Geissmann, T. 1996: New sounds from the crested gibbons (Hylobates concolor group): First results of a systematic revision. In: Abstracts, XVIth Congress of the International Primatological Society, Madison, Wisconsin, U.S.A., August 11-16, 1996, abstract no. 480, Wisconsin Regional Primate Research Center, Madison.

New sounds from the crested gibbons (Hylobates concolor group): First results of a systematic revision

T. Geissmann

Anthropological Institute, University Zürich-Irchel

The crested gibbons have traditionally been regarded as consisting of a single species, Hylobates concolor, containing 6 subspecies (concolor, hainanus, lu, leucogenys, siki, gabriellae). More recent studies suggested that this group should be split into two species, H. concolor and H. leucogenys, with concolor, hainanus and lu being subspecies of the former. Some even suggested recognition of a third species, H. gabriellae, with some debate as to whether siki is a subspecies of H. leucogenys or of H. gabriellae. Also more recently, two new black gibbon subspecies have been described from the Chinese Province of Yunnan (H. c. furvogaster and H. c. jingdongensis). The present study describes and compares crested gibbon vocalizations and fur characteristics. First results based on museum skins and vocalizations of captive gibbons clearly support the recognition of the species H. concolor, H. leucogenys and H. gabriellae, with siki being more closely related to H. leucogenys than to H. gabriellae. Tape-recorded songs of wild populations, however, suggest the existence of an intermediate population between siki and gabriellae. No clear vocal or color differences were found among Chinese populations of H. c. concolor, H. c. jingdongensis and H. c. furvogaster, making the recognition of the latter two taxa questionable. Two unnamed forms of crested gibbon were identified based on Zoo and Museum specimens from northeastern Vietnam. At least one of them produces a radically distinct song, and the same type of song was found in the population from Hainan island. Although these three populations have been previously attributed to H. concolor, they should be recognized as three subspecies of a distinct species. It is unclear whether the two mainland subspecies still survive in the wild, and the Hainan form is probably down to less than 20 individuals, suggesting that this may be one of the rarest primate species worldwide.