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- Foraging behaviour of four albatross species by night and dayPublication . Phalan, Ben; Phillips, Richard A.; Silk, Janet R. D.; Afanasyev, Vsevolod; Fukuda, Akira; Fox, James; Catry, Paulo; Higuchi, Hiroyoshi; Croxall, John P.We integrated information from satellite transmitters, GPS loggers and wet/dry activity loggers to compare the at-sea behaviour of 4 sympatric albatross species by night and day: wandering Diomedea exulans, grey-headed Thalassarche chrysostoma, black-browed T. melanophrys and light-mantled sooty Phoebetria palpebrata (in total, 350 foraging trips by 101 individuals). Trip duration, distance and maximum range varied more within species between stages (incubation, broodguard and post-brood) than between species at the same stage, implying that reproductive constraints are more important than interspecific competition in shaping foraging behaviour. Wandering albatrosses spent more time on the water in fewer, longer bouts than other species. The proportion of time spent on the water was similar among the 3 smaller species. The partitioning of foraging activity between day and night varied little between species: all landed and took off more often, but spent less time overall on the water during the day than at night. This supports observations that albatrosses forage most actively during daylight, even though many of their fish and squid prey approach the surface only at night. Albatrosses were more active on bright moonlit nights, seem to have no fixed daily requirement for sleep, rest or digestion time on the water, can navigate in darkness, and are probably unhindered by the slight reduction in mean wind strength at night. They are probably less active at night because their ability to see and capture prey from the air is reduced and it is then more energy-efficient for them to rest or to catch prey using a ‘sit-and-wait’ foraging strategy.
- Movements, winter distribution and activity patterns of Falkland and brown skuas: Insights from loggers and isotopesPublication . Phillips, Richard A.; Catry, Paulo; Silk, Janet R. D.; Bearhop, Stuart; McGill, Rona A R; Afanasyev, Vsevolod; Strange, Ian J.In the first published study of the wintering ranges and activity patterns of skuas from any colony, we combined tracking (geolocator) and stable isotope analysis in a comparison of migration behaviour of brown skuas Catharacta lonnbergi and Falkland skuas C. antarctica from South Georgia and the Falkland Islands, respectively. Brown skuas, particularly failed breeders, departed and returned to the colony much earlier than Falkland skuas, and 2 of 3 brown skuas performed a pre-laying exodus. During winter, brown skuas were distributed widely over deep, oceanic water within the Argentine Basin (37 to 52° S) between the Antarctic Polar Front and the northern sub-tropical Front. Falkland skuas, by comparison, wintered mainly in subantarctic waters around the central Patagonian shelf-break (40 to 52° S). Much greater overlap existed among core areas within than between species, and sex did not influence distribution. The partial inter-specific spatial segregation was also reflected in a divergence in activity patterns, with brown skuas in flight for a greater proportion, and more time on average, during both daylight and darkness. Both species of skua spent far more time on the water than do foraging albatrosses, and there was limited overlap between their nonbreeding distributions and those of large procellariids from the same archipelagos. Stable isotope signatures of brown skua feathers indicated that distributions of tracked birds were typical of most or all of the breeding population, and were consistent from year to year. None was characteristic of species that winter on adjacent continental shelves or off south-west Europe. Isotope values also suggested a mixed diet for brown skuas of zooplankton, low trophic-level squid and fish, with little or no reliance on seabird predation or fisheries.