Song repertoire size correlates with measures of body size in Eurasian blackbirds

In most oscine bird species males possess a repertoire of different song patterns. The size of these repertoires is assumed to serve as an honest signal of male quality. The Eurasian blackbird's (Turdus merula) song contains a large repertoire of different element types with a flexible song organisation. Here we investigated whether repertoire size in Eurasian blackbirds correlates with measures of body size, namely length of wing, 8th primary, beak and tarsus. So far, very few studies have investigated species with large repertoires and a flexible song organisation in this context. We found positive correlations, meaning that larger males had larger repertoires. Larger males may have better lighting abilities and, thus, advantages in territorial defence. Larger structural body size may also reflect better conditions during early development. Therefore, under the assumption that body size is linked to overall male quality, our results are in accordance with the hypothesis that repertoire size represents an honest signal in Eurasian blackbirds that has evolved in response to sexual selection.