Dallmann, R., and Geissmann, T. (2009). Individual and geographical variability in the songs of wild silvery gibbons (Hylobates moloch) on Java, Indonesia. In Lappan, S. M., and Whittacker, D. (eds.) The gibbons: New perspectives on small ape socioecology and population biology, Springer, New York, pp. 91-110.

Individual and geographical variability in the songs of wild silvery gibbons (Hylobates moloch) on Java, Indonesia

Robert Dallmann¹, and Thomas Geissmann^2
1 Department of Neurobiology, University of Massachusetts Medical School,
Worcester, MA, USA, E-mail: robert.dallmann@umassmed.edu
² Anthropological Institute, University Zürich-Irchel, Winterthurerstr. 190, CH-8057 Zürich, Switzerland, E-mail: thomas.geissmann@aim.uzh.ch

Abstract: All gibbon species (Hylobatidae) produce loud, long, and relatively stereotyped morning call bouts usually referred to as song bouts. Gibbon songs are known to exhibit species- and sex-specific characteristics. In addition, it has frequently been suggested that these songs exhibit a high degree of individuality. However, quantification of vocal variability between individuals or populations has rarely been attempted in gibbons, and a comparison of vocal characteristics and their variability across the distribution area of a species has not to our knowledge been carried out for any primate. We investigate geographic variability in the female great-calls of the silvery gibbon (Hylobates moloch) from Java, Indonesia. Our results suggest: (1) Individuals can be distinguished by their great-calls. (2) Some, but not all, populations can be distinguished by their great-calls. (3) Vocal distances between populations are not consistent with geographic distances. (4) If two gibbon subspecies exist on Java, as suggested in a few recentby previous publications, the boundary between them should be located somewhere between West and Central Java. In this respect, our vocal data support biogeographical evidence but appear to contradict recent molecular evidence.