Current Impact of DDE on Black-Crowned Night-Herons in the Intermountain West

Abstract

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. J. WILDL. MANAGE. 48(1):1-13 DDT and its metabolites may have played a role in the decline of blackcrowned night-herons in the northeastern United States (Ohlendorf et al. 1978). For example, Anderson and Hickey (1972) reported 18% shell thinning by 1952 in New Jersey. The use of DDT in the United States was banned in 1972, and by the midto late 1970's, production rates at several locations in eastern North America (Wisconsin, Qu6bec, Rhode Island, and Massachusetts) appeared normal, eggshell thickness was normal or near-normal, and/ or residues of organochlorine pesticides were lower (Hoefler 1980, Tremblay and Ellison 1980, Custer et al. 1983), with the possible exception being Lake Ontario (Price 1977). Similar improvements have been reported for other species, including the osprey (Pandion haliaetus) (Henny 1977, Spitzer et al. 1978). An adult black-crowned night-heron died at Ruby Lake National Wildlife Refuge near Elko, Nev., in 1975-3 years after the DDT ban. Its brain contained 230 ppm DDE and 1.1 ppm DDT (wet weight) (Ohlendorf et al. 1979). Although DDE concentrations in eggs from the northeast were diminishing in the late 1970's, the mortality at Ruby Lake in 1975 led us to suspect that DDE was still a problem for bird populations in the Intermountain West. Most birds nesting in the region are migratory, and many winter in Latin America. We studied two colonies in 1978 and extended our efforts to eight colonies by 1980. This study was designated to (1) determine levels of DDE and other organochlorine residues in black-crowned nightheron eggs; (2) evaluate the most common contaminants in relation to shell thickness and egg breakage; (3) evaluate regional patterns and trends of DDE residues; (4) evaluate DDE in eggs in relation to productivity; (5) evaluate the source of the contaminants; and (6) evaluate residues in herons found dead to determine if pesticides were implicated. National Wildlife Refuge personnel who provided field assistance included S. H. Bouffard, J. E. Cornely, and S. P. ThompJ. Wildl. Manage. 48(1):1984 1 This content downloaded from 40.77.167.80 on Mon, 13 Jun 2016 06:09:49 UTC All use subject to http://about.jstor.org/terms 2 DDE IN BLACK-CROWNED NIGHT-HERONS * Henny et al.