By Richard Black
Environment Correspondent, BBC News website
Scientists will meet this weekend to launch an action plan aimed at stemming the global decline in amphibians.
Almost a third of amphibians are in difficulty (Image: Conservation International)
About a third of frog, toad and salamander species are facing extinction; threats include fungal disease, pollution and habitat loss.
The Washington DC meeting is expected to call for the establishment of a large-scale captive breeding programme.
The cost of preserving amphibians from extinction may run into tens of millions of US dollars per year.
The extent of amphibian decline was revealed in October last year, with the publication of a comprehensive worldwide survey, the Global Amphibian Assessment.
It revealed that almost a third of the 5,743 known species are categorised as Critically Endangered, Endangered or Vulnerable according to criteria established by IUCN, the World Conservation Union.
Thirty-four species are extinct, and more than a hundred other species have not been seen for so long that scientists believe they may be extinct as well.
Establishing the reasons behind this decline has proved more difficult than finding out the numbers.
The biggest single threat appears to be a fungus, Batrachochytrium dendrobatidis; first identified just six years ago, it is firmly established in parts of the Americas, Australia and Europe.
The disease which it causes, chytridiomycosis, appears to kill amphibians by damaging their sensitive skins, blocking the passage of air and moisture.
Other threats include viral diseases, habitat loss, drought, pollution, and hunting for food.
WHAT ARE AMPHIBIANS?
Group includes frogs, toads, salamanders and caecilians
First true amphibians evolved about 250m years ago
Adapted to many different aquatic and terrestrial habitats
Present today on every continent except Antarctica
Undergo metamorphosis, from larvae to adults
It is believed that environmental stresses, including drought and pollution, may make the animals more vulnerable to the chytrid fungus, perhaps by weakening their immune system or reducing their birth weight.
"The smoking gun in all this is the fungus," the chair of IUCN's amphibian group Claude Gascon told the BBC News website.
"We have some idea what it's doing, but we don't know where it's coming from and how it's being moved around, and there is no way of controlling it in the wild.
"That leaves us with few options but to go and rescue some populations at risk from disease, and then re-introduce them in the wild when we've cleaned up or found ways of allowing them to live in the wild with the fungus."
Paying the price
The scale of the rescue programme set out in discussion papers for this weekend's meeting is staggering in scale.
They suggest that specimens of several hundred species of frogs, toads, salamanders and caecilians - legless amphibians - could as a priority be taken from the wild into captive breeding programmes.
When further data is gathered on little-known species, about a thousand more could also become candidates.
"The price-tag for all this is going to be enormous - tens of millions of dollars per year for at least a decade," said Claude Gascon, who is also senior vice-president for regional programmes with the charity Conservation International.
"But when you break this down and look at what different stakeholder groups can do - one thing we need for example is more capacity in zoos around the world to run these captive breeding programmes, and that's something that governments might be quite willing to address."
Papers before this weekend's meeting also address issues other than fungal attack.
Amphibians have now been evaluated on a global scale (Image: Conservation International)
There will be calls for more protected habitats, for increased testing of agricultural chemicals to discover whether they are toxic to amphibians, and for the establishment of a central laboratory to study the fungus and other pathogens.
Because of their sensitivity to environmental factors, amphibians are sometimes referred to as the "canary in the coal mine", an early-warning system for ecological decline which will also impact other species, including humans.