By Rebecca Morelle
Science reporter, BBC News, Costa Rica
First-known footage of rare frog
An incredibly rare frog has been filmed for the first time, scientists believe.
The red-eyed stream frog is found in Costa Rica, but it is now thought to be critically endangered.
The tiny, vividly coloured frog was spotted by a team from the University of Manchester, Chester Zoo and Costa Rican naturalists.
The frog was caught on camera by BBC News, which is following the researchers as they are working on frog conservation programmes.
Andrew Gray, from Manchester Museum at the University of Manchester, who is leading the expedition, said: "This frog has been classified as being one of the most critically endangered frogs in Costa Rica.
By any measure, this is a rare frog
Mark Wainwright Costa Rican naturalist
"They are so rare and locating them is extremely difficult - we have been very lucky to find it. We believe that this particular species has never been filmed before."
The red-eyed stream frog, or Duellmanohyla uranochroa, measures just 2-3cm in length, and has bright red eyes and a vivid green colour.
This male was discovered in the Monteverde cloud forest area where it was sitting above a stream calling for a female.
The team played a recording of the soft, whistle-like call of another male red-eyed stream frog, which prompted him to call back, enabling them to locate the little amphibian.
Finding the red-eyed stream frog
Mark Wainwright, a naturalist from Costa Rica who has joined the team, said: "This frog is endemic to the mountains of Costa Rica and western Panama. It was very common before the [amphibian] population crash of the late 1980s but now it maintains only very small populations.
"By any measure, this is a rare frog. And if you do not know the call, you probably aren't going to see one."
He added that there were many rare species in Costa Rica, where little is known about them.
"The vast majority of frogs here have never really been studied," he said.
Amphibian numbers have fallen dramatically in the last few decades - but highland areas like Monteverde seem to have been particularly hard hit. Some believe this may be to do with a fungus that has swept through the area.
The team from the University of Manchester took a spectrometer into the forest to look at the properties of this frog's skin. This non-invasive technique allows them to see how much light the frog is reflecting.
The researchers believe that the ability to sit out in the sun may allow the frogs' skin to heat up just enough to kill off chytrid - preventing the disease from taking its grip.
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