A devastating outbreak of H5N1 bird flu has wiped out more than three-quarters of newborn southern elephant seals on Australia's remote Heard and McDonald Islands in the Southern Ocean, scientists have confirmed. The virus killed an estimated 13,000 pups, along with several hundred adult king penguins and other seabirds, in one of the world's most isolated wildlife sanctuaries.
Mass Mortality Among Seal Pups
Drone surveys conducted by the Australian Antarctic Program in October and January captured what senior research scientist Jarrod Hodgson described as “sobering” scenes of seal pup carcasses scattered across the grey shorelines. Scientists estimate that pup mortality reached 76% from a cohort of around 17,000 born on the islands, with one high-density area recording a concentrated death rate of 97%.
“The thing we don’t know from our surveys so far is what the impact was on the breeding adult population of southern elephant seals,” Hodgson warned, highlighting uncertainties about the longer-term fallout.
Spread to Penguins and Seabirds
The damage was not limited to seals. Data gathered in January found “several hundred” adult king penguins on Heard Island had died, with researchers noting the mortality appeared higher than normal levels. Wildlife biologist Julie McInnes said the outbreak marks a grim milestone for Australia’s remote territories.
“These observations of H5 bird flu at Heard Island and McDonald Island are the first detection in an Australian external territory and show the continued eastward movement of the virus around the sub-Antarctic,” McInnes said. She added, “Our results show a similar pattern to other sub-Antarctic islands, such as South Georgia, where elephant seals have been hardest hit.”
Origin and Genetic Analysis
Genetic analysis suggests the virus may have arrived via wildlife from the French sub-Antarctic Crozet Islands, around 1,800 kilometres away, with researchers believing it likely reached Heard and McDonald around August 2025. As of February, there had been no confirmed cases of the H5N1 strain on the Australian mainland or in New Zealand, despite the virus spreading widely among birds globally and infecting some mammals.
The findings were shared on the scientific preprint site BioRxiv and have not yet been peer reviewed.
