The global decline in frogs and toads is a genuine phenomenon that began long before biologists first suspected it.
Scientists have conducted the biggest study yet into the drastic fall in amphibian numbers and have concluded that the trend is real and shows no signs of reversing. The findings will fuel the belief that amphibians are the world's "canary in the coalmine" and that their demise is a warning that other large groups of animals are the next to go.
An international team of biologists led by Jeff Houlahan, of the University of Ottawa in Canada, found that the many anecdotal accounts of declining frogs and toads can be backed up by an analysis of 936 separate populations studied over the past 50 years. They detected no significant fall in numbers during the Fifties but a sharp decline in the early Sixties, which continued as a more modest yet significant dwindling up to the late Nineties.
"Our results suggest the most dramatic declines - from which amphibian populations seem not to have recovered - occurred several decades before herpetologists sounded the alarm," the scientists report in the journal Nature.
Scientists first began to suspect that frogs, toads, newts and salamanders were suffering population falls in the Eighties but the reports were often anecdotal or too poorly documented to conclude they were part of a global phenomenon.
For instance, biologists counted hundreds of populations of golden toad and harlequin frog in the Monteverde cloud forests of Costa Rica in the mid-Eighties. A decade later they had disappeared. Similar disappearances were seen as far apart at the American Rockies, the English meadows and Australian rainforests. There were no easy explanations for the declines.
Dr Houlahan and his colleagues from the University of Zurich and the Russian Academy of Sciences gathered all the available data from published and unpublished amphibian studies from around the world. They found amphibian numbers had declined by an average of about 5 per cent over the past 40 years and that 61 of the 936 populations under study were now completely extinct.
Dr Houlahan said: "We've presented pretty convincing evidence that amphibians have been declining for at least the last 40 years and continue to do so." Amphibians, which breathe through their skin and lay eggs in water, may be more vulnerable to pollution and habitat loss than other animals, he said.Reuse content