Abstract
When allocating investment among offspring, parents might maximize their fitness by biasing investment toward offspring with the best direct fitness prospects. The observed preferences of avian parents for carotenoid-rich mouth colors that advertise good condition has been interpreted as support for this hypothesis. However, because these condition-dependent visual signals might also make offspring more visually conspicuous, active parental preferences for carotenoid-rich traits are difficult to distinguish from passive responses to differences in detectability among offspring. Here, we used a visual model to examine how mouth colors influence the visual conspicuousness of nestling house sparrows (Passer domesticus) to parents under a suite of realistic ambient light conditions. We found little evidence that mouths rich in carotenoids provided more conspicuous targets to parents than mouths poor in carotenoids. While other features of mouth color may have evolved to increase conspicuousness, our results suggest that carotenoid-based coloration is not a product of detectability pressures and rather may serve as a signal of nestling quality.
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Acknowledgments
We thank Jennifer Place for assistance with field work and Doug Mock and P.L. Schwagmeyer for generously providing access to birds. The Institutional Animal Care and Use Committee of the University of Oklahoma approved all protocols (R06-012). Research was funded by a George Miksch Sutton Scholarship in Ornithology to MD, who was also supported by an Alumni Fellowship and Adams Scholarship in Zoology from the University of Oklahoma. Doug Mock, P.L. Schwagmeyer, Rosemary Knapp, Ingo Schlupp, Anne Magurran, Marty Leonard, Tatiana Czeschlik, several anonymous reviewers, and the ZEEB Graduate Review all provided helpful critiques of manuscript drafts.
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Loadings of contrast values under each ambient light condition on the principal components representing achromatic and chromatic (located in individual tabs) contrast of the flange against the palate and nesting material. (XLS 24 kb)
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Dugas, M.B., Rosenthal, G.G. Carotenoid-rich mouth colors influence the conspicuousness of nestling birds. Behav Ecol Sociobiol 64, 455–462 (2010). https://doi.org/10.1007/s00265-009-0861-z
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DOI: https://doi.org/10.1007/s00265-009-0861-z