The beak shape variation of Neotropical passerines is explained more by body size than diet

Abstract Beak morphology in birds is often linked to diet. In this study, we aimed to analyse whether diet or other drivers, such as allometry or species relatedness, explain the morphological beak variation of Neotropical passerines and whether there are specific predictors for beak shape variation for the two passerine suborders, Oscines and Suboscines. We analysed beak measurements (length, width, and depth) as response variables and body size, diet, and phylogenetic distance as predictor variables. After controlling for allometry which had major impact on beack shape, beak length and depth exhibited significant differences across diet categories and between suborders. Compared with Oscines, the beak shape of Suboscines is more influenced by species relatedness, probably owing to niche conservatism. Our findings suggest an adaptive convergence between the two passerine suborders in the Neotropics, driven mainly by allometric constraints rather than by the trophic niche.