For well over 100 years, only two pigments have been identified in avian eggshells: rusty-brown protoporphyrin (e.g., brown chicken eggs) and blue-green biliverdin (e.g., turquois eggs of robins). However, tinamou (chicken-like forest dwellers of South America) eggshells display unusually colored eggshells, suggesting the presence of other pigments. The Brückner Group, in collaboration with the ornithologists and eggshell and bird color experts Daniel Hanley (Long Island University) and Richard Prum (Yale University), investigated this. Through extraction, derivatization, spectroscopy, chromatography, and mass spectrometry, they identified two novel eggshell pigments: yellow–brown bilirubin and red–orange uroerythrin from the guacamole-green and purplish-brown eggshells of two tinamous species. Both pigments are known porphyrin catabolites and were found in the eggshells in conjunction with biliverdin. A colour mixing model using the new pigments and biliverdin reproduced the respective eggshell colours. These discoveries expand our understanding of how eggshell colour diversity is achieved. The ability of these pigments to photo-degrade may have an adaptive value for the tinamous – this is the subject of follow-up studies for the ornithologists.
Hamchand, R.; Hanley, D.; Prum, R.O.; Brückner, C. ‘Expanding the Eggshell Colour Gamut: Uroerythrin and Bilirubin from Tinamou (Tinamidae) Eggshells’ Sci. Rep. 2020, 10, 11264.