Australia is confronting what experts are calling a critical escalation of the H5N1 avian influenza outbreak, with aerial surveillance revealing dozens of dead and sick seabirds off the South Australian coast in what may become the country's first confirmed mass mortality event from the virus — just six weeks after bird flu was first detected on the continent.

Helicopter surveys identified 49 dead greater crested terns on Baudin Rocks, near Robe on South Australia's southeastern coast, along with 35 more sick birds. Samples are being tested, but South Australia's chief veterinarian Skye Fruean said it was likely the first mass mortality event caused by the disease in Australia. The total number of confirmed detections across the country has now reached 53, spread across five states — Western Australia, South Australia, New South Wales, Queensland and Victoria, which recorded its first case this week. Authorities emphasised that confirmed detections represent only a fraction of actual infections, as many affected animals are never found or tested.

Of particular concern is the detection of silver gulls carrying the virus. Unlike the greater crested tern, the silver gull — the bird most Australians picture when they think of a seagull — ranges widely across coastal, urban and inland environments. It scavenges from dead or dying animals, frequents wetlands, rubbish tips and flooded areas, and thrives in cities, making it a potential vector for spreading the disease far beyond the coastline. A suspected positive case at Monarto, inland South Australia — an area home to several poultry farms — has heightened concerns. Five infected terns have also been confirmed at Seal Bay on Kangaroo Island, a critical breeding site for the endangered Australian sea lion. Overseas, H5N1 killed more than 17,000 southern elephant seals in Argentina in 2023, and tens of thousands of seals have died globally from the disease.

Experts warn Australia's experience may mirror that of South America, where early isolated detections were followed by rapid spread and mass mortality events. Because Australia has an exceptionally high proportion of unique bird species, the susceptibility of many native animals to the virus is unknown, though there is little reason to expect they will fare better than affected species elsewhere. Every other continent, including Antarctica, has recorded H5N1 deaths numbering in the millions over the past five years. There are currently no confirmed cases in Australian poultry or livestock, but biosecurity authorities say the risk is rising as infections among resident wild birds increase.

Conservation groups describe the situation as a bleak turning point. Kate Millar of BirdLife Australia called it