Sexual segregation in tropical seabirds: drivers of sex-specific foraging in the Brown Booby Sula leucogaster

Sexual segregation in the behaviour, morphology or physiology of breeding seabirds can be related to divergent parental roles, foraging niche partitioning or sex-specific nutritional requirements. Here, we combine GPS tracking, dietary and nutritional analysis to investigate sex-specific foraging of Brown Boobies breeding on Raine Island, Great Barrier Reef, Australia. We observed sex-specific segregation in: (1) foraging location: females undertook longer trips, foraging at more distant locations than males; (2) foraging time: male activity and foraging occurred throughout the day, while female activity and foraging increased from midday to an afternoon peak; and (3) prey type, females mostly consumed flying fish, whereas males consumed equal proportions of flying fish and squid. Brown Booby diets contained five tropical prey species that significantly differed in their nutritional composition (Protein, Lipid and Water, wet mass). Despite this variation we found no differences in the overall nutritional content of prey caught by each sex. The observed sex-specific differences in prey type, location and time of capture are likely driven by a combination of a division of labour, risk partitioning and competition. However, Brown Boobies breeding on Raine Island, and other populations, might flexibly partition foraging niches by sex in response to varying competitive and environmental pressures. In light of such potential foraging dynamism, our inconclusive exploration of nutritional segregation between sexes warrants further investigation in the species.