A new study finds that frogs, toads, salamanders and other amphibians in the U.S. are dying off so quickly that they could disappear from half of their habitats in the next 20 years. For some of the more endangered species, they could lose half of their habitats in as little as six years. The nine-year study, published on May 22 in PLoS One by scientists from the U.S. Geological Survey (USGS), examined population trends for 48 species at 34 sites across the country.

The researchers found that on average amphibian populations were shrinking a surprising 3.7 percent per year. "Even though these declines seem small on the surface, they are not," lead author Michael Adams, a USGS ecologist, said in a prepared release. "Small numbers build up to dramatic declines with time. We knew there was a big problem with amphibians, but these numbers are both surprising and of significant concern."

Worse yet, the scientists found that species currently classified as "endangered," "vulnerable" or "near threatened" on the IUCN Red List of Threatened Species were declining much faster, at an average of 11.6 percent. Species listed as "least concern" on the Red List were declining at a slightly slower-than-average rate of just 2.7 percent.

The researchers did not look at specific causes of death—although past experience tells us amphibians suffer from habitat loss, climate change, pollution, invasive species and the deadly chytrid fungus. But they did discover that populations dwindled throughout the country, even in national parks and wildlife refuges that are supposedly protected for conservation purposes. "The declines of amphibians in these protected areas are particularly worrisome because they suggest that some stressors—such as diseases, contaminants and drought—transcend landscapes," Adams said. "The fact that amphibian declines are occurring in our most protected areas adds weight to the hypothesis that this is a global phenomenon with implications for managers of all kinds of landscapes, even protected ones."

A FAQ published in conjunction with the study explains why the drop in amphibian species matters: "[Amphibians] control pests, inspire new medicines, feed other animals and help make ecosystems work. They are inherently valued by people of all ages—watching tadpoles and listening to frog calls are some of the most accessible interactions we have with the natural world."

The study was conducted under the auspices of the USGS Amphibian Research and Monitoring Initiative, which was established by congressional mandate in 2000 to monitor, research and conserve the country's amphibian populations.

Previously in Extinction Countdown:

Photo: A Sierra Nevada yellow-legged frog (Rana sierrae) in Yosemite National Park. By Devin Edmonds , USGS