The Department of Natural Resources confirmed highly pathogenic avian influenza, or bird flu, was found in a merganser recovered in early February on the Lake Michigan shoreline in Milwaukee County.
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| A hen red-breasted merganser feeds on a crayfish Feb. 9 in the Milwaukee harbor. Paul A. Smith |
A wild duck found in January along the Lake Michigan shore in Milwaukee County tested positive for highly pathogenic avian influenza, or bird flu, according to a Friday announcement by the Department of Natural Resources.
The bird, a red-breasted merganser, was among 21 birds taken in by the Wisconsin Humane Society's Wildlife Rehabilitation Center in Milwaukee between Jan. 2 and Feb. 10.
All were dead or so severely ill they were euthanized, said Mary Landry, WHS wildlife rehabilitator.
Bird flu was suspected in all the birds the center received. The merganser was submitted for confirmatory testing at the U.S. Geological Survey's National Wildlife Health Center in Madison.
The virus, which has circulated in wild and domestic birds in North America since late 2021, has caused the largest loss of poultry in the U.S. in at least 50 years and has killed untold numbers of wild birds.
As of Wednesday the U.S. Department of Agriculture reported 157.7 million poultry have been lost due to HPAI in the current outbreak. The toll on wild birds is much more difficult to estimate; 11,966 wild birds have tested positive for the disease so far, according to a USDA report. Experts say that number is a small fraction of the number of wild birds affected.
In 2022 Sumner Matteson of the DNR and other scientists documented the loss of at least 1,000 Caspian terns to bird flu on islands along the Door Peninsula in northeastern Wisconsin. That same year the virus was documented in dead adult and hatchling bald eagles in southeastern Wisconsin.
Internationally, many thousands of cranes have died during bird flu outbreaks in recent years at sites in Israel and Japan, according to the International Crane Foundation.
In recent regional events in wild birds, bird flu was found in a die-off of hundreds of waterfowl along the Lake Michigan shore in Chicago. From 200 to 300 dead birds, mostly red-breasted mergansers, were reported by observers in Illinois. The Michigan Department of Natural Resources has also reported 300 dead birds, mostly Canada geese, suspected with bird flu in five Michigan counties since Jan. 1.
The disease also has shown effects, but more limited, in wild birds in the Milwaukee area in recent weeks.
Since Jan. 2 the WHS wildlife staff received 21 birds suspected of having bird flu, Landry said. The total included nine red-breasted mergansers, three Canada geese, three Herring gulls, two red-tailed hawks and one each American crow, great-horned howl, mallard and ring-billed gull.
Birds that gather in flocks and breeding colonies are particularly affected by H5N1, as are raptors that scavenge on sick or dead birds infected with the virus.
Ducks, geese, swans, eagles, hawks, pelicans, cranes, gulls and terns are among the types of birds found dead and have tested positive for bird flu during the current outbreak.
The virus has also affected mammals, including dairy cows, domestic cats, red fox, otter, bobcat and fisher in Wisconsin. Human cases of bird flu, including one in Wisconsin, have been documented but the virus poses a low risk to humans, according to the Centers for Disease Control.
The most common type of HPAI seen in wild and domestic birds is H5N1. Sequencing results are pending on samples from the merganser obtained in Milwaukee. Scientists are monitoring the virus for potential changes.
Since mid-December, the DNR said HPAI has been detected in wild birds in six Wisconsin counties: Brown, Dane, Milwaukee, Racine, St. Croix and Wood. The majority of mortality reports have been for waterfowl, including various duck species, tundra and trumpeter swans and Canada geese.
"It is important to remember that avian influenza is still present in Wisconsin, and we are seeing it affect birds in isolated areas around the state," said Jasmine Batten, DNR Wildlife Health Supervisor. "However, this winter's HPAI detections in wild birds have remained relatively low. The best advice we can give is to remain aware and avoid handling wild birds as much as possible."
According to public health officials, the risk to the human health from avian influenza remains low. However health officials recommend people avoid handling sick or dead wildlife and, when possible, prevent their pets from coming into contact with sick or dead wildlife.
If you must touch a dead bird, the DNR recommends you follow guidance provided on the the agency's Avian Influenza webpage. More information on HPAI and public health can be found on the Wisconsin Department of Health Services' Avian Influenza A Virus webpage.
The DNR is interested in groups of five or more sick or dead wild birds. Depending on the specifics of the case, DNR staff will decide whether to collect a sample.
The public can report sick or dead wild birds through the DNR’s Sick or Dead Bird Reporting Form or by contacting the Wildlife Switchboard at DNRWildlifeSwitchboard@wisconsin.gov or 608-267-0866.
More information on avian influenza viruses and the ongoing response to this HPAI strain is available on the DNR’s Avian Influenza webpage. The DNR will continue to update the webpage with any future HPAI findings in wild Wisconsin birds.
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