HEARD AND MCDONALD ISLANDS — An H5 avian influenza outbreak killed approximately 13,000 southern elephant seal pups on Australia's Heard and McDonald Islands. The outbreak also resulted in deaths among penguins and seabirds in the same region, marking the first confirmed detection of the virus in an Australian external territory.

Drone surveys conducted by the Australian Antarctic Program in October and January recorded seal pup carcasses scattered across the volcanic coastlines of the islands. The mortality rate for southern elephant seal pups was estimated at 76 percent among a total population of 17,000 pups. In one specific section of the islands, the southern elephant seal pup mortality rate reached 97 percent.

Data collected in January indicated that several hundred adult king penguins died on Heard Island. These deaths occurred at rates exceeding historical averages. Researchers estimate the virus likely reached the islands around August 2025.

Genetic analysis indicates the virus likely arrived at the islands via wildlife migrating from the French sub-Antarctic Crozet Islands, located 1,800 kilometers away. The islands are approximately 4,000 kilometers southwest of mainland Australia. As of February, mainland Australia and New Zealand had not reported any cases of the H5N1 strain.

Wildlife biologist Julie McInnes said, "These observations of H5 avian influenza on Heard Island and McDonald Island constitute the first detection in an Australian external territory and demonstrate the continued eastward displacement of the virus in the sub-Antarctic zone." McInnes added, "Our results show a similar pattern to other sub-Antarctic islands, such as South Georgia, where seals have been more affected."

Senior research scientist Jarrod Hodgson said, "What we currently do not know from our studies is what the impact has been on the breeding adult southern elephant seal population." The study data were published on the preprint server BioRxiv and have not yet undergone peer review.