How Are Migrating Wild Birds Affected By H5N1 Infection In The U.S.?

MICHAEL WARD

URBANA, ILLINOIS

Each spring, roughly 3.5 billion wild birds migrate from their warm winter havens to their breeding grounds across North America, eating insects, distributing plant seeds and providing a variety of other ecosystem services to stopping sites along the way. Some also carry diseases like avian influenza, a worry for agricultural, environmental and public health authorities. University of Illinois Urbana-Champaign professor of natural resources and environmental sciences Michael P. Ward, an expert on wild bird migration and conservation, spoke with U. of I. News Bureau life sciences editor Diana Yates about how H5N1 affects wild birds and how they contribute to its distribution across the U.S.

How is the H5N1 bird flu virus affecting wild bird populations in the U.S., and Illinois, specifically?

H5N1, avian flu, is of concern for wild birds, especially birds that congregate in large numbers. According to the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service, more than 11,000 wild birds have been found with H5N1 infection across the U.S. since January 1, 2022, with more than 114 detections in 2025 so far.

In Illinois, we saw a die-off of several dozen waterfowl, most of them snow geese, at Baldwin Lake in Randolph County late last year. This month already, hundreds of waterfowl were found dead on Chicago beaches, likely a result of bird flu. There are likely many more uncounted infections and mortality among wild birds.

At this point, however, I do not think H5N1 infection is having a large impact on wild avian populations, but we need to continue to monitor colonial breeding birds and other species that gather in large numbers.

Do the four migration flyways – Pacific, Central, Mississippi and Eastern – differ in how they affect or are affected by bird flu?

The different flyways have some different species, and, in some cases, there are locations where large numbers of individuals will stop during migration or in winter. Currently one of the concerns is for waterfowl. Most of the infected wild birds over the last year in Illinois have been ducks and geese. In the Mississippi flyway many waterfowl species have large populations along large rivers and thus we expect those areas might be impacted.

Do times of peak bird migration coincide with an uptick in bird flu infections in birds and other species in the U.S.?

The highly pathogenic avian flu can be difficult to detect and most often we notice the impact when the public finds dead birds. Because birds congregate in winter and during migration, the flu is more likely to spread. However, birds that breed in groups such as herons, egrets and other colonial waterbirds may also experience high infection rates. Given that we have been seeing more avian flu than usual, we need to be on the lookout for dead birds during all seasons.

What human activities contribute to or prevent the spread of diseases like H5N1 in wild birds or from wild birds to humans or other animals?

As with humans, flu can move between individuals, and when birds gather in large groups in close proximity to one another, there is the possibility that many individuals will become infected. Humans should avoid attracting large numbers of birds to one location, particularly waterfowl. Some people have been known to feed geese or ducks with bread in parks. This is a bad idea for many reasons, but an added concern is the possibility of geese and ducks infecting each other.

The largest economic issue is associated with avian flu getting into poultry farms, and many farms take precautions to keep wild birds away from their flocks. While extremely rare, there are documented cases of humans getting avian flu so people should avoid handling dead birds and areas with a large number of roosting birds.

Is the spread of new viruses among – and via – wild birds an inevitable fact of life?

Diseases continue to spread around the world, often being facilitated by humans. Therefore, we expect that new diseases will occasionally outbreak in wild birds. One way to reduce the probability of disease outbreaks is by maintaining large tracts of quality habitat, where birds can stay healthy and maintain natural spacing between individuals.

What should people do if they see dead birds on their property?

I would encourage people to report bird mortalities to the Illinois Department of Natural Resources. Do not touch dead or sick birds. If you decide to collect them or dispose of them, use gloves and enclose them securely in plastic.

Bird feeders are unlikely to be an issue, but it is also a good idea to disinfect bird feeders every few weeks. It is also very important to keep wild birds away from captive birds.   ∆

MICHAEL P. WARD: University of Illinois