Foraging and provisioning strategies of the light-mantled sooty albatross at South Georgia: competition and co-existence with sympatric pelagic predators
Foraging and provisioning strategies of the light-mantled sooty albatross (LMSA) Phoebetria palpebrata were studied during chick-rearing at Bird Island, South Georgia, in January to May 2003. Virtually all trips of satellite-tracked birds were restricted to Antarctic waters. Individual birds followed a diversity of foraging routes, the majority to shelf and shelf-slope areas along the southern Scotia Arc or to oceanic waters in the mid Scotia Sea, with only a few trips extending as far south as the marginal ice zone in the Weddell Sea. Sympatric white-chinned petrels Procellaria aequinoctialis, black-browed Thalassarche melanophrys and grey-headed albatrosses T. chrysostoma also exploit these areas. Unlike LMSA, these species and the wandering albatross Diomedea exulans, also forage on the shelf and shelf-slope waters surrounding South Georgia, or at the Antarctic Polar Front (APF), where the larger albatrosses and smaller, more manoeuvrable white-chinned petrel may out-compete LMSA for access to prey. As a consequence, foraging distances and maximum ranges are greater, chick-feeding frequencies are lower and chick growth rate is slower in LMSA than in sympatric Thalassarche albatrosses, and adult LMSA appear to have little capacity to regulate provisioning according to chick condition. Nonetheless, LMSA seem well-adapted to exploitation of distant foraging grounds, apparently using the wind to reduce flight costs and, in comparison with other albatrosses, spending more of the night on the wing and returning with food loads that represent a greater proportion of adult mass.