Delayed release improves site fidelity but has little effect on survival or breeding success of reintroduced western quolls (Dasyurus geoffroii)

Reintroductions of threatened species can fail due to a lack of site fidelity and dispersal of individuals away from the release site. Delayed-release techniques are commonly used in reintroduction programmes to acclimatise animals to novel sites to improve site fidelity and survival following release. However, some studies have found negative or little effect of initial containment on post-release outcomes, suggesting that the benefits of a delayed release may be species-specific or dependent on the methods used. The western quoll (Dasyurus geoffroii) is a 900-1300 g carnivorous marsupial that has previously been found to travel long distances after release, potentially contributing to reintroduction failure. We investigated the effect of immediate versus delayed release on the survival, site fidelity and breeding success of western quolls reintroduced to the Ikara-Flinders Ranges National Park in South Australia. Delayed-release animals were confined to individual 10 x 10 m outdoor release pens and provided with supplementary food and water for ten days prior to release. Immediate-release animals were released without any additional assistance provided. Monitoring of 39 radio-collared quolls for three months after release failed to detect a difference in survival probability between release treatments. There was also no evidence to suggest that the success or timing of breeding differed between immediate- and delayed-released quolls. However, a delayed release did significantly improve site fidelity. On average, delayed-release quolls remained within a linear distance of 1.6 km (SE = 0.348, 95% CI = 0.98-2.39) of their release site over three months, compared to 3.26 km (SE = 0.36, 95% CI = 2.57-4.03) for immediate-released animals. In unbounded release sites, delayed releases may assist with keeping western quolls within predator-controlled release areas. Results from this study may be used to guide future reintroductions of this threatened species.