Gesture Use in Communication between Mothers and Offspring in Wild Orang-Utans (Pongo pygmaeus wurmbii) from the Sabangau Peat-Swamp Forest, Borneo

Abstract

Research on captive and wild great apes has established that they employ large repertoires of intentional gestural signals to achieve desired goals. However, gestural research has focused on African great apes, with orang-utan data limited to a few captive studies. We address this gap by describing gesture use in wild Southwest Bornean orang-utan (Pongo pygmaeus wurmbii) mother and offspring pairs. We conducted focal follows on 16 individuals in the Sabangau peatswamp forest in Borneo, Indonesia. The resulting 681 h of video footage yielded 1299 communicative signals: 858 vocal signals and 441 gestural signals. Eleven vocal signal types and 21 gesture types met the criteria for inclusion in the repertoire; however, the gestural repertoire did not approach asymptote and further gesture types will likely be identified in the future. Signalers used gestures of any modality in higher frequency when the recipient was paying visual attention, and took the recipient's visual attention into account when selecting gesture modalities. Orang-utans employed hands and arms more than legs and feet in gesturing, but were more flexible in their choice of limb than chimpanzees using the same gestures. Orang-utans were highly responsive to gestural requests, using them to achieve eight goals and, where successful, responding either before gesturing ended or in <1 s in 90% of communications. Our findings on the range of gesture types and impact of visual attention support findings from captive orang-utans; and those on responsiveness and limb use highlight the importance of studying ape communication in the social and ecological context to which it is adapted.

Red-capped mangabeys (Cercocebus torquatus) adapt their interspecific gestural communication to the recipient’s behaviour

“…Intentionality markers accompanying non-human primates’ gestural communication can be studied by observing intraspecific interactions (e.g. 15 – 20 ), however control of the recipient’s behaviour cannot be applied practically in this context to evaluate rigorously the effects of different characteristics. Consequently, intentionality of non-human primate gestures is often investigated at an interspecific level through an experimental approach, using setups in which subjects produce learnt begging or pointing gestures directed towards a human, in order to obtain a food reward (e.g.…”

“…Then this trait was reported for all great ape genera based on both observational and experimental data (e.g. chimpanzees 19 , 22 , 34 , 53 , 54 ; bonobos 15 , 55 ; orangutans 16 , 20 , 56 ; and gorillas 18 , 56 ). Another strategy to deal with recipient’s attentional state is to move to a position in the recipient’s visual field before gesturing.…”

Use and Function of Multi-Articulator Versus Multi-Sensory Acts in the Close-Range Communication of Orang-Utans

“…It is important to note that gaze, even though it de nitely has a communicative function, often acts as a social cue rather than an intentionally produced signal. However, we do know that orang-utans are capable of controlling their gaze for bouts of intentional communication 32,33,67 , suggesting that eye gaze serves as important communicative articulator just as it does in humans. As important component of social interactions, gaze can be directed at speci c individuals (thereby being less ambiguous than auditory and olfactory signals), and may be used to predict another individual's behaviour 68 .…”

“…due to differences in social tolerance and familiarity 30,31 . Although mothers are the most important communication partner of infant orang-utans 10,32,33 , temporary associations during feeding or travelling occur, particularly if food is abundant 34,35 , thus providing opportunities for social interactions beyond the mother-infant unit [36][37][38] . We expect that the reduced familiarity of these dyads, and thus the greater uncertainty of tolerance, would lead them to use more multi-articulator signals.…”

Multicomponent and multisensory communicative acts in orang-utans may serve different functions

“…due to differences in social tolerance and familiarity 45 , 46 . Although mothers are the most important communication partner of infant orang-utans 10 , 47 , 48 , temporary associations during feeding or travelling occur, particularly if food is abundant 49 , 50 , thus providing opportunities for social interactions beyond the mother–infant unit 51 – 53 . We expect that the reduced social tolerance of these dyads, and thus the lower predictability of interaction outcomes, would lead them to use more multicomponent signals.…”