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Wisconsin River Bald Eagle syndrome

Wisconsin River Bald Eagle syndrome is a name given to a specific group of signs which have consistently been found in sick or dead bald eagles in certain locations in Wisconsin, but for which a specific cause of those signs has not yet been found.

During the winter of 1994-95, 14 bald eagles were found sick or dead along the lower Wisconsin River in Sauk and Columbia Counties. Thirteen sick or dead bald eagles were found during the winter of 2000-2001 and the area had expanded to include Dane and Adams Counties. Fewer eagles with specific signs and lesions for this syndrome were identified in the subsequent years. However, in 2017, five bald eagles were found dead along the Fox River and Little Lake Butte des Morts in Winnebago, Outagamie and Calumet counties and one bald eagle found dead along the Branch River in Manitowoc county was determined to have died from this syndrome.

Extensive diagnostic testing for bacteria, fungi, viruses, parasites, and contaminants has not yet identified the cause. DNR staff continue to monitor bald eagles for this syndrome.


The cause and transmission of this syndrome are unknown.


Sick eagles are weak and show signs of neurological disease including incoordination, tremors and seizures. At necropsy, all the eagles have abnormal spaces in the cytoplasm of cells of the liver when observed under the microscope (microscopic hepatocellular cytoplasmic vacuolation). Some eagles also have microscopic lesions in the brain.


Because the cause of the syndrome is unknown, there are no management actions to take at this time.


There is no evidence to suggest this syndrome affects people.


Winter Mortality of Bald Eagles Along the Lower Wisconsin River, Mclaughlin, et al., 2004 Proceedings AAZV, AAWV, WDA Joint Conference, pages 312-313 [PDF exit DNR]