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

Abstract

BackgroundBreeding pelagic seabirds feed over wide areas. Their diet and space use can therefore provide proxies for otherwise be difficult to observe environmental conditions but interpretation of these proxies requires knowledge of foraging range. Antarctic sea ice regulates global climate, but a paucity of data on its past extent causes uncertainty in climate reconstruction and prediction. Deposits of stomach oils, produced defensively by snow petrels Pagodroma nivea (near-obligate sea-ice foragers), reflect sea ice conditions, sometimes over tens of millennia, but spatial interpretation of these biological archives is hampered by lack of data on foraging range, and how this varies seasonally, among colonies and with sex. MethodsWe tracked 34 and 60 snow petrels using light-based geolocators and GPS loggers, respectively to estimate foraging ranges at three colonies located 180-200 km inland in Dronning Maud Land. We tested whether foraging latitude is associated with ice edge latitude, estimated via satellite remote sensing. We then projected potential foraging ranges for all known colonies on the study area to reexamine assumptions made in paleoclimate studies. ResultsDuring most breeding stages, and across breeding seasons, core home ranges were centred approximately 2{degrees} south of the outer sea-ice edge and tracked this habitat as it receded during the spring melt. Females 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, median range was [~]1,400 km during the pre-laying exodus vs. [~]550 km during brood-guard. ConclusionsSnow 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 outer Marginal Ice Zone during the early summer when stomach oil deposition due to nest competition is likely greatest. Projected potential home ranges of snow petrel colonies in the western Weddell Sea suggest that breeding is limited by access to foraging habitat, such as coastal polynyas. We hypothesise that as sea ice fluctuated over previous glacial-interglacial cycles, this also regulated breeding distribution across the region.