The July 5 trip was routine: From the deck of an airboat, two wildlife biologists surveyed Cattell Swamp—one of several seasonal wetlands in Sacramento National Wildlife Refuge—in their weekly search for sick or dead birds. In the summer months, bird botulism is a major concern in California’s Central Valley, and removal of carcasses can limit its spread. But this year, there was an additional worry: a new and devastating strain of highly pathogenic avian influenza (HPAI) had been creeping west across the continent since December 2021, affecting millions of poultry and countless wild birds.
On that day, biologists carefully collected several of the carcasses, including two Canadian bison and two American white pelicans, and sent the remains to the US Geological Survey’s National Wildlife Health Center laboratory for routine testing. Days later, the laboratory and then the USDA confirmed that the H5N1 bird flu strain had finally reached California.
This year’s bird flu epidemic – the first in North America since 2015 – is caused by a version of this virus never seen before by virologists and wildlife managers. “It’s acting on a different set of rules,” said Brian Richards, emerging disease coordinator at the National Center for Wildlife Health. For the first time, it is widespread among wild birds, with far-reaching implications for wildlife and human health.
Wildlife is already facing unprecedented pressures, from drought to wildfires to habitat loss. Now, emerging and widespread infectious forms of avian influenza still exist Another new and dangerous threat An approach that wildlife biologists say requires a new approach to disease management in farms, shelters and landscapes across the country. “We are in the midst of an unprecedented outbreak of wildlife diseases in North America,” said Rebecca Paulson, a University of Georgia research scientist who has been studying bird flu for 15 years. “We’ve never seen anything like this before.”
Before 1996, It was widely assumed that highly pathogenic avian influenza only affected commercial poultry farms: these were virulent but contained outbreaks caused by on-farm mutations of the wild avian influenza virus. While it was devastating to those farms, the mutated strains seemed unable to spread again in the wild birds. This made it easier to deal with outbreaks through biosecurity prevention, isolation of exposed flocks, and rapid culling.
In 1996, virologists first discovered the H5N1 strain in domestic geese in Guangdong, China. This virus gained global attention in 1997 when it infected 18 people in Hong Kong, killing six. The outbreak has raised international fears of a human pandemic, but the virus has never mutated in a way that enables human-to-human transmission. The international media has paid less attention to the fact that by 2002, the H5N1 virus had acquired the ability to pass from domestic flocks to wild birds. The virus has been evolving since then.
Today, many types of highly virulent avian influenza are associated with “sporadic death events” in wildlife. In Newfoundland and Labrador in 2021, current stress has emptied coastal cliffs from Thousands of gannets, puffins and morays. In August, killed 700 black eagles in the Georgia Reserve. Waterfowl, shorebirds, raptors, and scavengers are most at risk. In western states hit by the virus recently, these species include threatened and endangered birds such as the California condor and snow plover, although agencies have not yet documented infections in either species. Canadian geese, urban and suburban corals and nationally symbolic bald eagles are also at risk, as are hundreds of millions of waterfowl whose migration is now beginning to peak in northern states and will continue south until late October.
“I think we’re on the tip of the iceberg. We’re kind of holding our breath to see what happens.”
The last major outbreak – caused by a related strain, H5N8 – reached North America in 2014, causing $3 billion in losses to US farmers, who had to cull 50 million chickens, turkeys and waterfowl. This year’s outbreak so far has affected a similar number of commercial birds, but is much larger in wild landscapes. Via wild bird transmission, it has reached nearly 10 times the number of backyard domestic birds, and while the 2014-15 outbreak has been documented in only 18 wild bird species in 16 states, this year it has been confirmed in at least 108 wild bird species. , with cases in nearly every state. In another unusual development, several cases of mammalian crosses and deaths have also been confirmed in foxes, skunks, opossums, raccoons, bobcats, mink, harbor seals, small black bear and bottlenose dolphin. The labs are so overwhelmed that wildlife officials say they have stopped sending carcasses of species already documented in their county. They also only deliver a small number of birds per mortality event, which makes official wild bird death numbers an understatement.
The next few months could be worse. Flocks migrate across the continent now towards Central and South America, home to the greatest diversity of bird species on Earth. “I think we’re at the tip of the iceberg,” Paulson said. “We’re kind of holding our breath to see what happens.”
Among the western states this fall, California is likely to feel the brunt of the effects: It is one of the largest producers of eggs in the country, and commercial poultry meat is the sixth largest commodity in the state, worth $1 billion annually. California’s Central Valley provides primary migration and wintering grounds for wild birds: The Sacramento National Wildlife Refuge alone is visited by tens of millions of immigrants each fall. It supports nearly 40% of the continent’s northern pentecostal (one of the world’s most numerous species of duck), and hosts nearly 1.5 million winter birds.
This year’s drought means that winter herds may be unusually crowded and especially mobile, increasing the risk of spreading the virus, said Michael Derico, the sanctuary’s chief wildlife biologist. Because the refuge’s wetlands are half their normal size, the birds will have to get closer and may move more frequently to find resources, which Derico thinks may push the birds further south.
“Once the disease has solidified in a free population, you really lose the upper hand.”
Derico’s concern about birds in the Pacific flyway is mitigated somewhat by the fact that, so far, the country’s westernmost migration channel does not appear to have as much virus as other areas. But he and other wildlife managers are very limited in what they can do to mitigate the potential impacts.
“Once the disease has solidified in a free population, you really lose the upper hand,” Richards said, from his USGS home office near Madison, Wisconsin. “We’re really good at documenting disease on the landscape, but we’re less efficient at changing disease outcomes.” Instead, he said, “Some of us are starting to shift toward a conversation about wildlife health rather than wildlife disease.”
For Derico, in the Sacramento Shelter complex, promoting health rather than disease prevention may involve increasing investment in wetland management to ensure birds reach the largest possible habitat, and minimizing human disturbance to prevent birds from scattering into new areas. In many parts of the country, bald eagles and other birds of prey are already experiencing widespread deaths from lead poisoning and hunting tackle, and Richards said tackling this problem may be a better use of resources.
“This is something we can control, right?” He said. Besides improving biosecurity measures on farms, by addressing environmental factors that are within human reach, Richards believes that wildlife managers may be able to increase birds’ resilience even in the face of deadly new diseases.
The pressure to change wildlife disease management is only increasing. “When you look globally at emerging infectious diseases, we see some very interesting trends,” Richards said. “We’ve seen more new diseases, more outbreaks, more frequent, greater impacts.” This includes some species that have the potential to cause species extinction and, as we’ve seen recently with COVID-19, species that can mutate to become widely infectious and transmissible in humans. Virologists believe the risk of this happening in the H5N1 strain is low, but they are advising hunters, farm workers and other bird handlers to take extra precautions this year anyway. Of all the emerging diseases that threaten people, the majority have originated in the wild, Richards said.