Data and code from: Song complexity in suboscine birds: Evolutionary drivers and ecological constraints

Acoustic signal complexity varies widely in animals from single notes to
highly sophisticated vocal displays. In birds, vocal complexity can evolve
as an honest signal of individual quality driven by sexual selection.
However, this hypothesis is rarely explored in conjunction with
alternative drivers, including competition for ecological resources
(social selection) and intra-group communication, both of which may favour
increased signal complexity. Using Bayesian phylogenetic models, we test
whether these alternative mechanisms predict the complexity of innate
songs in 1,288 species of suboscine passerine birds, while accounting for
ecological constraints on sound production, transmission and detection. We
found that overall song complexity was reduced by sexual selection
(estimated from mating systems), and declined with body size and
vegetation density. Conversely, note count and song length increased in
territorial species, particularly those using song to defend year-round
territories during the non-breeding season. These findings challenge the
common assumption that sexual selection is the main driver of increased
signal complexity, and highlight the role of social selection via
territorial competition as a factor increasing the temporal complexity of
songs. Our results suggest that signal complexity depends on social,
cultural and ecological contexts, reflecting a combination of multiple
inter-related drivers and constraints.