Page 117 - Emotions through the eyes of our closest living relatives- Exploring attentional and behavioral mechanisms

Self-scratch contagion observed in orangutans
orangutans show increased frequencies of social behavior, including agonistic interactions (Edwards & Snowdon, 1980; Tajima & Kurotori, 2010; Zucker, 1987). This suggests that orangutans show a certain degree of behavioral flexibility under social contexts which makes them an interesting case for a study on mimicry and its possible social function.
Research on mimicry in orangutans, however, is scarce. One study found that
orangutans show rapid facial mimicry during play events (Davila-Ross et al., 2008),
while another study did not find evidence of yawn contagion in an experimental
setup (Amici et al., 2014). In this study, we aimed to enhance our understanding of
the function of mimicry in the orangutan. To do so, we focused on yawning as this
behavior is commonly studied in mimicry research. In addition, we decided to focus
on self-scratching behavior because of its possible link to arousal (Elder & Menzel,
2001). As such, we recorded all yawning and self-scratching events in a group of zoo‐
housed Bornean orangutans (P. pygmaeus) with the aim to investigate whether (a)
yawning and self-scratching is contagious and (b) whether contagion has a social 5 function in this species. Based on a previous study reporting the presence of rapid
facial mimicry (Davila-Ross et al., 2008), we hypothesize that mimicry is present in orangutans in the forms of yawn and self-scratch contagion. Furthermore, if these behaviors have a social function, we expect that the contagion of yawning and self- scratching will be influenced by the relationship quality of the expresser and observer and that contagion is higher between kin and friends.
Method
Participants and data collection
Behavioral data were collected from February to May 2017 on nine adult Bornean orangutans (three males and six females, mean age= 23.2, range= 7–52 years old, all born and raised in captivity. See Table S1) living in primate park Apenheul, The Netherlands. The animals were housed in a building consisting of four indoor enclosures that were each connected to outdoor islands. The four enclosures could be disconnected from and connected to two adjacent enclosures, which allowed the zookeepers to alter group composition on a daily basis, based on the animals’ preferences.
Usually, there were four separate groups (ranging from one to four individuals) that differed in composition and occasionally three groups (ranging from two to five
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