Geissmann, T. & Chan, B. 2004: The Hainan black crested gibbon: Most critically endangered ape. Folia Primatologica 75, Supplement 1: 116 (Abstract only).

The Hainan black crested gibbon: Most critically endangered ape

Thomas Geissmann ¹ & Bosco Chan <sup>2

1</sup> Anthropological Institute, University Zurich-Irchel, Switzerland;
² China Programme, Kadoorie Farm & Botanic Garden (KFBG), Hong Kong, China
Email: thomas.geissmann@aim.unizh.ch

Key Words: Hainan black crested gibbon, extinction, Indochina

In October 2003, we carried out a large-scale survey of the remaining gibbon (Nomascus sp.) habitat in the Bawangling National Nature Reserve (Bawangling) in order to determine the size of the gibbon population. Up to 17 teams surveyed all suitable habitat in Bawangling using a fixed listening point method specially adapted for gibbon surveys. In addition, group compositions were established through direct sightings.

We were able to find evidence for the occurrence of two gibbon groups and two solitary males in Bawangling (i.e. 13 gibbons, including three infants). In comparison, an earlier survey by one of us (TG) 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. Apparently, young or dispersing gibbons die. Newborn infants have been observed in the groups repeatedly during the last ten years, and no confirmed hunting of gibbons is known to have occurred during the same time interval. 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. Inbreeding does not appear to be a convincing cause for the stagnation of the gibbon population, because other almost extinct mammal populations with even smaller population sizes bounced back to viable numbers following protection. We suspect that low habitat quality may be a cause for gibbon mortality and discuss the options available to save this most critically endangered of apes.