Sexual segregation in foraging behavior varies with breeding site and year in seabirds

In many animals, behavioral sex differences can produce spatial or temporal segregation, known as sexual segregation, which is thought to reduce competition and satisfy sex-specific physiological demands. In seabirds that engage in central-place foraging during the breeding season, such sexual segregation is likely to be accentuated by spatiotemporal constraints. Among the potential drivers of these behavioral sex differences are interannual variation in resource availability and environmental heterogeneity among breeding sites. However, it remains unclear whether sex differences in seabird foraging represent consistent species-wide traits or instead emerge only under particular local environmental conditions, because most studies focus on sexual size dimorphism or a single breeding site. We collected and analyzed GPS tracking data from streaked shearwaters ( Calonectris leucomelas ) breeding at three colonies located in oceanographically distinct regions (the Sea of Japan and the Pacific Ocean) from 2018 to 2024. We tested for sex differences by year and breeding site for behavioral metrics, including maximum distance from the colony, total travel distance, and behavioral states. In addition, we extracted oceanographic variables such as sea surface temperature and chlorophyll a concentration experienced by birds during each trip to evaluate their association with observed sex differences. Males were consistently larger than females, but behavioral sex differences were not universal. Clear sex differences in movement emerged mainly at the Sea of Japan colony, where birds can access both the Sea of Japan and the Pacific Ocean, whereas few or none were detected at colonies that forage exclusively in the Pacific. Patterns of sex differences varied among years within the same colony. Our findings indicate that the expression of behavioral sex differences varies with the spatial context in which birds forage, with clearer differences observed at colonies spanning multiple marine regions. By integrating multi-colony and multi-year data, this study highlights the importance of considering environmental context when evaluating sexual segregation in seabirds.