Coloniality of Brown Booby (Sula leucogaster) in Gorgona National Natural Park, Eastern Tropical Pacific

Abstract

Many hypotheses have been considered to explain how colonial breeding can benefit individuals who practice it; however, these hypotheses are supported by weak evidence. On Gorgona island, during October 2002 through October 2003, Brown Booby (Sula leucogaster) nest sites were physically characterized and periodically visited in order to describe the reproductive cycle and explain coloniality hypotheses and nest site position (center-periphery, center-satellite or at random). We found a reproductive population of 300 individuals breeding asynchronously. Nest sites followed an aggregated pattern with an average nearest neighbor distance of 1.6 m. Hatching success of population during the whole year was 28.2%, and reproductive success 17.3%. This success was closely related to nest site position in the colonies. The center-periphery model, which suggests that variation in survival is generated by the fact that central individuals are less accessible to predators and have better physical conditions and higher reproductive success than periphery individuals, was not supported by Brown Booby colonies in Gorgona. The spatial disposition of quality of pairs shows a negative autocorrelation in the first distance interval (0 to 1.5 m), which indicates that there was an attraction of pairs of low quality towards pairs of high quality. This suggests that center-satellite patterns and aggregated patterns were predominant. The central-satellite model which predicts the attraction of individuals of low quality towards the best breeding places already occupied by individuals of high quality was consistently observed throughout the year. In conclusion, the center-periphery pattern derived from the predation-dilution hypotheses does not fit all the colonies of marine birds as proposed. © The Neotropical Ornithological Society