Use of stable isotopes to investigate individual differences in diets and mercury exposures among common terns Sterna hirundo in breeding and wintering grounds
Nisbet, Ian C. T.
Montoya, Joseph P.
Hatch, Jeremy J.
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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 (‘southern’ feathers) and in the breeding area (‘regrown’ 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.