Population recovery of the yellow-footed rock-wallaby following fox control in New South Wales and South Australia

Abstract

Context Introduced herbivores and carnivores have significantly altered ecosystems across Australia and have been implicated in the decline and extinction of many species, particularly in the arid and semiarid zones. The experimental confirmation of agents of decline is a fundamental step in threatened species management, allowing for an efficient allocation of resources and effective species recovery. Aims Following unsuccessful attempts to increase the abundance of yellow-footed rock-wallaby populations through concerted goat control across the southern extent of their range, the primary aim of our study was to determine whether fox predation was limiting the recovery of wallaby populations. Methods Intensive fox-control programs (1080 baiting) were initiated around wallaby subpopulations in New South Wales and South Australia. Wallaby numbers were monitored for a three-year period before and after the initiation of fox control, and ANCOVA used to examine for differences between the subpopulation’s rate of increase (r). Observational data were used to determine the demographic effects of fox predation on wallaby colonies in New South Wales. Key results Wallaby subpopulations that were treated with fox control increased significantly, while experimental control subpopulations remained at consistently low levels. Juvenile and subadult wallabies were apparent within the treated New South Wales subpopulation, but almost absent from the control subpopulation, suggesting that fox predation focussed primarily on these age classes. Conclusions Fox predation is a major limiting factor for southern wallaby populations and fox control should be the primary management action to achieve species recovery. Implications Although a significant limiting factor, the regulatory effect of fox predation was not assessed and, as such, it cannot be confirmed as being the causal factor responsible for the historic declines in wallaby abundance. The determination of whether fox predation acts in a limiting or regulatory fashion requires further experimentation, but its resolution will have significant implications for the strategic allocation of conservation resources.