Where have the diggers gone? The occupancy and distribution of the long-nosed potoroo and the southern brown bandicoot in the Gariwerd landscape.

Context: Australia's critical weight range mammals are declining in abundance at an accelerating rate, predominantly due to predation, habitat clearing, and irregular fire regimes. 'Ecosystem engineers' or 'diggers' are responsible for a vital process called biopedturbation and contribute to the health of native vegetation. The Grampians National Park (Gariwerd) is a diverse and unique landscape surrounded by vast mountain ranges and isolated by agriculture. Two of the Grampian's diggers, the long-nosed potoroo (Potorous tridactylus) and the southern brown bandicoot (Isoodon obesulus), are considered at risk of local extinction, as extensive research in the last decade has failed to detect either species. Aims: (1) to develop species distribution models to identify potential habitat for long-nosed potoroos and southern brown bandicoots within the Grampians National Park; (2) to validate these species distribution models through camera trapping to try to detect potoroos and bandicoots and (3) recommend conservation strategies for the Grampians National Park based on any detections of these two species. Methods: Species distribution models were developed using historic detection records of southern brown bandicoot and long-nosed potoroo. Based on the models, 180 sites were selected across the Gariwerd landscape for targeted surveys. Motion sensor cameras were deployed at all 180 sites for 21 nights. All animals detected on the cameras were identified, and occupancy models were built for potoroos and bandicoots. Results: Cameras detected the southern brown bandicoot at 42 sites and the long-nosed potoroo at six sites. Site occupancy for bandicoots was positively influenced by structure density 40-100cm and wiregrass percentage covering and negatively influenced by NDVI and 4 the percentage coverage of fern. Site occupancy for the long-nosed potoroo was positively influenced by structure density 40 to 100cm. Conclusion: We were able to demonstrate the utility of species distribution models to detect low-density populations of potoroos and bandicoots in the landscape and identify factors that influence occupancy. This research highlights that whilst undetected for many years, bandicoots and potoroos remain in the Gariwerd landscape. Land managers need to prioritise predator management, continually monitor populations, consider future translocation or captivity breeding plans, and release programs to disperse species into the broader landscape to re-establish the species back into their former ranges. In doing so, we could dramatically reduce the risk of local extinction and improve the Grampian's landscape's health.