SEX RECOGNITION BY MALE PIED FLYCATCHERS IN A POPULATION WITH LITTLE SEXUAL DIMORPHISM IN PLUMAGE COLOR

In Central and Eastern Europe most breeding male Pied Flycatchers Fice dula hypoleuca have a brown, female-like plumage colour, whereas north ern and southern populations are darker. Recent studies in a dark popu lation have demonstrated the importance of sexual dimorphism in plumag e colour for sex recognition; female-like males are treated as females . In the present study I tested whether male Pied Flycatchers have evo lved an improved ability to discriminate between the sexes in an area where flycatchers show little sexual dimorphism in plumage colour. I f ound that resident, male Pied Flycatchers responded with courtship dis play to a caged, female-like male, as if the caged intruder was a visi ting female. This result demonstrates that sex recognition by visual c ues is imperfect in the Pied Flycatcher. Possible adaptive explanation s for the evolution of light-coloured populations of Pied Flycatchers are discussed.