Competitive Family Dynamics in a Breeding Population of Black-faced Cormorants (Phalacrocorax fuscescens) at Outer Harbour, South Australia

Abstract

This study aimed to investigate the competitive family dynamics of breeding Black-faced Cormorants (Phalacrocorax fuscescens) at Outer Harbour, South Australia. Mating and parental care behaviours are complex yet fundamental to family dynamics. Family interactions are highly influenced by access to resources and the degree of relatedness between individuals. Competition between family members is expected to increase when access to resources is limited. Individuals within a family have different degrees of relatedness and thus compete for resources because they do not necessarily share the same reproductive interests. Resource limitation and relatedness are thus sources of intra-familial conflict that was a focus in my study. All family members are affected by resource shortages. Adults insure against reproducing in an uncertain world by laying optimistic clutches. Adults may then play favourites and trim the size of the brood if access to resources decreases. Hatching asynchrony facilitates this brood reduction because adults provide first-hatched core nestlings with physical and developmental advantages over later-hatched marginal nestlings. Core nestlings compete with marginal nestlings by begging and/or using overt aggression to dominate adult food supply, generally resulting in weaker marginal nestlings dying from starvation or siblicide. Marginal nestlings thus bear the brunt of resource shortages.