Populations of frogs, salamanders and other amphibians are declining at an average rate of 3.7 percent each year, according to a U.S. Geological Survey study released this week. Researchers say the study is the first to calculate how quickly amphibians are disappearing in the United States.

"If the rate observed is representative and remains unchanged, these species would disappear from half of the habitats they currently occupy in about 20 years," according to the USGS.

The negative findings held true in regions around the country, including on federally protected lands such as national parks.

To conduct the study, geologists analyzed reports of the presence of 48 species of amphibians at ponds and other habitats that were monitored between 2002 and 2011. The sampling data came from 34 different sites. The results were published in the journal PLOS One.

While the average decline was estimated at 3.7 percent, the study found that for species on the International Union for Conservation of Nature's the news was even worse, with an 11.6 annual decline.

Amphibian species that had been seen as robust, capable of sustaining themselves amid global declines that have concerned scientists since the 1980s, were found to dwindle at a rate of 2.7 percent each year, a finding the researchers called "alarming."

"Overall, the trends we documented suggest that amphibian declines may be more widespread and severe than previously thought," the geologists wrote.

The data collected did not include possible causes of the declines. In their report, the scientists write that possible factors include climate change, disease, and drought. They also noted that the study covered a comparatively short period of time.

"Amphibians have been a constant presence in our planet's ponds, streams, lakes and rivers for 350 million years or so, surviving countless changes that caused many other groups of animals to go extinct," says USGS Director Suzette Kimball. "This is why the findings of this study are so noteworthy; they demonstrate that the pressures amphibians now face exceed the ability of many of these survivors to cope."

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