Egg Mass and Clutch Size Relationships in Geese, Eiders, and Swans

Abstract

We examined the relationship between egg mass and clutch size for five species of waterfowl. None showed decreasing egg mass with increasing clutch size. Brant Branta bernicla nigricans laid slightly heavier eggs in larger, rather than smaller clutches. These results were contrary to predictions of the hypothesis that egg production limits clutch size in waterfowl. Clutch size declined with later laying, both within years and between years. The intra-seasonal rates of clutch size decline were similar among years for each species, but were not similar for three species of geese nesting at the same site in Alaska, U.S.A. Egg mass did not vary with laying date, nor did egg mass vary with year, except in Brant. Trumpeter Swans Cygnus buccinator in Alaska laid larger eggs but not larger clutches than swans in Montana, U.S.A. Intra-clutch egg mass variation accounted for 17-37% of the total variation in egg mass. Intra-clutch variation in egg mass was independent of clutch size, except in Emperor Geese, Chen canagica.