Social network changes during the development of immature capuchin monkeys (Sapajus spp.)

Immature indivuduals influence the formation and maintenance of social relationships within groups in diverse ways. Because of the increased interest of group members toward newborns, lactating females may use infants as social tools to temporally gain rank positions in matrilineal societies, and differential support received by the mothers may bias the network of immatures born to females of different ranks. In this study, we investigated the changes in proximity, grooming, play, and agonism networks of lactating females and immatures of different developmental periods, sex, and mothers' dominance rank. A semi-free-ranging group of 22 capuchin monkeys (Sapajus spp) was monitored for 12 months, totaling over 300 hours of observation. During this period, the age changes of 13 immatures were monitored and recorded. Best regression models showed that an increased number of grooming partners while lactating did not translate into changes in the proximity or agonistic network positions for females. Age was the main predictor of social network changes, while sex had a minor influence on the play network and no influence on the grooming or agonistic networks. Finally, mothers' rank predicted differences in the affiliative but not the agonistic social network. This pattern points to a more affiliative and individual-based rather than agonistic and nepotism-based strategy for social network insertion, which can be explained by the decreased competition faced by the focal group and by the behavioral flexibility of the clade.