Some of springtime's more notable heralds appear to be fading away, as a new study finds frogs, toads and salamanders disappearing at an alarming rate across the United States.
In what they say is the first analysis of its kind, scientists with the U.S. Geological Survey and a couple of universities report that declines in environmentally sensitive amphibians are more widespread and more severe than previously thought. Even the most common critters, such as the spring peepers that make Maryland marshes ring with their mating cries, appear to be losing ground.
What's more, they also seem to be vanishing from ponds, streams, wetlands and other supposedly protected habitat in national parks and wildlife refuges.
"What we found was a little surprising," said Evan Grant, a USGS wildlife biologist and study co-author who monitors amphibians in the Northeast.
If the trend continues, the researchers say, some of the rarer amphibians could disappear in as few as six years from roughly half the sites where they're now found, while the more common species could see similar declines in 26 years.
Researchers have known for some time that some frog, toad and salamander species were in trouble, but until now they hadn't developed a broad national picture of how fast they were disappearing.
Besides fascinating children of all ages, amphibians help control mosquitoes and other insect pests. They're also important sentinels for changes in the environment, because they spend part of their lives in water and part on land. They're cold-blooded, depending on the sun's warmth to stay active, and breathe through their skin, which makes them sensitive to changes in water quality.
"Amphibians are a good indicator of what's going on," said Joel Snodgrass, a professor and chairman of biology at Towson University.
He's seen declines locally, which he attributed mainly to development eliminating or altering their habitat, but noted that such observations are limited because of the innate elusiveness of creatures that tend to lurk in water or under rocks. The value of the USGS study, he said, is that it accounted for variability in sightings by making repeated checks over many locations and a long period.
Researchers hadn't expected to see declines in many of the more common species that they looked and listened for over nine years at nearly three dozen sites around the country, including Patuxent Research Refuge in Laurel and along the Chesapeake & Ohio Canal in the Washington area. Based on earlier studies that indicated perhaps one-third of the nation's species were losing ground, researchers had expected to find some species improving while others faced trouble.
But looking at results for 48 species across all the sites, the study charted a "consistently negative" trend in how often they were found where they normally live. On average, the number of locations where amphibians could be found shrank by 3.7 percent per year, meaning that if that continued, they would be in half as many places in about 20 years.
"We don't know how long it's been going on or whether it's a trend that will continue," said Michael Adams, the study's lead author and USGS research ecologist in Oregon.
The study did not attempt to identify the cause or causes for the declines. Amphibian losses have been linked previously with development, disease, chemical contaminants, climate change and even introduced species. While a fungal disease blamed for frog die-offs in other countries is found in the United States, Adams said, "we're not seeing patterns that would help us make that link."
The researchers limited their monitoring to sites controlled by the U.S. Department of the Interior, so development likely had little direct impact on the amphibians' habitat.
"The fact we see declines even in protected areas means there is some larger-scale issue going on with amphibian populations," Grant said.
Parts of the nation experienced severe but not unprecedented drought during the study, the researchers noted, which might have reduced the amount of rain sustaining their wetlands and ponds.
In Maryland, state biologists say that with a few exceptions they have not seen drastic declines in the past 20 years or so in the 20 species of frogs and toads or in the 21 species of salamanders and newts found in the state. Glenn Therres, a wildlife biologist with the Department of Natural Resources who oversees an annual volunteer-driven census of the state's amphibians and reptiles, noted that there has not been any systematic sampling done for most of the state's species, so it's hard to draw overarching conclusions.
But Scott Stranko, a DNR biologist who oversees an ongoing statewide survey of Maryland streams, said it has tracked declines in some of the salamanders more sensitive to disturbances in landscape or water quality.
"It's pretty conclusive that where you have urban development you lose salamanders and probably some frogs as well," said Mark Southerland, a private consulting ecologist who has worked with DNR on the stream survey. The Northern two-lined salamander, for instance, appears to be pretty tolerant of changes to its habitat, so it is still found pretty widely, he said. But other apparently more sensitive species show up less often.
Another factor likely contributing to amphibian declines in urbanized areas such as Baltimore is the widespread use of salt to keep roads clear of ice and snow, Snodgrass said. Changes in salinity can kill the freshwater aquatic insects on which salamanders and frogs feed.
And the salt also poses a direct threat to amphibians. Because they breathe through their skin, increases in water salinity can cause them to lose vital fluid from their bodies.
"Basically, they die of thirst in an aquatic environment," Snodgrass said.