In fact, Monteverde's entire amphibian fauna had collapsed, while reports from other mountain areas around the world told of strikingly similar accounts. The patterns at Monteverde however, do not support such a view. Long-term data strongly imply that the amphibian declines are not an isolated phenomenon. Instead, they appear to belong to a broader suite of population changes involving birds, reptiles, amphibians, and others. Because it is highly unlikely that a fungus, which attacks the moist skin of frogs, would also attack reptiles, a search was begun for a common denominator.
Evidence now points to climate change, particularly a change in moisture availability.
In a cloud forest moisture is ordinarily plentiful. Even during the dry season, which at Monteverde lasts from January through April, clouds and mist normally keep the forest wet. Trade winds, blowing in from the Caribbean, carry moisture up the mountain slopes, where it condenses to form a large cloud deck that surrounds the mountains. It is hypothesized that a climate warming, particularly since the mid-1970s, has raised the average altitude at which cloud formation begins thereby reducing the clouds' effectiveness in delivering moisture to the forest. Observational evidence and instrumental records indicate that the incidence of days without mist during the dry season has quadrupled over recent decades.