Australia has recorded its first confirmed case of the deadly H5 strain of bird flu in a local resident seabird, marking what experts are calling a significant escalation in the disease's spread across the continent. A greater crested tern — a common coastal bird — was found dead by a member of the public at Robe Marina, on South Australia's Limestone Coast, on Tuesday. Laboratory testing confirmed the bird had tested positive for H5 avian influenza, federal Agriculture Minister Julie Collins announced on Friday.

Until now, all 12 confirmed cases of H5 bird flu in Australia since June had been detected in migratory subantarctic seabirds, principally giant petrels, found along the coasts of South Australia, Western Australia and New South Wales. Those birds were believed to have carried the virus from sub-Antarctic regions, including Heard and McDonald Islands — remote Australian external territories — where the strain was found in June to have killed more than 13,000 elephant seal pups. The greater crested tern, by contrast, is a permanent Australian resident, suggesting that local transmission has now occurred. "Those earlier detections were like little spot fires, but this suggests transmission has occurred on or near our beaches," said Chris Purnell, wetland and migratory shorebird program manager at BirdLife Australia.

The discovery has alarmed conservation groups. Greater crested terns live in large mixed flocks alongside other species, creating conditions in which a disease can spread rapidly. The bird was found near a network of coastal lakes and in close proximity to habitat of the eastern hooded plover, a species listed as vulnerable. Jack Gough, chief executive of the Invasive Species Council, warned that international experience showed H5 could travel further and faster than anticipated. In France, hundreds — and potentially thousands — of sandwich terns died within days of the first reports of sick birds. "I'm concerned that if we get persistent spread to Australian wildlife, this could quickly turn up all over the Australian continent," Gough said.

South Australian authorities have launched enhanced surveillance across the state's coastline, following what officials described as the largest aerial survey of its coast, islands and reefs in 40 years, which found no widespread evidence of mass mortality. Separately, a young fur seal found unwell at Blue Bay on the New South Wales Central Coast died on Thursday and has been submitted for H5 testing as a precaution; results are pending. Minister Collins sought to reassure the public, stressing there is still no evidence of mass wildlife mortality, no sign of spread to poultry or agricultural systems, and that the risk to human health remains low.

The stakes are particularly high for Australia, which was considered the last major continental landmass free of the H5 strain. Nearly half of Australia's wild bird species and 83 per cent of its mammals are found nowhere else on Earth, making the potential consequences of a sustained outbreak especially severe for global biodiversity. Authorities say the investigation into how the virus reached the greater crested tern is ongoing.