Bald eagles serve as bio-sentinels of ecosystem health

posted Aug. 7, 2017 9:06 a.m. (CDT)
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by / Thomas Nicholls | Nature Education Center, Fifield

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    A Wisconsin DNR tree climber approached an American bald eagle nestling to be captured for banding and data processing on the Turtle-Flambeau Scenic Waters in Iron County as part of the DNR’s Wildlife Bio-sentinel Program.
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    Wisconsin DNR biologists prepared to “bag” an American bald eagle nestling to hoist it by rope back up into its nest after banding and data collection for the DNR’s Wildlife Bio-sentinel Program.
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    Biologists need to secure the feet of bald eagles while banding and data processing to protect themselves from sharp talons. The oldest banded nestling American bald eagle was banded in Minnesota and lived to be 38 years old.
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    An American bald eagle parent intently watched from a nearby white pine while its eaglet was processed by Wisconsin DNR biologists and returned to its nest.

The American bald eagle, our national bird, is once again on the front lines of providing important ecological information that will help people understand the health of the environment.

This fact was demonstrated to group of about 25 people who participated in a Natural Resources Foundation of Wisconsin-sponsored eagle-banding field trip in June on the Turtle-Flambeau Scenic Waters in Iron County. The flowage contains the seventh-largest body of water in Wisconsin and was acquired by the state in 1990. It comprises more than 35,500 acres of land and water, including 114 miles of mainland shoreline and 195 islands, many with campsites. The flowage is known for its scenery, fishery and high density of bald eagles, osprey and common loons.

People on the field trip were split into two groups and taken on a boat tour of the flowage by Wisconsin Department of Natural Resources biologists and managers to learn about the management of the area and see its scenery, forests and fishery and to watch the banding of nestling bald eagles.

The banding of eaglets in nests in Wisconsin is part of a larger effort called the Wildlife Bio-sentinel Program. This program, also part of a Great Lakes initiative, is designed as an “early warning system” in which sensitive wildlife are monitored to identify populations impacted by toxic substances such as PCBs, mercury, lead and dioxin, among others. The bald eagle, being at the top of the food chain, is an excellent sentinel species because, if toxins are present, they will often be concentrated in the tissues and blood of affected birds. Banding eaglets in nests and monitoring them over time can tell a lot about ecosystem health upon which all people depend to stay healthy. This day, three eaglets from two different nests were banded, and data was taken.

Being a bird bander myself, but of smaller birds, I was excited to witness the banding of a young eagle from a nest on the flowage. From a safe distance in a boat, a group watched as a DNR tree climber inched his way up a huge white pine, a favorite tree species of nesting bald eagles. It must be quite a feeling to come nose to beak with a large eaglet in a huge nest with parent eagles circling or perched nearby, intently watching as a nest intruder the size of a human approached their nest. The single young eagle was carefully caught, being mindful of its sharp talons and beak. Young eagles are transported from/​to their nest in a canvas bag by a rope. Once the bird was on the ground, the group was allowed to land their boat and watch the biologists do their work.

Once on the ground, DNR biologists banded the eagle with an official U.S. Geological Survey individually numbered lock-on band that needs to be riveted because eagles are so strong, they could otherwise remove it. After banding, many biological measurements were taken which indicated the eagle was a female and about seven to 10 days away from fledging. Tissues and blood samples were also taken for later toxicology tests as part of the Bio-sentinel Program.

After processing, some were allowed to touch the eagle. I have allowed hundreds of kids to touch or hold wild birds I had banded before being released, a great way to connect kids with nature, and to see kids’ eyes and faces light up with excitement is truly rewarding. When I touched this magnificent bald eagle being held by a DNR researcher, I felt an excitement and connection with nature that most people don’t have an opportunity to have. As the eagle was placed in the canvas bag and pulled back up into its nest by the tree climber, I thought what a privilege it was to have witnessed dedicated Wisconsin DNR research biologists doing their work to study and conserve wildlife and to monitor the health of the environment.

This isn’t the first time bald eagles and other raptors like ospreys have served as bio-sentinels of environmental health. Remember when raptors were almost decimated by the use of DDT, which thinned their egg shells to the point they broke before their young could successfully hatch? After DDT was banned in the 1970s, Wisconsin’s bald eagle population has grown dramatically. According to the Wisconsin DNR, there were only 175 nesting bald eagle pairs in the state in 1980, compared to 1,504 occupied nests in 2016, the largest number ever recorded in the state. Of the counties that were surveyed, occupied eagle nests were observed in 69 of 72 (96 percent) Wisconsin counties.

The bald eagle was removed from Wisconsin’s endangered species list in 1997 and from the federal list in 2007, a conservation success story. However, it remains protected by the Bald Eagle Protection Act of 1940. Now, bald eagles are common again in Wisconsin skies, helping provide information on environmental contaminants. This information will be used in scientific research to develop management plans and regulations to protect ecosystem health.

For more information about the Natural Resources Foundation of Wisconsin’s educational effort to protect and conserve the natural resources of Wisconsin or to sign up for their field trips, visit

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