Multiple signals for multiple messages: great tit, Parus major, song signals age and survival

Birdsong is a well-known sexually selected trait that plays a major role in female choice and male – male interactions. Although birdsong has been studied for many years, it has only recently been suggested that it is a multifaceted signal that could encompass multiple sexually selected traits. According to the theories on the evolution and maintenance of multiple sexually selected signals, the different components of birdsong may signal multiple, redundant or unreliable information on male quality. We used a cross-sectional approach to examine whether the expression of song in the great tit was differentially related to any of three measures of quality: age, condition and survival. We analysed several informative characteristics in great tit song concerning diversity, output, performance and consistency to see whether different traits were simultaneously related to the studied quality parameters, or if, in contrast, each song trait was related to only one of the measures of quality. Song consistency and repertoire size were strongly related to only one of the studied parameters (age and survival, respectively), indicating that different song traits signal specific quality characteristics, and providing, therefore, evidence to support the multiple-signal hypothesis. Moreover, measures of song performance and song output (phrase and strophe rate) correlated positively with repertoire size, which might indicate that, at the same time, great tit song is signalling redundant information. In addition, some song characteristics did not correlate with any of the quality parameters measured, suggesting that those song traits might provide unreliable information.