Reintroduction biology of the eastern quoll (Dasyurus viverrinus)

Biodiversity loss in the Anthropocene, driven by human-induced environmental change and destruction, threatens ecosystem function and the health of all living beings. Translocations are a critical tool used to reverse this biodiversity loss, and their outcomes hinge on a population’s passage through the establishment (where post-release effects drive population dynamics), growth (characterised by high rates of expansion), and finally, regulation phases (where density dependence limits survival and recruitment). However, management decisions are always made in the face of imperfect knowledge, which have historically led to low levels of translocation success.

In this thesis, I explored tactics, behaviour, movement, and species recovery related to reintroductions (translocation to a species’ indigenous range from which it has disappeared), using the model system of eastern quolls (Dasyurus viverrinus, ‘murunguny’ in the Indigenous Ngunnawal language) at a conservation-fenced, ‘outdoor laboratory’; Mulligans Flat Woodland Sanctuary (MFWS) in the Australian Capital Territory (ACT). The eastern quoll is an endangered carnivorous marsupial of high conservation priority with an indigenous range that included the ACT, and the potential to fulfil the ecological role of a ground-dwelling mesopredator. I aimed to harness the best available knowledge relating to the eastern quoll’s biology and ecology to improve reintroduction outcomes, as well as develop frameworks that could be applied to translocation programs for other species across the globe.

To establish a population of eastern quolls at MFWS, we conducted a reintroduction program in a series of iterative trials from 2016 to 2018, followed by a reinforcement translocation in 2019. We designed each trial to maximise the knowledge we could gain to our inform strategies and tactics for the next trial. Throughout the establishment, growth, and regulation phases of the reintroduction, I assessed eastern quolls using pre-release behavioural assays (Chapter 3), monitored their post-release survival and dispersal using VHF (Chapters 2–4) and GPS collars (Chapter 4), and monitored their population dynamics using capture-mark-recapture methods (Chapter 5).

In Chapter 1, I summarised the literature relating to reintroductions, conservation fencing, and the eastern quoll species. I then presented an overview of the eastern quoll reintroduction to MFWS, to provide the context for understanding the project and the relationships between its different aspects.

In Chapter 2, I demonstrated the value of iterative trials in achieving the reintroduction milestone of establishment. By comparing survival- and dispersal-related measures across three trial reintroductions of eastern quolls to MFWS, I showed how we can use learnings from such trials to adapt tactics in a way that could lead to positive outcomes in later trials.

In Chapter 3, I investigated whether behavioural measures in reintroduced
eastern quolls could predict post-release survival and dispersal using the ‘behavioural reaction norm’ approach. Personality (consistent individual variation in behaviours) and plasticity (ability to adjust behaviour over time) can play a pivotal role in determining post-release performance. By integrating novelty into behavioural assays, I found that they offer significant value as a conservation tool.

In Chapter 4, I investigated how movement, habitat use and preference, and conspecific association differed between eastern quoll residents (established individuals) and reinforcers (individuals translocated to reinforce demographic, behavioural, and genetic diversity of a population) at MFWS. The results revealed movements at a greater spatio-temporal resolution than has ever been achieved for this species. These findings offer important insights into appropriate habitat structure for future reintroduction sites, and highlight the need for intensive post-release monitoring to inform adaptive management interventions to ensure the success of reintroductions and reinforcements.

In the Chapter 5, I demonstrated how demographic parameters can reveal threats to persistence, inform thresholds for management, and create targets for removing species from the IUCN Red List. To avoid the pitfall of long-term restoration goals being limited by short-term human memory of ecosystems (‘shifting baseline syndrome’), I visualised an ambitious end point (‘stretch goal’, i.e., recovery of the eastern quoll species within 10 years), and projected the population size and habitat required to achieve this goal (‘back-casting’). While the targets may appear daunting, our goals must be ambitious to inspire the innovation needed to achieve long-term outcomes that currently seem impossible.

In the penultimate Chapter 6, I took the learnings from this thesis and developed the ‘Translocation Continuum Framework’. The framework creates clarity around translocation ‘phases’, their criteria, strategies, tactics, evaluation measures, and expected outcomes. I discuss the limitations of ‘success’ and ‘failure’ labels in translocation science, and the importance of parsimonious decision making that balances objectives to maximise learning with the least amount of loss. By avoiding ‘short-termism’ and managing expectations of the likelihood of establishment, growth, and regulation throughout a program’s lifetime, we can galvanise trust and investment in translocations so they can contribute meaningfully to long-term restoration.

In the final Chapter 7, I provide a summary of the key findings from each of my Chapters, synthesise how these substantially contributed to the conservation and translocation sciences, and recommend future studies to build on this body of work.