Yawning and scratching contagion in wild spider monkeys (Ateles geoffroyi)

Abstract

Behavioural contagion is a widespread phenomenon in animal species, which is thought to promote coordination and group cohesion. Among non-human primates, however, there is no evidence of behavioural contagion in Platyrrhines (i.e. primates from South and Central America) yet. Here, we investigated whether behavioural contagion is also present in this taxon, by assessing yawning and scratching contagion in a wild group (N = 49) of Geoffroy's spider monkeys (Ateles geoffroyi). We conducted focal samples to examine whether individuals observing the triggering event (i.e. a naturally occurring yawning or scratching event in the group) would be more likely to yawn or scratch in the following 3 min, as compared to individuals who did not observe the triggering event. We ran generalized linear mixed models using a Bayesian approach, and found that the probability of yawning and scratching was higher for individuals observing others yawning and scratching, respectively, as compared to individuals who did not observe such an event. Behavioural contagion did not vary depending on the observer's sex, kinship or relationship quality with the individual performing the triggering event. These findings provide the first evidence for yawning and scratching contagion in a wild group of spider monkeys, and importantly contribute to the debate about the evolutionary origins of behavioural contagion in primates.

Figure 1

Thick lines represent the median estimated probability of individuals yawning after observing or not the yawning triggering event, back-transformed from the logit scale, and averaged over the level of maternal kinship and observer’s sex. Boxes represent the lower and upper 95% highest posterior density (HPD) interval probabilities.

Figure 2

Thick lines represent the median estimated probability of individuals scratching after observing or not the scratching triggering event, back-transformed from the logit scale, and averaged over the level of maternal kinship and observer’s sex. Boxes represent the lower and upper 95% highest posterior density (HPD) interval probabilities.