Geissmann, T.; Bohlen-Eyring, S. & Heuck, A. 2004: The male song of the Javan silvery gibbon (Hylobates moloch). Folia Primatologica 75, Supplement 1: 266-267 (Abstract only).

The male song of the javan silvery gibbon (Hylobates moloch)

Thomas Geissmann¹, Sylke Bohlen-Eyring² & Arite Heuck<sup>2

1</sup> Anthropological Institute, University Zurich-Irchel, Switzerland;
² Institute of Zoology, Tierärztliche Hochschule Hannover, Germany
Email: thomas.geissmann@aim.unizh.ch

Key Words: Hylobates moloch, song function, Hylobatidae

This is the first study on the male song of the Javan silvery gibbon (Hylobates moloch) and the first quantitative evaluation of the syntax of male solo singing in any gibbon species carried out on a representative sample of individuals. Because male gibbon songs generally exhibit a higher degree of structural variability than female songs, the syntactical rules and the degree of variability in male singing have rarely been examined. In contrast to most other gibbon species, mated silvery gibbons do not appear to produce duet song bouts but solo song bouts only, and male singing is exceptionally rare, making this study particularly challenging.

For the present study, we tape-recorded and analysed several solo song bouts of eight silvery gibbon males, including both wild and captive individuals.

Males exhibit significant individual preferences in the order of different note types used in their phrases. Phrase structure was found to exhibit unusually low degrees of stereotypy and high degrees of variability. As a surprising finding of our study, male phrase variability - both within and between individuals - appears to be higher in H. moloch than in most, perhaps all, other gibbon species. This high variability appears to be a derived characteristic among the Hylobatidae. We discuss the implications of this finding for the interpretation of song function and present new and testable functional hypotheses. Our study demonstrates that song function cannot be identified for ìthe gibbonî. Gibbon songs appear to be multi-functional, and the relevance of these functions appears to exhibit strong differences among gibbon species.