Morphological traits influence food choice by coexisting New World warbler (Parulidae) species

New World wood warblers (Parulidae) represent one of the most dramatic adaptive radiations in North America. However, the ecological bases for these species' evolved morphological differences remain poorly understood, especially considering how many foraging and habitat studies the family has inspired. We hypothesized relationships between morphology and diet in parulids. We combined a principal component analysis (PCA) of 18 external morphological traits from 11 species with stomach content data from coexisting species in one breeding community in Louisiana and three wintering communities in Jamaica. The primary morphological differences, corresponding with the first three PCA axes, were body size, morphological adaptations for aerial foraging versus gleaning, and arboreal versus ground adaptations. Our analysis revealed little morphological overlap among all 11 species. Diet differences among the bird species showed a significant relationship to the first two PCA axes of morphological traits. For five coexisting, foliage-gleaning species wintering in Jamaican wet limestone forest, larger warblers ate larger beetles and Orthopterans but not larger ants. In analyses including all four communities, warbler species with aerial foraging morphologies consumed a greater proportion of winged insects than other warbler species. Overall, our results indicate that food and foraging have likely played an integral role in the morphological diversification and coexistence of Parulidae.