The Flexibility of Gestural Communication in Bornean Orangutans (Pongo pygmaeus) in Kalimantan Tengah

Presenter: Cudmore (Anthropology)

Mentor: Kirstin Sterner

Great ape communication research attempts to reveal the cognitive abilities of our closest living relatives and to inform our understanding of the evolution of human language. Although great ape gestural communication has been well documented, relatively few studies are specific to the orangutan. The aim of this study was to determine if rehabilitant orangutans (Pongo pygmaeus) at the Orangutan Care Center and Quarantine (Pasir Panjang, Indonesian Borneo) use distinct gestures toward other orangutans versus toward humans. Because orangutans are tree-living species whose arms are typically not free to gesture, we predicted that orangutan gestures are adapted to employ the whole body. Using 59 sub-adults in 18 different home enclosures, we examined gestural types and frequencies in comparisons of orangutan-orangutan and orangutan-human communication. Orangutan-human trials were run with both the experimenter facing and non-facing to further measure gestural flexibility. Our results show that 92% of orangutan-human gestures were made with the limbs, while the majority (46%) of orangutan- orangutan gestures were facial. When the human experimenter was facing, 76% of gestures were visual, while when non-facing, only 7% were visual. Our results suggest that limb gesturing toward the experimenter may be partly due to rehabilitant orangutans learning that caretakers respond more readily to anthropocentric gestures, like arm/hand pointing. Our findings demonstrate that these orangutans use gestures flexibly.