Identification of the landscape and bioclimatic characteristics that contribute to maintaining the allopatric distribution ranges of the Northern Black Korhaan Afrotis afraoides and the Southern Black Korhaan Afrotis afra

Abstract

The Northern Black Korhaan Afrotis afraoides and the Southern Black Korhaan Afrotis afra were previously considered conspecific, but were subsequently separated based on habitat, plumage, displays and vocalisations of the males and genetic differences. The Northern Black Korhaan is endemic to predominantly north of the Great Escarpment in southern Africa. In the southern part of its range in South Africa, it inhabits mostly the Nama-, Succulent Karoo and Grassland Biomes. The Southern Black Korhaan is a South African endemic and inhabits the Fynbos, Nama- and Succulent Karoo and Grassland and Albany Thicket Biomes to the west and south of the Great Escarpment. The purpose of the present study is to determine which bioclimatic and topographical characteristics contribute to maintaining the allopatric distribution ranges of the Northern and Southern Black Korhaan. The bioclimatic and topographical characteristics of the birds' distribution ranges and the area between them were described using habitat suitability modelling and by sampling these variables at the localities of the presence and pseudoabsence records of the birds in their respective breeding ranges and absence records from the area between their respective distribution ranges. The Northern and Southern Black Korhaan do not occupy the area between their respective distribution ranges, because some of the terrain in this area has a slope >6°. The remainder of the area is on terrain with a slope ≤6°, but the precipitation is too low (median of 216 mm), which may result in an insufficient food supply to the birds, especially when breeding, because they are polygynous. In addition, the low precipitation results in reduced ground cover by the Nama-Karoo and succulent Karoo vegetation, which in turn results in a possible increase in the predation rate of the birds. Consequently, the area is therefore not suited to and therefore not occupied by either species.