Image caption The Rio Pescado stubfoot toad was the only one on the "top-10 wanted" list to be rediscovered

A mission to discover whether any of 100 amphibian species believed to be extinct are still alive has ended with few successes to report.

The five-month project took researchers to 21 countries; but only four of the targeted 100 were found.

Researchers describe these as "glimmers of hope" in a group of animals severely threatened by changing land use, disease, pollution and climate change.

Particularly galling was the failure to find the golden toad of Costa Rica.

This is a reminder that we are in the midst of what is being called the 'Sixth Great Extinction' Dr Robin Moore, CI

This beautiful and iconic animal has not been seen since 1989 - killed off, it is thought, by the fungal disease chytridiomycosis.

The project team had previously announced the rediscovery of three species - the Mexican cave splayfoot salamander (last seen in 1941), the Mount Nimba reed frog from Ivory Coast (last seen in 1967), and the Omaniundu reed frog from Democratic Republic of Congo (1979).

The only addition to the final list is the Rio Pescado stubfoot toad (Atelopus balios), a critically endangered Ecuadorian species that frequents lowland rainforest streams.

But they did also rediscover by chance a few amphibians not on the original list; and a parallel search in India also turned up some "lost" species, including one found in a rubbish bin.

Image caption The scarlet frog of Venezuela is one that was not re-discovered

"Rediscoveries provide reason for hope for these species, but the flip side of the coin is that the vast majority of species that teams were looking for were not found," said Robin Moore, the conservation scientist who conceived the project.

"This is a reminder that we are in the midst of what is being called the 'Sixth Great Extinction', with species disappearing at 100 to 1,000 times the historic rate - and amphibians are really at the forefront of this extinction wave."

'Brilliant colours'

More than 100 scientists took part in the project, which concentrated principally on Africa and South and Central America.

It was funded and managed by the charity Conservation International (CI) and the Amphibian Specialist Group of the International Union for the Conservation of Nature (IUCN).

Image caption The re-discovered elegant tropical frog of India is threatened by a proposed dam

The Indian project, co-ordinated by SD Biju from the University of Delhi, found five missing species, including the chalazodes bubble-nest frog (Raorchestes chalazodes) that was last seen in 1874.

It is a striking creature with blue thighs and eyes of gold-flecked black, which lives inside reeds during daytime.

And the Silent Valley tropical frog (Micrixalus thampii) turned up in a rubbish bin at a field station.

"I was so excited to see the Chalazodes bubble-nest frog in life after 136 years," said Dr Biju.

"I have never seen a frog with such brilliant colours in my 25 years of research."

The Indian project is set to continue, as is a parallel mission in Colombia.

Overall, amphibians are the most threatened group of life-forms on the planet, with about two in five species on the internationally-recognised Red List of Threatened Species.