Birds of the highlands and escarpments of Angola and Namibia: ornithological significance, avifaunal patterns and questions requiring further study
Keywords:Angola, avifauna, endemism, escarpments, highlands, Namibia
The highlands and escarpments of Angola and Namibia are recognised as an important region for the evolution and conservation of birds. However, no comprehensive study of the avifauna, and its potential evolutionary origins and links, has been made. As a basis for further study, we draw up a comprehensive list of birds largely confined to the region, together with details of links to nearest relatives, including birds from all relevant levels of the evolutionary process and taxonomic hierarchy (isolated populations to genera). A total of 233 Evolutionarily Significant Units were identified, comprised of four genera, 37 species, 71 subspecies and 121 taxa with isolated populations. The escarpment holds a richer diversity of ESUs than the Afromontane region, although most escarpment ESUs are separated from relatives by a break in the forest zone of about 320 km. Hence few Northern Escarpment ESUs are differentiated even subspecifically (15 of 111; 14%), and most (n = 92; 83%) involve isolated but undifferentiated populations. However, further south along the escarpment distinctiveness increases; 15 of 64 (23%) forest ESUs on the Central Escarpment are differentiated subspecifically. In contrast, the ESUs of the highlands are typically isolated from their nearest vicariants by a much larger gap. Although only 44 ESUs are found here, 26 of them have differentiated to the subspecies level and seven to species level. In the highlands, lower diversity is paired with a greater degree of differentiation, both of which are known to be the result of extreme isolation. Preliminary research has shown that the Angolan Afromontane forests are located in an area of high climatic stability, and that they constitute an important historical link between the montane bird communities of East Africa and the Cameroon mountains. Our simple analysis reveals some potentially interesting patterns but relies on largely-untested assumptions regarding the closest relatives of the region’s significant bird taxa (ESUs). More detailed and extensive studies of the origins and relationships of key bird taxa are needed to explore whether counterintuitive patterns exist that are currently being masked.
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