Habitat use and life-history of Hall's babbler (Pomatostomus halli) - a group-living passerine of the Australian arid zone

Australo-Papuan babblers have been the focus of considerable research in avian behaviour and ecology, yet our knowledge of this group is biased toward two species: grey-crowned (Pomatostomus temporalis) and white-browed (P. superciliosus) babblers (Chapter 1). In this thesis, I investigated the geographic range, habitat use, morphology, social organisation and life-history of Hall's babbler (P. halli), the least-studied Australian species. To define the geographic range and examine habitat use therein, I used a novel approach that combined species locality records, climatic envelope modelling, vegetation maps, and existing bird survey data (Chapter 2). Hall's babbler occurred primarily in vegetation communities dominated by mulga (Acacia aneura) and those of Acacia species occurring on residual soils. In the remainder of this thesis, I present results from an intensive three-year study of colour-banded individuals within a population in south-western Queensland. At a macrohabitat scale, multivariate analyses of vegetation structure and floristic composition indicated the distribution of Hall's babbler within my study site was primarily associated with increased abundance of mulga trees and coarse woody debris. At the microhabitat scale, nest-site selection appeared to be influenced principally by tree density (Chapter 3). I found the species is sexually size dimorphic with males slightly larger than females, and dimorphism was disproportionally greater in bill length than other traits (Chapter 4). This sexual size dimorphism has practical utility in that the sex of individuals could be identified with 88% accuracy using linear discriminant analysis. Hall's babblers bred cooperatively in small (2-5 adults), kin-structured breeding units, which usually coalesced to form social groups when not breeding (Chapter 5). A comparison of the social organisations of all babbler species revealed they varied markedly in many fundamental attributes. Life-history characteristics of Hall's babbler – nestling growth rate and development (Chapter 6), clutch size, incubation and nestling periods, annual productivity, and survival – were generally similar to those of other babblers species, and typical of the 'slow' life-history strategy of old endemic Australian passerines (Chapter 7). I conclude by discussing the implications of my research on our understanding of the behavioural ecology of Australo-Papuan babblers and suggest future avenues of research within this group (Chapter 8)