The causes and consequences of group living in the crimson finch (Neochmia phaeton)

Abstract

This thesis consists of five chapters, each investigating an aspect of breeding biology, sociality or behaviour of a group living species of an Australasian grassfinch, the crimson finch (Neochmia phaeton). It primarily focuses on the effects of habitat structure and group size on reproductive behaviour, and the role of signalling in mediating conflicts. Much of our knowledge of the breeding behaviour of the crimson finch is based on observations in captivity, little is known about wild populations. Captive crimson finches are known for their highly aggressive nature. However, free-living birds live and breed in large social colonies, which seems counterintuitive. The first three chapters explore the ecology and colony structure of wild crimson finches, providing insight into the breeding system, nest predation and dispersal strategies. In chapters 4 and 5, we used field observations and experimental manipulations in captivity to determine the factors that cause, facilitate and maintain aggression and sociality in this species. Chapter One describes aspects of habitat use and breeding ecology from 14 distinct colonies, and contrasts these findings with other populations living in different habitat, which have been examined previously. Although we found many similarities between the populations in breeding biology, we also found some pronounced differences in the way crimson finches organise themselves socially and geographically in the divergent habitat structures. Chapter Two investigates the factors influencing nesting success, specifically the influence of nest site location and adult behaviour (predator defence) on nest success. Though there was no evidence that adult behaviour influences nest success, we found three features of nest site choice that were related to nest survival; nest visibility, vegetation height and distance to other vegetation. Chapter Three provides the first study of dispersal in crimson finches. We report that contrary to previous speculations, long-distance movements between colonies are common. The primary factor predicting two key decisions, whether to leave the natal group, and where to settle, was primarily related to the adult sex ratio of the colony. Chapter Four explores aggressive behaviour between adult males. Here we use correlative and manipulative approaches to understanding how plumage signals mediate aggressive behaviour. In particular, we investigate the role of melanin and carotenoid plumage pigments in signalling dominance and fighting ability. Chapter Five experimentally examines aggressive behaviour of both males and females at the nest, using mounts of conspecific and heterospecific intruders. Although crimson finches are said to be non-territorial they are known to defend the area immediately around their nest. We found no difference in levels of aggression between males and females, or towards conspecific and heterospecific intruders. The final section of this thesis summarises our findings and provides suggestions on future research to further investigate the costs and benefits of group living. Show more