Scientists are set to begin a hunt for the some of the world's rarest frogs in Costa Rica, including the iconic golden toad, last seen some 20 years ago.

A team from Manchester University and Chester Zoo are in Costa Rica to track down the highly endangered creatures. BBC News will follow their trek deep into the cloud forests of Monteverde.
Amphibian numbers around the world have crashed, in part because of a deadly fungus. Costa Rica has been particularly badly hit. Expedition leader Andrew Gray, from the University of Manchester's Manchester Museum, said: ""Costa Rica's highlands used to be major biodiversity hotspots - but in many areas, amphibian populations have been completely decimated.""
In the late 1980s, herpetologists around the world found that amphibian populations were suffering unprecedented declines, but they struggled to understand exactly why.
A decade later, researchers isolated a previously unknown fungus, Batrachochytrium dendrobatidis, which was infecting amphibians, effectively suffocating them by making it impossible for them to breathe across their skin.
Recently, the scientists working on the Global Amphibian Assessment estimated that one-third of all amphibians were threatened with extinction and about 120 species had already become extinct since the 1980s.
Many believe the disease caused by the chytrid fungus is a key factor for this crash. Other causes are thought to include habitat destruction and changes in climate.
Countries in Central America have been particularly badly affected by the deadly chytrid fungus, which is widespread there. A great deal of effort is now being put into place to safeguard any remaining species.
Andrew Gray said: ""For the last 10 years, I've been working with others to ensure the future for frogs that have so far escaped extinction.
""One of the main things I have been doing is establishing breeding populations in Manchester Museum for a number of very, very rare species - including the splendid leaf frog (Cruziohyla calcarifer), the yellow-eyed leaf frog (Agalychnas annae) and the lemur leaf frog (Hylomantis lemur).
""I've also been working with the Costa Rican authorities and scientists to put conservation measures into place at the sites where any rare frogs are found.""
Last year, Mr. Gray caught a glimpse of the Ithsmohyla rivularis in the cloud forests of Monteverde - a frog that was thought to have gone extinct about 20 years ago.
He said: ""To find this species last year that was thought to have become extinct at the same time as the golden toad was incredible - it is the rarest tree frog in the world."" He has now been given special permission by the Costa Rican authorities to collect some of the frogs to take back to Manchester.
He told the BBC: ""We are returning to thoroughly search the site in the hope of finding more specimens.
The rediscovery of Ithsmohyla rivularis has spurred the team on to also try to seek out a golden toad (Bufo pereglines).
(Source: BBC)