Title: Complex Society of a Colonial Cooperatively Breeding Bird in a Fluctuating Environment
Description: Sociality represents one of the major evolutionary transitions in life: a transition from individuality to societies as complex as our own. Animals exhibit a wide variety of societies, from temporary aggregations, such as schools of fish, to complex organizations where individuals maintain stable relationships, such as cooperative groups in birds, mammals, and eusocial ants. However, the diversity of social systems and the mechanisms driving the formation of complex societies remain unclear. In this dissertation, I aim to understand a less known complex social system, a colonial cooperatively breeding bird on the African savannah, grey-capped social weavers (Pseudonigrita arnaudi). I monitored daytime and nighttime relationships among more than 600 birds in over 100 colonies across three subpopulations for five breeding seasons using an auto-tracking system. In Chapter 1, I examine the social organization of this species and test the role of kinship in the organization of the society. In Chapter 2, I focus on the inter-annual variation in the fission-fusion process of colonies and test how social factors (i.e., group membership and colony membership) and ecological conditions (i.e., rainfall) may underlie individual and group decisions about settlement of colonies.

In Chapter 3, I investigate the conflict in the form of infanticide behavior (i.e., egg tossing) in this social system and test nest predation as an alternative hypothesis against a presumed hypothesis that group conflict is the cause of the tossing behavior. In sum, my dissertation provides the first detailed study of a colonial and cooperatively breeding bird with high resolution of movement at the individual level. Understanding a new social system will not only expand our knowledge of the variety of animal societies, but will also give insight into how social complexity has evolved, including our own.