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

Abstract 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 breeding central-place foraging seabirds, sexual segregation may be accentuated by spatiotemporal constraints and influenced by environmental heterogeneity among breeding sites. However, because most studies have focused on either sexual size dimorphism or a single breeding site, it remains unclear whether sex differences in seabird foraging are consistent species-wide traits or emerge only under specific local environmental conditions. We analyzed GPS tracking data from 1,179 foraging trips by 73 male and 69 female streaked shearwaters ( Calonectris leucomelas ) breeding at three colonies in oceanographically distinct regions across four study years: 2018, 2019, 2023, and 2024. We examined sex differences in broad-scale trip-level movement metrics, spatial overlap in 95% full-trip utilization distributions and 50% core-use areas, and trip-level proportions and rates of behavioral states. We also compared experienced oceanographic conditions based on sea surface temperature (SST) and chlorophyll-a concentration (Chl-a). We found that males were consistently larger than females, with body mass approximately 18–25% higher across colonies. Behavioral sex differences varied among breeding site–year combinations. At the breeding site where birds could access two oceanographically distinct regions, males reached maximum distances from the breeding site up to 1.6 times those of females in some years, consistently experienced cooler SSTs than females, and showed significant segregation in 95% full-trip space use across all study years. In contrast, at breeding sites where birds foraged primarily within a single oceanographic region, sex differences were weaker and varied among breeding sites and years. At one breeding site, significant segregation in 95% full-trip space use was detected only in 2024, whereas females experienced higher Chl-a than males only in 2023. These results indicate that sexual segregation in streaked shearwaters is not a fixed species-level trait but varies with breeding context and environmental setting, highlighting the importance of considering environmental context when evaluating sex differences in seabird foraging behavior.