The deadliest avian flu virus in history, responsible for the deaths of hundreds of millions of birds in the last five years, has once again jumped to mammals and decimated the world’s largest population of elephant seals, located on the remote island of South Georgia, a British-controlled territory about 1,500 kilometers (932 miles) from the Antarctic mainland. The British Antarctic Survey estimates that more than 50,000 females — half the total — have disappeared from one year to the next. “The scale of this decline is staggering,” warns marine ecologist Connor Bamford, who led the research.
The virus’s journey reportedly began in 1996 on a goose farm in Sanshui, southern China, a humid region teeming with poultry farms: the ideal breeding ground for new pathogens. After several less intense waves, a new version of the virus, dubbed 2.3.4.4b, emerged in 2020 and began sweeping across the Americas from north to south, with unprecedented lethality. The highly pathogenic avian influenza killed or forced the culling of nearly 150 million birds in 84 countries in 2022 alone, according to data from the World Organization for Animal Health. On September 16, 2023, on Bird Island, near South Georgia, a group of British scientists stumbled upon a giant Antarctic petrel — a bird with a wingspan of two meters — that was unable to move. The plague had reached the gates of Antarctica, the last virgin continent on the planet.
The virus quickly spread to mammals there. Connor Bamford’s team used drones to count the female southern elephant seals in the three main colonies on South Georgia Island. Before the avian flu outbreak, there were about 10,000. After the virus arrived, almost half disappeared. If the results are extrapolated to the entire island population, that’s 53,000 fewer females — a devastating blow to the southern elephant seal, a species that until now was not considered at-risk. Two decades ago, there were about 700,000 individuals worldwide, according to the last population census.
Spanish virologist Antonio Alcamí led two expeditions in 2024 and 2025 to try to measure the impact of avian flu in Antarctica. Aboard a sailboat converted into a laboratory, the scientists explored the coast of the Antarctic peninsula, the region of the continent closest to South America, at the beginning of this year. The virus had spread everywhere: it was found in practically every location visited and in one out of every four animals analyzed. Penguins were more resistant than feared, but the pathogen was devastating other birds, such as skuas. Two journalists from EL PAÍS documented for the first time the ravages of avian flu in Antarctica, accompanying the Spanish expedition.
Southern elephant seals can weigh up to four tons.Steve Gibbs / Servicio Antártico Británico
“Just because we don’t see marine mammal carcasses doesn’t mean they aren’t dying, because they are possibly dying at sea, where we can’t see them,” Alcamí argued at the time, on the deck of his sailboat in the dangerous Antarctic waters. Now, he warns that the 50% drop in the number of females in just one year “is an extremely high figure,” especially in a species where individuals, weighing up to four tons, can live for more than 20 years under normal conditions. “It’s a huge impact, especially considering that 50% of their breeding population is located in South Georgia,” warns the virologist from the Spanish National Research Council (CSIC). The new study was published Thursday in the specialized journal Communications Biology.
Alcamí criticizes the lack of support for analyzing the effects of avian flu in Antarctica. “It’s worrying that the impact on other marine mammal species could be similar, but we simply don’t have any information about what’s happening,” he laments. His mission last year was made possible by a €300,000 ($349,000) donation from the Spanish Union of Insurers and Reinsurers, in addition to logistical support from the CSIC Antarctic base, which is financially supported by the Spanish Ministry of Science. This year, he hasn’t been able to find funding to continue his research. “It’s a bit disheartening,” he says.
Biologists Antonio Alcamí (right) and Begoña Aguado, at a penguin colony on Livingston Island (Antarctica), on February 22.Luis Manuel Rivas
Veterinarian Ralph Vanstreels witnessed the most heartbreaking scene of his career in October 2023 on a beach in Península Valdés, a protected area in Argentine Patagonia. The sand was so covered with dying or already dead elephant seals that it was difficult to walk. He and his colleagues estimated that the virus killed some 17,000 individuals in just a few weeks, including more than 95% of the pups. “The new study in South Georgia is very alarming because it points to a pattern that’s very similar to what happened here in Argentina. It suggests that all elephant seal populations where the virus has already caused outbreaks may be affected to the same degree. It’s extremely serious,” reflects Vanstreels, from the University of California, Davis. “This is a species that wasn’t threatened, and suddenly its population is cut in half. It has very serious implications for the conservation of the species,” he emphasizes.
The analysis of the outbreak in Argentina pointed to a disturbing possibility: the virus not only jumped from birds, it was spreading from elephant seal to elephant seal. Having such a contagious and deadly avian flu virus evolving in mammal populations is the scenario most feared by public health experts, as the World Health Organization’s chief scientist, British physician Jeremy Farrar, warned after an outbreak of avian flu on a mink farm in the Spanish region of Galicia in October 2022. The organization, however, considers the risk to humans to be “low,” unless the virus mutates and begins to spread among humans.
Ecologist Connor Bamford says that the pathogen remains in elephant seal populations. His colleagues are analyzing the virus’s genetic material from different animals to try to determine its path across the island and what mutations it has undergone along the way. “There has been mammal-to-mammal transmission, via the air, with contaminated droplets carrying the virus between hosts. That is probably why the elephant seals, which form dense colonies in South Georgia every year, have been so severely affected,” says the British Antarctic Survey researcher. Bamford acknowledges that other factors may have contributed to the disappearance of the females, such as some local weather anomalies, but stresses that natural year-to-year variations can account for at most a 10% drop, not 50%. “Declines like the one we have observed can only be attributed to highly pathogenic avian influenza,” he concludes.
Elephant seals are divided into two species: the more numerous southern elephant seal and the less common northern species, which has so far been relatively unaffected by the virus. Biologist Michelle Wille manages the avian influenza database for the Scientific Committee on Antarctic Research, the international body that coordinates science investigations in the Antarctic. “Highly pathogenic avian influenza has been catastrophic for southern elephant seals,” she states. “These mortality rates are shocking, but not surprising, because we’ve seen similar figures in numerous bird species. The implications are considerable,” continues Wille, from the University of Melbourne, Australia. “One wonders if this species will survive this.”
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