Sierra Nevada Yellow-legged Frogs Feeling the Heat

The Sierra Nevada yellow-legged frog once was common in these high elevation lakes and slow moving streams at altitudes ranging from 4,500 to 12,000 feet. But its range has decreased more than 80 percent in the last 90 years.

In a long-term study funded by the Forest Service, the researchers found that the combination of the shallow lakes drying up in summer and predation by introduced trout in the larger lakes limits the frog's breeding habitat, and can cause its extinction.

These lakes and streams were not inhabited by fish until the hybrid trout were introduced.

"Environmental factors that increase summer drying of small lakes are likely to bring further population decline because the larger lakes are off limits to breeding," said study co-author Kathleen Matthews a Forest Service scientist at the Pacific Southwest Research Station.

The researchers studied lakes in Kings Canyon National Park's Dusy Basin that are mostly fed by snowmelt. Climate change models suggest one of the effects of climate change on Sierra Nevada water balance will be a decreased snow pack, with more than half of the current snow water equivalent gone by 2090.

Sierra Nevada yellow-legged frog (Photo by Gary Nafis courtesyCalifornia Herps)

Sierra Nevada yellow-legged frogs need two to four years of permanent water to complete their development, so repeated tadpole mortality from lakes drying up in summer leads to population decline. The warmer and drier the climate, the more the frogs would be affected, the scientists concluded.

In addition, they believe it was unlikely the frogs were historically restricted to small lakes in Dusy Basin as they are today. Larger lakes free of introduced fish would have provided refuge for the frogs and tadpoles in dry years.

The U.S. Fish and Wildlife Service has determined that listing of the Sierra Nevada yellow-legged frog as an endangered species is warranted but precluded by the need to complete other listing actions of a higher priority.

Matthews co-authored the 10-year study with Krishna Feldman, another Pacific Southwest Research Station scientist and Igor Lacan, of the Berkeley Department of Environmental Science, Policy and Management.

Their findings appear in the current issue of the journal "Herpetological Conservation and Biology."

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