Cassey, P., Portugal, S. J., Maurer, G., Ewen, J. G., Boulton, R. L., Hauber, M. E., & Blackburn, T. M. (2010). Variability in Avian Eggshell Colour: A Comparative Study of Museum Eggshells. Public Library of Science.

Cassey, Phillip, Steven J. Portugal, Golo Maurer, John G. Ewen, Rebecca L. Boulton, Mark E. Hauber, ja Tim M. Blackburn. Variability in Avian Eggshell Colour: A Comparative Study of Museum Eggshells. Public Library of Science, 2010.

Cassey, Phillip, et al. Variability in Avian Eggshell Colour: A Comparative Study of Museum Eggshells. Public Library of Science, 2010.