Hundreds of red-breasted mergansers have been found either dead or sick over the past few days along Lake Michigan in Chicago and into the northern suburbs.
Officials suspect that highly contagious bird flu is the cause of the illnesses found in the mergansers, a species of diving duck that winters in the Great Lakes region.
Chicago Bird Collision Monitors, a volunteer conservation group, began receiving reports Friday from people finding “large numbers” of mergansers along the shores from Hyde Park to Wilmette, the organization’s director, Annette Prince, said.
Two of the largest concentrations of sick mergansers — roughly 50 each — were found Saturday at North Avenue Beach and Oak Street Beach, Prince said. About the same number, if not more, were seen floating in the lake.
Prince estimated that around 200 to 300 infected mergansers were reported to her organization between Friday and Sunday.
It’s the first time that such a large number of mergansers has been suspected of bird flu infections, which has been on the rise in waterfowl and other birds throughout Illinois and the U.S. in recent months.
Last month, a bald eagle found in Hinsdale was euthanized after it appeared to be infected with bird flu, and in south suburban Matteson, a family-run farm lost its entire flock of nearly 3,000 hens to the disease.
“The spread has seemed to reach out to another species here with the huge number of mergansers that are currently showing all the symptoms of bird flu,” Prince said. “This is a real change in the kind of bird and in the numbers that we had seen.”
The majority of mergansers picked up by Prince’s organization were dead, she said, and the sick ones were “not surviving well,” but volunteers have picked them up to avoid other animals approaching them and getting infected.
Prince said seeing a merganser on land is the first clue that something may be amiss.
“They really shouldn’t be on land,” she said. “These birds only come on land when they’re in distress and no longer strong enough to fly or navigate the waters of the lakes, so it’s concerning if anyone notices these birds out of place from their typical aquatic environment.”
A couple other mergansers sick with suspected bird flu were found over the weekend in parking lots at Lincoln Park Zoo and the Old Orchard Center in Skokie, Prince said.
Symptoms of bird flu include weakness, inability to stand up and move, tremors, green diarrhea and general respiratory and neurological problems.
“We know this virus does very well in cold weather, and it’s going to stay around, as far as we know, until we get a break and warmer temperatures, so we’re worried that this could continue to spread to other species, other kinds of birds,” Prince said.
The U.S. Centers for Disease Control and Prevention has reported 67 cases of bird flu in humans since 2024, with almost all of the cases in people who worked with livestock or poultry. One human death from the virus has been reported — a Louisiana man with underlying health conditions who died last month.
As of Jan. 28, infections had been detected in more than 11,000 wild birds across the country since the outbreak started in 2022, according to the CDC.
Backyard and commercial poultry have suffered greatly from the disease, with nearly 150 million chickens, turkeys and other birds affected, the CDC said. It is also forcing farmers to slaughter millions of chickens a month, pushing U.S. egg prices to more than double their price from the summer of 2023.
Associated Press contributed.