This study will investigate the determinants of group size, cohesion, and inter-group spacing in two mangabey species, Cercocebus galeritus agilis and Cercocebus albigena, that live in the same areas of the Mondika Research Station, Central African Republic. These two mangabey species reportedly differ in their grouping patterns despite their morphological and ecological similarities. C. albigena reportedly lives in relatively stable social units, whereas C. galeritus groups often fragment into subgroups, yet at other times aggregate into large hordes (or 'supergroups'). The study proposed here will test hypotheses of how specific ecological factors (such as fluctuations in food availability) and social factors (such as dominance hierarchies, and the presence of infants and estrus females) influence group size, cohesion, and spacing. Methods will include behavioral sampling of the two mangabey species as well as ecological sampling to monitor the availability of food in their environment. Results of this study will enhance our understanding of the evolution of primate sociality. In addition, this study will provide the first long-term data on social organization and foraging strategies in two sympatric mangabey species. The behavioral data collected can be used with morphological and molecular data to address the puzzling issue of mangabey phylogeny and affinities with other old world monkeys such as baboons and macaques.
