WASHINGTON (Reuters) - Frogs, toads and salamanders have been in trouble for decades, but a new U.S. government study shows just how quickly many amphibians are disappearing from ponds and creeks across the United States.
The average rate of decline for U.S. amphibians is about 3.7 percent a year, which may sound small but compounds over time, scientists with the U.S. Geological Survey reported on Wednesday in the peer-reviewed online journal PLOS One.
Biologists recognized an international amphibian crisis in 1989, when scientists' compared their disparate tales of vanishing species in locations around the world.
A global assessment in 2004 suggested nearly one-third of the amphibians species in the world, and the United States specifically, were declining.
The new USGS study is the first to present detailed monitoring data on how various populations of U.S. frogs, toads and salamanders are faring in an analysis of nine years of information collected from 34 sites across 48 species.
The news is not good: Even the best-off species of U.S. amphibians have seen an average annual decline of 2.7 percent in the number of animals; those considered at highest risk have an average annual decline of 11.6 percent, which means that if declines continue on their current path, they would vanish in six years from half the patches they now occupy.
USGS biologists consider an amphibian "patch" to be something as small as a pond or specific stretch of a stream or river where a species resides.
Because amphibians develop in water and on land, and because they generally sit at the middle of their respective food chains - they eat small things like insects, while bigger predators including fish eat them - they are an integral piece of their ecosystems.
Particularly worrisome is the decline of amphibians in protected areas including national parks and refuges, according to Mike Adams, a USGS ecologist and the study's lead author.
"It may well be that amphibians are getting the worst of a number of global patterns," Adams told Reuters. "We're seeing things like climate change and disease and invasive species that are affecting amphibians."
The study did not evaluate the cause of the amphibian crisis, but a USGS blog released last week - available here - cited a trio of studies that suggest increasingly erratic rainfall linked to a changing climate could play a role.