Bird Flu Affecting Migratory Birds, Especially Waterfowl

Recently, more than 100 dead birds—mostly merganser ducks—were found along Lake Michigan in Chicago, likely caused by bird flu.

Ducks, along with other waterbirds such as swans, gulls, geese and terns, are natural hosts for avian influenza viruses, according to a January 2025 abstract published by the National Library of Medicine.

The authors state that infection in other water birds, such as pelicans, herons and egrets, has been rarely reported. However, at least two American white pelicans in Minnesota were recently diagnosed with avian flu.

“The potential role of many water bird species in the ecology and epidemiology of these viruses remains undefined,” the authors wrote.

The Illinois Department of Public Health is monitoring waterfowl mortality throughout the state and has determined that these bird deaths were most likely caused by avian flu. The department advises the public not to handle or attempt to capture waterfowl or other wild birds displaying signs of illness.

The public is asked to report groups of five or more dead birds found in one location to Illinois Department of Natural Resources district wildlife biologists at WildlifeIllinois.org/idnr-district-wildlife-biologist.