The mountain coqui once lived in the western part of the island and across its central mountain range, but numbers there have since dwindled, and in some cases disappeared, said Jan Zegarra, a Puerto Rico-based biologist for the U.S. Fish and Wildlife Service.
"People love the coquis of Puerto Rico, but they don't realize what's going on," Joglar said. "We don't need more investigations to protect this species. There is enough evidence to warrant protection."
While the coqui is originally from Puerto Rico, it has been found in Costa Rica and has formed large colonies in Hawaii, where it has no natural predators.
Joglar previously rejected the idea of breeding frogs in captivity to ensure their survival in Puerto Rico, noting they have died when introduced into the wild as adults, but he said that may be the only alternative now.
Scientists are using breeding programs in an attempt to save another one of the island's endangered species, the Puerto Rican crested toad. The Nashville Zoo in Tennessee has sent more than 5,000 tadpoles to the U.S. territory, while the Buffalo Zoo in New York has sent hundreds of tadpoles in an effort to rebuild the wild population.