Under the Biological Species Concept, eight species of Accipiter breed in sub-Saharan Africa. The point of view that all African Goshawk A. tachiro populations belong to one biological species may be compared to that for Shikra A. badius, the only other strongly polytypic African Accipiter. The latter's two African populations differ slightly from each other in migratory and transitional moult strategies, but markedly from some of the Asian races . Populations of the widespread African Goshawk are even more geographically distinct in size and plumage characteristics (intensity of coloration and pattern) than those of Shikra . This variation is, in part, individual but mostly related to age and sexual dimorphism. Birds of Africa  grouped all populations into one species, whereas Handbook of the Birds of the World  recognised two, although Kemp, in a subsequent work, also treated them as a single species . Dowsett & Dowsett-Lemaire  stated that the southern and eastern tachiro group 'can be every bit as much a forest bird' as the equatorial toussenelii group. These authors also remark that both do have a similar, peculiar display flight (contra Birds of Africa  and Kemp ).
Louette [8, 9] observed that morphological characteristics of this bird vary according to habitat (and apparently also according to the presence of the similar Chestnut-flanked Sparrowhawk A. castanilius!). In evergreen forest habitat, African Goshawks are rather small, with colourful adults in both sexes, the females being quite 'masculine' in this respect. Louette  concluded from a detailed study of specimens that size and plumage morphology follow a west-east cline in West Africa (the presence of the smallest birds in the West being the reason for unsubstantiated claims that Chestnut-flanked Sparrowhawk occurs there). In the larger eastern and southern African woodland races, the female is more cryptically coloured.
African Goshawk is the only Accipiter with endemic circum-African island (Pemba, Bioko) and Ethiopian montane races. These three subspecies, like the evergreen forest-belt birds, show enforcement of colourful advertising plumage and loss of sexual plumage dimorphism, and are also rather small (this is especially true for the island birds, the Ethiopian race takes a more intermediate position). A habitat-related trade-off in morphological characteristics comes to mind as an explanation (possibly also, in part, character displacement). This may be the result of adaptation to a relatively closed environment in which the needs for sexual attraction overrule the benefit of crypsis in the female .
The monotypic Chestnut-flanked Sparrowhawk, on the other hand, is only present in the Lower Guinea forest region. It has been claimed to occur in Upper Guinea and in Ethiopia, but without proof. The photograph included here, which was taken on 29 April 2003, at Wondo Genet, Ethiopia, by Paul Ellis, clearly shows the following characteristics, all typical of the adult of the endemic race of African Goshawk A. t. unduliventer in comparison with adult Chestnut flanked Sparrowhawk:
- Smallish head (noticeably broader in castanilius)
- No bare yellow skin in front of the eye
- Throat grey, not white
- Barring on breast rufous-brown, not dark grey (note that the barring in castanilius is erroneously described as 'chestnut' in Birds of Africa )
- Flanks rufous, not dark red
- Back grey, not blackish
- Feet plain orange, not overlaid with blackish green (colour in museum skins).
The tail pattern fits both species. The Ethiopian race of African Goshawk is rarely mentioned in the literature and no photographs of the bird in life were previously known to me. The bird depicted here is probably a male, the female being slightly less colourful and more bulky.
- Brown, L.H., Urban E.K. and Newman, K. (eds) 1982. The Birds of Africa. Vol 1. London, UK: Academic Press.
- Dowsett R.J. and Dowsett-Lemaire F. 1993. A Contribution to the Distribution and Taxonomy of Afrotropical and Malagasy Birds. Tauraco Research Report No. 5, Liège: Tauraco Press.
- Herremans, M. & Louette, M. 2000. A partial post-juvenile molt and transitional plumage in the Shikra Accipiter badius and Grey Frog Hawk Accipiter soloensis. J. Raptor Res. 34: 249-261.
- Kemp, A. 1994. African Accipiters. In: del Hoyo, J., Elliott, A. and Sargatal, J. Handbook of birds of the World. Vol 2. Barcelona: Lynx Edicions.
- Kemp, A. and Kemp, M. (1998) SASOL Birds of Prey of Africa and its Islands. London, UK: New Holland.
- Louette, M. 1992. The identification of forest Accipiters in central Africa. Bull. Br. Ornithol. Cl. 112: 50-53.
- Louette, M. 2000. Evolutionary exposition from plumage pattern in African Accipiter. Ostrich 71: 45-50.
- Louette, M. 2001. Redescription of African Goshawks Accipiter tachiro on Bioko Island and the adjacent mainland. Ostrich 72: 24-27.
- Louette, M. 2003. Size, plumage, moult and supposed hybrids of African Goshawks (Accipiter tachiro/toussenelii group) in DR Congo. Ostrich 74: 18-29.