Since 1987, at least 20 of the 50 amphibians found in the forests surrounding Monteverde, Costa Rica, have declined. Evidence has mounted that climate change is a culprit in Monteverde. Scientists including J. Alan Pounds of the Monteverde Cloud Forest Preserve and Tropical Science Center think that climate change has raised the altitude of the clouds that typically hang over the mountains in the winter dry season. Temperatures have increased, and moisture levels have decreased, causing changes in bird, reptile and amphibian populations. All of that is potentially bad news for amphibians, with their need for a certain moisture level.
Most amphibians lay eggs that have a gelatinous coating but no shell.
The eggs must stay moist to develop, and a long dry period could desiccate not only an adult but its eggs as well. During a dry period in the 1980s, Pounds noticed that harlequin frogs along one stream grouped together more closely than usual as they vied for space. The frogs became easy targets for a parasitic fly that patrols streams. Pounds says it is possible that the effects of two decade's worth of climate change may have made amphibians in the Monteverde area more susceptible to parasites and disease. The conditions could have stressed the amphibians' immune systems, caused behavioral changes that put them in harm's way or increased the virility of diseases or parasites.