Effect of Infant Presence on Social Networks of Sterilized and Intact Wild Female Balinese Macaques (Macaca fascicularis)

SIMPLE SUMMARY: In primates, social interactions are significantly influenced by the female reproductive cycle and the presence of infants. In particular, unweaned infants act as amplifiers of social interactions: they facilitate contact between group members while also triggering occasional conflicts. Sterilized females no longer having young offspring could see their social integration modified. We studied intact and recently sterilized wild female long-tailed macaques (Macaca fascicularis) to see if infant presence was influencing the females’ place and role in the social group. We used the social network analysis tool to compare grooming and proximity to other females for females in three nursing conditions (with young infant (YI), with old infant (OI), and non-nursing (NN). YI females were less involved in grooming but stayed in closer proximity to other females than OI and NN females. We suggest that YI females keeping proximity to others was a way to maximize their infants’ protection, while avoiding too direct social interactions, such as grooming, to protect them from kidnapping risk. Overall, sterilization did not deteriorate female social integration, at least shortly after the surgery. Further research should track the social status of non-nursing females over a long time period, in aid of making sound population management decisions. ABSTRACT: Contraception is increasingly used to control wild animal populations. However, as reproductive condition influences social interactions in primates, the absence of new offspring could influence the females’ social integration. We studied two groups of wild macaques (Macaca fascicularis) including females recently sterilized in the Ubud Monkey Forest, Indonesia. We used social network analysis to examine female grooming and proximity networks and investigated the role of infant presence on social centrality and group connectivity, while controlling for the fertility status (sterilized N = 14, intact N = 34). We compared the ego networks of females experiencing different nursing conditions (young infant (YI) vs. old infant (OI) vs. non-nursing (NN) females). YI females were less central in the grooming network than other females while being more central in proximity networks, suggesting they could keep proximity within the group to protect their infant from hazards, while decreasing direct grooming interactions, involving potential risks such as kidnapping. The centrality of sterilized and intact females was similar, except for the proximity network where sterilized females had more partners and a better group connectivity. These results confirm the influence of nursing condition in female macaque social networks and did not show any negative short-term effects of sterilization on social integration.