Female-Female Pairing in Ring-Billed Gulls

Abstract

Abstract Female-female pairs of Ring-billed Gulls (Larus delawarensis) were recorded attending supernormal clutches (5-8 eggs) on Granite Island, northern Lake Superior in 1978. Female-female pairs complete their clutches usually before the peak of egg-laying in the colony. Supernormal clutches completed after the peak are thought to result from egg-dumping by several unpaired females. Compared to normal 3-egg clutches, laid early in the season, the average hatching success of supernormal clutches was lower (8-20% vs 80-90%) and over 50% of the embryos showed depressed growth and development. Although the phenomenon of homosexual pairing is likely not recent in Ring-billed Gulls, as compared to the situation in Western Gulls, the adaptive significance of such pairs is currently unknown.