Diet and long-term changes in population size and productivity of brown skuas Catharacta antarctica lonnbergi at Bird Island, South Georgia

• Published in: Polar Biology
• Main Authors: Phillips, R.A., Phalan, B., Forster, I.P.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Springer 2004
• Subjects: Zoology; Ecology and Environment; Antarctic; Austral; Bird Island; Antarc*; Antarctic Fur Seal; Antarctica; Arctocephalus gazella; Polar Biology
• Online Access: http://nora.nerc.ac.uk/id/eprint/12340/; http://www.springerlink.com/content/4g1gjpnyel3lkfvm/fulltext.html

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 km(2) of suitable habitat (132 pairs per km(2)), 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.