The population of the world's rarest ape has doubled after a new survey. There are now thought to be 110 Cao Vit gibbons in forests on the China-Vietnam border.
Until the latest survey by Fauna and Flora International (FFI) there were thought to be only 50 surviving gibbons.The Cao Vit is listed as a critically endangered species and the new study will help with its future conservation.
Survey teams of biologists, government rangers and local villagers led by FFI surveyed forest on both sides of the China-Vietnam border in September last year for Cao Vit gibbon groups, counting them either by sight or by recording their evocative songs.
Preliminary estimates suggest that as many as 20 family groups survive and the team were able to take pictures and make videos of the gibbon in the wild for the first time.
Gibbons were also reported in parts of the forest they had not previously been recorded in. People from Lung Hoai Village in Vietnam told project staff that they are now hearing gibbon songs near their village where they didn't before.
FFI, which works to save threatened species and ecosystems, has been working to save the Cao Vit gibbon - a sub-species of the eastern black crested gibbon, scientific name Nomascus nasutus nasutus - since staff members found a small remnant sub-population in Cao Bang Province, Vietnam in 2002.
FFI began conservation efforts despite the scarcity of data on the species. Four years later, three more family groups were discovered across the border in Guangxi Autonomous Region, China, where they were believed to be extinct.
FFI Vietnam project coordinator Paul Insua-Cao said: "When we realised the gibbon was rare enough to demand urgent action, we immediately began protection measures, even though we lacked the results from an exhaustive census. We didn't want the Cao Vit gibbon to go the way of the Yangtze river dolphin, which was declared extinct last year."
Gibbons are apes, like chimps, gorillas and orangutans, and are closely related to humans. They are native to the forests of Southeast Asia live in close-knit family groups comprising a male, 1 - 2 females and 2 - 5 offspring.
They make distinct and complex bird-like calls, called a 'song', which they can project up to two kilometres through the forest canopy. Adult family members sing both duets and solos (with the male and female singing different parts) in the early morning to defend their territory.
The loss of suitable habitat is one of the main threats to the gibbons due mainly to villagers felling trees for firewood and charcoal making and clearing forest for grazing.
FFI has established community groups to patrol and protect the gibbon's forest habitat and is working with local people to prevent habitat loss. Simple and cost-effective measures such as providing villagers with simple fuel-efficient stoves are helping to relieve pressure on the gibbon's habitat.