Song complexity in suboscine birds: evolutionary drivers and ecological constraints

Area of Science:

• Animal Behavior
• Bioacoustics
• Evolutionary Biology

Background:

• Vocal complexity in animals varies greatly, with bird songs often cited as examples of honest signals driven by sexual selection.
• Alternative drivers like social selection and intra-group communication may also favor increased signal complexity, but are less explored.

Purpose of the Study:

• To investigate the drivers of innate song complexity in 1288 species of suboscine passerine birds.
• To test whether sexual selection, social selection, or ecological factors best predict song complexity.
• To challenge the assumption that sexual selection is the primary driver of vocal complexity.

Main Methods:

• Utilized Bayesian phylogenetic models to analyze song complexity in a large dataset of suboscine passerine birds.
• Accounted for ecological constraints on sound production, transmission, and detection.
• Estimated sexual selection from mating systems data.

Main Results:

• Song complexity was reduced by sexual selection and decreased with larger body size and denser vegetation.
• Note count and song length increased in territorial species, particularly those defending territories year-round.
• Social selection via territorial competition emerged as a significant factor increasing temporal song complexity.

Conclusions:

• Sexual selection is not the sole or primary driver of increased signal complexity in bird songs.
• Social selection, particularly territorial competition, plays a crucial role in shaping song complexity.
• Song complexity is a result of multiple interacting social, cultural, and ecological factors and constraints.