Dominance and Communication in a Cooperatively Breeding Bird

Abstract

Social dominance can influence the allocation of resources in animal groups and has important consequences for individual fitness. In my thesis, I examined the structure, formation, maintenance and consequences of dominance, in the cooperatively breeding pukeko (Porphyrio melanotus melantous: Aves). I first describe a quantitative analysis of pukeko dominance networks (Chapter 2), which included one of the first applications of exponential random graph models in behavioural ecology. This study demonstrated that pukeko form highly ordered dominance hierarchies, and that dominance relationships were influenced by both the attributes of individual birds, as well as self-organizational processes such as winner and loser effects. Additionally, I demonstrated that hatching order has an important influence on the formation of dominance relationships, with earlier hatched chicks achieving higher dominance ranks as adults (Chapter 3). To maintain dominance relationships, pukeko use their red frontal shield as a ‘status signal’, with larger frontal shields indicating more dominant individuals. I showed that sexual dimorphism in frontal shield size is dramatically different in two pukeko populations, probably due to differences in the intensity of intrasexual competition (Chapter 4). Furthermore, by manipulating apparent frontal shield size, I demonstrated that shield phenotype both influences, and is influenced by, social interactions (Chapter 5). This bi-directional relationship between signals and social interactions challenges conventional signalling theory, and has important implications for how honesty is maintained in this signalling system. Finally, I expanded my findings on pukeko colour traits by exploring interspecific patterns of bill colouration in over 1600 bird species (Chapter 6). This study revealed that colourful bills likely evolved as a signal used in competitive interactions, rather than as a sexual signal. Taken together, my research provides a significant advancement in our understanding of the complex nature of dominance in a wild bird, and provides both a methodological and theoretical basis for future studies on animal social behaviour.