Concentrations of metals in feathers and blood of nestling Black-Crowned Night-Herons (Nycticorax nycticorax) in Chesapeake and Delaware Bays
Over the past decade, destruction and degradation of wetland habitat has contributed to the decline of wading bird colonies on the Atlantic Coast. In 1998, an initial assessment of the possible contribution of metal pollution to declining heron populations in Chesapeake and Delaware Bays was conducted. Study sites included two heronries in industrialized locations (Pea Patch Island, DE and Baltimore Harbor, MD), and a reference site (Holland Island) remotely located in the southern Chesapeake Bay. Concentrations of 19 metals, metalloids, and trace elements were examined in blood and breast feathers of 14-16 day old nestling black-crowned night-herons. Metal concentrations in blood were low and showed few site differences, though mercury was elevated at Pea Patch Island as compared to other sites. In feathers, metal concentrations appeared to be in the low to moderate range at all sites, though limited data exist for interpreting pollutant concentrations in feathers of nestling wading birds. Where differences were detected, concentrations at Pea Patch Island were consistently greater than those at Baltimore Harbor and Holland Island. Feathers collected at Pea Patch Island had significantly greater concentrations of aluminum, barium, iron, lead, magnesium, and manganese, but were generally found to be within the range of concentrations detected in other nestling birds, where that information was available. Based on these results, metal pollution does not appear to be an immediate threat to BCNH colonies at these two locations, though future monitoring of some elements (Pb, Mn, and Al) may be warranted.