Primate societies are diverse in terms of social organization and structure (Smuts et al. 1987; Boesch et al. 2002). The society, or social unit, is the set of conspecific animals that interact regularly and more commonly with each other than with members of other societies (Kappeler and van Schaik 2002). Traditionally, social organization, which has been the basis for characterizing primate societies, can be classified into three types: solitary, pair-living, and group-living (Kappeler and van Schaik 2002). Social units, including mature males, fertile females, and their offspring, function as the reproductive unit and are linked via two processes (Itani 1985). First, sex-biased dispersal across social units is a near-ubiquitous feature of the life history of mammals and birds (Handley and Perrin 2007). Second, different groups in a population occasionally come together during intergroup encounters.