A tactics-based approach for improving the outcomes of eastern bettong (Bettongia gaimardi) reintroductions

Abstract

Reintroductions aim to re-establish self-sustaining populations of the focal species within its indigenous range, but their outcomes are variable. An issue commonly perceived as limiting reintroduction success is the tendency for decisions to be based on personal opinion and general assumption. Reintroduction outcomes are ultimately determined by the relative forces of mortality, dispersal and recruitment; but these are influenced by a myriad of proximate factors that may need to be managed. This has led to a diverse array of management techniques being developed; however, comprehensive records of these are rarely available. As certain techniques can induce unpredictable effects they need to be tested to ensure that they are used appropriately. In the initial part of this thesis, I develop the concept of Translocation Tactics which I define as “techniques capable of influencing post-release individual performance or population persistence” (Paper I). This concept is founded on a review of 195 peer-reviewed scientific articles, the IUCN/SSC Guidelines for reintroductions and other conservation translocations (‘the Guidelines’), and 73 case-studies from the IUCN/SSC Global Reintroduction Perspectives Series. Through this review, I identified 30 tactics used during bird and mammal translocations which I organised into The Translocation Tactics Classification System (TTCS) providing a structural framework to help practitioners anticipate threats, and identify appropriate tactics. I use the TTCS to assess the coverage of tactics in the Guidelines, and conclude that they offer an extensive, but not exhaustive coverage. The absence of six tactics reinforces the benefit of developing context-specific resources to support their broadly applicable approach. I expand upon this concept by outlining the theoretical basis of common release tactics (e.g. delayed- and immediate-release, the number of founders, behavioral training) and provide examples of their application and evidence of their effectiveness during Australasian reintroductions (Paper II).

The second part of this thesis empirically investigates the biological, behavioral and physiological effects of pre-release captivity on reintroduced eastern bettong (Bettongia gaimardi), to evaluate the potential use of captivity as a tactic. This research focuses on founders at Mulligans Flat Woodland Sanctuary (MFWS) a mainland-island and outdoor laboratory in southeast Australia. Founders were released using three tactics (1) wild-wild or immediate-release, (N=16) incorporating wild founders without captive experience, (2) wild-captive-wild or delayed-release, (N=16) incorporating wild founders released after 3-18 months in captivity, (3) captive-wild, (N=6) incorporating captive-bred founders. Founders were monitored for up to 18 months post-release, and the data were used to compare a range of variables including performance (survival and reproduction), physiology (stress and body-mass), and behaviors (movement and nesting). My results suggest that exposing wild founders to captivity did not alter their performance or body-mass post-release, despite being heavier and having fewer pouch young when released. However, the lack of a population-level effect may reflect the high-quality and low-risk (e.g. predator-free) release-site which resulted in optimum performance irrespective of release tactic (Paper III). Pre-release captivity did induce a range of sub-lethal responses including influencing the stress physiology of wild founders which may be associated with chronic stress (Paper IV). In addition, wild and captive-bred founders tended to display wider exploratory movements, and higher rates of activity when released with captive experience; while the wild-captive-wild group also tended to build poor quality nests (Paper V). I interpreted these results based on their expected effect on establishment during subsequent reintroductions beyond-the-fence which carry a greater risk of failure. Overall, I recommend captivity is avoided when possible to reduce the risk to founders, except during reintroductions requiring pre-release quarantine.