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Marine Ecology Progress Series

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MEPS 345:281-291 (2007)  -  DOI:

Movements, winter distribution and activity patterns of Falkland and brown skuas: insights from loggers and isotopes

R. A. Phillips1,*, P. Catry2, J. R. D. Silk1, S. Bearhop3,6, R. McGill4, V. Afanasyev1, I. J. Strange5

1British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 0ET, UK
2Unidade de Investigação em Eco-Etologia, Instituto Superior de Psicologia Aplicada, Rua Jardim do Tabaco 44, 1149-041 Lisboa, Portugal
3Quercus School of Biology & Biochemistry, MBC, Queen’s University of Belfast, Lisburn Road, Belfast BT9 7BL, UK
4Scottish Universities Environmental Research Centre, Scottish Enterprise Technology Park, East Kilbride G75 0QF, UK
5New Island Conservation Trust, The Dolphins, Stanley, Falkland Islands
6Present address: Centre for Ecology & Conservation, School of Biosciences, University of Exeter, Cornwall Campus, Tremough, Penryn, Cornwall TR10 9EZ, UK

ABSTRACT: 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.

KEY WORDS: Foraging behaviour · Habitat preferences · Niche specialisation · Migration · Spatial segregation · Site fidelity

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Cite this article as: Phillips RA, Catry P, Silk JRD, Bearhop S, McGill R, Afanasyev V, Strange IJ (2007) Movements, winter distribution and activity patterns of Falkland and brown skuas: insights from loggers and isotopes. Mar Ecol Prog Ser 345:281-291.

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