Socioecological correlates of social play in adult mantled howler monkeys

The study of animal play is highly complex since its potential functions vary with social and environmental circumstances. Although play is generally characteristic of immature animals, it may persist in adults in its social form, particularly when interacting with young individuals, and less often with other adult playmates. We measured the amount of social play in 62 wild adult howler monkeys, Alouatta palliata, belonging to seven different groups in Mexico and Costa Rica. Overall, adult play represented a small mean proportion of observation time across all groups, but it was present in all study groups. Generalized linear mixed models revealed that group size correlated with both adult–adult and adult–immature play, supporting the hypothesis that more individuals provide more play opportunities. While play between adults decreased with increases in the immature to adult ratio, we did not find a clear preference for adults to play with immatures, emphasizing the importance of playing with other adult peers. Conversely, adults played more with immatures as the immature to adult ratio increased, which may correspond with the role adult–immature play may have in the socialization process of young individuals. More time dedicated to foraging on fruits corresponded with more adult–adult play. This finding, aside from being associated with more energy being available to engage in play, supports the hypothesis that play is a mechanism for solving conflicts associated with contest competition by either reducing social tension and/or fighting for a limited resource. The range of factors affecting social play indicates that this behaviour in adult howler monkeys is facultative, having affiliative, socializing and competitive roles, depending on the socioecological context.