2 days ago
- Health
- Scientific American
The Invisible Toll of Bird Flu on Wildlife
25,669 Northern Gannets in Canada.
134 harbor and gray seals along the coast of Maine.
21 California Condors in the western U.S.
These are just a tiny fraction of the wild victims of a strain of high pathogenicity avian influenza—what we colloquially call bird flu. The virus, which scientists call H5N1, has spread like wildfire around the globe in recent years, surprising and horrifying scientists at every unpredictable turn. And while most people have fretted about the rising price of eggs, the possibility of viruses in our milk and the risk of a pandemic in humans, countless wild animals are dying almost entirely out of our view—so many that even the limited tallies scientists can make are incomprehensibly large.
'It's easier to treat the numbers as numbers and not think too hard about what they really represent,' says Stephanie Avery-Gomm, a conservation scientist at Environment and Climate Change Canada. 'But if you do take that time to think about it, it's pretty sad.'
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She lived that reality firsthand in early 2022, soon after the killer strain of bird flu arrived in North America. Northern Gannets, which span the Atlantic and spend most of their year out to sea but breed every spring at six colonies in eastern Canada, started washing up on beaches. Hundreds of their massive white bodies littered the shorelines across the region. Scientists couldn't figure out the source, so they enlisted a helicopter to fly over the largest breeding colony in the region, capturing footage that still makes Avery-Gomm emotional years later.
'It showed absolute devastation,' she says. 'Just so many dead gannets.'
Extrapolating from reports of dead birds, she and her colleagues calculated that in six months avian influenza killed 25,669 of Canada's 213,704 tallied breeding Northern Gannets—literally decimating the population. Totaling across all species, her team calculated more than 40,000 wild birds died in the region's monthslong outbreak. Common Murres were the second most heavily affected species, with more than 8,000 dead. 'I don't think anything could have really prepared us for this mass mortality event,' Avery-Gomm says.
But the numbers that came later were even harder to bear. Wildlife scientists knew all along they weren't seeing every bird flu casualty on land, much less at sea, where it is more difficult to monitor species. And since avian influenza's devastation began, they haven't seen nearly as many birds at the breeding colonies as previous years. At the largest Common Murre breeding site in her area, Avery-Gomm says tallies are down 9 percent from before the outbreak; Northern Gannet reductions are more like 40 percent of the Canadian population. 'We have a lot fewer gannets in North America than we did in 2021,' Avery-Gomm says quietly.
A Totally New Bird Flu
7,000 Snow Geese in Idaho.
2,712 Humboldt Penguins in Chile.
9,600 Sandwich Terns in the Netherlands.
Bird flu viruses have been circulating for a couple centuries, popping up in historical records as 'fowl plagues,' says Wendy Puryear, a scientist at Tufts University, who tracks influenza viruses in wildlife. Ducks and geese tend to act as reservoirs for the virus, but domestic poultry are also susceptible.
In crowded modern farming operations, poultry are very susceptible. Killer strains of bird flu can wipe out 75 percent or more of a flock in just days, earning them the designation of high-pathogenicity avian influenzas—a classification that's traditionally only reflected fatality in farmed birds, not wild ones.
Puryear is among a host of scientists who have been monitoring avian influenza strains in wild birds for decades now, on guard for potential spillovers into poultry and humans. How wildlife weathered the virus has historically been of little concern—wild birds and waterbirds particularly have been carrying flu strains for ages without serious issues. 'There's this huge variation of influenza viruses that circulate out there in nature, in wild birds, and most of those, as far as we're aware, really don't cause much in terms of disease,' Puryear says. 'You don't see die-offs; you don't see an impact on their migration patterns—any sort of thing that we've been able to pick up.'
'We are in uncharted territory.' —Wendy Puryear, scientist, Tufts University
But influenza viruses are slippery beasts. Their genetic material is packaged on eight segments of RNA that can easily get swapped around into new arrangements when two different flu viruses infect the same animal. Sometimes this trading results in novel strains that cause more severe illness, spread more easily or survive better in particular species.
Scientists trace the heritage of the H5N1 virus that decimated Northern Gannets back to a goose in southern China in 1996. In the three decades since that infection, the virus has hopped around the world, swapping genes with local influenza viruses all along the way. In 2020—while the virus that causes COVID devastated humans worldwide—a group of bird flu viruses that scientists call 2.3.4.4b emerged and spread across swaths of Africa, Asia and Europe. By the late days of 2021, a virus in that killer strain made the leap across the Atlantic Ocean, showing up first in Canada, then the U.S.
And this bird flu strain is a whole new bird flu. 'We are in uncharted territory,' Puryear says. 'It's doing things that we had not observed with flu ever in the past, and it doesn't show signs yet of going away.'
