Frogs, toads and newts face worldwide environmental threats, according to a new study by more than 500 scientists from over 60 nations.

The Global Amphibian Assessment is a comprehensive look at the threat to the world's 5,743 known types of amphibians, including frogs, toads, salamanders and legless creatures called caecilians.

Conservation researchers analysed the distribution and conservation status of the amphibians.

Scientists first described this frog from the Western Ghats Mountains of India in 2003. (Courtesy S. D. Biju)

They concluded 1,856, or almost one-third, qualify as vulnerable, endangered or critically endangered under the World Conservation Union (IUCN) Red List criteria.

In comparison, 12 per cent of bird species and 23 per cent of mammal species are threatened.

Scientists consider amphibians to be "canaries in the coal mine," offering an early warning of threats since their permeable skin is so sensitive to environmental changes, such as polluted air and freshwater.

"Amphibians are one of nature's best indicators of overall environmental health," said Russell Mittermeier, president of Conservation International, one of the sponsors of the study.

"Their catastrophic decline serves as a warning that we are in a period of significant environmental degradation," he added in a release.

At least nine species have gone extinct since 1980, and another 113 species are considered to be possibly extinct, the researchers said.

The report lists some reasons for the decline:

• Overharvesting of frogs for food in East and Southeast Asia.
• Widespread habitat loss, especially in Southeast Asia, West Africa and the Caribbean.
• A fungal disease called chytridiomycosis is associated with amphibian deaths at higher elevations and streamsides.

The report appears in Friday's online issue of Science Express.