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Rarest ape species rediscovered in Vietnam

Thomas Geissmann
Institute of Zoology, School of Veterinary Medicine, Hannover, Germany

La Quang Trung & Trinh Dinh Hoang
FFI Asia Pacific Programme, Hanoi, Vietnam

Vu Dinh Thong, Dang Ngoc Can, Pham Duc Tien
Institute of Ecology and Biological Resources, Hanoi, Vietnam

Unlike what most people believe, the rarest apes of the world are not the popular great apes which include chimpanzees, gorillas and orangutans. The gibbons or small apes are usually overlooked by media and scientists alike. Yet, several gibbon species are much more critically endangered than even the rarest of the great apes. Whereas even the rarest great ape (the Sumatran orangutan Pongo abelii) still exhibits a population size of 12,000 individuals, the populations of several gibbon species are about one to three orders of magnitude smaller.

The rarest ape species - and actually the most critically endangered primate species of the world - is a gibbon, the eastern black crested gibbon (Nomascus sp. cf. nasutus). This gibbon was recognized as a species distinct from the western black crested gibbon (Nomascus concolor) in 1997 by the Swiss primatologist Thomas Geissmann. Originally, the species was widely distributed in northeastern Vietnam east of the Red River, in southeastern China and on Hainan Island. However, the species became extinct on the Chinese mainland in the 1950's, and the Hainan population has become reduced to less than 20 individuals. In Vietnam, the last reliable record for the occurrence of the species stems from the 1960's. Since the recognition of the eastern black crested gibbon as a distinct species, numerous surveys were carried out in all areas where the species had previously been recorded. In spite of these efforts, no live individual was sighted or heard, and it became increasingly likely that the species may actually have become extinct in Vietnam.

In January 2002, however, a small remnant population of the eastern black crested gibbon was re-discovered by FFI biologists La Quang Trung and Trinh Dinh Hoang in Trung Khanh district of Cao Bang Province (NE Vietnam). In August 2002, a small team of Vietnamese scientists and Thomas Geissmann - supported by FFI's (Fauna and Flora International) Asia Pacific Programme - carried out the first overall population survey. They discovered that at least 5 groups comprising at least 26 individuals survive in the remaining forest area of less than 3000 hectares. As a result, the gibbons in Cao Bang do not solely represent the only population of the species in Vietnam but also the most important population of the whole species. Moreover, because these Vietnamese gibbons and their Hainan island counterparts differ in both fur colouration and their territorial calls, they also represent two distinct subspecies.

Because of its characteristic morning songs, the Vietnamese subspecies is termed the Cao-Vit black crested gibbon. It is the only ape taxon endemic to Vietnam. However, its future seems highly uncertain. Not only is the size of their remaining forest area very small, but the gibbons are highly threatened by hunting and by illegal logging for firewood and for charcoal production, both from the neighbouring villages as well as from the neighbouring Chinese communities. In order to save the Cao-Vit, FFI together with FPD is proposing to create a species/habitat conservation area for the area and to develop a joint forest protection system with local communities.