Impacts of extrinsic threats on swift parrot population dynamics

Abstract

Attaining species population viability (i.e. averting extinction, stable growth) is a key goal of many conservation programs globally. Many species, however, do not progress towards population recovery despite their threatened status. A review of the IUCN Green Status of Species has found that species with poor conservation legacies are due to failure to address the most significant and key threats and the implementation of actions which are not effective at the population-level. Failure to address threats may be because threats are not known, are poorly understood or may seem insurmountable because they are driven by socio-economic factors. Research on extrinsic threats and their impacts on populations are therefore vital to i) identify mechanisms of threats and interactions; ii) identify impacts on population growth rates, iii) identify steps to reduce and remove threatening processes, iv) recommend effective management-actions, and; v) inform evidence-based changes to policy and legislation which may currently pose barriers to species recovery.

This thesis focuses on the Critically Endangered swift parrot Lathamus discolor and closing knowledge gaps hindering effective species recovery. The swift parrot is a forest-dependent nomadic parrot and it is threatened primarily by habitat loss and predation by invasive sugar gliders Petaurus notatus in their breeding range within Tasmania, Australia. The swift parrot has been listed as Critically Endangered for nearly ten years but has precipitously declined over the same time period because key threats remain unmitigated. Swift parrot life history traits (i.e. tree-cavity dependence, nomadism) elevate their extinction risk from anthropogenic change and make them a difficult species to conserve, as incremental threats across their range cumulatively impact the entire population. However, the swift parrot has been well-studied for over a decade and has unusually rich demographic-data for a scarce species. This makes them an excellent model to investigate the impacts of extrinsic threats on population dynamics.

The goal of this thesis was to inform conservation management aimed at recovery of the swift parrot. I aimed to do this by improving our understanding of key threatening processes and updating our knowledge of life history parameters and population dynamics. The thesis has five data chapters. The new contributions in these chapters included investigating habitat-predation relationships, synthesising a decade of field data, updating swift parrot nest survival and population models, a meta-analytical review of prevalent methods to trap sugar gliders and a field-trialled solution to improve detectability and density estimation, quantifying habitat loss at landscape and fine scales and integrating stochastic habitat resources and habitat loss into population modelling. I conclude the thesis by discussing the implications of unaddressed extrinsic threats on swift parrots and possible future directions for aiding species recovery for this Critically Endangered species. Show more