Abstract
Breeding ecology of brown skuas (Catharacta antarctica lonnbergi) was studied at Bird Island, South Georgia in the austral summers of 2000/2001–2003/2004. A complete census recorded 467 breeding pairs in 3.55 km2 of suitable habitat (132 pairs per km2), and an additional 312 nonbreeders at club-sites. Comparison with previous counts indicates two phases of population change: an initial rapid increase (3.6% per annum) from the late 1950s to early 1980s, probably attributable to increased carrion availability from the expanding Antarctic fur seal (Arctocephalus gazella) population, followed by slower growth (0.9% p.a.). Currently, seal carrion dominates the diet of skuas during incubation, with a switch to seabird prey during chick-rearing. Breeding is now later, chick growth poorer, and productivity significantly lower than in the early 1980s. There is also a strong seasonal decline in adult attendance, and chicks that hatch later and are in poorer condition are less likely to fledge. These results suggest a long-term increase in competition for carrion that is particularly apparent once fur seal pupping has ceased.
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Acknowledgements
We are very grateful to Dafydd Roberts and Chris Green for helping with field work at Bird Island, Janet Silk for carrying out the spatial analyses, and John Croxall and two anonymous referees for helpful comments on the manuscript.
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Phillips, R.A., Phalan, B. & Forster, I.P. Diet and long-term changes in population size and productivity of brown skuas Catharacta antarctica lonnbergi at Bird Island, South Georgia. Polar Biol 27, 555–561 (2004). https://doi.org/10.1007/s00300-004-0633-1
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DOI: https://doi.org/10.1007/s00300-004-0633-1