ウミネコＬａｒｕｓ ｃｒａｓｓｉｒｏｓｔｒｉｓにおける過剰卵数の出現

Abstract

Super normal clutches were observed in the Black-tailed Gull Larus crassirostris at the colony on Kabu Island. I regarded clutches of 1-3 eggs as normal and those of 4 or 5 eggs as super normal. The super normal clutches were found in 31 nests (0.8% of 4, 034 nests examined): 5 in 1990, 5 in 1991, and 21 in 1992. Female-female pairings were reported for several species of genus Larus in USA as a cause of super normal clutches. Pairings of this type were not observed in Black-tailed Gulls, but instead, super normal clutches coincided with irregular sequences of egg-laying which suggested intraspecific nest parasitism.