National Park Service researchers are again turning to bald eagles to determine how pervasive contaminants like lead, mercury and perfluorinated chemicals are along the Mississippi River.
Park service scientists on Monday will begin their annual survey of bald eagle nests. They hope to reach 49 nests within the Mississippi National River and Recreation Area before conducting the survey along the St. Croix River and on the Apostle Islands of Lake Superior.
The survey, which began in 2006, enlists professional tree climbers who reach the nests with cameras on their helmets. The tree climber then puts an eaglet in a sack, brings it down to the scientists for blood and feather samples, and then returns it.
Katie Nyberg, executive director of the Mississippi Fund, a nonprofit that supports the efforts, said the researchers have found that adult eagles are noisy during the process but don't attack the tree climbers.
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"Once the eaglet's been put back into the nest, everybody settles down and it doesn't seem to be a problem for either the eaglets or the parents," she said.
The scientists are interested in how various contaminants affect the eagles, but they are also interested in learning about pollution in and along the river.
"We're really using them because they're at the top of the food chain," Nyberg said. "So they just happen to be a great study subject to monitor these pollutants that tend to affect animals and humans throughout the environment."
Over the years, the researchers have seen contaminants like DDT, mercury and polychlorinated biphenyls (PCBs) decline. But in Lake Superior, DDT levels are still higher than what researchers expected, said Bill Route, who coordinates the survey for the National Park Service.
"Probably because of the deep, cold waters of Lake Superior, they just don't break down very fast," he said. "It's been more than three decades since they've been banned and we're still seeing levels that are high enough that for individual eagles, it may be detrimental."
And even while many contaminants are declining, Route said researchers are keeping an eye on flame retardants and perfluorinated chemicals (PFCs).
"While [companies] have taken some of those off the market, we really don't know what others they're putting in," Route said. "It's a constant effort to find out."
Route said the eaglet survey is a good indicator of contaminants in the nearby environment because the adult eagles generally don't travel long distances to look for food for their young.