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Young Eagles Tell Story of Great Lakes Pollution

Eaglets in nest with Lake Superior in the background.

Apostle Island eaglets have a bird’s eye view of Lake Superior from their nest. Photo courtesy of Craig Thompson, Institute for Wildlife Studies

This summer, several professional climbers scaled over 60 trees in five of the region’s national parks, daring to look over the broad rim of eagle nests swaying slightly above the forest canopy. Parent eagles circled and dutifully fussed but didn’t attack as their offspring were gently tucked into handcrafted “eagle bags” and lowered to the ground. Touching terra firma for the first time didn’t seem to phase the plump 5 – 8 week old eaglets. Even when ecologist Bill Route measured and weighed them, then collected a blood sample and clipped a few feathers from their fuzzy chests, most eaglets acted as if such handling were routine, if not dull.

Route is coordinator of the Great Lakes Inventory and Monitoring Network, a National Park Service program based out of Ashland, Wisc. He’s leading an effort to monitor air quality, water quality, plant and wildlife populations, and land use throughout nine national parks in the Great Lakes. Vital signs selected for monitoring were chosen by scientists and natural resource managers. Several programs were initiated in 2006; one of these is the study of contaminants in eaglet tissues to track trends among the parks. Minnesota Sea Grant is helping the network explain their activities and findings to the public.

Map indicating the location of all 9 Great Lakes Inventory and Monitoring Network observatories./

The Great Lakes Inventory and Monitoring Network is one of 32 networks contributing to the National Park Service’s endeavor to monitor natural resources and manage them with science-based approaches. The Great Lakes Inventory and Monitoring Network involves nine areas that each have significant waterways:

  • Voyageurs National Park
  • Grand Portage National Monument
  • Isle Royale National Park
  • Apostle Islands National Lakeshore
  • St. Croix National Scenic Riverway
  • Mississippi National River and Recreation Area
  • Pictured Rocks National Lakeshore
  • Sleeping Bear Dunes National Lakeshore
  • Indiana Dunes National Lakeshore

The Anishinabe have long acknowledged that Mi-Ge-Zi, the American bald eagle, is a messenger — a conduit between humans and the creator. About 50 years ago, humans realized that these iconic birds also carried warnings from the environment about the effects of contaminants like DDT.

“It’s important to listen to the messages received from eagles and the other environmental indicators,” said Route. “The park service has embarked on a nationwide effort to monitor critical indicators. The more managers understand about how the environment is changing, the better they can react to preserve ecosystem integrity.

“Even at less than two months old, an eaglet’s tissues harbor contaminant levels that mirror the quantity and type in the surrounding waters,” Route said. “A few milliliters of blood and a couple of feathers can tell us a lot.”

Despite their youth, bald eagle chicks are particularly suited to their new role as ecological sentinels. The reasons for this include:

  • They are at the top of the food web
  • Persistent bioaccumulative toxins (PBTs) collect in their bodies quickly and young eagles are highly sensitive to them
  • Standardized methods for analyzing samples exist, saving time and money
  • Comparable data from the region dates back to 1989, providing a historic baseline

The park service’s monitoring team and cooperators from Clemson University collected blood and feathers from nearly 100 eaglets and sent the samples to laboratories where they will be analyzed for DDT, PCBs, mercury, and some new and emerging pollutants. One of these is perflourooctane sulfonate (PFOS), which was a key ingredient in Scotchgard™ before it was reformulated in 2002. Extremely resistant to decay, PFOS have accumulated in wildlife and people from the arctic to the equator. The human health risks of this persistent chemical and others like it are under investigation.

As in the case of DDT and PCBs, which are now banned from use in the United States but are still used elsewhere, it is clear that certain chemicals released into the environment through human activities accumulate in animal tissues to
concentrations that cause reproductive, developmental, and other complications. Scientists have difficulty showing biological and physical damage from PBTs for small, short-lived, plant-eating creatures, but plenty of evidence shows PBTs can build to harmful — sometimes lethal — levels in organisms at the top of the food chain, where animals live longer and eat more flesh.

For people, the main route of exposure to these toxins seems to be through eating contaminated meat. The same is true for bald eagles. Eagle nestlings inherit very little contamination from their mothers but after hatching, begin retaining PBTs with each meal.

In the 1960s, the levels of PBTs were high enough to cause shell failure and lethal abnormalities in chicks of some species of birds. Around Lake Superior, concentrations have declined significantly and are now at or below the “no observable adverse effect” level for reproductive impairment.

Bill Route testing an eaglet.

Bill Route tests a young eagle on the Apostle Islands for contaminant levels as part of a coordinated effort to monitor environmental conditions at nine national parks in the Great Lakes. Photo courtesy of Craig Thompson, Institute for Wildlife Studies

As some of the most devastating PBTs have waned, bald eagles, other birds of prey, and other fish-eating birds and mammals have fared well.

“Since this was our first summer in the field, we have little data to share,” said Route. “That will change.” The network is currently building a Web site where park managers, scientists, and the public will be able to access the information. Results of the eaglet PBT levels should be available in 2007.

For updates on the vital signs of the region’s national parks, continue checking the Great Lakes Inventory and Monitoring Network’s Web site or call their office, (715) 682-0631.


By Sharon Moen
October 2006

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