Bacterial degradability of white patches on primary feathers is associated with breeding date and parental effort in a migratory bird

We compared the in vitro bacterial degradability of the white patch and melanized area of primary feathers of breeding male and female Pied Flycatchers Ficedula hypo‐leuca and related this variation to laying date, brood size and brood mass. Bacterial degradability of male and female white feather patches, but not of melanized areas, was positively correlated with laying date. Male Pied Flycatchers showed a positive correlation between bacterial degradability of the white patch, though not of the melanized patch, and brood size and brood mass. Feather degradability appears to be negatively related to individual quality and positively related to reproductive effort.