Plumage convergence resulting from social mimicry in birds? A tetrachromatic view

Abstract

Social mimicry may lead to convergent evolution when interactions with conspecific and heterospecific individuals drive evolution towards similar phenotypes in different species. Several hypotheses accounting for convergence in communication signals based on mechanisms of social mimicry exist, but evaluations of how similar species are given the visual system of receptors of such signals have been ostensibly missing from tests of such hypotheses. We used plumage reflectance measurements and models of avian color discrimination to evaluate the efficacy of visual deception and therefore the plausibility of mimicry hypotheses accounting for plumage convergence among six species of passerine birds in the flycatcher family (Tyrannidae) with strikingly similar plumage. We rejected interspecific social mimicry hypotheses as an explanation for the similarity between one putative model species and putative mimics because deception seems unlikely given the visual system of passerines. However, plumage similarity was consistent with a role for selective pressures exerted by predators because dorsal coloration of putative model and mimic species was indistinguishable by visually oriented raptors. Experiments and behavioral observations are necessary to better characterize social interactions and to test predictions of alternative mimicry hypotheses proposed to account for convergence.