Current impact of DDE on black-crowned night-herons in the intermountain west

Organochlorine contamination was studied in eight black-crowned night-heron (Nycticorax nycticorax) populations nesting in Washington, Oregon, and Nevada in 1978-80. DDE was detected in 220 eggs sampled; eggshell thickness was negatively correlated with residues of DDE and polychlorinated biphenyls (PCB's). Other contaminants were detected in 35% or fewer of the eggs. Except for the two Columbia River colonies in which local DDE contamination was a probable compounding factor, a strong north-south clinal pattern of DDE residues among colonies existed. Southern colonies were most contaminated, and observed productivity was below population maintenance in one colony (Ruby Lake). At DDE levels in eggs above 8 ppm, clutch size and productivity decreased, and the incidence of cracked eggs increased. No evidence of breeding-ground DDE-DDT contamination was found except along the Columbia River.