Mississippi National River and Recreation Area - Eagle Nest Survey in the Mississippi River's National Park (U.S. National Park Service)

The bald eagle population has made an extraordinary recovery; in 1995 the bald eagle's status was upgraded from endangered to threatened by the US Fish and Wildlife Service. Several direct and indirect legal decisions paved the way: the National Emblem Act of 1940 (the Bald Eagle Protection Act), its listing on the Endangered Species Preservation Act of 1966 and subsequently on the Endangered Species Act of 1973, and perhaps most importantly, the Clean Water Act of 1972 and the banning of DDT the same year.

From May 12 – May 23, 2008, the National Park Service collected data from nestlings in the Mississippi National River and Recreation Area and the St. Croix National Scenic Riverway to determine the persistence of various chemicals in these rivers. Rivers and lakes are the eagles' primary food source; fish and other birds associated with the water environment make up the bulk of the meals. Consequently, chemicals present in the Mississippi and St. Croix rivers ultimately show themselves in the samples taken from these birds.

While mother eagles circled above, wildlife biologists climbed to nests precariously perched high above the water to take blood and feather samples from the nestlings that call this river home.

For the third year Bill Route, Program Coordinator for the Great Lakes Inventory and Monitoring Network of the National Park Service, assembled and headed the team: Eco-Ascension Research and Consulting's Senior Biologist and Canopy Scientist Jim Spickler, and Biologist and Canopy Specialist Giacomo Renzulloprovided the primary climbing expertise and Mississippi National River and Recreation Area park partners Dan McGuinness and Mark Martell of Audubon Minnesota provided water transportation and bird handling assistance.

The team surveyed 47 nests in the Mississippi National River Recreation Area and St. Croix National Scenic Riverway and most were active. A total of 74 nestlings were sampled for contaminants in blood and feathers. Four addled (non-viable) eggs were also collected and will add to our knowledge of how much contamination is passed on to the young from the mother. Data collected from the nestlings will provide critical information about the health of the eagle population, and consequently the water quality in the park. "Eagles are the river's version of canaries in the coal mine; unhealthy trends show up in the birds long before they would surface in the human population," says Paul Labovitz, Mississippi National River and Recreation Area superintendent.

Blood samples are used to sex the birds and are also analyzed for levels of targeted new and emerging contaminants Perfluorooctyl Sulfonates (PFOS), a key element in weatherproof clothing and Scotchgard before it was removed in 2002, and Polybrominated Diphenyl Ethers (PBDE), a flame-retardant. Samples are also analyzed to determine levels of Dichlorodiphenyltrichloroethane (DDT) ,p-dichlorodiphenyldichloroethylene (DDE), the breakdown of DDT and Polychlorinated Biphenyls (PCBs).

Feather samples are analyzed for levels of mercury and lead. Measurements of weight, foot pad, beak, and talon can be used to estimate the birds health, sex and age. DNA tests will later verify the birds sex, and when combined with measurements of the 8th primary [feather], biologists can calculate age. (There are 10 primary wing feathers; the sheaths are engorged with blood to feed the feather while it grows; it will eventually outgrow the sheath, which will essentially disappear).

While the completed report is not expected for more than six months, preliminary observations show a very productive eagle population on the Mississippi and lower St. Croix Rivers. There were an abundance of nests in 2008 that had three healthy nestlings, something Route attributes to "very productive river systems, which reflect the success of the Clean Water Act and the banning of DDT." There was also a more varied age pattern compared to the two previous years with chicks ranging from one to 10 weeks-old. This may have been the result of a highly varied spring weather pattern. The abundance of food the river provides made for healthy looking nestlings. Compared to some populations, there appeared to be remarkably little evidence of competition between nestlings (nestlings of dramatically different sizes and/or having injury inflicted by their larger nestmate).

Laboratory analysis of the blood and feather samples will provide insights into the levels of contaminants in the water, which may not affect these long-lived birds until later in life. Stay tuned for updates as information, images and video clips become available and are added to the site.

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