Understanding the drivers of individual and group-level movements in gregarious species

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The intricate movements of animal groups across landscapes and of individuals within groups are not well understood. Ostensibly these are the outcome of individuals' manoeuvering relative to others to best meet their current needs but further study is needed to clarify the strategies of different classes of individuals. There are both costs and benefits of associating with individuals of the same species; and the costs may be mitigated and the benefits increased by controlling group size, inter-individual proximity, sex-ratios, and group movement direction. However, depending on their sex and life stage, animals vary in their abilities to control these variables. When choosing their individual movement paths animals must also consider their resource needs, the multiple ways that food sites vary, and the locations of competitors and allies. This project aims to understand the important factors underlying group-level and individual-level movements using two species of group-living nonhuman primates at Lake Nabugabo, Uganda. Angolan black-and-white colobus monkeys (Colobus angolensis ruwenzorii) form large aggregations made up of individuals and subgroups that frequently fission and range apart before coming together again. Angolan colobus will be used to understand group-level movements and this project will determine whether there is structure to this subgrouping, what factors influence fission and fusion events, the ways that subgroups synchronize their movements, and the spatial organization of subgroups. Vervet monkeys (Chlorocebus pygerythrus) form smaller, cohesive, matrilineal groups and provide the perfect system to examine individual-level movements. This project will examine why individuals choose to join group progressions and how they decide which resources to visit based on specific food attributes and the presence or absence of competitors and allies. Foraging experiments can be done with single vervet monkeys and the same individuals as part of a social group, thus movement decisions can be compared in solitary and social contexts for the same individuals. This allows an analyses of how individual decision-making is altered by the presence of others. This project will aid in clarifying how gregarious animals balance the costs and benefits of living with others and the underlying drivers of animal movement patterns at multiple scales.