Avian eggshell pigments and their variability

Eggshell pigment constituents were determined by a high performance liquid chromatography method. Most of the work was done on whole clutches of red-backed shrike (Lanius collurio). In addition to the known pigments (protoporphyrin IX, biliverdin), a new pigment, zinc-containing protoporphyrin IX, was found as well. Its content was highly variable-from 0% to 100%. The content of total protoporphyrin IX (with and without zinc) ranged from 1.72 to 114.84 nmol (average for whole clutches was 39.93 nmol), while the content of zinc-deficient protoporphyrin IX was ND (not detectable) -110.46 nmol (average for whole clutches was 34.02 nmol) and the content of zinc-containing protoporphyrin IX was ND -32.28 nmol (average for whole clutches was 5.91 nmol). Zinc-containing protoporphyrin IX was absent in 33% of eggs, while zinc-deficient protoporphyrin IX was absent in a single case only (2%). If clutches from relatively ''polluted'' and ''unpolluted'' regions were compared, no differences have been found. Based on these findings is the conclusion that the high variability in eggshell pigment content is likely to reflect physiological influences (e.g. order of egg laying and the whole condition of the nesting female) rather than environmental interferences. This conclusion is in agreement with our previous findings. Additional data regarding the pigment content of seven other bird species are also included.