Among the now-extinct species is the Golden Toad, named for its shimmering yellow color, and two varieties of Harlequin frog, identified by their black and green stripes.

Scientists have yet to identify a precise mechanism for the disappearance of the amphibians, which began decades ago, but a prime suspect is a fatal fungus that has invaded their habitats, Herrero said.

"It is believed climate change is raising temperatures allowing a skin fungus to enter the places where the amphibians resided," he said.

Several studies in recent years have linked the rapid disappearance of many of the world's frog and toad species to global warming.

About a third of the 5,743 known species of frogs, toads and other amphibians are classified as threatened, according to the Global Amphibian Assessment survey.

Human activities are wiping out three animal or plant species every hour, the United Nations said on Tuesday, the International Day for Biological Diversity.

A strong consensus of scientists believe that global warming is the result of the release of greenhouse gases like carbon dioxide into the atmosphere.

Scientists say the amphibian die-off is a harbinger of things to come in the biologically rich tropical forests of Costa Rica.

"It's going to be a fact that we see a large extinction," said Rodrigo Gamez, president of the biodiversity institute.

In La Selva, a biological station in northern Costa Rica run by Duke University's Organization of Tropical Studies, scientists have found a 75 percent decline in amphibian population over the last 35 years.

The precise reason for the La Selva decline is not known, but scientists suspect that higher temperatures are inhibiting plant growth and thus diminishing the volume of decomposing leaves in which the amphibians thrive.

Populations of reptiles and insects also seem to be on the decline around the biological station, he said.

Another disturbing trend in the country is the decline of Costa Rica's monkeys. Monkey populations have fallen by 30 percent in recent years, according to Alfo Piva, executive director of the biodiversity institute.

He said a lot was unknown about the changes in Costa Rica's jungles. "Much study is still lacking," he said.