Breeding synchrony and paternity in the barn swallow (Hirundo rustica)

The barn swallow (Hirundo rustica) is a socially monogamous passerine which usually breeds in colonies where extra-pair copulations are frequent. Male s intensively guard their mates during the female fertile period. Since mal es are more likely to be available for extra-pair copulations when their ma te is not fertile, synchrony in timing of breeding may affect paternity of individual males. In this study, we analysed the change in mate-guarding ra te by males in relation to the fertility condition of the female, and the r elationships between breeding synchrony and density with paternity in first broods of 52 male barn swallows. Paternity (proportion of nestlings father ed in own brood) was assessed by typing of three highly polymorphic microsa tellite loci. Mate guarding by males peaked during the fertile period of th eir mates. Paternity increased as breeding synchrony in the colony increase d. Paternity of barn swallows is positively associated with the degree of e xaggeration of male tail ornaments. The relationship between male ornamenta tion and paternity was partly mediated by an effect of ornament size on bre eding synchrony. We suggest that females might delay breeding with low-qual ity males to enhance their opportunities for being fertilised by high-quali ty extra-pair males.