Feathers as a means of monitoring mercury in seabirds: Insights from stable isotope analysis

Mercury concentrations, together with nitrogen and carbon stable isotope signatures, were determined in body feather samples from northern fulmars Fulmarus glacialis and great skuas Catharacta skua, and in different flight feathers from great skuas. There were no significant relationships between trophic status, as defined using isotope analysis, and mercury concentration in the same feather type, in either species. Mercury concentrations in body feather samples were markedly different between fulmars and skuas, reflecting differences in diet, but there was no corresponding difference in trophic status as measured through nitrogen stable isotope signatures. We conclude that mercury concentrations and stable isotope values in feathers are uncoupled, mercury concentrations apparently reflecting the body pool of accumulated mercury at the time of feather growth whilst stable isotope values reflect the diet at the time of feather growth. There were significant positive correlations between the different flight feathers of great skuas for all three parameters measured. These were strongest between primary 10 and secondary 8, suggesting that these two feathers are replaced at the same time in the moult sequence in great skuas. Stable isotope analysis of different feathers may provide a means of investigating moult patterns in birds.