Every spring, more than 200,000 northern gannets — stocky seabirds with dazzling white feathers — journey to the coast of eastern Canada. There, they blanket oceanside cliffs and rocky outcroppings, breeding in enormous colonies before flying back south for the winter.
But in May 2022, as many females were getting ready to lay their eggs, the birds began dying in droves. “Thousands of northern gannets started to wash up on our shores,” said Stephanie Avery-Gomm, a seabird biologist and research scientist at Environment and Climate Change Canada.
The culprit: a bird flu virus, known as H5N1, that had recently arrived in North America. Over the months that followed, the virus raced through the region, killing tens of thousands of northern gannets.
The carnage was “devastating,” Dr. Avery-Gomm said. “You have to harden your heart to work on this kind of scale of mortality.”
Since a new version of H5N1 emerged in 2020, scientists have become increasingly concerned that the virus might set off the next pandemic, infecting people around the globe. But for the world’s wild birds, the prospect of a deadly, uncontained outbreak is not theoretical. The virus has already decimated avian populations around the globe, with body counts that can sometimes be staggering: an estimated 24,000 Cape cormorants killed in South Africa, more than 57,000 pelicans reported dead in Peru.
“The scale of the mortalities is truly unprecedented,” said Johanna Harvey, an avian disease ecologist at the University of Maryland. “There’s nothing comparable historically.”
Wild birds are poorly monitored, and the true global toll remains unknown, as do the long-term consequences. But a few years into the avian outbreak, it is clear that the virus is an unwelcome new danger to animals that are already under intense threat from climate change, habitat loss, overfishing and other human activities.
“This disease isn’t being popped into a lovely, pristine, resilient ecosystem,” said Ruth Cromie, the coordinator of a United Nations task force on avian influenza and wildlife. “This is a disease that is adding pressures to species that are already really up against it.”
She added, “I feel like the worst isn’t done yet.”
‘Falling out of the sky’
Historically, the H5N1 virus, which has been around for decades, has primarily affected farmed poultry. But the virus is constantly evolving, and the version that emerged in 2020 “was a different sort of beast,” said Rebecca Poulson, an expert on avian influenza at the University of Georgia. It seemed much better adapted to wild birds, which soon carried the pathogen all over the world, to places as remote as Antarctica.
Wild birds weren’t just vectors for the virus — they were also victims of it, and reports of dead gulls and geese began to pile up. “We had many early reports of these birds quite literally falling out of the sky as they were succumbing to illness,” Dr. Poulson said.
Since October 2021, more than 117,000 dead wild birds — from 315 species in 79 countries — have been reported to the World Organization for Animal Health. But because many wild bird deaths are never detected, let alone reported, the true scope of the problem is likely to be much larger — what could be the biggest threat to wild birds “in a generation,” said Gregorio Torres, who leads the organization’s science department.
So far, the toll has been uneven, with some types of birds suffering from especially heavy losses. Seabirds, for instance, “are taking a hammering,” said Michelle Wille, an avian flu expert at the University of Melbourne in Australia.
Those disparities may stem from differences in biological susceptibility and behavior. Most seabirds breed in large colonies, giving the virus ample opportunity to spread. Northern gannets have 53 breeding colonies on both sides of the Atlantic; in 2022, unusually high mortality rates were documented at 75 percent of them.
The virus also tore through the world’s gull and tern populations. It wiped out roughly 36 percent of Peru’s namesake pelicans and 13 percent of Chile’s Humboldt penguins. It killed so many great skuas that Britain added the birds to its “red list” of species of highest conservation concern.
There is no evidence that the virus has driven any of these species to the edge of extinction, and experts have seen encouraging signs of immunity in some survivors. But large-scale losses could make these populations more likely to succumb to whatever threat pops up next, whether it’s another outbreak, a heat wave or an oil spill. “They may be pushed further to the brink,” said Dr. Samantha Gibbs, a veterinarian at the U.S. Fish and Wildlife Service.
Seabirds also tend to be slow to reproduce, which means that it could take some populations decades to recover, scientists said.
H5N1 has also taken a heavy toll on raptors, which can become ill after preying on other infected birds or scavenging their carcasses. In the United States, the virus has hit the national emblem itself: the bald eagle. The once-endangered species mounted a vigorous comeback after the pesticide DDT was banned in the 1970s.
But since the arrival of H5N1, scientists have seen spikes in bald eagle deaths and sharp declines in the birds’ reproductive success. “The last time we saw that was the DDT era,” said William Bowerman, a wildlife ecologist at the University of Maryland who has been studying bald eagles for more than 40 years.
Another species of national concern has been the critically endangered California condor. During the 1980s, the entire species dwindled down to just 22 individuals. By the end of 2022, an intensive conservation program had built the wild population back up to nearly 350 birds.
Then, bird flu killed more than 20. Federal officials were so concerned that they agreed to start a vaccination effort. “It was an effort to put everything we could toward saving them,” Dr. Gibbs said.
So far, roughly 250 birds have received at least one dose of vaccine, but the long-term effectiveness remains unclear, and vaccination will not be a feasible strategy for most wild bird populations, experts said.
Beyond Birds
Birds aren’t the only wild animals that have been pummeled by the virus. Some species of marine mammals have also suffered significant losses, especially in South America, where at least 24,000 sea lions died last year.
In Argentina, the virus killed roughly 17,400 southern elephant seal pups, scientists estimated. The outbreak, which erupted during last year’s breeding season, also appears to have eliminated many of the most reproductively successful adults, which typically dominate the beaches at that time of year.
This year, the breeding colonies are just one-third the typical size, and the seals that have shown up are young, small and inexperienced, said Dr. Marcela Uhart, who directs the Latin American wildlife health program at the University of California, Davis.
That could result in lower rates of breeding success or have other ripple effects that are difficult to predict. “It’s this reminder that we can be monitoring populations that were doing well,” Dr. Uhart said, “and then all of a sudden one thing, like avian influenza, comes along and really messes things up for the long term.”
Even in populations that have now developed some immunity to the virus, it’s not clear how long that protection will last, especially as H5N1 continues to evolve.
“We should take this lull as just that — a potentially normal part of this process — but really be prepared for these viruses to burn through animals again,” Dr. Poulson said.
Scientists remain gravely concerned about the prospect of mass die-offs in Antarctica, where H5N1 arrived only recently. “This virus is not done in that part of the world yet,” Dr. Wille said. And it has not yet reached Australia or New Zealand, both of which are home to unique and highly endangered birds.
At this point, experts agree, the virus has become so widespread in wild birds that it can’t be stamped out. But conservationists and officials can work to ensure that bird populations are big, healthy and resilient enough to survive it. That will require tackling the other threats they’re facing, such as pollution and overfishing, and ensuring that birds have access to ample habitat, said Ashleigh Blackford, the California condor recovery coordinator for the U.S. Fish and Wildlife Service.
Those actions, she said, can help make sure that wild birds “are more resilient to climate change, to viruses, to whatever this earth throws their way or we throw their way.”
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