How bird flu affects the welfare of birds and other wild animals
January 16, 2025
Bird flu is emerging as a potential public health concern, with increasing cases and notable mutations among farmed animals, companion animals, animals in zoos, and humans. But for wild animals, avian influenza has already taken its toll.
The current strain of bird flu, H5N1, is spreading more quickly and prolifically than any previous outbreak of the disease. It began in Europe in 2020, where it initially impacted wild bird populations. Bird flu tends to have low pathogenicity when it first emerges in wild populations, with afflicted birds often presenting with mild or no symptoms. But when it spreads to farmed birds, that changes. On industrial animal farms, where very large numbers of chickens and turkeys are kept indoors in crowded and unsanitary conditions, the disease quickly spreads and mutates. When wild birds pick up the mutation, it becomes highly pathogenic. This is exactly what happened with H5N1, which has now become a panzootic — an animal pandemic.
At least 485 bird species have so far been affected, as well as 48 mammal species. Due in part to the migratory activity of wild birds carrying the virus, H5N1 has now spread to animals on every continent except Australia. In the air, on land, and at sea, hundreds of millions of wild animals have died of H5N1 since the outbreak began.
This has had severe consequences for wild animal populations, but also for the individual wild animals suffering with the disease.
Diseases likely have a detrimental effect on the welfare of many wild animals. Although much more research is needed to understand how specific diseases affect different species and individuals, we know that birds carrying some diseases exhibit behavioral signs of significant stress that correlate with their symptoms.
Symptoms of bird flu in wild birds
Symptoms of bird flu vary depending on the species an animal belongs to. In wild birds, the highly pathogenic H5N1 strain typically results in severe, noticeable symptoms. Some of the most common are:
Swollen head
Closed, runny eyes
Unresponsiveness
Lack of coordination, loss of balance, and tremors
Drooping wings
Dragging legs
Twisting of the head and neck
Discolored or watery droppings
Bleeding and redness of the legs and neck
Other symptoms may include breathing and respiratory difficulties like sneezing, coughing, and gurgling; lethargy and lack of movement, shaking of the head and body; and blue discoloration of the comb or wattle. Any sudden or dramatic increase in dead birds in an area can be a strong indicator of an avian influenza outbreak.
The spread of zoonotic diseases like bird flu has severe consequences for all animals: When it comes to H5N1, the welfare of humans, wild animals, and captive animals is intertwined. Without sufficient disease monitoring and strong efforts to control the virus, bird flu may continue to spread and mutate, threatening the health and welfare of people and animals.
How researchers can help
If you’re a scientist interested in the intersection of welfare and epidemiology, there are several ways you can incorporate wild animal welfare into your work. These include:
Incorporating a welfare metric into experiments: If you’re studying how a particular disease affects animals by cataloguing symptoms, you can score the welfare costs of those symptoms at the same time. To find out what metrics are available for your study species, take a look at our papers on metrics and do a broader literature search.
Including information about all animals in your study: If you’re researching disease spread or ecology, be sure to include information about all of the animals who are affected by diseases, including juvenile animals. This can help wild animal welfare researchers better understand the total welfare impact of a disease.
If you’re curious about how to apply your particular expertise to a research project on welfare and disease, get in touch with us. We can offer advice, direct you to funding opportunities, or introduce you to our network of researchers to help you find other scientists who are interested in welfare and epidemiology.
Learn more about bird flu
We’ve compiled a list of resources to help answer your questions about bird flu.
What’s going on with bird flu?
“Bird Flu, Explained” (The New York Times)
What is being done about the spread? Could bird flu be the next pandemic?
“A Bird Flu Pandemic Would Be One of the Most Foreseeable Catastrophes in History” (The New York Times)
“Inside the Bungled Bird Flu Response, Where Profits Collide With Public Health” (Vanity Fair)
“How Worried Should We Be About Bird Flu?” (Rolling Stone)
What to know to help protect yourself and the animals you live with (NPR)
How has bird flu affected wild animal populations?
Avian influenza resources (World Organisation for Animal Health)
Effects on avian biodiversity (The Guardian)
How bird flu affects marine animals (Dialogue Earth)
Minimising the risk of infectious diseases in garden birds (UFAW)
How do bird flu and disease affect wild animal welfare?
Bird flu symptoms in mammals (Centers for Disease Control and Prevention)
Understanding disease in birds (British Trust for Ornithology)
The impact of disease on avian welfare (Butterworth & Weeks, Animal Welfare)