Within months of bird flu reaching North America, scientists began detecting the virus in wild mammals—terrestrial and marine alike—in both the U.S. and Canada, as wild birds continued to turn up dead. Next, the virus zipped down into South America, then finally breached Antarctic islands and even the mainland in early 2024. And the harsh Antarctic winter didn't clear the disease, which returned with a vengeance during this year's southern summer. 'The entire Antarctic peninsula is covered in outbreaks,' says Marcela Uhart, a wildlife veterinarian at the University of California, Davis.
Today at least 406 wild bird species and 51 wild mammals globally have been infected. Australia is the only continent to remain free of the virus.
As it has spread, the virus has devastated some species and regions while leaving others unaffected. 'What's emerged is just this really complex picture,' says Brian Millsap, a raptor ecologist at New Mexico State University. 'It flares up in a place kind of out of the blue and then fades away.... Then it pops up somewhere else.'
The Hidden Declines
17,400 southern elephant seal pups in Argentina.
2,286 Dalmatian Pelicans in Greece.
24,463 Cape Cormorants in South Africa.
Scientists have seen glimpses of the virus's devastation, but the public has been largely unaware of the death unfolding often in the far reaches of the planet.
'This is a massive event, but I think it's pretty much invisible,' Uhart says. She watched as avian influenza blazed through a massive breeding colony of southern elephant seals in Argentina in late 2023. Of the year's pups, 96 percent died—some 17,400 animals. Even a few adults died at the colony, which is an unusual occurrence.
And much like Avery-Gomm's team, Uhart and her colleagues have only gotten worse news in the virus's wake. In late 2024 only one third as many adult females arrived at the colony's most densely populated beaches to breed as researchers were used to seeing. 'Instead of seeing long lines of animals, hundreds of animals and listening to their vocalizations,' says Claudio Campagna, a wildlife conservationist, 'it was a silent beach with a few animals and that's it.'
The huge reduction in animals at the colony suggests that many adult elephant seals had died of avian influenza at sea, out of scientists' view, says Campagna, who worked with Uhart to model potential recovery scenarios. 'It could take a century before we get back to 2022,' he says.
Fortunately, many of the mammals in the U.S. being reported ill or dead with avian influenza are of common species. Infected red foxes, coyotes and raccoons, for instance, are appearing relatively frequently—but not at nearly the scale of the marine mammal mass mortalities. And these are plentiful species, says David Drake, an urban wildlife ecologist at the University of Wisconsin-Madison, so he isn't too concerned.
Other species aren't as fortunate. Bald Eagles were one of the early species to suffer from bird flu, and scattered populations continue to fall ill. Between January and June of 2022, 136 dead eagles were confirmed to have avian influenza across 24 states. Rebecca Poulson, a wildlife disease researcher at the University of Georgia, watched the outbreak unfold along the Georgia coast. 'The reports of devastation from the field were just really sobering and daunting,' she says.
Bird flu has also hit Bald Eagle populations in the Great Lakes region, where Bill Bowerman, a wildlife ecologist and toxicologist at the University of Maryland, has been studying the animals for 40 years. Here, too, devastation. In Minnesota's Voyageurs National Park—dubbed 'eagle nirvana'—the iconic bird is now much harder to find than just a few years ago. Across the park, researchers found only four chicks last year.
Breeding adults are scarce, too. 'Two thirds of the nesting pairs are gone,' Bowerman says. 'It may take three decades for them to recover.'
The Limits of Data
5,500 Peruvian Pelicans.
600 Arctic Tern chicks in the U.K.
At least one walrus, plausibly six, on the Norwegian Svalbard islands in the Arctic.
The tallies of known dead animals and the calculations of missing breeders at colonies are heartbreaking, but there's a third number that's more distressing: the number of invisible deaths. 'A lot of mortality happens in wildlife and no one sees it,' Poulson says. 'These events might be happening in expanses of the country where there just aren't a lot of human eyeballs to see them and characterize them.'
Much of what Bowerman knows about Bald Eagles in the Great Lakes, for example, comes from the national park and from five sites he's monitoring as part of a pollution remediation project, watching eagles as a signal for the health of the ecosystem overall. The rest of the nation doesn't have that kind of monitoring in place.
And the problem isn't limited to Bald Eagles, Millsap says. Quite the opposite: Bald Eagles and Peregrine Falcons have more monitoring in place than most species he studies, after their near extinction in the 20th century. Other species—Merlins, Cooper's Hawks, Sharp-shinned Hawks—may be equally vulnerable bird flu but have never come as close to extinction. That means they don't have any dedicated surveys at all, so there's no sense of local or even regional declines. 'The bottom line is we're in a place where we don't know, and we may not have a mechanism to really know unless it's hugely catastrophic,' Millsap says.
And in order to really see the real effects of avian influenza, scientists needed these programs in place before the outbreak began, says Frank Baldwin, a waterfowl biologist at the Canadian Wildlife Service who studies Snow Geese. Because hunters target these birds, the government tracks them with a program that involves putting ID bands on individuals at their nesting sites across the Arctic. When a hunter kills a banded Snow Goose, they report it to the government, allowing scientists a glimpse of that animal's story.
