MALE COLORATION AND SPECIES RECOGNITION IN SYMPATRIC FLYCATCHERS

Currently favoured views for explaining ornaments in males emphasize female preference such that females benefit from increased offspring production, good genes of the offspring, or the attractiveness of sons. Results from long-term studies in the pied flycatcher Ficedula hypoleuca suggest that factors associated with species recognition may also be important for male coloration. In sympatry the collared flycatcher F. albicollis is dominant in competition for nesting sites over the pied flycatcher. Bright pied flycatcher males resemble collared flycatcher males and suffer from interspecific interference, whereas dull. and female-like males can acquire nesting sites close to those of the collared flycatcher. (A similar aggression release mechanism had previously been suggested to influence the evolution of colour differences in coral reef fishes.) Additionally, the risk of hybridization was low for the dullest pied flycatcher males, resurrecting the idea that avoiding mating with wrong species might currently be under selection. Thus interspecific effects related to species recognition can probably explain the dull plumage colour of pied flycatcher males in sympatry. In allopatry, intraspecific sexual selection for bright coloration in males seems to be weak, and even a low level of gene flow between sympatric and allopatric populations may maintain the high variation in this highly heritable trait.