LAYING-SEQUENCE VARIATION IN YOLK CAROTENOID CONCENTRATIONS IN EGGS OF YELLOW-HEADED BLACKBIRDS (XANTHOCEPHALUS XANTHOCEPHALUS)

Abstract

Abstract Asynchronous hatching creates a size hierarchy among siblings and a survival disadvantage for last-hatched nestlings. Female birds can influence this disadvantage by differentially investing maternal resources, such as carotenoids, across the laying sequence. We studied intraclutch variation in carotenoid concentrations in Yellow-headed Blackbirds (Xanthocephalus xanthocephalus) and predicted that yolk concentrations would decrease across the laying sequence, because nestling mortality is inversely related to hatching order in this species. We quantified intraclutch variation in the concentrations of total and individual identifiable carotenoids (β-carotene, β-cryptoxanthin, lutein, and zeaxanthin) in Yellow-headed Blackbird eggs collected from five breeding colonies, and correlated these concentrations with egg mass, yolk mass, and yolk water content. Carotenoid concentrations were not related significantly to any of the egg metrics measured. The concentration of total identifiable carotenoids i...