There are an estimated 7,000 different species of amphibians -- and scientists say one-third of them are on the endangered list. Many species of frogs are especially at risk. Their unusually thin skin, which allows them to absorb oxygen and water, makes them particularly sensitive to climate change and environmental hazards. So frogs can serve as a natural kind of "early warning system." Frog species aredying out the world over -- and this phenomenon has gone largely unnoticed by the general public. We accompany two Berlin specialists as they search the rain forest that covers the slopes of Mount Manengouba in Southwest Province of Cameroon. They're trying to find out why so many frogs are dying, and how to protect those that still remain.