Climate change and montane refugia: predicted distribution range contractions of the Drakensberg Rockjumper Chaetops aurantius and Mountain Pipit Anthus hoeschi

Summary

Climate change alters species distributions, and range-restricted species are particularly vulnerable. Our study used species distribution modelling under climate change for two montane bird species categorised as Near Threatened by the IUCN. The Drakensberg Rockjumper Chaetops aurantius and Mountain Pipit Anthus hoeschi are confined to the high-elevation mountains of South Africa and Lesotho. Understanding how their life histories mediate climate vulnerability is essential for conservation prioritisation. We used ensemble species distribution models within the BIOMOD 2 framework to predict changes in habitat suitability for both species under the high-emission SSP5-8.5 scenario for the years 2050–2080, relative to the current climate (1970–2000). The models predicted that both species are likely to experience contractions in their distribution ranges by the 2080s, with suitable climatic space persisting primarily in high-altitude areas of Lesotho and lower Drakensberg slopes. The Drakensberg Rockjumper exhibited severe declines, with mean suitability decreasing by 36.4% by 2050 and 63.5% by 2080, while the Mountain Pipit showed moderate declines of 4.4% and 18.9%, respectively. In terms of variable importance, the Drakensberg Rockjumper distribution is limited by temperature (22.4% importance), whereas the Mountain Pipit is limited by elevation (32.7%). Elevation-dependent patterns showed greater losses at lower elevations (1,500–2,000 m) for both species, with the Lesotho Highlands (>2,500) serving as climate refugia. Even within optimal high-elevation habitats, the Drakensberg Rockjumper’s distribution is projected to contract further. Its greater vulnerability to range loss than the Mountain Pipit is directly attributable to its sedentary life history and narrow habitat specificity, which limit its capacity to track shifting climatic conditions. We recommend reassessing the Drakensberg Rockjumper’s IUCN status, prioritising protection of high-elevation refugia, and considering assisted colonisation as a last-resort conservation measure. Future studies on physiological and ecological constraints will enhance understanding of their capacity to cope with climate change.