Effect sizes of predictors of difference in plumage colour between the sexes. Effect size of (a) sexual dichromatism and (b) sexual difference in colour elaboration based on single predictor models. Effect size of (c) sexual dichromatism and (d) sexual difference in colour elaboration based on multiple predictor models (N = 273 species). Shown are the means of the model coefficients for the 1,000 phylogenetic linear models and the corresponding 95% confidence intervals. N indicates the number of species included in the analyses (determined by data availability)