Survey of the world's rarest gibbon


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Thomas Geissmann, Gibbon Research Lab., Zürich

November 2003, updated April 2005

Bawangling National Nature Reserve lies in southwestern Hainan Island, China and is believed to be the last and only refuge in the world for the Hainan gibbon Nomascus nasutus hainanus, an endemic subspecies of the rarest ape in the world, the eastern black-crested gibbon. A complete census was carried out in the humid October 2003 by local reserve staff, with the participation of experts from Hainan Forestry Bureau, Kadoorie Farm and Botanic Garden, local institutes and FFI.

After six days training in gibbon census techniques provided by Dr. Thomas Geissmann, 37 participants in 15 teams were dispatched into their respective one-square kilometre grids of forest. Each team was required to record gibbon vocalization at the same time each day from the listening post within its grid. Gibbons were located by sound triangulation. In addition, group compositions were established through direct sightings.

The 12-day survey revealed that just 13 confirmed individuals, including two social groups and two solitary males, are now restricted to a small patch of old-growth seasonal rainforest of about 400 ha. In comparison, an earlier survey by Thomas Geissmann using the same method found three groups in Bawangling ten years ago. The low population size found in the new survey is particularly surprising considering that the earlier survey had used only three survey teams and had covered a smaller area.

The reason for the restricted range of the gibbons is not known.

Apparently, young or dispersing gibbons die. Newborn infants have been observed in the groups repeatedly during the last ten years and survive to become subadults. However, no gibbon pairs have established new territories in Bawangling since 1987.

No confirmed hunting of gibbons is known to have occurred during the last ten years, but hunting by villagers of local Li and Miao (Hmong) ethnic groups continues inside the reserve and gunshots were heard almost every day during the survey.

The reserve area is bigger than the area required by the existing gibbon groups. Some accessible areas of good habitat are not used by gibbons, suggesting that the habitat size is not the limiting factor.

It is unknonw whether inbreeding may play a role in the stagnation of the gibbon population, but other almost extinct mammal populations with even smaller population sizes bounced back to viable numbers following protection.

I suspect that low habitat quality may be a main cause for gibbon mortality, but illegal hunting may also be a priority threat to the survival of gibbons. With the cooperation of local partners, Kadoorie Farm & Botanic Garden (Hong Kong), FFI-China, and the Gibbon Conservation Alliance support an emergency programme which includes patrolling, habitat mapping, community awareness building, and creating tree nurseries to grow food plants for gibbons. The trees will be used to reforest forest gaps.


Anonymous: The plight of the world's rarest gibbon. Fauna & Flora International Asia-Pacific Programme
(28 Aug. 2004,

Geissmann, T. (2005): Auf der Suche nach den letzten Gibbons von Hainan. Gibbon Journal 1: 18-22 (German text, English abstract). Available from at

Geissmann, T. (2005): Der Hainan-Schopfgibbon: Der bedrohteste Menschenaffe der Welt. Gibbon Journal 1: 10-12 (German text, English abstract). Available from at


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