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. We studied in the canary (Serinus canaria) whether eggshell blue-green and brown pigmentations are associated with experimentally elevated anemia, female hematocrit level, immature erythrocyte percentage, and feces and plasma pigment levels during egg laying to find out the possible origin of eggshell pigments. We found no significant effects of hematocrit level or experimentally elevated anemia on intensity of eggshell blue-green and brown pigmentations; therefore, we consider it less likely that eggshell pigments are derived from erythrocytes. In addition, we found no significant associations between female feces biliverdin concentration during egg laying and intensity of eggshell blue-green pigmentation, suggesting that eggshell biliverdin may not originate from the spleen or liver. We found a negative association between plasma and feces protoporphyrin concentrations during egg laying and eggshell brown chroma. This result suggests that an increased production of protoporphyrin in the liver, which could have elevated plasma and feces protoporphyrin concentrations, could inhibit eggshell protoporphyrin pigmentation, probably through affecting enzymatic activities. We suggest that both pigments are produced de novo in the shell gland in the canary, but circulating pigment levels may influence shell gland pigment synthesis, thus connecting the physiological status of the female to eggshell coloration.

Protoporphyrin pigment causes the red-brown eggshell colors; however, for many species, the function of this pigment is unknown. It has been proposed that eggshell pigmentation may strengthen the shell or that it may be a sexually selected signal, which advertises the quality of the female and that of her offspring to the male parent. In this study, we aimed to discover whether protoporphyrin-based eggshell pigmentation patterns of Eurasian Great Tits (Parus major) were related to female or egg quality. Additionally, we tested whether different methods of eggshell pigmentation estimation could be reliable predictors of eggshell protoporphyrin levels. We found that spot intensity, spot size, spotting coverage, and brown spot chroma indicated the protoporphyrin pigment concentration of the eggshell. Our results revealed that Eurasian Great Tit females that laid eggs with darker pigmentation had more lymphocytes in their circulation and had paler yellow breast and lower UV plumage reflectance, possi... RESUMEN El pigmento protoporfirina causa el color marrón rojizo de la cáscara de huevo; sin embargo, para muchas especies, la función de este pigmento es desconocida. Se ha propuesto que la pigmentación de la cáscara de huevo fortalece la cáscara o que puede ser una señal seleccionada sexualmente, la cual publicita la calidad de la hembra y la de sus polluelos al macho paterno. En este estudio, nuestro objetivo fue determinar si el patrón de pigmentación de la cáscara de huevo basado en protoporfirina de Parus major estuvo relacionado a la calidad de la hembra o del huevo. Además, evaluamos si diferentes métodos de estimación de la pigmentación de la cáscara de huevo podrían ser predictores confiables del nivel de protoporfirina en la cáscara de huevo. Encontramos que la intensidad de las manchas, el tamaño de las manchas, la cobertura de las manchas y el color marrón de las manchas indicaron la concentración del pigmento protoporfirina de la cáscara de huevo. Nuestros resultados revelaron que las hembras...