Egg spottiness reflects female condition, physiological stress, and ornament expression in a common rallid species

Abstract

Lay Summary • There is equivocal support for direct associations between maternal quality and deposition of protoporphyrin pigmentation (dark spots and blotches) in avian eggshells. • Research on protoporphyrin eggshell pigmentation has primarily focused on a single avian order (Passeriformes). • We examined associations of protoporphyrin-based eggshell pigmentation with female phenotypic and genetic traits in a non-passerine species, the Eurasian Coot. • Deposition of protoporphyrin in eggshells (total number per area of egg spots) positively correlated with female condition and expression of a putative bare-part ornament (frontal shield), while it was negatively associated with the level of physiological stress. • Protoporphyrin-based eggshell pigmentation acts as a reliable signal of female phenotypic (but not genetic) traits in the Eurasian Coot. • Signaling properties of protoporphyrin-based egg coloration are likely to largely differ between different evolutionary lineages of birds.