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

The Black Harrier (Circus maurus) is listed as Endangered by the IUCN and
is an endemic, range-restricted habitat specialist within southern Africa.
Our study aimed to assess the current and potential future changes in the
distribution of the Black Harrier, 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 Black
Harriers during breeding and non-breeding periods). Using tracking data of
13 tagged adults and 307 nest locations collected from 2000-2015, we
implemented a Species Distribution Modelling workflow, making use of 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 three
Shared Socioeconomic Pathways to assess the potential impact of climate
change on the geographical distribution of the Black Harrier. Our study
shows that a disproportionately low percentage (32%) of the area currently
climatically suitable for the Black Harrier hosts suitable breeding
habitat for the species. Climate change modelling projects extensive range
contractions (up to 83%) of both Black Harrier 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 ca. 20% and 10% of Black
Harrier’s breeding and all-year-round ranges, respectively, fall within
Protected Areas (PAs). Prioritising, protecting, and managing the
remaining habitat patches within the projected future range by including
them within PA networks, will be critical to promote the persistence of
the Black Harrier.