SPATIAL PATTERNS OF PERSISTENT CONTAMINANTS IN BALD EAGLES NESTING ON THE ST. CROIX NATIONAL SCENIC RIVERWAY WITH COMPARISONS TO THE MISSISSIPPI RIVER AND LAKE SUPERIOR

Bill Route and Rebecca Key, National Park Service Great Lakes Inventory & Monitoring Network
Paul Rasmussen, Wisconsin Department of Natural Resources
Mike Meyer, Wisconsin Department of Natural Resources
Mark Martel, Audubon Minnesota

From 2006 through 2009 the National Park Service Great Lakes Inventory & Monitoring Network and its partners assessed levels of targeted environmental contaminants in bald eagle (Haliaeetus leucocephalus) nestlings from the St. Croix National Scenic Riverway, the Mississippi National River and Recreation Area, and the Apostle Islands National Lakeshore. Adjacent study areas were also added when funds were available, including a section of the Mississippi River from Hastings to the southern end of Lake Pepin and the entire south shore of Lake Superior in Wisconsin.

Over the four years of monitoring we conducted annual productivity surveys and collected a total of 154 plasma and 142 feather samples from 288 nestlings. From these samples we evaluated levels of six contaminants: total mercury, lead, DDT (and metabolites DDE and DDD), PCBs (75 congeners), PBDEs (9 congeners), and PFCs (16 different analytes).

All study areas produced ≥1.0 (range 1.0 to 2.2) young per occupied nest, which is considered the threshold for a healthy bald eagle population. Eagles nesting on the Mississippi and lower St. Croix Rivers were more productive than those on the upper St. Croix Riverway and on Lake Superior. Productivity was likely due to differences in prey availability and not contaminant levels.

Patterns in contaminant burdens provide insights into the sources, mechanisms of transport, and biomagnification through the food web. Generally, contaminants associated with industry and municipal waste (PCBs, PBDEs, PFCs, and lead) were found to be highest in nestlings near large population centers which included those from the lower St. Croix River. By contrast, nestlings from the upper St. Croix Riverway had the lowest levels of most contaminants with the exception of mercury. Higher mercury levels there are linked to the high density of wetlands in the upper watershed. Nestlings from remote islands of the Apostle Islands archipelago had higher levels of industrial contaminants and pesticides than expected. It is believed that Lake Superior receives these pollutants through aerial transport from global sources and that the Lake retains them for longer periods of time. We hypothesize that some "hot spots" we observed resulted from an additional trophic step in the food web at individual nest territories.