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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 2 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 nonlactating 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. [ABSTRACT FROM AUTHOR]

Social organisms make collective decisions during group movement, thereby remaining cohesive and providing the ecological and evolutionary benefits of sociality. The ability for groups to make successful collective decisions is dependent on relationships between leaders and followers. We investigated how consistent followers (a fan structure) facilitated successful group movement in a group of Tibetan macaques, Macaca thibetana , at Mt. Huangshan in Anhui, China. We used structural equation modelling to determine the relative influences of sex, age, number of maternal familial connections within the group, dominance and social network centrality on the number of fans that an individual had and the number of other group members that an individual was a fan of (fandom). Our structural equation modelling revealed that dominant females had more fans, while younger, dominant individuals with more familial connections were fans of more individuals. Fans and fandom were most strongly influenced by dominance, displaying a strong network of females occupying top positions in the dominance hierarchy who consistently followed each other. In addition, we examined the relationship between fan structure and movement speed and success. Using regression, we found a positive relationship between fans and speed and a negative correlation between fans and number of unsuccessful movements, suggesting a link between the social connections maintained in a movement and the speed of the movement. Dominant females with more fans initiated slower movements, perhaps because the complex fan structure slowed the joining process. However, individuals with more fans led fewer unsuccessful movements, suggesting a relationship between fans and initiation success. Our findings show a network of social relationships within Tibetan macaque groups that are used during movement organization to maintain cohesion and mediate the benefits of sociality. Highlights • We studied Tibetan macaque decision making during collective movement. • Dominant females had the most consistent followers during movement. • Dominant, younger individuals with more kin consistently followed more individuals. • Individuals with more consistent followers led slower movements. • Individuals with more consistent followers had fewer unsuccessful movement initiations. [ABSTRACT FROM AUTHOR]