Today the squawks, shrieks, and whistles of parrots reverberate through the rainforest of Puerto Rico. But a few decades ago, these sounds almost disappeared.

In a last-ditch effort to pull the species back from extinction, conservationists began to breed the parrots in captivity. It was a successful gambit: Though the chatty emerald-green birds are still considered critically endangered, today more than 600 exist.

Now there may be a new threat to their survival, conservations say. Captive parrots have developed an entirely new dialect, a phenomenon that has not been observed before in other captive bird populations, says study leader Tanya Martínez, a conservation biologist with the Puerto Rico Department of Natural and Environmental Resource's Puerto Rican Parrot