Do female pied flycatchers seek extrapair copulations with familiar males?A test of the incomplete knowledge hypothesis

In birds with biparental care, great variation exists in the frequency of e xtrapair paternity. Several hypotheses have been proposed to account for th is variation. We tested the incomplete knowledge hypothesis, which states t hat females are constrained in their knowledge of male quality and that thi s influences their willingness to engage in extrapair copulations (EPC). By selective removal and release of female pied flycatchers Ficedula hypoleuc a, we created a situation where females finally settled with a social mate close to the site where a former social mate was breeding. According to the incomplete knowledge hypothesis, this would lower the threshold for female s to seek extrapair copulations in cases where their former social mate was of higher quality than the one finally chosen. The hypothesis was not supp orted because manipulation of female settlement did not increase frequency of extrapair paternity, not even in cases where the female nested close to the previous mate and the current mate apparently was of lower quality beca use he was younger and more dull colored. However, we found that when extra pair paternity did occur, the cuckolder tended to be a familiar male (i.e., the female's initial social mate).