Predicting potential climate-driven changes in activity time for the critically endangered Kaputar rock skink (Egernia roomi)

High-elevation ectotherms are vulnerable to climate change due to their restricted ranges, limited dispersal capacity, and reliance on external temperatures for physiological regulation. In Australia, montane regions are limited in extent and elevation, making their cold-adapted fauna especially sensitive to warming. Egernia roomi (Kaputar rock skink) is a Critically Endangered, crevice-dwelling lizard endemic to the high-elevation areas of Mount Kaputar, New South Wales, Australia. Despite its elevated conservation status, little is known about its thermal ecology or climate sensitivity. We projected potential impacts of climate change on thermal activity by quantifying the thermal buffering capacity of rock crevices, and modelling changes in activity time under future climate scenarios. Field-deployed operative temperature models were used to compare crevice and exposed microhabitats across the species' activity season. These data were combined with biophysical modelling (NicheMapR) to simulate body temperature, activity time, and water loss under present and projected climatic conditions. Crevices consistently provided strong thermal buffering, remaining up to 28 °C cooler than exposed surfaces during the day. NicheMapR model predictions aligned with observed temperatures, and predicted substantial increases in daily thermal activity time under moderate to high emissions scenarios (up to +1.6 h/day by 2090 under RCP8.5). These findings offer insight into the species’ thermoregulatory potential and highlight the importance of fine-scale microhabitat features in shaping climate vulnerability.