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When closely-related species are sympatric, there will be a coevolutionary selection pressure for species-specific characteristics to be developed, e.g. in plumage-colour. Because the three European Ficedula flycatchers have similar ecological requirements, we expected that some kind of interspecific signalling system had been evolved in sympatric regions of species of this genus. By using museum specimens we studied the seasonal and geographical variations in plumage-colour of the males of the three European species of the genus, and found that in areas of sympatry with F. albicollis, the subdominant species, F. hypoleuca, was lighter coloured than in allopatric areas. The plumage-colour of F. hypoleuca gradually changes from light in sympatric areas to dark in allopatric areas. A similar pattern was found for the eastern species F. semitorquata. The results of this paper, therefore, support the character displacement hypothesis.