MEPS 242:267-274 (2002)  -  doi:10.3354/meps242267

Use of stable isotopes to investigate individual differences in diets and mercury exposures among common terns Sterna hirundo in breeding and wintering grounds

Ian C. T. Nisbet1,*, Joseph P. Montoya2,**, Joanna Burger3, Jeremy J. Hatch4

1I.C.T. Nisbet & Company, 150 Alder Lane, North Falmouth, Massachusetts 02556, USA
2Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138, USA
3Department of Biological Sciences, Rutgers University, Piscataway, New Jersey 08855, USA
4Department of Biology, University of Massachusetts, Boston, Massachusetts 02125, USA
*E-mail: **Present address: School of Biology, Georgia Institute of Technology, Atlanta, Georgia 30332, USA

ABSTRACT: We measured variations in stable isotope signatures (δ13C and δ15N) and concentrations of mercury (Hg) in breast feathers from pairs of common terns Sterna hirundo and their chicks at a breeding site in Buzzards Bay, northwestern Atlantic Ocean. By collecting 2 sets of feathers from the same adult birds, we compared values of δ13C, δ15N and Hg in feathers grown in the wintering area in the South Atlantic Ocean (Œsouthern¹ feathers) and in the breeding area (Œregrown¹ feathers). Regrown feathers had lower δ13C, higher δ15N and higher Hg than southern feathers. Values of δ13C, δ15N and Hg were much more variable in adults than chicks. Within families, δ13C and δ15N were correlated between parents and chicks; Hg was correlated between male and female parents. Among regrown feathers, Hg was positively correlated with δ13C and negatively correlated with δ15N. These findings suggest that high individual exposure of common terns to Hg results from consumption of inshore prey at low trophic levels in restricted parts of Buzzards Bay and that members of pairs have similar diets in the breeding season but not in winter. They demonstrate the power of stable isotope analyses in revealing individual differences in foraging habits, diet and contaminant exposure in generalist predators.

KEY WORDS: Common tern · Diet · Feathers · Foraging · Mercury · Stable isotopes · Sterna hirundo · Trophic web

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