Don and Duncan playing (Chimfunshi Wildlife Orphanage, Group 2). Credit: Dr Jake Brooker, CC-BY 4.0 (https://creativecommons.org/licenses/by/4.0/).

Chimpanzees are more likely to groom or play with each other if they see others partake of friendly social behaviours first.

Chimpanzees are more likely to engage in play or groom each other if they see others performing these social behaviours first, Georgia Sandars and colleagues at Durham University.

Whether it’s yawning or keeping watch for predators, many animals — including primates and ravens — find certain behaviours contagious: after seeing another member of their group performing one of these behaviours, they will instinctively perform it too.

This ‘behavioural contagion’ is thought to help animal groups reinforce their social bonds and stay in sync.

Chimpanzees’ behaviour and emotions can be influenced by those around them, but whether they experience contagion of friendly social behaviours, such as grooming and play, has not previously been investigated.

Grooming and play

To address this knowledge gap, researchers observed the behaviour of 41 chimpanzees living in a sanctuary in Zambia.

They found that chimpanzees of all ages, ranks and sexes displayed contagion of grooming and playful behaviours.

Chimpanzees were more likely to find grooming behaviour contagious when they observed it in another individual that they had a close relationship with.

In contrast, play behaviour was more contagious in younger chimpanzees, but this contagion was unaffected by the strength of the social bond.

Behavioural contagion of friendly behaviours like grooming and play may help to strengthen social bonds, the authors say.

Play is an important part of social and behavioural development for young chimpanzees, whereas adults tend to build and repair social relationships by grooming each other, which may explain the differences in contagion between the two behaviours.

There are several possible explanations for why adult chimpanzees find the behaviour of individuals they have a close social relationship with more contagious: they may pay more attention to or be more strongly influenced by their close friends, or seeing a close friend grooming someone else may cause jealousy.

The authors add: “Chimpanzees ‘catch’ social behaviour from each other; they are more likely to start grooming and playing after having just seen others groom and play.”

The research is published in PLOS ONE.