Social Interactions in Wild Black-Fronted Titi Monkeys (Callicebus nigrifrons)

Social species live in groups that vary in size and composition for many reasons, including resource availability, predation risk, and space restrictions. Their social interactions reflect intraspecific interactions, social bonding, rank, reproductive status, and relatedness. Titi monkeys (Callicebus, Cheracebus, and Plecturocebus) are a diverse group of pitheciid primates that are widely distributed throughout South America. Typically, they live in small groups composed of a breeding pair and their offspring. Although social structure and interactions have been studied in captive titi monkeys, there has been much less research on free-ranging groups. We used all occurrence sampling during a 16-month period to investigate group composition and within-group social interactions in five wild groups of black-fronted titi monkeys, Callicebus nigrifrons living in an Atlantic Forest fragment at the Caraça Private Natural Heritage Reserve in Minas Gerais, Brazil. Unusually for the species, we found more than one adult male in three of our study groups (three adult males in one group and two in the other two groups). As reported for other titi monkeys, the breeding pair interacted more with each other than with any other group members. We also observed that breeding males interacted more with their offspring than breeding females did. Our results expand the existing literature on the social structure of titi monkeys, demonstrating their flexible social organization, providing further evidence of the breeding pair as the nucleus of the group and showing evidence for strong paternal care and stable attachments between breeding pairs in free-ranging C. nigrifrons.