Breeding Biology of a Small Colony of Western Gulls (Larus occidentalis wymani) in California

Abstract

The breeding biology of some gull species has been fairly well studied. A notable exception is the Western Gull ( Larus occidentalis), a resident of the west coast of the United States, Baja California and Sonora, Mexico, and British Columbia. The difficulty of reaching island nesting colonies has deterred investigators until recently. Reports by Schreiber (1970) and Coulter (1969) have added much to our understanding of the nesting biology of the species, especially the egg-laying and hatching phases. During 1965 and 1966 I studied a small colony of Western Gulls (L. o. wymani) on Bird Rock, Santa Catalina Island, California. Emphasis was given to population ecology of the colony from egg laying through fledging, nest site preference, nest distribution pattern, and territoriality. Also examined were the nesting success of this small colony and the effect of colony size on survivorship for this and other gull species.