Understanding the Importance of Bird Migration as it Relates to Avian Influenza

I have been deeply involved in the avian influenza space and especially interested in the interconnectedness of the disease across all species. It is concerning the impact that migratory birds have on spreading the Highly Pathogenic Avian Influenza (HPAI) virus to other animals and how their migration patterns can be tied to outbreaks at poultry operations.

As fall is upon us and the weather is cooling down, I realize that most people are focused on school and homework, sporting events, and work. Unless you are a poultry producer or veterinarian, you may not be thinking too much about H5N1, an HPAI virus more commonly known as avian or bird flu, especially since the media coverage of the virus has lessened and the price of eggs has dropped over the summer months. We should not be lulled into complacency. Avian flu outbreaks tend to fluctuate up and down during the year—peaking in the fall through spring months due to bird migration patterns. The HPAI virus is still lurking behind the scenes and gaining ground in spreading disease, destruction and economic devastation in the coming months. We are already seeing upticks and devastation in cases that are reported including in the Dakotas, Minnesota and most recently Michigan. Experts in collaboration are projecting that this migratory season is gearing up to be the worst ever in the US.

Each year, thousands of wild birds, including waterfowl (ducks and geese), shorebirds (sandpipers, red knots and sanderlings), gulls, raptors (falcons and osprey) and scavenger species (vultures) migrate across North America in search of food and suitable nesting conditions.¹ Like human “snowbirds,” some fly south in the fall to stay warm and north in the spring to return to their seasonal home to breed. They traverse up and down migratory bird flyways across the US and Canada, stopping along the way to eat insects and nectar, as well as to disperse plant seeds.² Even if they show no signs of illness, wild birds that are infected with the H5N1 virus can easily spread the disease through their droppings as they mingle with other birds, including domestic poultry, each time they stop.

Even with these seasonal migrations, the number of birds affected in 2025 continues to rise—from 169 million in May to 174 million in June, and avian flu has been detected in flocks in all 50 states and Puerto Rico, according to the Centers for Disease Control and Prevention (CDC),⁵ which began tracking the disease in conjunction with the USDA in commercial poultry and backyard flocks in the US in February 2022.⁶ Since we are entering the peak months for the normal fall/winter migration of birds,¹ we are seeing a rise in the number of cases as the risk of spread increases.

And I feel with this increase comes the potential for more animals, and people, to become infected as HPAI is a zoonotic disease, meaning it is transmissible between animals and humans. Zoonotic diseases can spread when a person comes into direct contact with an infected animal, its bodily fluids, feces or respiratory droplets, as well as via contaminated food, water or insects like fleas and ticks.⁷ Direct or close exposure to any animal with HPAI is a potential risk for human infection.

 There is an economic toll to consider as well. At the end of 2024, American poultry and egg producers had already suffered $1.4 billion in losses.⁸ The ever-increasing threat and economic impact make animal surveillance and biosecurity all the more critical, not just from fall to spring, but year-round. The US Fish and Wildlife Service has increased its avian influenza surveillance of wild birds across the country through an Interagency Steering Committee for Avian Influenza Surveillance in Wild Migratory Birds.⁹ The committee is focused on end-to-end surveillance, including early detection, rapid communications, and broad reporting back to the field, to implement prevention and management actions swiftly, if needed.

In its $1 billion dollar comprehensive strategy to curb HPAI, the USDA has recognized the need for increased bio-surveillance and other innovative solutions to get ahead of outbreaks in commercial and backyard poultry flocks.¹⁰ APHIS is working closely with state animal health officials on surveillance efforts to look for the virus in commercial, backyard and wild birds.¹¹ Through its Defend the Flock Resource Center, it is also encouraging all bird owners to practice strong biosecurity by reducing opportunities for wildlife to spread the virus to their birds and preventing the spread of the virus from one location to another.¹²

Geolocation-linked diagnostics are critical for wild bird surveillance, where tracking HPAI’s spatial movement is essential to protecting domestic poultry.

Tests for various pathogens are key, as migrating wild birds have the potential to introduce new variants of avian flu into the highly susceptible poultry population, giving it opportunities to evolve. These birds are “hosts” to many different types of flu viruses categorized as low pathogenicity avian influenza (LPAI) or HPAI, depending on the severity of disease in poultry. In March, APHIS confirmed the presence of an HPAI, H7N9, in a broiler chicken breeder flock in Mississippi. ¹³ Although an H7 LPAI had been previously documented in US wild bird surveillance this year and in the past, it is the first HPAI H7 case in commercial poultry in the US since 2017. 

A June 23, 2025, podcast for Scientific American’s Science Quickly, highlights how “virus detectives” from St. Jude Center of Excellence for Influenza Research and Response are finding diverse, genetically new strains of bird flu that have evolved over time by collecting the droppings of shorebirds along the Delaware coastline.¹⁴ They do this to stay current with the viruses actively present in the flocks of migrating shorebirds.

