Nearly one in three species of frogs and toads in the world is under threat of extinction, according to the most comprehensive global study of amphibians ever conducted. The report shows that 122 amphibian species have disappeared since 1980. The discovery, reported in the journal Science, is seen by researchers as an early warning of imminent environmental disaster.

Amphibians act like "natural barometers" since their highly permeable skin makes them very sensitive to the effects of climate change and pollution. Any drastic change in the natural world is likely to affect them first. Over the past three years, scientists analysed the distribution and conservation status of all 5,743 known amphibian species. Of these, 1,856 -32 per cent- were threatened with extinction. In comparison, only 12 per cent of bird species and 23 per cent of all mammal species are considered to be endangered. The president of Conservation International, who co-led the research, said: "Amphibians are one of nature's best indicators of overall environmental health. Their catastrophic decline serves as a warning that we are in a period of significant environmental degradation."

Amphibians were the first terrestrial vertebrates to colonise the land successfully about 350 million years ago. They have developed a remarkable diversity by adapting to many different aquatic and terrestrial habitats. Amphibians are present today in every continent except Antarctica, and can be found in almost all habitat types from dry, inhospitable deserts to lush tropical rainforests and temperate climates such as Britain's.