Multiple factors affect the evolution of repertoire size across birds

Changes in signaling repertoires across species allow for insight into the macroevolutionary forces that control signaling systems. Signaling systems are theorized to be affected by both the social and ecological environments of species. With respect to social variables, increased social complexity is thought to lead to increased vocal complexity. Although ecology can affect signaling systems in numerous ways, one potential effect of ecology is that more cluttered habitats should lead to greater reliance on non-visual (e.g. vocal) signals. To test these concepts on a macroevolutionary scale, we compiled a large dataset of avian vocal repertoires. We amassed vocal repertoires for 821 species of birds and for many of these species categorized their vocalizations into usage categories (e.g. alarm, contact). To analyze the social and ecological forces that act on repertoire evolution, we incorporated datasets with several social variables (e.g. cooperative breeding and length of social bond...