Bald Eagles

Highly pathogenic avian influenza EA H5N1 affecting domestic and wild birds

A bald eagle is shown being treated at the Wisconsin Humane Society in Milwaukee.  The bird was found flightless on Friday in Bay View.  It is believed to be part of a pair that built a nest in the neighborhood.

The 2021-22 bird flu epidemic in North America is already the worst in seven years among US domestic flocks and evidence is mounting that it could be the deadliest ever documented among wild birds in America, including bald eagles.

The highly pathogenic avian influenza (HPAI) strain, called EA H5N1, has been circulating since late 2021. It had been detected in 38 states as of Monday, according to the US Department of Agriculture.

So far about 38 million domestic birds died in the outbreak, primarily through depopulations in infected poultry farms, according to federal figures.

This is the largest since 2015, when the H5N2 subtype of HPAI affected an estimated 49 million domestic birds. At a cost of $1 billion, the outbreak was the costliest animal health emergency in US history, according to the USDA.

The balance sheet of wild birds is much more difficult to assess.

During the last major avian flu outbreak, 98 HPAI-positive wild birds were detected between December 2014 and June 2015, according to the USDA. Most were waterfowl captured by hunters in the Pacific Flyway.

This number has increased more than 10 times in wild birds during the current epidemic, according to USDA figures released on Monday.

Of the 1,156 wild birds documented with bird flu in the past six months, three states have more than 100 cases (212 in North Dakota, 143 in North Carolina and 108 in Florida); Wisconsin had 51.

A map shows the 38 states with 2022 detections of highly pathogenic avian influenza (HPAI) in wild birds.

But wildlife experts say the number of birds tested is a tiny fraction of the number likely to be affected by the disease.

“It’s just not possible to find every diseased bird in the wild,” said Sumner Matteson, an avian ecologist with the Wisconsin Department of Natural Resources. “The tests tell us the disease is there, but not how many birds have it. The trend this year is certainly concerning.”