Wild chimpanzees modify modality of gestures according to the strength of social bonds and personal network size

Abstract

Primates form strong and enduring social bonds with others and these bonds have important fitness consequences. However, how different types of communication are associated with different types of social bonds is poorly understood. Wild chimpanzees have a large repertoire of gestures, from visual gestures to tactile and auditory gestures. We used social network analysis to examine the association between proximity bonds (time spent in close proximity) and rates of gestural communication in pairs of chimpanzees when the intended recipient was within 10 m of the signaller. Pairs of chimpanzees with strong proximity bonds had higher rates of visual gestures, but lower rates of auditory long-range and tactile gestures. However, individual chimpanzees that had a larger number of proximity bonds had higher rates of auditory and tactile gestures and lower rates of visual gestures. These results suggest that visual gestures may be an efficient way to communicate with a small number of regular interaction partners, but that tactile and auditory gestures may be more effective at communicating with larger numbers of weaker bonds. Increasing flexibility of communication may have played an important role in managing differentiated social relationships in groups of increasing size and complexity in both primate and human evolution.

Social Brain Hypothesis: Vocal and Gesture Networks of Wild Chimpanzees

“…We therefore examined the predictors of reciprocated close proximity between pairs of chimpanzees i.e., what predicts the presence of a reciprocated close proximity bond between Chimpanzee A and Chimpanzee B? In previous research, we have shown that the presence of a reciprocated close proximity bond is predicted by a longer duration of mutual grooming and received grooming between pairs of chimpanzees (Roberts and Roberts, 2016). Here we extended these findings and showed that a specific set of signals—greetings, gestures to initiate mutual grooming, gestures to initiate receiving grooming, gestures to initiate travel, and synchronized low intensity pant-hoot—predicted the presence of a reciprocated close proximity bond between pairs of chimpanzees.…”

“…Here we show that joint coalitionary aggression in the form of synchronized high intensity pant-hoots may be one way in which these relationships are maintained. On the behavioral level, aggressive signals, particularly those that are deep, sharp, sudden, and high volume gestures, are associated with high arousal and induce arousing, fear reactions in the recipients (Bryant, 2013; Roberts and Roberts, 2015, 2016). On the physiological level, aggressive signaling can affect the recipient's nervous system by inducing an increase in plasma cortisol release (Beerda et al, 1998).…”

“…A recent study showed that the presence of reciprocated close proximity bonds between pairs of chimpanzees (i.e., those pairs who spent larger amounts of time in close proximity, per hour spent in the same party) was associated with several behavioral indices. These included a longer duration of visual attention directed at the dyad partner, a longer duration of mutual grooming and received grooming, and a longer duration of time spent resting and traveling, per hour the pair of chimpanzees spent in close proximity (within 10 m; Roberts and Roberts, 2016). Moreover, chimpanzees use a communication system consisting of gestures (Leavens et al, 2004; Forrester, 2008; Hobaiter and Byrne, 2011; Roberts et al, 2012a,b, 2013, 2014a; Smith and Delgado, 2013; Bard et al, 2014) and vocalizations to maintain their relationships (Van Lawick-Goodall, 1967, 1968; Goodall, 1986; Mitani and Nishida, 1993; Mitani et al, 1999; Roberts and Roberts, 2016).…”

“…Moreover, chimpanzees use a communication system consisting of gestures (Leavens et al, 2004; Forrester, 2008; Hobaiter and Byrne, 2011; Roberts et al, 2012a,b, 2013, 2014a; Smith and Delgado, 2013; Bard et al, 2014) and vocalizations to maintain their relationships (Van Lawick-Goodall, 1967, 1968; Goodall, 1986; Mitani and Nishida, 1993; Mitani et al, 1999; Roberts and Roberts, 2016). For instance, chimpanzees use visual gestures with strongly bonded individuals and tactile or auditory gestures with weakly bonded individuals (Roberts and Roberts, 2016). Gestural communication that has previously been suggested to be important in relation to social bonds includes gestures made when encountering each other after a natural period of separation, in response to the threat of aggression or after receiving aggression (Roberts et al, 2014a; Taglialatela et al, 2015).…”

The ontogeny of intentional communication in chimpanzees in the wild

“…We aimed to expand Plooij's (, ) early descriptive work by conducting the first systematic, quantitative study on behavioural markers of intentional communication and taking into account potential within‐species variability. Recent work on chimpanzees living in different study populations has shown that social factors such as context, familiarity and social bond (Fröhlich et al., ; Fröhlich, Wittig, & Pika, ; Luef & Pika, ; Roberts & Roberts, ; Schel et al., ), and also individual or demographic factors (mother's experience in rearing offspring, sex and study site) can have a profound influence on signal production (Fröhlich et al., ; Fröhlich, Wittig et al., , ). We therefore need more systematic data on the communicative behaviour of great apes in the wild to better understand how communicative development relates to social opportunities in the environment.…”