The social dynamics of complex gestural communication in great and lesser apes (Pan troglodytes, Pongo abelii, Symphalangus syndactylus)

Abstract

Gestures play an essential role in primate communication. However, little is known about how complexity of gestural use (in terms of repertoire size, intentional use, flexibility and use of gestural sequences) relates to individual and dyadic measures of sociality and whether more complex gestural use is more effective in eliciting a response. We observed 19 captive chimpanzees (Pan troglodytes), 16 Sumatran orangutans (Pongo abelii) and 18 siamangs (Symphalangus syndactylus) to assess the complexity and effectiveness of their gestural use. We found that, beyond interspecies variation, the number of gesture types used in a dyad was higher when individuals had stronger social bonds; the probability of accounting for others' attention increased with age, especially for visual gestures; and sequences were more likely used by younger or socially less integrated individuals. In terms of effectiveness, older individuals and those using fewer sequences were more likely to be responded to, while across dyads, the probability of obtaining a response was higher when both individuals accounted for the other's attention and when they used fewer sequences. Overall, this confirms the link between sociality and complex gestural use and suggests that more complex forms of communication, at least in terms of intentional use, may be more effective at achieving communicative goals. This article is part of the theme issue 'Cognition, communication and social bonds in primates'.

Keywords: chimpanzees; complex gesture use; orangutans; siamangs; sociality.

Figure 1.

Cumulative number of gesture types observed in the study groups, as a function of the number of gestures coded, separately for each species ((a) chimpanzees, (b) orangutans, (c) siamangs) and group (circles: chimpanzees in Atlanta; light and dark grey squares: orangutans at the Leipzig and Zürich Zoos, respectively; black crosses and black diamonds: siamangs at the Howletts Wild Animal Park, groups A and B, respectively; light grey asterisks and dark grey diamonds: siamangs at the Krefeld Zoo, groups 1 and 2, respectively).

Figure 2.

For all species, individual proportion of gestures in which the individual accounted for the recipients’ attentional state when gestures were produced in the visual or in the non-visual modality, as a function of the individual's age (in years). Circles represent individual proportions in the visual modality, and grey asterisks in the non-visual modality. The two lines represent the fitted model, which is like Model M2-Ind, but unconditional on the other predictors that were standardized.