( CNN ) -- An estimated 125,000 Western lowland gorillas are living in a swamp in equatorial Africa , researchers reported Tuesday , double the number of the endangered primates thought to survive worldwide . Forest clearings draw large numbers of Western lowland gorillas searching for food . `` It 's pretty astonishing , '' Hugo Rainey , one of the researchers who conducted the survey for the U.S.-based Wildlife Conservation Society , told CNN Tuesday . The last census on the species , carried out during the 1980s , estimated that there were only 100,000 of the gorillas left worldwide . Since then , the researchers estimated , the numbers had been cut in half . WCS survey teams conducted the research in 2006 and 2007 , traveling to the remote Lac Tele Community Reserve in northern Republic of Congo , a vast area of swamp forest . Acting on a tip from hunters who indicated the presence of gorillas , Rainey said that the researchers trekked on foot through mud for three days to the outskirts of Lac Tele , about 80 kilometers ( 50 miles ) from the nearest road . `` When we went there , we found an astonishing amount of gorillas , '' said Rainey , speaking from the International Primatological Society Congress in Edinburgh , Scotland . Though researchers did spot some gorillas , they based their estimate on the number of gorilla nests found at the site , Rainey said . Each gorilla makes a nest to sleep in at night . `` This is the highest-known density of gorillas that 's ever been found , '' Rainey said . Watch a glimpse of gorilla life in African swamp » . Western lowland gorillas are listed as critically endangered , the highest threat category for a species . Their populations are declining rapidly because of hunting and diseases like Ebola hemorrhagic fever , whose symptoms include diarrhea , vomiting and internal and external bleeding . Take a closer look at the Western lowland gorilla » . While the discovery in northern Congo indicates that the gorilla population remains stable in some areas , it is likely that gorillas will remain critically endangered because the threats facing the species are so great , Rainey said . iReport.com : Share photos and video of gorillas in zoos or the wild . `` We know very little about Ebola and how it spreads , '' he said . `` We do n't even know the animal that spreads it around . '' The goal now , Rainey said , is to work with the Congolese government and donors to protect the areas in which the gorillas are known to be living . Western lowland gorillas , which are found in Cameroon , the Central African Republic , Equatorial Guinea , Gabon and Nigeria as well as the Republic of Congo , are the most numerous and wide-ranging of the four gorilla subspecies , each of which is threatened by extinction , the WCS says . See where the gorillas live » . Illegal hunting and habitat loss have also threatened the Cross River gorillas , found in the highlands of Cameroon and Nigeria . Only about 250 to 300 are estimated to remain in the world , the WCS says . War , habitat loss , poaching and disease are the major threats to the mountain gorillas , made famous by researcher Dian Fossey and the film `` Gorillas in the Mist . '' The mountain gorilla population is starting to recover after decades of conservation work . From a population of around 230 in the 1970s , the mountain gorillas now number around 700 , the WCS says . Poaching and war have also threatened populations of Grauer 's gorillas in the eastern Democratic Republic of Congo , the former Zaire . The WCS estimates their population to be around 16,000 . News of the discovery of the Western lowland gorillas in northern Congo comes the same week as a report that almost 50 percent of the world 's primates are in danger of extinction . Watch what gorilla expert thinks of find » . The report , also delivered to the Edinburgh conference , cites habitat loss and hunting as the greatest threats . The situation is especially dire in Asia , where the report says more than 70 percent of monkeys , apes , and other primates are classified as vulnerable , endangered , or critically endangered . Conservation International and the International Union for Conservation of Nature issued the report .
Researchers feared only around 50,000 Western lowland gorillas left worldwide . Now 125,000 primates have been discovered in northern Congo . Score: 6 Expert : This is the highest-known density of gorillas that 's ever been found .