The 300 Kihansi spray toads residing in a small room at the Bronx Zoo chirp cheerily as they bask in a light sprinkling of water 14 times a day. Until a few years ago, the tiny, mustard-colored toads existed only in a river gorge in Tanzania. Now the survivors are confined to the Bronx and Toledo zoos, having gone extinct in the wild.

With thousands of amphibian species facing unprecedented threats to their survival, scientists have launched a global effort to collect them in zoos to save them from disappearing altogether. Named Amphibian Ark, the program aims to keep 500 species in captivity and breed enough to eventually reintroduce them into the wild.

“In terms of scope, I think this is the biggest conservation project that humanity has ever tried to tackle,” said Kevin Zippel, the program’s director, who said the initiative is testing zoos’ ability to raise and maintain animals with specialized needs. “In the course of the last four years, we’ve realized how badly off amphibians are,” he said.

Scientists have been tracking the rapid disappearance of amphibians for two decades, but new evidence suggests the animals face increasingly grave peril. A third to a half of all amphibians are now threatened with extinction; 165 species have already vanished. In Latin America and the Caribbean alone, three of every four amphibian species are critically endangered.

Research published Wednesday in PLOS One, a journal of the Public Library of Science, estimated that in the neotropic region, which spans from the Mexican deserts to Patagonia in southern Argentina, 35% of amphibians “are threatened by habitat loss, habitat fragmentation, and habitat split.”