Intensive monitoring, the key to identifying cat predation as a major threat to native carnivore (Dasyurus geoffroii) reintroduction.
Successful fauna reintroductions occur when the original causes of decline are addressed. When these causes are unclear, intensive post-release monitoring could help identify unknown threats and new management actions. We present an Australian case study involving a reintroduction of the threatened western quoll (Dasyurus geoffroii), a species whose decline was thought to have been caused primarily by predation from introduced foxes and habitat alteration. Intensive post-release monitoring occurred for 5 years after releasing 93 quolls into a semi-arid environment where foxes (Vulpes vulpes) were controlled but quolls had been absent for 130 years. Radiotracking and trapping results indicated that breeding occurred in all years after reintroduction, sufficient shelter sites were present and home ranges (245 ha for females, 2778 ha for males) were similar to other sites. Although cats (Felis catus) were previously considered a threat mainly to juveniles, they were a major threat to population establishment, responsible for the majority of adult quoll deaths recorded after each of three annual releases. Predation impacts were higher in smaller female quolls and quolls living in open habitats. Evidence for selective hunting was supported by the increasing male bias and declining population recorded during trapping. Monitoring results led to an intensification of cat control and suggested that feral cat predation was likely a significant contributor to the historical decline of the western quoll and previous reintroduction failures. This threat would not have been identified without intensive post-release monitoring. Quolls are still extant 7 years after release suggesting that reintroductions can be successful without identifying all causes of decline. Our intensive monitoring program and flexible management strategy were essential for understanding the factors influencing reintroduction success and implementing appropriate mitigation methods. Although logistically challenging and expensive, we urge other practitioners to conduct intensive post-release monitoring and flexible management for reintroductions of formerly widespread species where the original causes of decline are unclear.