Abstract
Understanding the evolution of multilevel societies is important for elucidating our own social evolution. The Rwenzori Angolan colobus (Colobus angolensis ruwenzorii) multilevel society is unique in its high prevalence of multi-male/multi-female core units and rare occurrence of all-male units. However, little is known about male-male social behaviour within multi-male core units or how male-female bonds are distributed among the males. We used social network analysis to examine spatial-proximity networks for identifiable colobus within eight multi-male/multi-female core units at Nabugabo, Uganda. Over a 12-month period, we found variation in the structure of male-female relationships, showing one of three patterns; (1) one male was preferred by females while others remained peripheral to the network (N = 3 units), (2) males and females were divided into social clusters where each male monopolized the social relationships of two to three females (N = 2 units), (3) all males invested equally in their associations with females and more significantly in each other (N = 3 units). Importantly, each of these social structures showed evidence of strong male-male bonds. Pairing these data with co-residency and parallel dispersal data from five subsequent years showed that males with more equitable patterns of proximity to females stayed together significantly longer and transferred together more in the future. We conclude that the variation in social network structure between core units reflects different strategies used by males to access the benefits of group-living and defend resources, mates, and offspring. Our study demonstrates that male Rwenzori colobus form lasting bonds that can transcend multiple dispersals between units.