ORIGINAL ARTICLE

Abstract Birds have brains that are comparable in size to those of mammals. However, variation in relative avian brain size is greater in birds. Thus, birds are ideal sub-jects for comparative studies on the ecological and behavioral influences on the evolution of the brain and its components. Previous studies of ecological or behavioral correlates in relative brain size were mainly based on gross comparisons between higher taxa or fo-cussed on the relationships between the sizes of specific brain structures and the complexity of different tasks. Here we examine variation in dimensions of the brain-case, relative overall brain size and size of its compo-nents, in reference to one general ecological and behavioral task: migration. We used data from three lineages of closely related species (14 Acrocephalines, 1