Eggshell coloration reflects both yolk characteristics and dietary carotenoid history of female mallards

1. Avian eggshell coloration has frequently been examined in a functional context (e.g. mimicry, camouflage), but in recent years, an interest has emerged in identifying the mechanisms that drive eggshell colour variation. 2. Eggshell coloration is predominately caused by pigment deposition; one such pigment is the antioxidant biliverdin, and deposition of biliverdin into eggshells may be costly to mothers due to depletion of their antioxidant reserves. Previous work has shown that dietary supplementation during laying with another type of antioxidant – carotenoid pigments – induces females to produce more biliverdin-rich eggshells. However, the impact of pre-laying nutrition – including the developmental period early in life – on eggshell coloration has not been investigated. 3. Here, we raised female mallards (Anas platyrhynchos) from hatching, supplemented their diets with carotenoids during early-, mid- or late-developmental periods, and at adulthood measured female circulating caro...