South Australia declares significant escalation in H5 bird flu after more than 1,000 seabird deaths

South Australian authorities have declared a significant escalation in H5 bird flu after three mass mortality events were detected on offshore islands. The deaths involve more than 1,000 greater crested terns, with the cause presumed to be the virus. Officials said the events were found through aerial surveillance on Wednesday and are being treated as the biggest detected mass casualty events linked to suspected H5 bird flu since the strain reached the Australian mainland in June.

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Premier Peter Malinauskas told state parliament that the development was of particular concern. He said there have still been no detections in poultry or livestock, and no mass deaths involving mammals have been reported. State authorities are also investigating a suspected case in a little penguin found on Kangaroo Island, while Tasmania is separately examining 28 little penguin deaths on King Island.

The confirmed deaths were found across Troubridge Island off the Yorke Peninsula and the Pages Islands, known as North Page and South Page, off Kangaroo Island. The islands are important breeding sites for seabirds and other wildlife, including little penguins, black cormorants, Australian sea lions and long-nosed fur seals. Authorities said aerial patrols, using helicopters, planes and drones with support from field crews, are not limited to coastal birds and are also looking for signs of illness in mammals that could be affected.

The escalation matters because H5 bird flu has already been detected in recent weeks on offshore islands, and the latest deaths suggest the outbreak is affecting a wider area of South Australia's marine bird populations. Greater crested terns have been the most affected local species so far, according to officials. The presence of endangered Australian sea lions near the Pages Islands has also raised concern about possible spillover into other wildlife.

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Biosecurity authorities in Australia have been monitoring the strain since it arrived on the mainland in June. The current detections add to a developing picture in which seabird colonies on offshore islands appear to be among the most exposed sites. Officials have not reported any confirmed cases in poultry or livestock, which remains an important distinction for the wider agricultural sector.

What remains unclear is whether the suspected little penguin cases in South Australia and Tasmania will be confirmed as H5 bird flu. It is also not yet known whether mammals on the affected islands have been exposed. Further testing and surveillance are under way, and authorities are expected to continue monitoring offshore islands for additional deaths or new detections.

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