Food chain differences affect heavy metals in bird eggs in Barnegat Bay, New Jersey

There is an abundance of field data on levels of mercury in a wide variety of birds and on a suite of heavy metals in single species of birds, but few studies examine a suite of metals in a suite of birds that represent different trophic levels. Thus it is often difficult to determine whether food chain differences exist and have ecological relevance for the birds. In this paper I examine the levels of seven metals in the eggs of five species of marine birds that nest in Barnegat Bay, New Jersey to determine whether there are differences among species and whether such differences reflect food chain differences. There were significant differences among species for all metals, except cadmium, with black skimmers (Rynchops niger) having the highest levels of all metals except manganese and selenium. Metal concentrations in eggs mainly represented food chain differences. Mercury exhibited the greatest interspecific difference, with skimmer eggs having five times higher mercury levels than the eggs of great black-backed gulls (Larus marinus). Although there were significant interspecific differences in the other metals, they were generally less than an order of magnitude. There were few high, significant correlations among metals, although mercury was positively correlated with arsenic overall. Mean mercury levels exceeded the level known to adversely affect development in bird eggs for common (Sterna hirundo) and Forster's (Sterna forsterii) terns and for skimmers and exceeded the mean for eggs of fish-eating birds reported from 68 studies.