Climate change modelling indicates extensive range contractions for a scarce southern African endemic and minimal protected area network within its future climatically suitable range

Circus maurus (Black Harrier) is a globally endangered, endemic, range-restricted habitat specialist within southern Africa. Our study aimed to assess the current and potential future changes in the distribution of the C. maurus, as well as to quantify the most suitable areas within both the “breeding range” (i.e., areas used for nesting) and the “all-year-round range” (i.e., areas used by C. maurus during breeding and nonbreeding periods). Using tracking data of 13 tagged adults and 307 nest locations collected from 2000 to 2015, we implemented a species distribution modelling workflow, using a data-driven process of variable selection and model optimization. Model optimization included hyper-parameter tuning, which is the process of finding the optimal settings for model parameters to improve predictive performance. Additionally, we used general circulation models and 3 shared socioeconomic pathways to assess the potential impact of climate change on the geographical distribution of the C. maurus. Our study shows that a disproportionately low percentage (32%) of the area currently climatically suitable for the C. maurus hosts suitable breeding habitat for the species. Climate change modelling projects extensive (up to 83%) range contractions of both C. maurus breeding and all-year-round ranges by 2061–2080. Core areas of the projected future range are in the coastal, Overberg and mountain Fynbos/Renosterveld regions of the Western Cape province of South Africa. Furthermore, only ~20% and 10% of C. maurus’s breeding and all-year-round ranges, respectively, fall within protected areas. Prioritizing, protecting, and managing the remaining habitat patches within the projected future range by including them within protected area networks, will be critical to promote the persistence of the C. maurus.