The July 5 trip was routine: From the deck of an airboat, two wildlife biologists scanned the reed swamp, one of many seasonal wetlands in the Sacramento National Wildlife Refuge, in their weekly search for sick or dead birds. In the summer months, avian botulism is a major concern in California’s Central Valley, and removing carcasses can stop its spread. But this year, there was an added concern: A devastating new strain of highly pathogenic avian influenza (HPAI) had been spreading west across the continent since December 2021, affecting millions of poultry and countless wild birds.
That day, biologists carefully collected several carcasses, including two Canada geese and two American white pelicans, and sent the remains to the US Geological Survey’s National Center for Wildlife Health laboratory for routine testing. Days later, the lab and then the US Department of Agriculture confirmed: the H5N1 strain of bird flu had finally arrived in California.
This year’s bird flu epidemic, the first in North America since 2015, is caused by a version of this virus unlike any virologists and wildlife managers have seen. “It’s behaving by a different set of rules,” said Bryan Richards, coordinator of emerging diseases at the National Center for Wildlife Health. For the first time, it is spreading widely among wild birds, with far-reaching implications for wildlife and human health.
Wildlife are already facing unprecedented stressors, from droughts to wildfires to habitat loss. Now, the emerging and widely infectious forms of avian influenza are still another new and serious threat — one that wildlife biologists say requires a new approach to disease management on farms, refuges and landscapes across the country. “We are in the midst of an unprecedented wildlife disease outbreak in North America,” said Rebecca Poulson, a research scientist at the University of Georgia who has been studying bird flu for 15 years. “We’ve never seen anything like it.”
BEFORE 1996, Highly pathogenic avian influenzas were generally assumed to only infect commercial poultry farms: they were virulent but contained outbreaks caused by on-farm mutations of an influenza virus originating in wild birds. While they devastated those farms, the mutated strains seemed incapable of spreading back to wild birds. This made outbreaks easy to manage with biosecurity prevention, isolation of exposed flocks, and rapid culling.
In 1996, virologists first detected the H5N1 strain in domestic geese in Guangdong, China. That virus received worldwide attention in 1997 when it sickened 18 people in Hong Kong and killed six. The outbreak sparked international fears of a human pandemic, but the virus never mutated in a way that allowed person-to-person transmission. The international media paid less attention to the fact that, by 2002, H5N1 had acquired the ability to pass from domestic flocks to wild birds. The virus has been evolving ever since.
Today, several HPAI variants are associated with “sporadic mortality events” in wildlife. In Newfoundland and Labrador in 2021, current stress emptied the coastal cliffs of thousands of gannets, puffins and guillemots. This August, he killed 700 Black Vultures at a Georgia Sanctuary. Waterfowl, shorebirds, raptors, and scavengers are most at risk. In western states more recently affected by the virus, such species include threatened and endangered birds such as the California condor and snowy plover, though agencies have yet to document infections in either species. Urban and suburban common Canadian geese and corvids and the nationally symbolic bald eagles are also at risk, as are the hundreds of millions of waterfowl whose migrations are beginning to peak now in the northern states and will continue toward the south until the end of October.
“I think we are at the tip of the iceberg. We’re just holding our breath to see what’s going to happen.”
The last major outbreak, caused by a related strain, H5N8, reached North America in 2014, causing US farmers in losses of $3 billion, who had to cull 50 million chickens, turkeys and waterfowl. This year’s outbreak has so far affected similar numbers of commercial birds, but it is much larger in wild landscapes. Through transmission from wild birds, it has reached nearly 10 times the number of backyard poultry, and while the 2014-15 outbreak was documented in just 18 wild bird species in 16 states, this year it was confirmed in at least 108 species of wild birds. with cases in almost every state. In another unusual development, many cases of mammalian interbreeding and deaths have also been confirmed in foxes, skunks, opossums, raccoons, bobcats, mink, harbor seals, a juvenile black bear, and a bottlenose dolphin. Labs are so overwhelmed that wildlife officials say they have stopped shipping carcasses of species that have already been documented in their county. They are also shipping only a few birds per mortality event, making the official wild bird death figures a gross underestimate.
The next few months could be even worse. Flocks from across the continent are now migrating to Central and South America, home to the greatest diversity of bird species on Earth. “I think we are at the tip of the iceberg,” Poulson said. “We’re just holding our breath to see what’s going to happen.”
AMONG THE WESTERN STATES THIS FALL, California is more likely to feel the brunt of the impacts: It’s one of the nation’s largest egg producers, and commercial poultry is the state’s sixth-largest commodity, worth $1 billion annually. . California’s Central Valley provides essential migration and wintering grounds for wild birds: the Sacramento National Wildlife Refuge Complex alone is visited by tens of millions of migrants each fall. It supports nearly 40% of the continent’s northern ruddy ducks (one of the world’s most numerous duck species) and supports a total overwintering population of about 1.5 million birds.
This year’s drought means wintering flocks can be unusually crowded and especially mobile, raising the risk of viral spread, said Michael Derrico, the refuge’s senior wildlife biologist. Since the refuge’s wetlands are half their normal size, the birds will be forced to move closer and may move frequently to find resources, which Derrico believes may also push the birds further south.
“Once a disease becomes established in a population in the wild, then you really lose the advantage.”
Derrico’s concern for birds in the Pacific flyway is somewhat tempered by the fact that, so far, the country’s westernmost flyway does not appear to have as much virus as other regions. But he and other wildlife managers are also severely limited in what they can do to mitigate potential impacts.
“Once a disease becomes established in a population in the wild, you really lose the advantage,” said Richards, from his USGS headquarters near Madison, Wisconsin. “We’re very, very good at documenting disease in the landscape, but we’re less good at altering disease outcomes.” Instead, he said, “some of us are starting to turn towards a conversation about wildlife health rather than wildlife disease.”
For Derrico, at the Sacramento refuge complex, promoting health rather than preventing disease could mean investing more in wetland management to ensure birds have access to the largest possible habitat and minimizing human disturbance to prevent birds from disperse to new areas. In many parts of the country, bald eagles and other birds of prey are already experiencing widespread mortality from lead poisoning from bullets and fishing gear, and Richards said addressing that issue might be a better use of resources.
“That’s something we can control, right?” he said. Combined with improving biosecurity measures on farms, by addressing environmental factors beyond the reach of humans, Richards believes that wildlife managers can increase the resilience of birds even in the face of new deadly diseases.
The pressure to change wildlife disease management is only increasing. “When you look at emerging infectious diseases globally, we’ve seen some pretty interesting trends,” Richards said. “We have seen more new diseases, larger disease outbreaks, more frequently and with greater impacts.” That includes some with the potential to cause species extinction and, as seen recently with COVID-19, those that could mutate to become widely infectious and transmissible in humans. Virologists believe the risk of that happening in this H5N1 strain is low, but they recommend that hunters, farm workers and other bird keepers take extra precautions this year anyway. Of all the emerging diseases that threaten people, Richards said, the majority originated in wildlife.