Nutrient Content of Eggs and the Energetics of Clutch Formation in the Boat-Tailed Grackle

Abstract

Shell, yolk, and albumen represent 10.5%, 21.9%, and 67.6%, respectively, of fresh-egg weight of Boat-tailed Grackles (Quiscalus major). The proportion of egg composed of dry yolk increases as egg weight increases. The average 8.1-g egg contains 33.6 kJ of which 66.1% is in yolk and 33.9% is in albumen. The average three-egg clutch was estimated to cost 131 kJ for yolk development and albumen deposition. These costs were spread over a 6-day period, with a peak of 28 kJ occurring on the day before egg laying began. At hatching, the yolk sac represents 19% of hatchling wet weight. Only 10% of the energy present in the egg at laying is expended during incubation. Hatchlings have substantial yolk reserves that contain 49% of the hatchlings' energy.