Here comes the sun: multimodal displays are associated with sunlight incidence
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Conspicuousness of courtship signals in animals likely evolved to maximize mate attraction while minimizing predator detection. It is assumed, though largely unknown, that environmental and luminosity conditions affect the detectability of ornaments and motor displays and could thus strongly influence behavior. We combined visual models and behavioral observations to test whether the multimodal display of the blue-black grassquit (Volatinia jacarina) is influenced by environmental conditions, predicting that males should display more often in moments with high sunlight incidence upon their bodies. By displaying in such a context-dependent fashion, males would be able to maximize conspicuousness of their iridescent blue-black plumage and avoid displaying continuously, since the latter would involve higher energetic investment. We recorded the rates of both complete displays (leap with singing) as well as incomplete ones (singing while perched) for males during repeated 30-min focal observations in varying environmental situations in the field. We found that when bathed directly in sunlight, males increased their rates of displays, tending to exhibit more complete rather than incomplete displays in this condition and suggesting a potential trade-off between display types. Our results suggest that animals may adjust the timing and precise location of signal activity to improve the efficiency or likelihood of detection of some signal elements.
KeywordsBlue-black grassquit Contextual plasticity Courtship Iridescent plumage Motor display Sexual selection Visual signals
We thank Jeff Podos for numerous discussions about grassquit biology, display behavior, and the importance of light. For assistance with field work, we thank Marcela Manara, Renata Alquezar, Tainá Bernardes, and Paulo Henrique Veloso. We also thank two anonymous reviewers and Esteban Fernandez-Juricic, associate editor, for their excellent and detailed criticisms and suggestions. This work was funded by the Fundação Coordenação de Aperfeiçoamento de Pessoal de Nível Superior—CAPES and the Conselho Nacional de Desenvolvimento Científico e Tecnológico—CNPq. Logistic support was provided by Universidade de Brasília.
This study was approved by the Instituto Brasileiro do Meio Ambiente e dos Recursos Naturais Renováveis—IBAMA (under license no. 17765–1) and by the Centro Nacional de Pesquisa para Conservação das Aves Silvestres—CEMAVE (under license no. 1301).
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