Avian vocalizations and phylogenetic signal

The difficulty of separating genetic and ecological components of vocalizations has discouraged biologists from using vocal characters to reconstruct phylogenetic and ecological history. By considering the physics of vocalizations in terms of habitat structure, we predict which of five vocal characters of herons are most likely to be influenced by ecology and which by phylogeny, and test this prediction against a molecular-based phylogeny. The characters most subject to ecological convergence, and thus of least phylogenetic value, are first peak-energy frequency and frequency range, because sound penetration through vegetation depends largely on frequency. The most phylogenetically informative characters are number of syllables, syllable structure, and fundamental frequency, because these are more reflective of behavior and syringeal structure. Continued study of the physical principles that distinguish between potentially informative and convergent vocal characters and general patterns of homology in such characters should lead to wider use of vocalizations in the study of evolutionary history.