Female birds allocate high concentrations of biologically active carotenoid pigments to their egg yolks, which help to protect developing embryos against damage from free radicals and increase the rates of nestling survival after hatching. In most avian species studied to date, carotenoids are allocated in higher concentrations to the first-laid egg and lower to the last-laid egg in the laying sequence, which has been attributed to a limitation of carotenoids in avian diets. We studied laying-sequence variation in carotenoid concentrations and egg metrics (i.e., egg mass, yolk mass, shell mass, egg length, and egg width) in 15 full clutches of House Sparrow (Passer domesticus) eggs collected from nest boxes on the main campus of Columbus State University, in Columbus, Georgia, during the breeding seasons of 2014–2018. We identified 4 yellow dietary carotenoids in House Sparrow egg yolks, β-carotene, β-cryptoxanthin, lutein, and zeaxanthin, with lutein being the most highly concentrated. We found that concentrations of most carotenoids significantly decreased from first- to last-laid eggs, but we did not find significant differences in any egg metrics across the laying sequence. To our knowledge, this research is the first to report detailed information on laying-sequence variation in yolk carotenoids in House Sparrow eggs, making our results an important contribution to the understanding of variation in the allocation of carotenoids to songbird eggs.

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