Vocal Diversity of Kloss’s Gibbons (Hylobates Klossii) in the Mentawai Islands, Indonesia

Abstract

The Mentawai Islands – off the west coast of central Sumatra – are known to support four endemic primates, one each of the genera Hylobates, Macaca, Presbytis and Simias. Two distinct subspecies have been described for each of these endemic Mentawai primates, except for Kloss's gibbon (Hylobates klossii) for which no subspecies are recognized. In each case, one taxon is endemic to the northernmost island of Siberut, and the second taxon is distributed across the three remaining islands: Sipora, North Pagai and South Pagai. We studied the vocal diversity of wild Kloss's gibbons at four localities (two on Siberut and one each on Sipora and South Pagai) to assess whether vocal differences among populations warrant further investigation into the possibility of suggest the occurrence of a distinct subspecies on Siberut, and whether vocal differences among populations correspond to geographic distance or other recognizable patterns. Both female and male calls differ among localities and can be correctly assigned to their source population using discriminant analysis. Vocal differences among localities exhibit no relationship to geographic distance. In addition, differences between two localities on Siberut are at least as pronounced as those between Siberut and localities on other islands. Affinities among the island populations are of comparable degrees and recognition of a distinct Siberut subspecies is not warranted. We propose that gibbons may have spread across the Mentawai islands at a considerably later date than the other non-human primates. This and a longer generation span in gibbons may explain why only Kloss's gibbons do not exhibit distinct taxa on Siberut and the more southern islands of Mentawai.