Only in Mentawai: Unique primate vocalisations and songs in an isolated Indonesian island group

Abstract

Biogeographical isolation has produced a unique rainforest biome and indigenous culture in Mentawai. While its huge surf is famous worldwide, Mentawai's ecology and peoples remain comparatively unstudied. Alhough Mentawai evolved almost as many endemics as the Galápagos, its hunter-horticulturalists are surprisingly unrelated to Sumatran peoples. This study explores gibbon vocalisations and traditional animist beliefs and songs about gibbons and other primates in Mentawai's three southern islands and makes a case to document and preserve this intangible cultural heritage. The most important of Mentawai's six endemic primates is the Kloss's gibbon (Hylobates klossii, locally called bilou), a small, black, monogamous, singing ape. The bilou plays a significant role in the traditional animist cosmology of Mentawai: simultaneously considered a changeling human, a rainforest spiritual guardian and a resource for shamanic healing, at times the bilou spirit can also be an evil trickster or harbinger of death. Deep in the rainforests, mated female bilou sing solo or "duet" melodiously with each other along mutual territorial boundaries. While deforestation and modern hunting endanger all Mentawai primates, humans still imitate the bilou, and elderly (Si)Kerei (shaman) again can perform the endangered animist heritage of bilou songs.