Collective group movement and leadership in wild black howler monkeys (Alouatta pigra)

Maintaining social cohesion through coordinating traveling time and direction is a primary benefit of group living in mammals. During a 15-month study, we investigated socioecological factors underlying leadership of collective group movements in three multimale–multifemale groups of black howler monkeys (Alouatta pigra) at Palenque National Park (PNP), Mexico. A total of 691 independent group movements across a variety of contexts were collected. Leadership of group movements was partially shared, with adult females initiating and leading group movements significantly more often than did adult males and juveniles, an outcome that has been observed among a diverse set of group living taxa. Adult females did not lead their group more often to feeding sites nor did they lead group movements more frequently when pregnant or lactating compared to when cycling, providing little evidence that energetic demands were the primary drivers underlying female leadership in this primate species. Instead, only one adult female in each social group was identified as a habitual leader of their group. These ‘leader’ females had the highest centrality eigenvectors among the adult group members in their group, suggesting an embedded leadership with the spatially widest connected adult group member emerging as recurrent leader of collective group movements.