Phylogeography and conservation biology of the Purple-crowned Fairy-wren, Malurus coronatus

Abstract

The purple-crowned fairy-wren (Malurus coronatus) is a declining passerine that is restricted to the dense patches of vegetation that grow along waterways in the wet-dry tropics of northern Australia. The species is threatened by ongoing degradation of riparian habitat caused by the grazing and trampling of introduced herbivores, intense fires and weed incursion. Although the western subspecies (Malurus coronatus coronatus) has been listed as endangered, conservation has been hampered by poor information regarding its distribution and what factors influence its fine-scale occurrence. This thesis aims to rectify these knowledge gaps and produce recommendations for management goals that could improve the conservation of M. c. coronatus, its riparian habitat, and other vulnerable species within the habitat. To validate the use of M. c. coronatus as a separate unit for conservation, we firstly affirmed the genetic and thus evolutionary distinctiveness of the morphologically defined subspecies of purple-crowned fairy-wren (M. c. coronatus and Malurus coronatus macgillivrayi). Because M. c. coronatus was of greater conservation concern it became the focus of the subsequent chapters. Extensive aerial and ground surveys, accompanied by an analysis of population genetics, revealed that M. c. coronatus occurs as six genetically divergent sub-populations on the Fitzroy, Durack, Drysdale, Isdell, Victoria and northern Pentecost catchments. The distribution of the species appears to be constrained by three factors: 1) fine-scale vegetation structure, 2) presence of threatening processes, and 3) the extent and spatial pattern of habitat across the landscape. The fine-scale probability of occurrence increased with increasing density of the mid-storey and increasing height of emergent trees, while the presence of potential threatening processes (cattle grazing, fire and weeds) were variously negatively correlated with decreased levels of these important habitat attributes. Suitable habitat for the species was extremely fragmented and widely dispersed along waterways in the Kimberley section of the species distribution. Suitable habitat occurred mainly on pastoral lands. The on-going decline of the purple-crowned fairy-wren signals the need for a targeted approach to conservation management; we suggest a regional plan that outlines management recommendations that are tailored to the specific requirements of each sub-population. The most urgent conservation attention may be required in the smallest subpopulations on the Isdell and Pentecost catchments. These populations are best managed through exclusion of herbivores and careful, fine-scale fire management. Elsewhere however, large and diffuse populations may be better maintained using landscape-scale conservation measures. Although reserves play a vital role in ecosystem conservation, landscape-scale environmental management, undertaken across properties of varying tenure, may be vital to manage widely dispersed species such as the purple-crowned fairy-wren that occur at low density across vast landscapes.