MOORHEAD, Minn. (AP) -- Scientists in northern Minnesota are trying to decode frogs' sounds, to understand why the amphibians' populations have been shrinking.
From 2002 to 2011, frog populations across North America were down 4 percent. Populations of at-risk species fell nearly 12 percent.
Michael Adams is a research ecologist with the U.S. Geological Survey. He says disease, pesticides and habitat loss are generally known to be factors, but scientists wanted more specifics.
They've been recording frog sounds in forests such as the Tamarac National Wildlife Refuge in Becker County. They set up audio recorders to capture months' worth of sound, and they're analyzing the findings to determine how populations are changing.
He says the biggest surprise so far is how the population of even healthy frog species is decreasing.