Mercury trends in herring gull (Larus argentatus) eggs from Atlantic Canada, 1972-2008: Temporal change or dietary shift?

► Monitored mercury in herring gull eggs from five sites in Atlantic Canada from 1972 to 2008. ► Egg mercury trends were adjusted for dietary shifts using stable C and N isotopes. ► Decreasing temporal trends in stable isotopes at four colonies suggested shifts in the gull diets. ► Diet-adjusted egg mercury levels were stable over the monitoring period at four sites. ► In Newfoundland gull eggs: mercury increased, then dropped abruptly, and rose again.