Rank reversal in females hierarchy in semi-free ranging capuchin monkeys (Cebus apella)

Benefits and costs of group living may not be equally distributed among all group members when they are organized in dominance hierarchies. In capuchin monkeys, higher-ranking individuals often have privileged access to food sources and reproductive partners. Other group members, particularly females, can benefit from proximity with the alpha male, gaining privileged access to the resources and also protection in the case of conflicts. In this study, a group with 17 individuals was observed for seven months and during this time data on activities and interindividual distances up to 10 meters were collected using animal-focal sampling method. Data were analysed through minimum spanning trees of interindividual distances and shortest directed trees of grooming and agonistic behavior. Dominance hierarchy in capuchins is generally considered stable, without reversions. However, during this study we observed a hierarchy reversal. It involved a period of increase in frequencies of agonistic behavior, caused mainly by conflict among females, and during this time the dominant female was threatened and sometimes attacked by a coalition of three other females. After this period the dominant female moved away from the group centre and the former beta female clearly took over the alpha position. The reversal was probably caused by transition to adulthood by one female and low grooming rates directed to the alpha male and adult females by the former alpha female.