ChimpanSEE, ChimpanDO: Grooming and play contagion in chimpanzees

Abstract

Behavioural contagion-the onset of a species-typical behaviour soon after witnessing it in a conspecific-forms the foundation of behavioural synchrony and cohesive group living in social animals. Although past research has mostly focused on negative emotions or neutral contexts, the sharing of positive emotions in particular may be key for social affiliation. We investigated the contagion of two socially affiliative interactive behaviours, grooming and play, in chimpanzees. We collected naturalistic observations of N = 41 sanctuary-living chimpanzees at Chimfunshi Wildlife Orphanage, conducting focal follows of individuals following observations of a grooming or play bout, compared with matched controls. We then tested whether the presence and latency of behavioural contagion was influenced by age, sex, rank, and social closeness. Our results offer evidence for the presence of grooming and play contagion in sanctuary-living chimpanzees. Grooming contagion appeared to be influenced by social closeness, whilst play contagion was more pronounced in younger individuals. These findings emphasise that contagion is not restricted to negatively valenced or self-directed behaviours, and that the predictors of contagious behaviour are highly specific to the behaviour and species in question. Examining the factors that influence this foundational social process contributes to theories of affective state matching and is key for understanding social bonding and group dynamics.

Fig 1. Proportions of attracted, neutral, and dispersed grooming PO-MC pairs, for each individual.

Attracted pairs correspond to grooming happening only in the PO, dispersed pairs correspond to grooming happening only in the MC, and neutral pairs correspond to grooming happening in neither or both. Data comprised of N = 120 matched focals of N = 32 individuals.

Fig 2. Proportions of attracted, neutral and dispersed play PO-MC pairs, for each individual.

Attracted pairs correspond to play happening only in the PO, dispersed pairs correspond to play happening only in the MC, and neutral pairs correspond to play happening in neither or both. Data comprised of N = 96 matched focals of N = 25 individuals.

Fig 3. Social closeness scores in focal follows where contagion did and did not take place.

The social closeness measure is the z-transformed dyadic sociality index between observer and stimulus individuals. The mean social closeness value for instances of no contagion vs contagion is shown with a black bar. Data comprised of N = 159 observations of N = 40 chimpanzees.

Fig 4. Histogram of latencies from observing grooming to first initiating grooming.

Data comprised of N = 54 observations across N = 21 individuals.

Fig 5. Mean rate of post-observation play across age categories.

Data is grouped into juveniles (3–7 years; N = 34 observations of N = 10 chimpanzees), subadults (8–11 years; N = 20 observations of N = 4 chimpanzees) and adults (12+ years; N = 82 observations of N = 27 chimpanzees). This categorisation is for visualisation purposes, but data were analysed with age as a continuous variable. Upper and lower quartiles are indicated by the box boundaries, and dots indicate outliers.

Fig 6. Histogram of latencies from observing play to first initiating play.

Data comprised of N = 48 observations across N = 28 individuals.