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The importance of white on black: unmelanized plumage proportion predicts display complexity in birds

Galván, Ismael
Behavioral ecology and sociobiology 2008 v.63 no.2 pp. 303-311
animal behavior, birds, correlation, phylogeny, plumage
Animal ritualized displays have been classically viewed as behavioral characters that decrease signal ambiguity or that facilitate the evaluation of costly exhibitions. It has been shown that their prevalence and level of complexity across species can reflect phylogenetic relationships between them, but the adaptive function of these behavioral traits is poorly known. Here, I hypothesize that, given that the efficacy of visual displays basically depends on conspicuousness and level of performance, species with low levels of conspicuousness may be forced to perform more complex varieties of a given display to get the same signal efficiency than other more conspicuous species. Thus, the evolution of display complexity, considered as the level of exaggeration of ritualized movements, may be explained as an adaptive trait and not only by phylogenetic inertia. I illustrate and test this hypothesis with the case of black-and-white plumage patches of pelecaniform birds. As predicted, there was a negative correlation between level of complexity and species conspicuousness (proportion of unmelanized plumage) for two different social displays. This indicates that classical ideas on the adaptiveness of ritualized displays should be considered to understand the present variation in signal form across species, which sheds light on the evolution of multiple signals.