Intraclutch Variation in the Size, Mass and Composition of Ring-Billed Gull Eggs

Abstract

In 1984, 94 complete three-egg clutches of Ring-billed Gull (Larus delawarensis) eggs were collected on Granite Island, northern Lake Superior. The fresh eggs (i.e., collected within 12 hr of being laid) were weighed, measured and frozen for later chemical analysis to determine if relationships existed between egg size, composition, and sequence. Egg size and mass decreased through the laying sequence. The average composition of fresh eggs was 35% yolk, 56% albumen, and 9% shell. Water accounted for 69% of fresh egg mass. Approximately 8% of fresh egg mass was yolk lipid. Dry yolk consisted of approximately 40% protein and 60% lipid. Caloric content averaged 1.55 kcal/g fresh egg mass. Within clutches, third-laid eggs contained absolutely less albumen and nutrients than earlier laid eggs. Albumen increased in proportion to the 1.2 power of egg mass, and the yolk in proportion slightly greater than the 0.66 power of egg mass. Results agreed well with egg composition studies of other semiprecocial species.