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Size, plumage, moult and supposed hybrids of African Goshawks (Accipiter tachiro/toussenelii group) in DR Congo

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Parapatric A. tachiro sparsimfasciatus and A. toussenelii canescens are in a size cline from large east African to small west African birds. While their plumage colour is different, the pattern of spotting (juvenile) and barring (adult) of the breast feathers is similar. No general hybridisation is found in the contact region in Kivu: the plumage of some aberrant individuals can be due to great age or to individual variation. One supposed hybrid was obtained far from the contact region. I consider them as paraspecies. Based on direct evidence and on annual moult I conclude that the breeding period is prolonged in both taxa in equatorial DR Congo, and that it is seasonal in tachiro sparsimfasciatus in southern DR Congo. In the latter population, the postjuvenile moult starts probably just before the age of one year but it lasts many months, leaving the juvenile upper tail coverts in place for one more year. Plumage characteristics are related to habitat. The female of the woodland sparsimfasciatus is cryptically coloured, with individual variation, possibly helpful for 'image avoidance'. The male is even more variable in colour, in part age related: a 'sepia' morph is described for the first adult plumage. Older birds are grey with reddish flanks, becoming darker with age. The adult evergreen forest canescens shows enforcement of colourful advertising plumage and loss of sexual plumage dimorphism. The first adult is advertised by the late moult of the barred juvenile flank feathers in both sexes. Its juvenile is peculiar; it lacks breast spots, suggesting image avoidance, but possibly also character displacement or mimicry.
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Document Type: Research Article

Publication date: June 1, 2003

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