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.
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.”
The global spread of bird flu is largely due to migrating waterfowl, according to the USDA.
Knowledge of migratory patterns and intercontinental associations of waterfowl, as well as genetic analyzes of virus strains, have supported the hypothesis that previous HPAI outbreaks entered North America from Asia via birds. migrants.
Wild waterfowl and other species shed the virus in the environment through their oral and nasal secretions and feces.
Scavenger and predatory species can also catch the virus by feeding on infected dead or alive birds.
Symptoms of birds with avian flu include swimming in circles, twisting of the neck and shaking.
Among Wisconsin domestic birds, the virus has been found in poultry in Barron, Dunn, Fond du Lac, Jefferson, Marinette, Pierce, Polk, Racine, Rock and Sauk counties, according to Monday’s USDA report. and affected eight commercial flocks, 13 backyard flocks for a total of 3,027,690 birds.
Among the state’s wildlife, the disease has been linked to the wild bird death in Milwaukee County (Canada goose), Brown County (herring gull), Columbia County (lesser scaup), Dane County (bald eagle, Cooper’s hawk, and red-headed vulture), the Grant County (red-tailed hawk), Polk County (trumpeter swan), St. Croix County (wood duck), and Winnebago County (American white pelican).
Other wild bird species documented with the disease across the continent include the common loon, double-crested cormorant, great horned owl, hen harrier, peregrine falcon and snow goose.
It has also been detected in wild red fox kits in Wisconsin, the first such finding in a mammal in the state.
The bird flu outbreak is raising concerns about its potential to significantly reduce the recruitment or survival of young birds, particularly bald eagles and other raptors.
Since May 15, the Raptor Center in Minneapolis had tested 283 birds admitted for care and 169 tested positive for HPAI. Only one affected bird survived to be released, according to the center.
Madison Audubon has run a Bald Eagle Nest Watch program since 2018 in Wisconsin. The citizen science effort includes frequent monitoring of eagles’ nests from winter mating season through spring and summer fledging.
From 2018-21, the program recorded 28 eagle nest failures out of 187 observed nests, or 15%. This year, the failure rate jumped to 35% out of 145 monitored nests.
The failures included cases where the adults left the nest, apparently because the chicks were dead, and at least one case where the adults disappeared, said Brenna Marsicek, director of communications and outreach for Madison Audubon.
In one well-documented case, an adult bald eagle was euthanized after it was found flightless near its nest in Bay View in Milwaukee County. It was later determined that the bird had bird flu.
Marsicek warned that since none of the chicks were tested for HPAI, the causes of the nesting failures cannot be attributed to bird flu.
“In the five years we’ve had this program in place, this year the percentage of failures is much higher,” Marsicek said. “Something seems to be happening. For now, we will continue to work to monitor the birds and assist with disease documentation efforts to learn more.”
Wildlife health experts at the Raptor Center hope the warmer weather will help slow disease transmission over the next few weeks.
The DNR recommends that people wear gloves if they must come into contact with a sick or dead bird. After contact, wash your hands with soap and water and discard the gloves.