Habitat suitability modelling of the North Flinders Ranges thick-billed grasswren Amytornis modestus raglessi reveals dynamic shifts at the landscape scale

Context The threatened subspecies of thick-billed grasswren, Amytornis modestus raglessi, occupies dense chenopod shrublands on the lower slopes and peripheral drainages of the North Flinders Ranges, South Australia. A decline in grasswren numbers was observed around 2012, after two preceding years of exceptionally high rainfall. Profound reduction in observed numbers was also evident in 2019, the second successive year of exceptionally hot and dry conditions, in areas where they had previously been numerous. Aims To identify environmental factors influencing A. m. raglessi habitat suitability using habitat suitability modelling, and to better understand possible drivers of grasswren decline and distributional changes between pre- and post-2012 periods. Methods Random forest modelling was used to predict grasswren habitat suitability in response to mapped environmental variables including remotely sensed vegetation, soil and landscape properties. Habitat suitability maps were produced for two separate periods, 1994–2011 and 2012–2023, and compared. An ornithological field survey was undertaken to validate the modelling, and vegetation time-series used to examine areas showing contrasting habitat suitability changes. Key results Mapped soil properties and the minimum green vegetation cover value were the most important habitat suitability predictors. The overall predicted area of habitat (suitability >50%) declined by 25% between the 1994–2011 and 2012–2023 periods. Changes included an expansion of high-suitability habitat in the west, and habitat contraction in south-eastern areas of the distribution. Time-series vegetation data showed that lower bare ground cover and higher non-green vegetation cover occurred in an area with marked reduction in predicted habitat suitability. Conclusions Habitat suitability modelling successfully identified key environmental drivers and demonstrated habitat shifts between periods. Soil properties and minimum green vegetation cover confirmed that water stress responses are fundamental to grasswren distribution. Modelling identified areas of habitat contraction that highlight conservation priorities, while also demonstrating management effectiveness in improving habitat quality. Implications These methods provide spatially explicit guidance for prioritizing conservation efforts for this subspecies and thick-billed grasswrens broadly. Demonstrated habitat improvement following reduced grazing at Witchelina illustrates the practical value of this modeling approach. Such methods are increasingly essential for land managers to understand biodiversity responses and species distributions under climate change.