The Greater Bilby (Macrotis lagotis) in Queensland, Australia: Distribution, Trends, and Threats

Medium-sized Australian mammals have suffered major declines since colonisation, with many now extinct or surviving only in intensively managed, predator-free fenced reserves or on islands. The greater bilby (Macrotis lagotis) in Queensland is an anomaly, persisting primarily in grazed rangelands with no targeted conservation management across most of its range. There has been limited field survey effort in recent decades, and very little is known about population trends or impacts of potential threats. We conducted surveys across the Queensland range of the bilby for the first time in 30 years, combining aerial surveys over 48 000 km² with 415 2-ha track plots surveyed between 2021 and 2023. We investigated the relative influence of predation, competition, and productivity on bilby presence using landscape variables and multivariate binary logistic models. The bilby's distribution, although greatly contracted since European settlement, has stabilised and perhaps expanded since the 1990s, with a current Extent of Occurrence in Queensland of 30 901 km². Temporal fluctuations in bilby presence were observed at 25% of survey plots visited at least three times, highlighting the importance of ongoing, standardised ground surveys. Within its current distribution, bilby presence was negatively correlated with distance to wooded alluvial land systems and, less strongly, effective distance to water, and positively correlated with relative greenness of the vegetation. The effects of distance to sand dune and residual land systems were not clear and are likely to be influenced by the bilby's preference for these habitats but inability to persist in them due to elevated predator densities. Predator control in wooded alluvial systems, dunefields, and residuals close to bilby populations may be more important to the bilby's persistence in the study area than limiting the spread of artificial water sources on grazing properties; however, field work is needed to inform predator density in these landforms. Ongoing monitoring and research are needed to distinguish inter-annual fluctuations from longer term population trends and better understand temporal and spatial predator dynamics. Our results provide vital context on the status of the Queensland bilby population and will underpin future research and conservation management.