No single hypothesis is likely to explain the diversity in eggshell coloration and patterning across birds, suggesting that eggshell appearance is most likely to have evolved to fulfill many nonexclusive functions. By controlling for nonindependent phylogenetic associations between related species, we describe this diversity using museum eggshells of 71 British breeding passerine species to examine how eggshell pigment composition and concentrations vary with phylogeny and with life-history and nesting ecology traits. Across species, concentrations of biliverdin and protoporphyrin, the two main pigments found in eggshells, were strongly and positively correlated, and both pigments strongly covaried with phylogenetic relatedness. Controlling for phylogeny, cavity-nesting species laid eggs with lower protoporphyrin concentrations in the shell, while higher biliverdin concentrations were associated with thicker eggshells for species of all nest types. Overall, these relationships between eggshell pigment concentrations and the biology of passerines are similar to those previously found in nonpasserine eggs, and imply that phylogenetic dependence must be considered across the class in further explanations of the functional significance of avian eggshell coloration.

Bird Group Department of Life Sciences Natural History Museum Akeman Street Tring Hertfordshire HP23 6AP UK

Centre for Ornithology School of Biosciences College of Life and Environmental Sciences University of Birmingham Edgbaston Birmingham B15 2TT UK

Department of Analytical Chemistry Faculty of Chemical Technology University of Pardubice Pardubice Czech Republic

Department of Animal and Plant Sciences University of Sheffield Sheffield S10 2TN UK

Department of Psychology Hunter College and the Graduate Center of the City University of New York 695 Park Ave New York City New York 10065

Division of Psychology Social and Health Sciences Abertay University Dundee DD1 1HG UK

School of Biological Sciences Royal Holloway University of London Egham Surrey TW20 0EX UK

School of Biological Sciences University of Adelaide Adelaide South Australia 5005 Australia

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