The decline is yet another indicator of the long-term decline in biodiversity on this planet

Jeff Houlahan

After a rapid shrinking then, the rate of population decline eased off, although it is still continuing.

The researchers say their findings support the widespread impression of amphibian decline, which has until now been largely based on anecdotal evidence.

The research team, whose work is reported in the science magazine Nature, was led by Jeff Houlahan, of the University of Ottawa in Canada. It also included scientists from Switzerland and Russia.

They used data from 936 separate amphibian populations, and unpublished data from herpetologists around the world.

'Conclusive proof'

The team says this was to avoid relying on evidence that was "either anecdotal or derived from short-term studies at small geographical scales".

It notes the persistent reports of catastrophic amphibian population crashes in Australia, south and central America, and high-altitude parts of the western US.

Declines are still continuing

These reports have suggested local climate changes, acid rain, disease, increased solar radiation, or a combination of several of these, as possible causes.

But most documented the disappearance of amphibians from small regions, making extrapolations to the global scale difficult.

The researchers say they think their work provides conclusive proof of the decline of amphibians, which include frogs, toads, newts and salamanders.

More than 200 scientists contributed data from 37 countries, covering 157 species from 21 families. The studies range from two to 31 years in duration.

The team found:

• no significant trend from 1950 to 1960
• a steep decline from 1960 to 1966 (an annual rate of about 15%)
• a shallower decline from 1966 to 1997 (about 2% annually).

Deformities worry scientists

The researchers say their analysis suggests that at a global scale "amphibians have declined over the past several decades and continue to do so."

Only 61 of the 936 populations studied became extinct, and only one of those during the period of most significant decline, from 1960 to 1966.

The team reports that this provides evidence that even existing populations have undergone strong declines.

It says its analysis also suggests recent declines, especially in North America and in Australia and New Zealand.