DDT and PCBs no longer hinder Bald Eagles of Lake Superior
Ann Arbor, Mich. — In the 1970s, DDT decimated bald eagle reproduction along the shores of Lake Superior. In the 1980s, although conditions improved, DDT and PCBs still depressed these eagles' chances of successfully raising eaglets. But no more.
"In the 1990s contaminant levels finally dropped to nearly insignificant amounts", states Cheryl Dysktra, a researcher formerly affiliated with the Department of Wildlife Ecology at the University of Wisconsin-Madison. "We believe that ecological factors such as food and weather are now more important than contaminants in determining how successful eagles are at reproducing."
Dykstra and fellow researchers studied contaminant levels and reproductive rate in eagles along the Wisconsin coast of Lake Superior in the 1990s. They measured concentrations of total PCBs and DDE (a metabolite of DDT) in the blood of nestling eagles, and monitored the number of eagle nests and eaglets produced.
They discovered that the contaminant levels in eaglets were similar to the levels found in some normal, healthy populations. The number of eagle nests along the Lake Superior shore in Wisconsin increased steadily from 15 to 24 per year throughout the study period, and the eagles' reproductive rate averaged 1.0 young produced per pair, which is typical of healthy eagle populations.
Original Publication Information
Results of this study "Contaminant concentrations and reproductive rate of Lake Superior Bald Eagles, 1989-2001" are reported by Cheryl R. Dykstra, Michael W. Meyer, Paul W. Rasmussen and D. Keith Warnke in the latest issue (Volume 31, No. 2, pp. 227-235) of the Journal of Great Lakes Research, published by the International Association for Great Lakes Research, 2005.
Contacts
For information about the study, contact Cheryl R. Dykstra, 7280 Susan Springs Drive, West Chester, OH 45069; cheryldykstra@juno.com, (513) 779-1744.
For information about the Journal of Great Lakes Research, contact Marlene Evans, Editor, National Water Research Institute, 11 Innovation Boulevard, Saskatoon, SK, S7N 3H5, Canada; marlene.evans@ec.gc.ca; (306) 975-5310.
Since 1967, IAGLR has served as the focal point for compiling and disseminating multidisciplinary knowledge on North America's Laurentian Great Lakes and other large lakes of the world and their watersheds. In part, IAGLR communicates this knowledge through publication of the Journal of Great Lakes Research, available to members in print and electronic form. A searchable archive of the journal is available online and includes the abstracts of articles from the journal's inception in 1975 through the most recent issue. In addition, complete articles are available to members who have signed up for an electronic subscription.
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