Waller, M. S. (2005). Vocal diversity of male Kloss's gibbons (Hylobates klossii) in the Mentawai islands, Indonesia. M.Sc. thesis in Primate Conservation, Oxford Brookes University, U.K., viii + 51 pp.

Vocal diversity of male Kloss's gibbons (Hylobates klossii) in the Mentawai islands, Indonesia

Melissa S. Waller


This is the first study to examine the vocal diversity of the male Kloss's gibbon (Hylobates klossii) endemic to the Mentawai Islands, Indonesia. The Kloss's gibbon is unusual because it is the only species that does not produce duets, with the exception of the silvery gibbon (H. moloch). Three other species of monkey are endemic to the islands and each has been classified into two subspecies; one on Siberut and the second spread over the three southern islands. This is based on morphological and some genetic differences, with the Siberut subspecies exhibiting a darker colouration. The Kloss's gibbon is completely black and exhibits no variation in pelt, so no subspeciation has previously been demonstrated. However, studies on the silvery and crested gibbons (Nomascus sp.) have shown that subspecies can be determined through examining vocal variation. Therefore Kloss's males were tape-recorded in four different locations; Simabuggai and Sikabae on Siberut island, Sipora and South Pagai islands. A total of 244 trill phrases from 27 individuals were examined using sonographic analysis (Raven 2.1) and non-parametric statistical tests (SPSS). The degree of variability was examined at the following levels; intra-individual, intra-population, intra-island and inter-population. Results from a Kruskal-Wallis one way ANOVA and post-hoc test indicated that the two populations within Siberut are significantly different to one another and that they are both significantly different to the Southern island populations, Sipora and South Pagai, which are very similar to one another. It was an unexpected result to find that Siberut contains two subspecies and this is most likely due to the prevention of dispersal by the numerous rivers, mountains and forest fragmentation. This division into three distinct units is supported by results from the discriminant function analysis; individuals can be classified back into their correct populations with an accuracy of 92.6%. Therefore, on the basis of male vocalisations it is concluded that the Kloss's gibbon is composed of three subspecies.

Site by Thomas Geissmann.
For comments & suggestions, please email to
Gibbon Research
Lab. Home: