Eggshell Biliverdin and Protoporphyrin Pigments in a Songbird: Are They Derived from Erythrocytes, Blood Plasma, or the Shell Gland?

Biliverdin and protoporphyrin pigments are deposited into the eggshell when the developing egg is in the shell gland. However, the site of synthesis of eggshell pigments is still uncertain, although it may influence the possible costs and potential functions of eggshell coloration in avian species. Eggshell pigments may be derived from red blood cells or be produced in other organs and then transferred to the shell gland, or they may be synthesized de novo in the shell gland.