Seabird sex differences in foraging shift with colony and year, study finds

Male and female streaked shearwaters do not follow a single, species-wide pattern when it comes to where and how they search for food. Instead, according to a new tracking study published in the journal Animal Biotelemetry, the degree of sexual segregation in their foraging behavior depends strongly on which breeding colony a bird belongs to and which year it is studied, pointing to environmental context as a decisive factor.

The research team, led by Chisaki Yashiki and colleagues including Ken Yoda, analyzed GPS tracking data from 1,179 foraging trips made by 73 male and 69 female streaked shearwaters (Calonectris leucomelas). The birds were tracked at three breeding colonies situated in oceanographically distinct regions, across four study years: 2018, 2019, 2023, and 2024.

Sexual segregation, the phenomenon in which males and females of the same species use different spaces or times, is thought in many animals to reduce competition between the sexes and to satisfy sex-specific physiological demands. In seabirds that must return to a fixed nest to raise chicks, so-called central-place foragers, these differences may be sharpened by the spatiotemporal constraints of breeding and by the varied ocean conditions surrounding different colonies.

Most earlier studies, the authors note, have focused either on sexual size dimorphism or on a single breeding site, leaving open the question of whether sex differences in seabird foraging are consistent traits of a species or emerge only under particular local conditions. The multi-colony, multi-year design of the new study was aimed squarely at that gap.

The analysis covered several levels of behavior. The researchers examined broad-scale trip-level movement metrics, measured spatial overlap in 95% full-trip utilization distributions and in 50% core-use areas, and quantified trip-level proportions and rates of behavioral states. They also compared the oceanographic conditions the birds actually experienced, using sea surface temperature (SST) and chlorophyll-a concentration (Chl-a) as indicators.

One finding was consistent everywhere: males were larger than females, with body mass approximately 18 to 25 percent higher across all colonies. But the behavioral consequences of that size difference were anything but uniform, varying among breeding site and year combinations.

The clearest segregation appeared at the breeding site where birds could access two oceanographically distinct regions. There, males reached maximum distances from the colony up to 1.6 times those of females in some years, males consistently experienced cooler sea surface temperatures than females, and the sexes showed significant segregation in 95% full-trip space use across all study years.

At the other breeding sites, where birds foraged primarily within a single oceanographic region, sex differences were weaker and less predictable. At one such site, significant segregation in 95% full-trip space use was detected only in 2024, and females experienced higher chlorophyll-a concentrations than males only in 2023, a single-year pattern rather than a persistent one.

The authors conclude that sexual segregation in streaked shearwaters is not a fixed species-level trait but varies with breeding context and environmental setting. For researchers studying sex differences in seabird foraging, the message is that environmental context must be part of the evaluation, because a pattern observed at one colony in one year may not hold elsewhere or at another time.

The study is published as an open-access article in Animal Biotelemetry, released on 28 September 2026 as a peer-reviewed, citable version of record in progress, subject to further editorial edits before the final version is posted.

Subject of Research: Sexual segregation in the foraging behavior of streaked shearwaters across breeding sites and years

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

Article References: Yashiki, C., Takeda, W., Koyama, S., Shiomi, K., Goto, Y., & Yoda, K. (2026). Sexual segregation in foraging behavior varies with breeding site and year in seabirds. Animal Biotelemetry. https://doi.org/10.1186/s40317-026-00500-1

Image Credits: AI Generated

DOI: 10.1186/s40317-026-00500-1

Keywords: streaked shearwater, sexual segregation, foraging behavior, GPS tracking, seabirds, central-place foraging, sea surface temperature, chlorophyll-a, breeding colonies, utilization distributions, animal biotelemetry, behavioral ecology