Disentangling the mechanisms of signal evolution in Tyrannidae flycatchers, part II: plumage elaboration evolved with migration behavior, but is also affected by diet, climate, and drift

. Animal coloration is an important communication signal that varies among taxa and affects survival and reproduction. Species-specific color is influenced by a variety of factors including phylogeny, predation, sexual selection, light and resource availability, ecological context, and/or species recognition. Tyrant flycatchers are useful to study color evolution because they are the largest family of birds, occur across broad environmental gradients, and although many genera are monomorphic with drab plumage, some are very colorful. Given the complexity of factors involved, the mechanisms influencing plumage color evolution in Tyrant flycatchers likely involve multiple drivers. In the second of our two-part paper on signal evolution in this avian family, we harnessed a large plumage color database of female and male Tyrannidae species (n = 399) to test the relative importance of geography (climate, latitude), ecology (migration behavior, forest cover, diet), and heterospecific proximity on plumage color evolution. From phylogenetically controlled analyses, we found that female color was largely driven by climate and male color was more exaggerated in migratory species. Sexual dichromatism was also affected by climate and diet, and was more pronounced in migratory species, possibly as a result of color loss in females. Pairwise comparisons between heterospecific color differences and geographic distance were generally weak and consistent with expectations under drift