Difference between the vocalizations of two sister species of pigeons explained in dynamical terms

Abstract

Vocal communication is an unique example,where the nonlinear nature of the periphery can giverise to complex sounds even when driven by simple neuralinstructions. In this work we studied the case of twoclose-related bird species, Patagioenas maculosa and Patagioenaspicazuro, whose vocalizations differ only in thetimbre. The temporal modulation of the fundamental frequencyis similar in both cases, differing only in the existenceof sidebands around the fundamental frequency in theP. maculosa. We tested the hypothesis that the qualitativedifference between these vocalizations lies in the nonlinearnature of the syrinx. In particular, we propose that theroughness of maculosa?s vocalizations is due to an asymmetrybetween the right and left vibratory membranes,whose nonlinear dynamics generate the sound. To test thehypothesis, we generated a biomechanical model for vocalproduction with an asymmetric parameter Q with which wecan control the level of asymmetry between these membranes.Using this model we generated synthetic vocalizationswith the principal acoustic features of both species. In addition, we confirmed the anatomical predictions bymaking post mortem inspection of the syrinxes, showingthat the species with tonal song (picazuro) has a more symmetricalpair of membranes compared to maculosa.