The blue tit's song is an inconsistent signal of male condition

Abstract

Sexually selected traits are often hypothesized to signal male condition or quality, though empirical evidence is mixed, and a number of alternative models of sexual selection do not require condition dependence. We examined the relationship between various measures of condition and dawn songs in male blue tits (Cyanistes caeruleus). We detected 6 largely independent measures of variation (i.e., variables) in these songs. None of these variables were related to blue tits' ultraviolet–blue plumage, a demonstrated sexual signal, thus failing to support the redundant signal hypothesis. We found some evidence that the song variables we measured signaled male quality. There were correlations between body size and certain song traits, though neither male age nor male recapture in the subsequent breeding season (apparent local survival) predicted any song variation. We combined our results with published effect sizes comparing blue tit song with male quality variables using meta-analysis and found that a few song measures are correlates of male quality, though as in our field data, neither male age nor survival appeared related to song. Our relatively large sample sizes (>60), combined with our meta-analytical integration of 89 effect sizes, make the results regarding the signaling value of our measured components of blue tit song robust. These results demonstrate that 1) only certain aspects of signal variation may be condition dependent and 2) even when components of a sexual signal appear correlated with condition in some studies, these signal components may be unrelated or inconsistently related to a variety of condition indices.