A conservation group in Chicago says hundreds of red-breasted mergansers, a species of diving duck that typically winters in the Great Lakes region, have been found sick or dead of suspected avian influenza — H5N1 bird flu — in the area over recent days.

From Hyde Park to Wilmette, wildlife monitors say they’ve discovered around 300 red-breasted mergansers dead or dying since Friday. The largest clusters were found at North Avenue and Oak Street Beaches.