Koalas on Australian Islands

Abstract Despite substantial conservation and research investments, populations of the endemic and iconic koala (Phascolarctos cinereus) continue to decline across much of their Australian range, resulting in their Endangered status. Island refugia may offer a crucial strategy for koala conservation but also have the potential to become ecological traps, leading to further population declines across the species’ range. Despite this, systematic efforts to map and record koala occurrences across Australian islands are lacking. This has left significant gaps in understanding the status, origin, and distribution of island koala populations, the factors influencing their persistence, and the extent of threats they face. This study aimed to address these gaps by creating the first comprehensive database of koalas on Australian islands, characterising their distribution, status, and history of occurrence. We integrated this database with spatial mapping software to analyse the geographic distribution and extent of anthropogenic and environmental threats across Australian island. Additionally, we applied path analysis to model the effects of abiotic, biotic, and anthropogenic factors on island koala persistence. We found records of koalas (historical and/or current) on 37 Australian islands, spanning subtropical to temperate climates, with > 15 islands currently supporting koala populations. Among the threats to extant island koala populations analysed, anthropogenic land use and overbrowsing exhibited a consistent spatial trend, both being more pronounced at lower latitudes. These findings can inform conservation and management actions by identifying islands where threat mitigation is required and highlighting those that may serve as suitable refuges for future translocation and koala conservation efforts.