Intraspecific variation in reproductive physiology and egg quality in the European Starling Sturnus vulgaris

Egg mass shows large intraspecific variation in birds and is repeatable wit hin individuals. The mechanisms underlying this variation are unknown. We h ypothesized that measures of egg quality (the mass of yolk protein, yolk li pid, and albumen protein) would be positively correlated with the plasma po ols of the yolk precursor vitellogenin, and the masses of the oviduct, meta bolic machinery (liver, heart, lungs, kidneys, gizzard, small intestine and pancreas), and endogenous stores of protein and lipid. We tested these pre dictions in European Starlings Sturnus vulgaris is collected at the peak of egg production effort. In contrast to our predictions, both yolk protein a nd yolk lipid were negatively correlated with plasma vitellogenin levels. A lbumen protein was positively related to oviduct mass, but other aspects of body composition failed to explain variation in egg quality. Hence, while we observed correlations between egg composition and peripheral systems (ci rculating precursor pools and the oviduct), we found no evidence that egg q uality is determined by more general processes, i.e., the supply and proces sing of nutrients.