Extra-pair paternity success relative to trill and male quality, with effects that remained significant after correcting for multiple testing in bold.

Trill and male quality measures were the dependent variables, and success siring offspring in other males’ nests (sired at least one offspring versus did not sire any) was the independent variable in mixed-effects models controlling for male identity and year, and (for trill measures only) trill type, pitch, trill duration, and the time of the trill in the song. Age, the only categorical dependent variable, was modeled with logistic regression; the estimated difference is the difference in log-odds of being an after-second-year male if the male is polygyous, and the effect size is partial r. For continuous variables, estimated differences are between successful and unsuccessful males, with a positive difference indicating that the more successful males had a higher score for quality, and the effect estimate is Cohen’s d. Abbreviations: obs., observations. CI, confidence interval. H:L, Heterophile:Lymphocyte ratio. PB, playback.