Soil and preen waxes influence the expression of carotenoid-based plumage coloration
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The signaling function of carotenoid-based plumage is mainly determined by the concentration of pigments in feathers. For this reason, most studies of the proximate control of coloration focus on processes during and preceding moult. In great tits Parus major, past research demonstrates that carotenoid-based plumage coloration honestly indicates male quality and, thus, may be a sexually selected signal. In this study, we investigate how dirt and preen oil influence the coloration of carotenoid-based feathers in the great tit. We collected six feathers from each individual bird; three feathers served as controls while the remaining three feathers were washed with a chloroform/methanol mixture to remove soil and preen waxes. We assessed plumage coloration using digital photography. This cleaning procedure slightly enhanced ornamentation; the experimentally cleaned feathers expressed hues shifted towards shorter wavelengths and expressed brighter overall coloration than control feathers. This is the first experimental study conducted on wild birds demonstrating that, in addition to pigment concentration, the presence of preen waxes and soils on feathers may contribute to variation in coloration.
KeywordsPlumage color Hue Uropygial gland secretions Plumage maintenance Sexual selection
Our survey would not have been possible without the help of many people. Volunteers working at ringing posts gathered biometric data. Monika Miller assessed preen wax and dirt load present on feathers. Ewa Waliszewska and Wojciech Kubasik supplied us with photographic equipment. Patrick Fitze and Alex Badyaev generously shared their knowledge about using photography in color measurements. Piotr Tryjanowski critically read early drafts of the manuscript. The manuscript was greatly improved by comments of Juan Carlos Senar and two anonymous referees. Special thanks are due to Lynn Siefferman for her valuable advices at various stages of this study and as well as help with language revision. All experiments done in the course of the study comply with the current laws of Poland.
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