Patterns of song evolution and sexual selection in the oropendolas and caciques

Although oscine bird song is widely thought to have evolved under the influence of sexual selection, few studies have used phylogenetic comparative methods to investigate how these vocalizations have changed historically. In the present study, we use a molecular phylogeny based on mitochondrial sequence data to reconstruct vocal evolution in the oropendolas and caciques, an oscine group with diverse taxon-specific song patterns and a wide range in levels of sexual size dimorphism. Our reconstructions show that large changes in song organization and structure have occurred on branches of the phylogeny with relatively high levels of size dimorphism. The particular vocal components that changed, however, often differed in different phylogenetic lineages. These patterns indicate that sexual selection has had important influences on song evolution in these birds, but has targeted different components of song in different taxa. Our results provide insight into how sexual selection influences bird song and suggest directions for future research to uncover the behavioral mechanisms driving vocal evolution.