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

Social mimicry may lead to convergent evolution when interactions with conspecific and heterospecific individuals drive evolution towards similar phenotypes in different species. Several social mimicry hypotheses accounting for convergence in communication signals exist. However, assessments of how similar species are given the visual system of signal receptors have been ostensibly missing from tests of such hypotheses. We used plumage reflectance measurements and models of avian colour discrimination to evaluate the efficacy of visual deception and 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 the interspecific social dominance mimicry hypothesis as an explanation for the similarity between one putative model species and putative mimics because deception seems unlikely given their visual system. 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 behavioural observations are necessary to better characterize social interactions and to test predictions of alternative mimicry hypotheses proposed to account for convergence.