Jacot, A., Romero-Diaz, C., Tschirren, B., Richner, H., & Fitze, P. S. (2010). Dissecting Carotenoid from Structural Components of Carotenoid-Based Coloration: A Field Experiment with Great Tits (Parus major). American Naturalist, 176(1), 55-62. doi:10.1086/653000.