Body Mass and Beak Size Drives Acoustic Evolution in Manakins

Abstract In this study we investigated the drivers of acoustic diversification in the advertisement calls of manakins (Pipridae), a Neotropical family of suboscine birds. We investigated how environment, morphological constraints, and sexually selected traits influenced spectral and temporal parameters in the advertisement calls of manakins. We analyzed 756 advertisement call recordings from 44 manakin species, and then used phylogenetic generalized least squares (PGLS) to test the influence of different drivers on these acoustic traits, along with generalized linear models (GLM) to test for Bergmann's rule. The results showed that body mass was positively related to call duration, consistent with the hypothesis that larger species have greater energy reserves for acoustic communication. Beak size was negatively related to call pace, as predicted by the biomechanical trade-off between force and speed in bill movement. Beak size also influenced peak frequency, with larger beaks producing lower peak frequencies. Lower average temperatures were directly related to call duration, suggesting energetic limitations on vocalization. No relationships were found between sexual dichromatism or display complexity and any call trait, although the smaller sample sizes for these analyses limit their conclusiveness. We also observed no evidence of Bergmann's rule acting on song variation. Significant phylogenetic signals were detected in peak frequency, frequency bandwidth, maximum frequency, and call duration, indicating that shared ancestry strongly influences these traits. We conclude that morphological constraints, particularly body mass and beak size, play important roles in shaping song differentiation in manakins, especially for call duration and pace. However, these drivers explain only a portion of the variation, with stochasticity likely accounting for much of the remaining song diversity. The lack of support for frequency allometry and sexual selection trade-offs highlights the complexity of acoustic evolution and the need for further study, particularly with larger datasets for sexually selected traits.