Infant attraction: why social bridging matters for female leadership in Tibetan macaques

Abstract

Leadership is a key issue in the study of collective behavior in social animals. Affiliation-leadership models predict that dyadic partner preferences based on grooming relationships or alliance formation positively affect an individual’s decision to follow or support a conspecific. In the case of many primate species, females without young infants are attracted to mother-infant dyads. However, the effects of mother-infant-female associations on affiliation-leadership models remain less clear. In free-ranging Tibetan macaques Macaca thibetana, we used social network analysis to examine the importance of “mother-infant-adult female” social bridging events as a predictor of who leads and who follows during group movement. Social bridging is a common behavior in Tibetan macaques and occurs when two adults, generally females, engage in coordinated infant-handling. Using eigenvector centrality coefficients of social bridging as a measure of social affiliation, we found that among lactating females, initiating bridging behavior with another female played a significant role in leadership success, with the assisting female following the mother during group movement. Among non-lactating females, this was not the case. Our results indicate that infant attraction can be a strong trigger in collective action and directing group movement in Tibetan macaques and provides benefits to mothers who require helpers and social support in order to ensure the safety of their infants. Our study provides new insights into the importance of the third party effect in rethinking affiliation-leadership models in group-living animals.

Individual Variation in the Use of Acoustic Signals to Coordinate Group Movements among Tibetan Macaques (Macaca thibetana)

“…Previous studies have shown that social centrality plays a key role in the success of collective movements in Tibetan macaques, where individuals demonstrating higher social centrality are more likely to succeed in initiating the group movement [ 28 ]. The eigenvector centrality coefficient measures how closely associated an individual is to others in group movements [ 42 ]. Thus, it is suggested that individuals with high social centrality possessed a stronger social affinity and could interact with more followers through vocal communication.…”

Sexual Interference Behaviors in Male Adult and Subadult Tibetan Macaques (Macaca thibetana)

“…This site consists of deciduous broadleaf and broadleaf evergreen mixed forests at altitudes from 600–1200 m [ 31 , 41 ]. Several wild groups of Tibetan macaques live in this area [ 31 , 42 ]. We focused our data collection on the Yulingkeng A1 (YA1) group (group size: 27–40 individuals), which has been provisioned and observed since 1986 [ 31 , 43 ].…”

Coordination and consensus: the role of compromisers in Tibetan macaques

“…We also calculated the eigenvector centrality coefficient via HWI matrices using SOCPROG 2.4. Eigenvector centrality coefficient measures how closely associated an individual is to others in group movements ( Wang et al 2015 , 2020 ). A higher score of the eigenvector centrality coefficient indicates that the individual possesses more movement partners ( Newman 2004 ).…”

“…Potential conflicts of interest in Tibetan macaques represent consensus costs. Individuals must regularly negotiate conflicting interests among group mates that vary in their optimality criteria ( Wang et al 2020 ). This prerequisite requires the majority of group members to choose between collective decisions and individual choice, representing a compromising process.…”