PLUMAGE MIMICRY IN AVIAN MIXED-SPECIES FLOCKS: MORE OR LESS THAN MEETS THE EYE?

Social mimicry was postulated as a possible evolutionary mechanism that would produce convergence in the characteristics of species that interact extensively and, thus, act as an opposing force to competition and character displacement. The examples for this hypothesis were drawn mostly from visual resemblances among bird species that flock together. We evaluated plumage mimicry among groups of birds, asking 31 raters to score the resemblances among 22 sets of putative mimicry postulated in the past four decades. The resemblance between the putative model and the mimic (if there was no one model hypothesized, we considered both species to be possible models for each other) was compared with that between the model and (1) a species closely related to the mimic and (2) another species that only occasionally associated with the mixed-species groups but lived in the same habitat. We found significant support for 14 of the cases. Our results emphasize the importance of assessing similarity by using multiple raters and that several mechanisms may drive phenotypic resemblance, some reflecting phylogenetic inertia or habitat constraints. Nevertheless, these mechanisms may be accentuated in groups of birds that interact extensively. Received 25 January 2011, accepted 18 May 2011.