Currently, wild bird testing in the US relies almost exclusively on polymerase chain reaction (PCR)-based diagnostics performed at authorized USDA laboratories. PCR is a highly precise test, but slow to return results due to the time it takes to ship samples to the lab and process them. Since many of these labs don’t have infinite capacity, bottlenecks occur in heavy outbreaks, which further delays the results.

While waiting days or weeks for results, the virus continues to spread through flocks, forcing health authorities to work with data from test results that are days to possibly weeks old. This is particularly problematic as clinical presentation in some wild bird species shifts from acute to delayed, and as sick or deceased birds increasingly enter rehabilitation and rescue networks. To address this gap, surveillance must expand to include decentralized testing directly at the point of collection, whether in the field, at a rehabilitation site, or during triage.

As wild birds continue to migrate across North America and infect poultry, the ability of knowing sooner, acting faster can allow producers, veterinarians, and government agencies to better manage spread and make better more informed decisions, quicker. By accelerating the development and deployment of innovative surveillance and biosecurity solutions, I feel strongly that we can protect the US poultry industry from a threat that is growing more serious as we progress through the migratory bird season. 

References
1.WSDA Blog. March 26, 2025. Accessed October 30, 2025. https://agr.wa.gov/about-wsda/blog-posts?article=42320.

2.Migratory bird flyways in North America., North Dakota Game and Fish Department, Public Domain. Accessed October 30, 2025. https://www.fws.gov/media/migratory-bird-flyways-north-america

3.APHIS. Confirmations of highly pathogenic avian influenza in commercial and backyard flocks.Accessed October 30, 2025.
Https://www.aphis.usda.gov/livestock-poultry-disease/avian/avian-influenza/HPAI-detections/commercial-backyard-flocks.

4. Bartels M. Bird Flu Is out of the News but Still Circulating. Scientific American. Published July 15, 2025. Accessed October 30, 2025. https://www.scientificamerican.com/article/bird-flu-is-out-of-the-news-but-still-circulating/.

5.USDA Reported H5N1 Bird Flu Detections in Poultry. CDC. June 13, 2025. Accessed October 30, 2025.
https://archive.cdc.gov/#/details?url=https://www.cdc.gov/bird-flu/situation-summary/data-map-commercial.html.

6.2020-2024 Highlights in the history of Avian influenza (Bird flu) timeline. Avian Influenza (Bird Flu). CDC. April 30, 2024. Accessed October 30, 2025. https://www.cdc.gov/bird-flu/avian-timeline/2020s.html.

7. Bird flu: causes and how it spreads. Avian Influenza (Bird Flu).CDC. April 23, 2025. Accessed October 30, 2025. https://www.cdc.gov/bird-flu/virus-transmission/index.html.

8. Avian influenza virus type A (H5N1) in U.S. Dairy cattle. Published September 15, 2025. Accessed October 29, 2025.https://www.avma.org/resources-tools/animal-health-and-welfare/animal-health/avian-influenza/avian-influenza-virus-type-h5n1-us-dairy-cattle

9. Avian Influenza.US Fish & Wildlife Service. Accessed October 30, 2025. https://www.fws.gov/avian-influenza.

10. USDA invests up to $1 billion to combat avian flu and reduce egg prices.USDA. February 26, 2025.Accessed October 30, 2025.
https://www.usda.gov/about-usda/news/press-releases/2025/02/26/usda-invests-1-billion-combat-avian-flu-and-reduce-egg-prices.

11. Confirmations of Highly Pathogenic Avian Influenza in Commercial and Backyard Flocks.USDA. Accessed October 30, 2025. https://www.aphis.usda.gov/livestock-poultry-disease/avian/avian-influenza/hpai-detections/commercial-backyard-flocks

12. Defend the flock. September 28, 2025. Accessed October 30, 2025. https://www.aphis.usda.gov/livestock-poultry-disease/avian/defend-the-flock/resources.

13. APHIS Confirms H7N9 Highly Pathogenic Avian Influenza (HPAI) in a U.S. Flock. March 2025.Accessed October 30, 2025. https://www.aphis.usda.gov/news/program-update/aphis-confirms-h7n9-highly-pathogenic-avian-influenza-hpai-us-flock.

14. Young LJ, DelViscio J, Mwangi F, Sugiura A, Feltman R. How H5N1 Went from an Illness in Wild Birds to a Global Pandemic Threat. Scientific American. https://www.scientificamerican.com/podcast/episode/how-h5n1-went-from-an-illness-in-wild-birds-to-a-global-pandemic-threat/. Published July 28, 2025.