Variability in foraging ranges of snow petrels and implications for breeding distribution and use of stomach-oil deposits as proxies for paleoclimate

Background: Pelagic seabirds forage over vast areas, and their movements and diet provide valuable insights into environmental conditions that are otherwise difficult to observe. Snow petrels Pagodroma nivea forage largely on sea-ice-associated prey, rendering the energy-rich lipids into stomach oil, some of which is spat defensively at nest sites where it accumulates over tens of millennia. These deposits contain chemical signatures of the foraging environment, providing a unique biological archive of sea-ice conditions in the pre-satellite era. Accurate interpretation of these proxies, however, requires detailed knowledge of foraging ranges—how far the petrels travel, the habitats they target, and how these behaviours vary with season, colony location, and sex. Methods: To estimate foraging ranges at three colonies located 180–200 km inland in Dronning Maud Land, we tracked 94 snow petrels (34 with light-based geolocators and 60 with GPS loggers). We tested whether foraging latitude is associated with the latitude of the ice edge, estimated via satellite remote sensing. We then projected potential foraging ranges for all known colonies in the study area to reexamine assumptions made in paleoclimate studies. Results: During most breeding stages, and across breeding seasons, core foraging areas were centred approximately 2° south of the outer sea-ice edge and tracked this habitat as it receded during the spring melt. Female snow petrels were approximately 7% lighter than males but foraged at similar distances and in similar areas. Foraging ranges differed little between colonies but substantially between breeding stages. For example, average median range was ~1400 km (95% CI 1340–1470 km) during the pre-laying exodus vs. ~530 (430–660) km during brood-guard. Conclusions: Snow petrel stomach-oil deposits potentially integrate environmental conditions over greater and more seasonally variable areas than previously assumed, probably with a bias towards conditions in the marginal ice zone (outer pack ice) during the early summer when stomach oil deposition due to nest competition is likely greatest. Our results are consistent with the hypothesis that snow petrel breeding range in the western Weddell Sea is limited by access to foraging habitat, such as coastal polynyas. Although tracking data from other colonies would be useful to confirm the generality of our foraging range estimates, we hypothesise that as sea ice fluctuated over previous glacial-interglacial cycles, this regulated breeding distribution across the region.

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