Volume 77, Issue 7, July 2023

Almost 200 years ago, Darwin found that Galápagos finches’ beaks were different shapes in birds with different diets. Today, it is well established that phylogeny, allometry, and ecology can also be key factors in shaping skulls. Yet, the influence of specific aspects of ecology, as well as life history, on morphological evolution remains poorly constrained. Here, we examined whether three novel factors also influence the shape of bird skulls and rates of evolution: habitat density, migration, or developmental mode. To do so, we combine high-resolution 3D quantification of skull shape with dense taxonomic sampling across living birds. Our analyses revealed that skull shape varies in birds based on vegetation density in their habitats and the extent to which they migrate, but not their developmental mode. Despite these differences, habitat density, migration, and life history all influence the rate at which bird skulls evolve. Birds evolved fastest if they live in densely vegetated habitats, migrate long distances, or are precocial. This adds to the growing body of evidence that avian skull evolution is affected by a diverse range of factors and suggests that habitat density, migration, and life history should be considered in future analyses on drivers of phenotypic evolution.