COMPOSITION OF EGGS OF COMMON EIDERS

The content of common elder (Somateria mollissima) eggs was studied in the colony on the Dutch island of Vlieland for 3 years. Mean wet mass was 108 g: ca. 9% shell, ca. 45% albumen, and ca. 45% yolk. Mean dry density (g . cm(-3)) was 0.086 for shell, 0.069 for albumen, 0.094 for lean yolk, and 0.169 for yolk lipids. The average energy value of the egg content was estimated at 10.45 . kJ cm(-3), and 1087 kJ for the c ontent of an average egg with a volume of 104 cm(3). The average energ y value of the shell membranes amounted to 15 kJ. The most common clut ch size is 5 eggs, which means that, on average, 5510 kJ is directly i nvested in a clutch. Corrected for volume, total dry mass and dry mass of lean yolk, albumen, and fat differed among females. Corrected for volume, lean yolk mass decreased with clutch size; other components we re not involved. This induced an increase in the ratio of lipid in the yolk to lean yolk with clutch size. Within a clutch, dry mass of the components varied isometrically with egg volume. Egg volume varies acc ording to the laying sequence, those laid in the middle of the sequenc e being largest. Therefore, the amount of energy allocated to individu al eggs in a clutch varies according to the same curvilinear relations hip.