The frogs have been hunted for their meat, and Smith says that they were served up to restaurants and hotels to tourists that visited the island.

Not only does the island’s active volcano threaten the species, but also the infectious disease known as Chytridiomycosis.

Only two uninfected populations remain, and conservationists from Durrell, London Zoo, Chester Zoo and Parken Zoo set out an emergency rescue mission to airlift 50 of the frogs from the island.

A dozen of the frogs were then relocated to Jersey, U.K., where herpetology keepers successfully bred them in captivity.

After breeding, the conservationists then released 33 healthy frogs back onto the island in January, and since then a field team has spent three months tracking their progress.

“Some of the frogs were calling in the forest in the first night,” Smith told BBC. “Three months later the fact that we still have live frogs in the release site looking healthy and calling is a very encouraging sign.”