Environmental Contaminant Exposure And Reproductive Success Of Black-Crowned Night-Herons (Nycticorax Nycticorax) Nesting In Baltimore Harbor (poster)

MCGOWAN, P.C., B.A. Rattner, J.S. Hatfield, C.S. Hong, and S. Chu.

The declining size of the Baltimore Harbor black-crowned night-heron colony has been hypothesized to be linked to PCB exposure as evidenced by high concentrations of toxic coplanar PCB congeners and cytochrome P450 induction in embryos, and substantial accumulation rates of PCBs in nestlings (Environmental Toxicology and Chemistry 16:2315-2322, 1997). In 1998, a "sample egg" was collected from 65 nests at the Fort Carroll heron colony for contaminant analysis, and the remaining eggs in these nests were monitored for hatching and fledging success. Eggs were also collected from 12 nests at a reference colony (Holland Island) in southern Chesapeake Bay. Samples were analyzed for 26 organochlorine pesticides and metabolites, total PCBs, and 145 PCB congeners. Pesticide and metabolite concentrations, including p,p'-DDE, were well below thresholds associated with adverse reproductive effects. Average concentration of total PCBs, 12 Ah receptor-active PCB congeners, and Toxic Equivalents (TEQs) in eggs from Baltimore were greater (average of 5 to >100-fold) than that observed at Holland Island. Despite substantial contaminant exposure, overall nest success in Baltimore Harbor was estimated by the Mayfield method to be 0.74. The mean number of young fledged/hen was 2.05, which exceeds the value necessary to maintain a stable heron population. Furthermore, concentrations of total PCBs, coplanar PCB congeners and TEQs were not found to be positively related with reproductive success. Processes other than poor reproduction (e.g., impaired post-fledging survival, emigration) may be responsible for the declining size of the Baltimore Harbor colony.