An epigenetic study of the social behaviour of the communally breeding pukeko (Porphyrio p. melanotus)

Abstract

The thesis addresses the general question of whether a functional approach is a useful or appropriate methodology for studying animal behaviour or whether an epigenetic approach might represent a more viable alternative for behavioural studies. The research itself contains a theoretical and empirical analysis of the social behaviour of communally breeding birds with particular emphasis on the polygynandrous pukeko (Porphyrio p. melanotus). The thesis commences with a critique of the functional approach used to investigate and explain the social behaviour associated with communal breeders, particularly, provisioning of nestlings by non-breeding members of communal groups. It is argued that a departure from functional-type explanations given to account for the occurrence of so-called 'helping' behaviour is needed. It is proposed instead that provisioning of nestlings in communal breeders is maintained by the same stimulus response mechanism that results in parents feeding their own young or host species feeding young of parasitic species. It was also found that asymmetries in provisioning behaviour develop within communal groups because different members of the group vary in the amount of previous experience they had in provisioning nestlings as well as varying in the degree of initial exposure to nestlings before and after they hatch. These results also suggest that provisioning behaviour by non-breeders should be viewed as a basic stimulus-response interaction. Differences in the tendency of breeders and non-breeders to incubate eggs are also examined. This asymmetry is best understood by looking at the circumstances which cause birds to realize their latent potential to exhibit incubation behaviour. The relationship between dominance and mating behaviour is then addressed. It is found that although dominance hierarchies are prevalent in breeding groups of pukeko, they play no direct role in biasing mating success among individuals differing in dominance status. Atypical behavioural interactions such as homosexual courtship and mountings by both males and females occur in the context of reproductive competition, but are insufficient by themselves to result in differential reproductive success and thus are of doubtful adaptive significance. The pukeko also exhibits a higher degree of incestuous mating than current functional theories on incest avoidance would predict. However, the unexpected nature of these results appears to be more a function of the limitations of the theories. It is proposed that high levels of inbreeding in communally breeding populations can be predicted on a theoretical basis and evidence is presented to support this view. Overall, the conclusions obtained within the thesis suggest that there is a general need for a reassessment of the functional approach used in communal breeding studies which generates the current theories and empirical data in this field of research.