The strategy has shortcomings: in the first few seasons of avian influenza, the team hadn't been able to band many birds as a result of the COVID pandemic, but the hunting data results looked normal. Then this spring, Baldwin began hearing more reports of dead geese, but he won't have any data until hunting season, beginning in the fall.
Still, it's better than no data at all. And it's exactly the sort of program that needs to be in place long before any unusual event begins in order to offer helpful insight. 'You can't just build these monitoring programs in a few years, the value of them is in their long-term nature,' Baldwin says.
Ecosystems in Flux
A polar bear in the North Slope of Alaska.
1,621 Caspian Terns in Washington State.
3,500 northern fur seals in southeast Russia.
Understanding the numerical impact on individual populations and species is only the first step of grasping the outbreak's scale.
Uhart worries that the devastated southern elephant seal colony in Argentina won't be able to breed as successfully into the future because of how many animals perished and that this can have larger repercussions. Already she's seen changes to the intricate harem system that governs breeding at the colony. 'The whole reproduction system was damaged,' she says. 'There was no social structure anymore.'
Large animal die-offs could also throw whole ecosystems in disarray, as deaths unfold within a network in which every species fills particular niches. The Northern Gannets of Canada, for example, act as apex predators for the ocean, Avery-Gomm says, feasting on fish such as mackerel and herring. With fewer gannets to eat them, fish populations may grow, potentially throwing off local balance.
'There's so many stressors that this is just an additional stressor that they really didn't need.' —Johanna Harvey, wildlife disease ecologist, University of Rhode Island
And during breeding season, the birds are on land, depositing nutrients they gobbled from the ocean into terrestrial ecosystems through their droppings. Each changed dynamic can send ripples deeper into the ecosystem, often in ways too subtle for scientists to detect.
And then there are the carcasses. Every ecosystem has ways to break down dead animals, but death at the scale of avian influenza can overwhelm that system. Indeed, scavengers such as Black Vultures and raccoons in the U.S. have been hit relatively hard by the virus, likely from trying to clean up infected corpses. 'Anything that might be feeding on infected individuals or mortalities, those are kind of sentinel species that give you an indication of how much virus is actually on the landscape that you're not detecting,' says Johanna Harvey, a wildlife disease ecologist at the University of Rhode Island.
A different ecological crisis highlights the potential costs of lost scavengers. In India, a veterinarian treatment used in cows decimated local populations of vultures that feasted on bovine carcasses. In much of the nation, vultures nearly disappeared—and now scientists have estimated that human death rates increased four percent in these areas from diseases spread by carcasses that vultures were no longer scavenging. Uhart worries similar issues may develop because of bird flu—particularly in Antarctica, where Brown Skuas that eat seal carcasses, penguin chicks and seabird eggs have been hard hit. Especially in Antarctica's harsh climate, 'if nobody is removing dead carcasses because there are no cleaners, well, the virus might just stay there,' she says. 'All those carcasses will be everywhere.'
Fears of Extinctions, Glimmers of Hope
It's not clear yet whether avian influenza will drive any species to extinction —but it's a close prospect for some. Overall, one in six of the bird species and fully a quarter of mammals affected by avian influenza are considered near threatened or worse by conservationists, according to research from Sergio Lambertucci, an ecologist at Argentina's national science agency, CONICET, and at the National University of Comahue.
Lambertucci also points to a California Condor—one of the rarest birds in the U.S.—was found dead of the virus in March 2023. Officials were so concerned that they took the unprecedented step of vaccinating condors against bird flu, but the damage was already done. Before the immunizations were ready to administer, 21 of the fewer than 600 living birds had died in the outbreak.
Uhart, meanwhile, worries particularly about the continuing toll of infections in the 22 species of albatross, which is one of the most threatened groups of birds in the world—and about what could happen if the virus finds its way into the about 1,600 living endangered Hawaiian monk seals.
After all, bird flu is not the only threat struggling species face. 'There are so many species that are already in decline,' Harvey says. 'There's so many stressors that this is just an additional stressor that they really didn't need.'
It's not all doom, though. Many researchers are finding protective antibodies to avian influenza in wildlife and have found them in some animals. 'There's good evidence from our group and many others that these animals, if they survive, can mount an immune response,' Poulson says of the eagles and many other species as well. No one knows yet how effective that immunity is or how long it can last, but it's a promising sign that some infected animals are surviving and may be better prepared to weather another infection. 'And that's true in lots of different species,' Poulson adds.
That's a small glimmer of hope as animals continue to get sick. Among the most recently reported infections of bird flu in U.S. wildlife: a round-tailed ground squirrel and a desert cottontail in Arizona. Red foxes in Colorado, New York and Massachusetts. A pair of Common Eiders in Maine. A Gambel's Quail and a Black-necked Stilt in Arizona. Five Black Vultures in South Carolina.
