Colorful ornaments in females are suggested to have evolved and be maintained by sexual selection. Although several studies have evaluated this idea evidence is still equivocal. Results from empirical studies have been compilated in reviews, but quantitative analyses have seldom been performed. Here, using a meta-analytic approach, we show that evidence from empirical studies conducted in birds, supports the ideas that colorful female ornaments are positively associated with individual condition, reproductive performance, and male-mate preferences. Hence, females’ colorful traits, in birds, likely evolved and are maintained by sexual selection.

A systematic search of literature was performed using PRISMA method (Preferred Reporting Items for Systematic Reviews and Meta-Analyses). We looked for literature trough the search engines Scholar Google and Web of Science, using the keywords: “female bird ornament”, “female bird ornamentation”, “female bird traits”, “female bird quality”, “female bird condition”, “female bird attractiveness”, “female bird color”, “female bird colour”, “female bird coloration”, “male bird choice”, “male bird preference”. References within papers were also checked. Last search was conducted on October 2020.

Studies with missing reports on statistical values, independent estimates for each sex, and type of coloration were excluded. Seventy-six studies were found but only 52 satisfied the inclusion criteria. Studies included were performed in 37 species with monogamous mating system, four with facultative polygamous, and only one with polygamous (eight species were used in more than one study). Carotenoid-dependent ornaments were present in 25 species, melanin based in 16, and structural colorations in 10. Intensity of coloration was estimated as number and/or size of colored structures/patches, spectrophotometry, digital image analysis (RGB or LBA), and visual rank scales (color charts and visual rank score).

Through independent meta-analyses we evaluated evidence for the association of colorful female ornaments with condition, reproductive performance, and male preferences. Studies assessing more than one of these associations were included in more than one meta-analysis. Effect sizes reported as Pearson’s correlation coefficients (r) were directly extracted from papers, otherwise were calculated using the square root of determination coefficients in regression models (R²). Pearson’s coefficients were subsequently transformed to Fisher’s z-values for statistical analyses. When studies reported t or F values, Hedges’ g was calculated to obtain effect size. All effect sizes were weighted using the variance value.