Charles Darwin first discovered the frogs while traveling in Chile in 1834. Scientists who later studied the mouth-brooding animals found that there are actually two species, naming one Rhinoderma darwinii (Darwin's frog) and the other Rhinoderma rufum (Chile Darwin's frog).

From 2008 to 2012, a team of researchers led by zoologist Claudio Soto-Azat surveyed 223 sites in the frogs' historical range, from the coastal city of Valparaíso south to an area just beyond Chiloé Island. R. rufum has not been seen in the wild since 1980, and despite the recent extensive search effort across every recorded location of the species, no individuals were seen or heard during the four-year survey, the researchers said. R. darwinii, meanwhile, was found in 36 sites, but only in fragmented and small populations, each with likely less than 100 individuals.

The findings suggest Darwin's frogs have disappeared from, or at least rapidly declined in, many locations where they were recently abundant, the researchers wrote in a paper published online June 12 in the journal PLOS ONE. Habitat loss and fragmentation may be the culprits.