Female white-handed gibbons (Hylobates lar) lead group movements and have priority of access to food resources

Abstract

One of the disadvantages of group life is competition over food. How this conflict is solved is an interesting issue for sexually monomorphic species, with co-dominant sexes. Since female mammals, particularly primate females with long gestation and lactation periods, have higher reproductive costs, the question arises how this increased need translates into leadership among group members and, thus, priority of access to food resources. We investigated seven wild, pair-living and six multi-male groups of white-handed gibbons ( N = 13), in which females are expected to experience even increased rates of food competition. We examined leadership tendencies in the context of group movement, travel order, access to food resources and feeding priority (i.e., monopolizing/sharing a food patch). We found that females consistently led travel by maintaining their position at the front of groups and that traveling order amongst the entire group remained consistent between journeys. Lead females usually arrived first at food sources and tended to feed alone when food resources were limited. Female reproductive stage appeared to influence their motivation to lead, as cycling females led movements more frequently than pregnant and lactating females did. We conclude that, although appearing co-dominant, gibbon females assume a greater leadership role in coordinating group activities.