Greeting Behaviors in Male Alouatta palliata at La Pacifica, Costa Rica

Abstract

Greeting behaviors are ritualized, nonaggressive interactions that serve as a form of tactile communication between two individuals; however, our understanding of the function of male greetings and how they vary inter- and intraspecifically is limited, particularly in Neotropical species. I examined greeting behavior in male Alouatta palliata to determine their social function by testing the tension reduction, social bonding, and formal dominance hypotheses. I collected 1751 h of behavioral data on two groups (G2 and G12/42) of similar size and sex ratio, with clear male dominance hierarchies. The overall number of greetings was low in both groups (N = 36 for both groups). More greetings occurred during times of social disruption (i.e., intergroup encounters, competition for food or females) than during neutral contexts (i.e., traveling or resting without potentially cycling females nearby), though frequencies varied by context in each group. Greetings occurred during all intergroup encounters in G2 but not in G12/42. With the exception of the competitive context in G12/42, alpha males and the higher-ranked male in the dyad initiated the majority of greetings in all contexts, though unidirectionality was not consistent. The pattern of greetings differed among dyads and between the groups. Subordinates in the dyad initiated more greetings than dominants only in G12/42 in the context of competitive activities, and the number of greetings decreased in G12/42 as rank distance increased. These results partially support the tension reduction hypothesis, and suggest greetings communicate nonagonistic intent among males. However, the nature of these encounters can vary by dyad and group within the same population, suggesting that greetings may also be partly driven by differing group histories, the social and ecological environments surrounding each group, and individual male temperaments.