'Astonishing' gorilla discovery in Republic of Congo

(CNN) - Researchers said Tuesday they have found 125,000 Western lowland gorillas living in a swamp in northern Republic of Congo, a rare positive discovery that adds significantly to the existing population of the threatened species.

The last census of Western lowland gorillas, done in the 1980s, estimated 100,000 worldwide - and researchers thought the number had been cut in half since then.

"It's pretty astonishing," said Hugo Rainey, one of the researchers who conducted the survey for the U.S.-based Wildlife Conservation Society.

Rainey spoke to CNN from the International Primatological Society Congress in Edinburgh, Scotland, where he and the other WCS researchers planned to reveal their findings Tuesday.