Once endangered, bald eagles flock to Wisconsin

Posted April 15, 2021

The bald eagle population in Wisconsin is seeing a promising uptick in numbers since the 1970s after measures were enacted to protect the nation’s bird.

The U.S. Fish and Wildlife Service said that the bald eagle population has quadrupled since 2009.

Bald eagles were added to the federal government’s endangered species list in 1978 and removed in 2007. Since being removed from the endangered species list, the bald eagle population in Wisconsin has continued to increase.

Laura Jaskiewicz, a research scientist with the Wisconsin Department of Natural Resources (DNR), said that one of the main reasons the bald eagle population has been increasing is the banning of Dichlorodiphenyltrichloroethane (DDT) within the United States in the early 1970s. DDT was a chemical commonly used to control the population of mosquitoes to reduce the diseases that they carry.

Despite the growing bald eagle population in Wisconsin, Jaskiewicz said that in the western part of the state, the population decreased when the last eagle survey was done in 2019. This decrease in population was most likely due to an extreme cold front that year. Jaskiewicz said that though there were fewer populated nests in western Wisconsin in 2019, bald eagles continue to nest where there are large food sources, such as near the Kinnickinnic River.

According to the DNR’s 2019 survey, Pierce County had 21 occupied bald eagle nests, while St. Croix County had 10. Farther north, observers in Polk County reported 37 occupied nests. Burnett County had 67. Across Wisconsin, the survey found 1,684 bald eagle nests in 2019, compared to just 108 in 1973.

Margarate Rheude, a biologist with the U.S. Fish and Wildlife Service in Minnesota, said that there is a long history of trying to help the bird, starting with the Bald Eagle Protection Act of 1940 and later the banning of DDT. The Eagle Act was created to stop people from harvesting bald eagles.

“What DDT did was make eagle eggshells very thin, so when eagles would sit on the eggs, they would break,” Rheude said. She said that while DDT did not kill eagles that were already alive, the population of bald eagles was aging because of thin eggshells and lack of new eagle offspring.

Aside from the banning of DDT, Rheude said that people were eager to help with the protection of bald eagles to see an increase in population. Protection measures for nesting eagles were put in place so that the eagles could not be disturbed while nesting, and some volunteers would take part in “hacking,” or raising eaglets in a controlled and safe environment that allowed them to return to the wild.

“Eagles did a really good job of recovering themselves,” Rheude said. Since 2007, when eagles were removed from the endangered species list, most states ceased monitoring their eagle population. Rheude said that Wisconsin is one of the few states that continues to monitor its eagles yearly, aside from the year 2020 due to COVID-19 complications.

Rheude said that bald eagles thrive in areas with bodies of water, and because the eagle population has grown so much, they have begun to nest in areas that are unexpected. She said that eagles are nesting closer together than usual and in areas that are more populated by humans.

“Fortunately in Wisconsin there is no shortage of habitat for eagles to nest,” Rheude added. “It is a really great success story.”

Rheude said that there are no outstanding concerns for bald eagles to return to the endangered species list in the future, and there is still uncertainty at what point the bald eagle population will top out in Wisconsin with so much habitat to be occupied.