Amphibians are experiencing a precipitous decline across the globe, according to the first comprehensive world survey of the creatures, which include frogs, toads and salamanders. As many as 122 species have disappeared since 1980, and 1,900 are in danger of becoming extinct.
The rapid drop -- the equivalent of tens of thousands of years' worth of extinctions in just a century -- is being caused by a range of factors that include deforestation, pollution, habitat loss and climate change, researchers said. But they added that the phenomenon also tells a disturbing tale of broad environmental degradation that may ultimately threaten humans and other animals, as well. Amphibians are often considered "canaries in the coal mine" because their permeable skin makes them especially sensitive to environmental changes.
"This is the first group being affected by a death by a thousand cuts in the way that we as humans have been affecting the biosphere in the past 50 or hundred years," said Claude Gascon, a scientific adviser to the study who serves as vice president for regional programs at Conservation International, an environmental group. "It's entirely possible other groups of biodiversity may go down the drain."
The survey found that 32 percent of all amphibian species face extinction, compared with 12 percent of bird species and 23 percent of mammal species. The three-year $1.5 million study, which involved more than 500 scientists from more than 60 countries, is being published today in the journal Science.
Scientists began noticing the disappearance of amphibians in the late 1980s and early 1990s, but before this study they had never conducted a worldwide assessment of the frogs, toads, salamanders and legless caecilians, also called rubber eels.
"We've never documented anything like this for any other species. When species become rare and begin disappearing, we nearly always know why," said Simon Stuart, leader of the global assessment team. "This has taken the scientific world completely by surprise."
Amphibians are under assault for three major reasons, according to the report. Habitat decline -- including deforestation, water pollution and wetlands destruction -- threatens them because the animals live both on land and in water. Overharvesting of amphibians for food and medication is a second threat. The third is more enigmatic, but it has resulted in catastrophic declines, often linked to a fungal disease called chytridiomycosis, particularly in cooler habitats experiencing drought.
Surveys showed the amphibian population of Costa Rica's Monteverde Cloud Forest, for example, was stable until 1987. The next year it began to crash, and by 1989, 40 percent of its amphibian species had gone extinct, including the striking golden toad. Stuart said it is now widely believed that chytridiomycosis played a pivotal role in the devastation, which took place during a dry period.
More than 200 amphibian species are showing rapid and enigmatic declines, which is alarming, Stuart said, because they probably are linked to recent disruptions in rain and storm patterns. "This is a wake-up call to us that we don't have a grip on the massive climate change that's going on," he said.
Humans are responsible for amphibians' decline in other regions of the world, including China, where many are sought as a delicacy. The Chinese giant salamander -- at six feet the largest amphibian in the world -- sells for at least $300 on the street and makes for several meals, and it has now disappeared from nearly all its range.
In the United States, habitat destruction poses the biggest challenge. Developers and environmentalists are feuding in central California over the fate of the California tiger salamander, a striking black animal with yellow spots. Federal officials estimate the salamander has lost 75 percent of its habitat over time, becoming a casualty of urbanization and agricultural development. The U.S. Fish and Wildlife Service decided in July to list the salamander as threatened and identified 383,000 acres of habitat as key to its survival.
Al Donner, an assistant field supervisor in Fish and Wildlife's Sacramento office, said federal officials are trying to "be sensitive to the interests of all affected parties" in the tiger salamander case, including developers, landowners and environmentalists, "while working to ensure the survival of the species."
Four years ago, the federal government launched a national program to research and monitor the state of amphibians in the United States, and it now devotes $4 million a year to identify threats to amphibians nationwide.
"We've had a leap in our understanding into the causes of amphibian decline," said Rick Kearney, national coordinator for the U.S. Geological Survey's amphibian research and monitoring initiative. "We recognize how there are connections between the decline in water quality [and availability] and amphibians. . . . Amphibians are a very important indicator of our environmental quality."
But Paul Ehrlich, a Stanford University ecologist, said the amphibian study is worrisome and shows that administration officials are "destroying the working supports of our life system" by exploiting rather than conserving habitat. "They're sawing off the limb that humanity is sitting on," Ehrlich said. "Without biodiversity, we'd be dead."
Gascon, at Conservation International, said: "There are some actions we can take today to prevent the immediate extinction of many species as we work on a longer-term solution." These include creating parks and ecological reserves, reducing emissions that contribute to climate change, and breeding animals in captivity to sustain vulnerable species.