Coordination of group movements in wild Verreaux's sifakas (Propithecus verreauxi)

Maintenance of group cohesion is of vital importance for group-living species. Individuals therefore need to coordinate their potentially divergent interests to maintain group cohesion. We studied behavioural aspects and mechanisms of coordinated group movements in Verreaux's sifakas (Propithecus verreauxi), an arboreal Malagasy primate living in small groups. During a field study in Kirindy forest, western Madagascar, we studied the initiation and course of Group movements, as well as vocalisations used in this context, in three social Groups. We found that both sexes initiated group movements, but females did so more often, lead groups further and enlisted more followers than males. Sex of the leader had no effect on the probability that a group would feed or rest after a successful movement, however. Grumble vocalisations were emitted by both leaders and followers at high rates, both before and during group progressions, but Grumbles uttered just before an individual moved were characterised by a significantly steeper frequency modulation at the beginning of the call and higher call frequencies in both females and males. The results of this study indicated that sifakas, which evolved group-living independently from other primates, converge with many other group-living primates in several fundamental proximate aspects of group coordination and cohesion. In contrast to many other primates, however, sifakas did not use a particular call or other signals to initiate or control group movements.