Experimental evidence that egg color indicates female condition at laying in a songbird

Abstract

The signaling hypothesis of eggshell coloration in birds is based on the assumption that females of species with blue-green eggs
\nsignal their phenotypic quality to their mates through deposition of the antioxidant biliverdin as pigment. Egg pigmentation may
\nbe an expression of the condition of females at laying or of genetic linkages between egg color and female performance variables.
\nWe have supplemented 16 pied flycatcher, Ficedula hypoleuca, females with mealworms before and during laying and compared the
\nmass and color of their eggs as measured on the day of laying to those of 16 control females with the same nest construction and
\nlaying dates and clutch sizes. Supplemented females laid significantly heavier and more intensely blue-green eggs than control
\nfemales. Egg blue-green chroma was significantly associated with the amount of biliverdin in eggshells. Egg color, and thus biliverdin
\ncontent, is an expression of female condition at laying.