Scientists have dramatically revised population estimates for gorillas after massive numbers of the animals were found in an area of central Africa the size of Switzerland.

More than 125,000 western lowland gorillas - one of four sub-species - are estimated to be living in two swampland areas in the north of the Republic of Congo, according to a census by the Wildlife Conservation Society published yesterday.

Scientists had previously estimated that the entire population of western lowland gorillas was between 50,000 and 100,000, but the discovery points towards a figure of about 200,000.

The gorillas, among the world's most romantic and secretive creatures, remain critically endangered, but the WCS survey suggests that attempts to protect them from threats, including poaching, deforestation and the ebola virus, are starting to pay off.

“These figures show that northern Republic of Congo contains the mother lode of gorillas,” Dr Steven Sanderson, WCS president, said. “It also shows that conservation in the Republic of Congo is working. This discovery should be a rallying cry for the world that we can protect other vulnerable and endangered species, whether they be gorillas in Africa, tigers in India, or lemurs in Madagascar.”

Yesterday The Times revealed that almost half the world's primate species were under threat of extinction.

Announcing the WCS findings at the International Primatological Society Congress in Edinburgh, Dr Emma Stokes, who led the survey, said: “We knew from our own observations that there were a lot of gorillas out there, but we had no idea there were so many.”

The census, conducted between 2006-07, counted the number of gorilla nests over 18,000 square miles in two adjacent areas in the Republic of Congo.

The survey, the most extensive carried out in the region, found about 73,000 western lowland gorillas living in the Ntokou-Pikounda area and another 52,000 in Ndoki-Likouala, including a previously unknown population of nearly 6,000 gorillas living in an isolated swamp. Scientists believe that the gorillas have thrived due to the remoteness of both areas - the nearest roads are more than 80km (50miles) away.

Gorillas build nests at ground level from leaves and branches to sleep in, allowing researchers to make fairly accurate estimates of population. The WCS scientists, who described the estimates as conservative, were also surprised by the density of population, which was as high in some areas as eight animals per square kilometre, among the highest ever recorded.

Dr Ken Cameron, of the WCS, said that as amazing as the discovery was, it should not be a reason for complacency.

Western lowland gorillas are one of four recognised gorilla sub-species. These also include mountain gorillas, of which fewer than 700 survive in the wild, Cross River gorillas, of which around 300 remain, and eastern lowland gorillas, whose population remains unknown, though thought to be in the thousands. All are classified as “critically endangered” except for eastern lowland gorillas, which are classified as endangered.

The western lowland gorilla has been found in the tropical rainforest and swamplands of eight central African nations: Nigeria, Cameroon, Central African Republic, Guinea, Gabon, Angola, Republic of Congo and Democratic Republic of Congo.

The western lowland gorilla has a wider skull than other gorilla subspecies and a brownish-grey coat. It can reach a height of 1.75metres (5.7feet) when standing, with the female weighing up to 140kg (308lb) and the male up to 275kg.

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