Biologist Steve Mierzykowski holding an eagle. Credit: USFWS

Are banned chemicals still impacting Maine's bald eagles?

The Problem and Effects:
Studies have found that contaminants accumulate quickly in the bodies of the top predators like bald eagles. Two of those contaminants are DDT, a pesticide used through the 1960s, and PCBs, polychlorinated biphenyls found in a number of products.

DDT was a major reason for the decline of the bald eagle in North America in the 1950s and 1960s. DDT and its breakdown products, DDD and DDE, are toxic to embryos and disrupt calcium absorption and impair eggshell quality.

What We're Doing:
For more than a decade, the U.S. Fish and Wildlife Service has kept an eye on Maine's bald eagles to monitor the changing levels of contaminants in different tissues. To date, Service biologists have collected more than 75 non-viable or abandoned eggs, 60 plasma samples from coastal nestlings, more than 300 whole blood samples from nestlings occupying inland nest territories, shed adult feathers from over 100 nest territories and more than 50 livers from carcasses found dead.

Levels of DDE, a leftover from DDT, have decreased 20-fold in bald eagle eggs. In addition, levels of polychlorinated biphenyls (PCBs) in eggs appear to have decreased at inland areas, but biologists are currently evaluating recently collected egg data from coastal sites. For comparison, biologists have also collected plasma from eaglets being reared at estuarine and offshore island nests since 2009. Levels of DDE and PCB in plasma will be compared to collections from the early 1990s in coastal nest areas.

Mercury levels in eggs collected statewide have stayed surprisingly stable since the 1970s. On average, mercury levels are below suggested toxicity thresholds. Some areas, however, exhibit chronically elevated mercury levels in eggs that could impact reproduction and productivity. Inland, mercury in whole blood from nestlings and adult shed feathers shows a distinctly higher level in nests located on lakes than in nests located along rivers.

Reports on contaminant levels in eggs and on the coastal monitoring are in development and should be available by early 2013.

Learn more

---

Return to Regional Issues