Organochlorine contaminant exposure and reproductive success of black-crowned night-herons (Nycticorax nycticorax) nesting in Baltimore Harbor, Maryland

The declining size of the Baltimore Harbor black-crowned night-heron (Nycti corax nycticorax) colony has been hypothesized to be linked to polychlorina ted biphenyl (PCB) exposure. In 1998, a "sample egg" was collected from 65 black-crowned night-heron nests (each containing greater than or equal to t hree eggs) for contaminant analysis, and the remaining eggs in these 65 nes ts, plus four two-egg nests, were monitored for hatching and hedging succes s. Eggs were also collected from 12 nests at Holland Island, a reference si te in southern Chesapeake Bay. Samples were analyzed for 26 organochlorine pesticides and metabolities and 145 PCB congeners. Pesticide and metabolite concentrations, including p,p'-DDE, were well below thresholds associated with adverse reproductive effects at both sites. Average concentration of t otal PCBs, 12 Ah receptor-active PCB congeners, and toxic equivalents in eg gs from Baltimore Harbor were greater (up to 35-fold) than that observed in Holland Island samples. Overall nest success at the Baltimore Harbor heron ry was estimated by the Mayfield method to be 0.74, and the mean number of young fledged/hen was 2.05, which is within published productivity estimate s for maintaining a stable black-crowned night-heron population. Using logi stic regression, no significant relationships were found between organochlo rine contaminant concentrations in sample eggs and hatching, fledging, or o verall reproductive success. Processes other than poor reproduction (e.g., low postfledging survival, emigration, habitat degradation) may be responsi ble for the declining size of the Baltimore Harbor colony.