SUMMARYWilliams, A. J. 1980. Variation in weight of eggs and its effect on the breeding biology of the Great Skua. Emu 80: 198–202.Eggs of the Great SkuaStercorarius skua lonnbergiat Marion Island had a mean weight of 111.7 grams (SD 7.7 g), with a maximum range of eighteen grams within a clutch. Differences in weight were related to composition and mortality of the eggs and to the weight of chicks at hatching but not to mortality of chicks. Positive relations were found between weight of eggs and the growth of chicks until forty-five days after hatching. Fast development of the primaries in chicks from heavy eggs suggested that these have a shorter fledging period than those from light eggs. Heavy eggs presumably provide more provisions for the hatchlings, which probably leads to an earlier start of the specific pattern of growth.