Abstract
The diet of brown skuas (Catharacta antarctica lonnbergi) on Bird Island, South Georgia was assessed using a combination of stable isotope analysis (SIA) and mixing model techniques. We found evidence that individual specialisation in diet of adult brown skuas was related to timing of breeding, which may reflect differences in intrinsic quality. Adults with more enriched 13C values hatched chicks earlier than those with depleted 13C values. Individuals with enriched 13C fed predominantly on Antarctic fur seal (Arctocephalus gazella) carrion and placenta while those with lower ratios appeared to rely more on burrowing petrels (e.g. Antarctic prions Pachyptila desolata). Individual foraging differences clearly influenced timing of breeding and potentially the reproductive output of breeding pairs. We confirmed that the main components of the diet of brown skuas during incubation are, in decreasing order of importance, Antarctic fur seal placenta, burrowing petrels and fur seal muscle. In addition, we identified fur seal faeces in the diet during this stage, which had not been detected previously by traditional sampling methods. Finally we identified a correlation in δ13C values between pair members, attributable to the influence of courtship feeding of females by males, or assortative mating according to foraging preference or intrinsic quality.
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Acknowledgments
Our thanks go to the field workers on Bird Island, South Georgia, and to B. Phalan and D. Roberts in particular. O.A. was funded by a Department of Employment and Learning Northern Ireland grant. Stable isotope analyses were conducted at SUERC, East Kilbride with financial support from a NERC Life Sciences Stable Isotope Facility Grant. Thanks also to R. Inger for help and advice on the application of IsoSource and IsoError programmes.
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Anderson, O.R.J., Phillips, R.A., Shore, R.F. et al. Diet, individual specialisation and breeding of brown skuas (Catharacta antarctica lonnbergi): an investigation using stable isotopes. Polar Biol 32, 27–33 (2009). https://doi.org/10.1007/s00300-008-0498-9
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DOI: https://doi.org/10.1007/s00300-008-0498-9