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Sub Antarctic skua, Stercorarius lonnbergi, roosting. Macquarie Island, Sub Antarctic, administered by Tasmania, Australia. (Photo by: Auscape\/Universal Images Group via Getty Images)<\/p>\n
Universal Images Group via Getty Images<\/p>\n
A brown skua, found dying on a remote stretch of the Western Australian coast, has done what years of surveillance had braced for. On June 20 the strain of highly pathogenic bird flu<\/a> that has killed wild birds and marine mammals on every other continent was confirmed in Australia for the first time.<\/p>\n Australia was the last continent on Earth free of the H5N1 lineage known as clade 2.3.4.4b<\/a>, the most destructive animal pathogen of the present era. The virus did not come down the Asian migratory flyways that biosecurity planners had watched for years. It came from the south, out of Antarctica, riding seabirds that had picked it up on subantarctic islands where it has been killing seals by the thousand.<\/p>\n The bird was found at Cape Le Grand National Park near Esperance<\/a>, about 700 kilometers southeast of Perth, and the detection was confirmed by CSIRO\u2019s Australian Centre for Disease Preparedness. A southern giant petrel found in the same region is suspected also to be positive, after a preliminary result at the Western Australian government lab, and was sent for confirmatory testing. The government reported no detections in poultry and no evidence of deaths in other species<\/a>, and said the finding does not change Australia\u2019s status as free from the disease in poultry under international standards. For now that holds.<\/p>\n This is not Australia\u2019s first encounter with avian influenza, though earlier episodes involved different strains of the virus. The country spent much of 2024 fighting bird flu in poultry, most of it the H7 subtype<\/a>, recording 16 outbreaks of highly pathogenic influenza that year against only seven in the preceding four decades<\/a> and culling roughly 1.8 million birds to stamp out infected and exposed flocks. It also recorded its first human H5N1 case<\/a> in 2024, a toddler infected in India who recovered fully.<\/p>\n Neither of the 2024 events was caused by this virus. The skua marks the first time the global 2.3.4.4b panzootic itself has reached Australian soil.<\/p>\n How Did It Get In?<\/p>\n For years the working assumption was that H5N1 would enter Australia from the north, carried by migratory birds moving down the East Asian flyway. Ducks and other waterfowl are the most common natural reservoir of avian influenza<\/a>, and their migrations had carried the virus across most of the world. Australia\u2019s isolation, and one ecological accident in particular, kept it out. As Marcel Klaassen of Deakin University, Meagan Dewar of Federation University and Michelle Wille of the University of Melbourne explain in The Conversation<\/a>, no duck species routinely migrate between Australia and Asia, and none migrate through Antarctica. The continent\u2019s reservoir hosts simply do not mix with the rest of the world\u2019s.<\/p>\n So the virus took the long way around, and its southern route was already on the record. It reached the Antarctic region in October 2023<\/a> in a brown skua at South Georgia, carried down from the tip of South America, then spread island to island across the Southern Ocean<\/a> over thousands of kilometers. In that case, the carriers were seabirds rather than ducks. Skuas, gulls and giant petrels cross enormous distances over the Southern Ocean, and the virus traveled with them.<\/p>\n By late 2025 it had reached Australia\u2019s subantarctic Heard Island, where it killed an estimated 13,000 elephant seal pups<\/a>, and from there it crossed to the mainland.<\/p>\n Why the Next Species Infected Is the One to Watch<\/p>\n The dead skua confirms the virus has reached Australia. It does not mean the virus is established here. Skuas and petrels patrol coastlines and feed on carcasses, which makes them useful sentinels but poor candidates to seed a continent on their own. The threshold that would change everything is freshwater ducks. \u201cOnce in ducks, the likely spread of the virus increases dramatically, and the outlook would be grim,\u201d the same researchers warned.<\/p>\n Grim because nothing in Australia has met this virus, its wildlife or its farmed flocks. For wildlife the threat is to conservation. Naive populations are where 2.3.4.4b does its worst. It killed up to 47 percent of some northern gannet colonies<\/a> in 2022, tore through South American sea lions and elephant seals, and gutted seabird cliffs across the North Atlantic. Australia\u2019s fauna is heavily endemic and often range-restricted, which is another way of saying many of its species have nowhere else to be. For poultry the threat is economic. The same strain has forced record culls and pushed up egg prices<\/a> across North America and Europe, and Australian flocks have no exposure to it.<\/p>\n PESCADERO, CA – MARCH 19: A view of elephant seals at Ano Nuevo State Park by the Pacific Coastline in Pescadero of San Mateo County, California, United States on March 19, 2026. A highly pathogenic avian influenza (H5N1) outbreak is affecting northern elephant seals at A\u00c3\u00b1o Nuevo State Park in San Mateo County, California. This is the first confirmed H5N1 outbreak in California elephant seals, with over 27 seals testing positive and causing over 30 deaths, prompting partially park closures. The virus causes severe respiratory and neurological symptoms in pups. (Photo by Tayfun Coskun\/Anadolu via Getty Images)<\/p>\n Anadolu via Getty ImagesWhere Wildlife, Livestock and Human Health Meet<\/p>\n The skua ties together three things usually managed apart. 2.3.4.4b is a wildlife virus, a livestock virus and a potential human virus all at once, and what it does in one of those worlds shapes the other two.<\/p>\n The wild-bird reservoir is the part no one can manage away. You can depopulate a barn. You cannot depopulate a flyway. Australia\u2019s poultry industry now lives with a standing risk of incursion from wild birds, and its conservation managers with the prospect of die-offs they can track but not prevent.<\/p>\n