Amphibians
Mountain Yellow-legged Frog
Rana muscosa · also called Sierra Nevada yellow-legged frog, southern mountain yellow-legged frog
The mountain yellow-legged frog used to be everywhere in the high Sierra Nevada — thousands of them ringing every alpine lake. Then it nearly vanished, in one of the sharpest amphibian collapses ever recorded. Its partial comeback is one of conservation’s better recent stories.
Overview
The mountain yellow-legged frogs — now split into the Sierra Nevada and southern mountain species — live in high-elevation lakes and streams of California, up to about 3,600 m. They are olive to brown with a yellow wash under the legs and a garlic smell when handled. Their tadpoles take two to four years to develop in the cold water.
Fish, then fungus
The Sierra’s high lakes were naturally fishless. Stocking them with trout for anglers, especially by aircraft in the twentieth century, removed the frog from most waters, because trout eat the slow-growing tadpoles. Then the amphibian chytrid fungus swept the survivors. Together they erased more than 90% of populations.
The turnaround
Removing trout from key lakes let frogs rebound in several basins, and some populations evolved enough chytrid resistance to persist and spread. A 2024 study found broad recovery across Yosemite over 20 years.
Status
Both species are Endangered. Recovery is real but confined mostly to protected wilderness; southern California populations remain very small.
Mountain Yellow-legged Frog: common questions
How did stocking trout nearly wipe out a frog?
The lakes and streams of the high Sierra were naturally fishless, cut off by waterfalls and steep gradients, so the animals living in them, including this frog, evolved with no fish predators. Starting in the nineteenth century and accelerating with aerial stocking in the twentieth, wildlife agencies filled thousands of these waters with trout for recreational fishing. Trout eat the frog's tadpoles, which are large, conspicuous, and present in the water for two to four years because of the cold, so a stocked lake typically loses its frogs entirely within a few years. Surveys found frogs almost only in the lakes that had somehow stayed fishless.
What is being done to save it?
Two main things. In parks and wilderness areas, crews remove non-native trout from selected lakes and their connecting streams by repeated gill-netting and electrofishing over several years, restoring the fishless conditions the frog needs; frogs have recolonised many of these on their own or with a helping hand. Separately, biologists have found that some frog populations carry enough natural resistance to the chytrid fungus to survive an outbreak and then grow, and they translocate frogs and rear tadpoles to seed recovery in suitable habitat. Yosemite and Kings Canyon have been centres of this work.
Is the recovery working?
In places, strikingly. A long-term study published in 2024 found that mountain yellow-legged frogs had increased substantially across Yosemite National Park over about two decades, driven by trout removal and by the spread of chytrid-resistant frogs, with the total population many times larger than at its low point. That does not mean the species is safe; recovery is confined largely to protected high country, southern California populations remain tiny, and the frog is still Endangered. But it is one of the more hopeful stories in the global amphibian decline.
Are the two yellow-legged frog species the same animal?
They were treated as one species, Rana muscosa, until genetic and call studies in the 2000s showed that the populations in the northern and central Sierra Nevada were distinct from those in the southern Sierra and the mountains of southern California. The northern and central form is now the Sierra Nevada yellow-legged frog, Rana sierrae, and the southern form keeps the name Rana muscosa as the southern mountain yellow-legged frog. They look very similar, share the yellow leg colour and garlic smell, and face the same threats, and both are federally Endangered.