Reproductive synchrony and extra-pair mating strategy in a socially monogamous bird,Dendroica petechia

Depending on the circumstances under which extra-pair mating occurs, theory makes opposing predictions about how reproductive synchrony should influence extra-pair paternity. This study investigated which sex initiated extra-pair mating in the yellow warbler, whether extra-pair behaviour and extra-pair paternity were related to reproductive synchrony, and whether synchrony affected the mating success of all males equally. Observations and captures of individuals making territorial intrusions indicated that males initiated extra-pair mating. Spatial patterns of male territorial intrusions and of extra-pair paternity were similar. Males’ extra-pair activity was reduced when their social partner was fertile. More offspring were sired by the extra-pair male when the female nested asynchronously with that sire's social mate. Neither population-wide synchrony, nor synchrony with neighbours, however, seemed to predict the incidence of extra-pair parentage or the identity of the sire, indicating factors other than synchrony were also important. Males with more breast streaking (a plumage ornament) were more successful as extra-pair sires, and were least affected by the constraint of synchrony. Larger males were less often cuckolded, and achieved extra-pair success mainly when their partner was not fertile. Thus, male yellow warblers apparently use different mating tactics depending on their plumage and size. More generally, the results suggest how mating strategies are affected by which sex initiates extra-pair mating and by the relative contributions of within-pair and extra-pair paternity to total reproductive success.