whereas adult frogs are mainly nocturnal.

Diet

The diet of California red-legged frogs is highly variable. Invertebrates are the most common food items, although vertebrates such as Pacific tree frogs and California mice can constitute over half of the prey mass eaten by larger frogs. Larvae likely eat algae.

Threatened

The California red-legged frog has been extirpated or nearly extirpated from 70 percent of its former range. Historically, this species was found throughout the Central Valley and Sierra Nevada foothills.

At present, California red-legged frogs are known to occur in 243 streams or drainages from 22 Counties, primarily in central coastal California. The most secure aggregations of California red-legged frogs are found in aquatic sites that support substantial riparian and aquatic vegetation and lack non-native predators.

Over-harvesting (for San Francisco restaurants),
habitat loss (due to agriculture and development),
non-native species introduction (bullfrogs), and
urban encroachment are the primary factors that have negatively affected the California red-legged frog throughout its range.

Ongoing causes of decline include
direct habitat loss due to stream alteration and disturbance to wetland areas,
indirect effects of expanding urbanization, and
competition or predation from non-native species.

References:

1. While most historians and frog scientists believe Twain’s Celebrated Frog was a California red-legged frog, there is a faint possibility the Northern Leopard Frog, Lithobates pipiens, could have been involved, but it is rarely seen West of the Eastern side of the Sierras. Treefrogs, particularly the Northern Pacific Treefrog, while gosh-darn cute, are likely far too small to fit Twain’s story. One other possibility is the Sierra Nevada Yellow-legged Frog (Rana sierrae).

2. All Federal Register Documents for the California red-legged frog

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