Amphibians of the Eldorado National Forest

Presented at the ENFIA General Meeting and Potluck on June 20, 2001

A number of amphibians are found or could potentially be found on the Eldorado National Forest. These species are the California Red-legged Frog, the Foothill Yellow-legged Frog, its up-country cousin, the Mountain Yellow-legged Frog, and the Yosemite Toad. At the ENFIA General Meeting on June 20th, this topic will be presented by the Amador Ranger District Biology Department.

The California Red-legged Frog (Rana aurora) is a federally listed threatened species that historically occurred on the forest and a known population now occurs just below the forest in the Placerville vicinity. It is the largest native frog of the Sierra and only found in a few streams in the foothills from El Dorado County south to the Merced River. Unlike the bellowing Bull Frog, this shy and uncommon creature slips silently into the depths of a pool to avoid detection. At night when the frog becomes active, a low, guttural growl might be heard. Its food is largely insects. This frog’s upper surface is dark brown to light olive with a whitish “mustache”. The lower side of the belly, undersides of the hind legs and feet may be a reddish hue. Its body measures about 5 inches in length. It does not adapt well to drought, requiring permanent bodies of water in which to survive. Breeding begins in January with peak egg laying around the end of February. In the summer, the tadpoles will metamorphose into frogs about 1 inch in size. The introduction of the Bullfrog has displaced the Red-legged The Foothill Yellow-legged Frog (Rana boylei) and Mountain Yellow-legged Frog (Rana muscosa), designated as a Forest Service sensitive species, occur in a number of locations on this forest.

The Foothill Yellow-legged Frog lives in lower elevation streams on the Sierra’s western slope and along the eastern base of the Sierra range north to near Mono Lake. When the swollen streams subside in springtime, this species lays its eggs in a round mass that attaches to rocks at the water’s edge. The tadpoles mature rapidly as seasonal moisture soon evaporates transforming into frogs about an inch long during July and August. The young adults seek pools in shady ravines or mountain springs in order to survive. One may find a number of these frogs perched beside a pool as if sunbathing. When disturbed they vanish seeking the shelter of rocks or the muddy bottom. This frog exhibits a chameleon-like quality in the coloring of its skin. It varies from reddish, yellowish or spotted. The underside and hind legs remain light yellow, from which the animal gets its name.

The Mountain Yellow-legged Frog’s natural habitat is lakes of the Mid to High Sierra. Walk around one of these lakes and observe this species leaping off the banks into the water. Their voice is weak and seldom heard. Orange-sized egg masses are laid in warmer water in early summer. Because of low water temperature and short summer, the larvae overwinter, most likely in water under ice, and transform when about a year old. Sometimes tadpoles are seen piled on top of one another as they lie near a lake’s edge in warmer water. This frog’s body and legs are brownish with blotches of green and darker brown. On the underside, it is dark yellow on the belly and inside of the hind legs. Mature frogs have a body length of about 3 1/2 inches. An odor of garlic is produced when the animal is handled. Its enemy is the Western Terrestrial Garter Snake. Large trout also prey upon tadpoles and mature adults. Its range is from near Mt. Whitney at 11,500 ft. to slightly beyond Lake Tahoe, mostly above the 7,000 ft. elevation. This frog has become a center of controversy regarding fish stocking in small, alpine lakes, many of which are in the Desolation and Mokelumne Wilderness areas.

The Yosemite Toad (Bufo canorus) is a sensitive species not known to currently occur on the Eldorado Forest, however potential habitat exists. Its present range is the 6,500-10,00o+ ft. elevation of the High Sierra from Ebbetts Pass south to Kaiser Pass. This toad has a very distinctive song much like that of a junco. Unusual for amphibians, its chorus can be heard in daytime as frigid nights of the high country hamper nocturnal activity. The Yosemite Toad lies dormant beneath winter’s snow until April or May. As winter’s hold on its habitat ebbs, the males converge around small warm-water pools and sing to attract mates. The eggs are laid in short strings soon hatching into tiny 1/4 inch toads. Adult males are olive-green. Females are larger than the males with back and sides having irregular sharp-edged patches of black rimmed with white.

All of these species are very important in the management of the Eldorado National Forest. Management practices are being implemented to improve habitat, protect known occurrences and educate the public on the importance of these species.