Abstract
In 1977, we studied nest-site selection and breeding success of Yellow-footed Gulls (Larus livens) at Bahia de los Angeles, Baja California. Seventy-five percent of the population nested colonially, a habit facilitating defense against egg and chick predation by Common Ravens (Corvus corax). The majority of these pairs selected beach-berm substrate where they obtained optimum visibility of surroundings. Beach-berm substrate also provided conditions that enabled them to place nests close to the water (advantageous for maintaining predator defense while practicing thermoregulatory activities necessary in a hot climate). The remaining 25% of the population nested noncolonially, probably in response to the threat of egg collecting by man. The majority of these pairs nested on talus-boulder substrate, a terrain difficult for man to negotiate, but which also provided suboptimum visibility of surroundings, and suboptimum conditions for nesting close to the water. Low reproductive success (0.12 young/pair) on Islas Coronado and La Ventana was attributed to predation by man on gulls nesting colonially, and ravens on gulls nesting noncolonially.
Published Version
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