Bird flu is spreading from pole to pole. Here’s why it matters.

In Alaska, a polar bear recently tested positive for a highly pathogenic strain of avian influenza for the first time ever in the species. Last week, several predatory seabirds died from the virus, known as H5N1, near Argentina’s research station on Antarctica—another first, this time as a novel record of bird flu on the icy mainland.

Now at both ends of the globe, bird flu has flared up once more, infecting dozens of bird and mammal species, from Africa to Asia to Europe. Evidence now points to the latest strain being “extremely deadly” and “increasingly infectious,” according to an article published in Nature.

Scientists first identified avian influenza on a commercial goose farm in Guangdong, China, in 1996, and periodic outbreaks have occurred since around the world. The potentially fatal virus, which is contracted through contaminated bodily fluids, spreads from wild birds, its primary vector, into poultry operations. These facilities then kill large quantities of their birds in an attempt to control the spread.

Since the first case was detected in the U.S. on February 8, 2022, the U.S. Department of Agriculture Animal and Plant Health Inspection Service (APHIS) has recorded avian influenza in either wild or captive birds in every state except Hawaii. As of March 6, 2024, the virus has affected more than 82 million birds in the United States, according to the U.S. Centers for Disease Control and Prevention.

While 20 countries have reported 882 cases of avian influenza leaping into humans since 2003—more than half of which were fatal—the CDC classifies the current risk to people as low. But other experts caution the recent developments as a stern wake-up call for the pathogen’s potential for becoming a pandemic. (Read about a bird flu outbreak in Israel in 2022.)

“Avian influenza is a wild card,” says Andrew Derocher, a biologist who’s been studying polar bears for 40 years at the University of Alberta in Canada.

For instance, while Derocher says it’s possible that the polar bear incident is a “one-off,” it could also be “a huge mess” for the species, which are already vulnerable to extinction. As the Arctic warms and sea ice breaks up earlier, more polar bears will be forced onto land, where they may scavenge birds that died from the virus.

“Disease in polar bears is an issue that smolders in my brain,” he says.

And it’s not only polar bears—H5N1 could have grave consequences for wildlife already suffering from a wide variety of human-caused stressors, such as pollution, climate change, habitat loss, and invasive species.

“Wildlife are definitely vectors,” says Jude Lane, a conservation scientist at the Royal Society for the Protection of Birds in the U.K. “But they’re also victims.”

“The sky was empty”

Most years, setting foot on Bass Rock in Scotland is an assault on the senses, says Lane.

This is because so many northern gannets nest on the rock each year that the crag, which rises out of the North Sea, literally turns white from the densely packed birds and their excrement. But in 2022, when scientists arrived to do their annual surveys of the seabirds, they stumbled upon a bizarre scene.

“Bass Rock was the biggest colony in the world. It was just alive. The whole rock was alive,” says Lane. “But when that virus hit, it was just immediately quiet.”

Over the course of several weeks and return visits, the scientists watched as what once used to be a living quilt of birds turned into a patchwork.

“I mean, there were birds dying at our feet,” says Lane. “And the sky was empty.”

In the aftermath, scientists estimate that a particularly aggressive strain of H5N1 killed thousands of birds in 40 out of 41 monitored northern gannet colonies across Europe—colonies that represent 75 percent of global northern gannet nesting sites. At Bass Rock, occupied nest sites plummeted by 71 percent.

A handful of GPS trackers also revealed a strange new behavior: As the virus raged, a few gannets flew off to visit neighboring rookeries—something the birds don’t usually do. If the birds had avian influenza, they could have carried the virus to new populations—an avian super spreader event.

“They don’t drown”

A year later and half a world away, a similar scene played out in Península Valdés, Argentina—this time, with southern elephant seals.

As the only continental colony for the species, these beaches typically look like a mosh pit with gigantic, 20-foot-long males bludgeoning each other over harems of squawking females and pups. But in 2023, the same beaches looked more like the aftermath of a shipwreck.

“We found silence and massive numbers of carcasses,” says Marcela Uhart, a wildlife veterinarian at the University of California Davis who has worked in Argentinian Patagonia for about 35 years. “All ages, new and old, just piled up on the beach where there should have been living, happy animals.”

Many of the animals still gripping to life were pups—clearly ill, and apparently alone.

“When the tide came in, as we were leaving the beach, some of those pups were actually in the water, unable to get out, and drowning,” says Uhart. “And these are elephant seals. They don’t drown.”

Back at the lab, samples confirmed the outbreak of highly pathogenic H5N1 avian influenza. Uhart and her team estimate the virus killed 17,400 pups, or approximately 96 percent of all young born in 2023. As with people, such severe cases of the virus can cause systemic organ failure and neurological issues.

The virus proliferated in seabirds that scavenged on the carcasses. At one point, she says, there were so many dead terns lying around that seagulls began using their corpses as nesting material.

Uhart was also an author on a report that found shocking numbers of wildlife deaths due to bird flu in South America. Between October 2022 and November 2023, the virus has killed nearly 600,000 birds of at least 82 species and more than 50,000 mammals of at least 10 species, mostly in Peru and Chile.

“We have never seen anything like this before in South America or Antarctica,” says Uhart.

Bird flu in poultry

While the virus has spilled over into wild mammals in North America, from bobcats and bottlenose dolphins to gray seals, coyotes, and skunks, and myriad birds, from bald eagles to mallards and great horned owls, there haven’t been any equally gruesome mass casualty events on that continent—yet.

The U.S. Department of Agriculture keeps running tabs on positive tests. For instance, between February 5 and 26 of this year, scientists detected avian influenza in wildlife in 15 states, from California to Florida to Maine.

At the same time, more than a dozen states have also confirmed infections in poultry flocks, both backyard and commercial, affecting more than 90,000 birds. That’s still a small number compared with the more than 9.5 billion broiler chickens and 208 million turkeys processed each year in the U.S., says Shilo Weir, a spokesperson for the USDA’s Animal and Plant Health Inspection Service.

“It is also important to note that we saw fewer cases of [bird flu] in 2023 than we did in 2022,” Weir says in an email.

This decrease may be due to tighter biosecurity measures, which prevent spread from farm to farm, she says. Fewer detections may also mean that “there’s less virus in the environment,” says Weir.

Lack of solutions

As for what can be done to stop bird flu, so far, the answer appears to be: not much.

While experts have experimented with vaccinating wild and critically endangered California condors against the virus, the logistics of vaccinating other populations, wild or domestic, have yet to be worked out.

“It’s not off the table,” says Lane, “but trying to vaccinate a colony of gannets would just blow my mind.” (Read why birds matter, and are worth protecting.)

Uhart says vaccines could be protect some wild animals, but that controversies around human health have thwarted those products’ development.

“At this point, I find it increasingly unacceptable that we’re willing to kill billions of chickens around the world to control a disease that we could manage differently,” she says.

Meanwhile, the virus will continue to spread, adapt, and evolve into new forms—some of which may be more targeted at mammals, including us, says Uhart.

“This is a number one zoonotic disease,” she says, “and a virus that has every single trait that makes it perfect for pandemic spread.”

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