Age-dependent expression of song in the collared flycatcher, **Ficedula albicollis**

Theory suggests that male ornaments should be reliable signals of age, with more elaborated ornaments reflecting superior quality in terms of experience and/or viability. Bird song is immensely involved in sexual selection, thus not-surprisingly, it usually shows age-dependent variation. Although the collared flycatcher Ficedula albicollis has been intensively studied for its sexual traits, and female preference for male age is expected to be strong, there is no quantitative information on age-dependent expression of song in this species. Here, we fill this gap and, based on phenotypic correlations, we report the relationship between age and several song features. Repertoire size was consistently smaller in yearlings than in older males, but it also tended to increase after the second year of breeding. In a meta-analysis of effect sizes using data from the literature, we found that the strength of the relationship between age and repertoire size in the collared flycatcher is similar to patterns observed in other passerines. Song rate was inversely related to age, as yearlings sang at higher rates than older males. Generally, effect sizes for the relationship between age and other song traits were of medium level on average, and had broad confidence intervals. Song traits covaried with survival in a direction suggesting that differences in song between age categories are unlikely to result from phenotype dependent survival. Our results generally support the hypothesis that song holds the potential to function as a reliable indicator of male age in the collared flycatcher. However, it seems that not all song traits are unambiguously more expressed in older males than in yearlings