About 1,700 kilometres north of Antarctica and 4,000 kilometres from mainland Australia, an island rises in the middle of the planet’s southernmost ocean. This is Heard Island, Australian territory, home to a large number of birds and marine animals, including penguins, seals and petrels.
However, despite, at first glance, being an isolated paradise, an outbreak of avian influenza is causing devastation among the animal populations living there.
study led by the Australian Antarctic Program, of the Australian government, reveals that, between October 2025 and January 2026, an estimated 13,359 southern elephant seal pups (Mirounga leonina) died due to the viral outbreak. Based on the data collected, government scientists estimate that, on average, 76% of the pups of this species died on Heard Island, and in a particular area the mortality rate reached as high as 97%.
Through laboratory testing, the investigators, who submitted their conclusions for publication in a scientific journal, reveal that of the nine vertebrate species tested, six tested positive for the highly pathogenic avian influenza strain that is spreading around the world, Influenza A H5N1.
Among the affected species, besides the southern elephant seals, are the king penguin (Aptenodytes patagonicus), the gentoo penguin (Pygoscelis papua), the Antarctic fur seal (Arctocephalus gazella) and the petrel Pelecanoides georgicus.
Drone observations also detected high mortality levels among penguins and also pups of the elephant seal on McDonald Island, which belongs to the same island group as Heard Island.
Julie McInnes, the first author of the study, says that the data on avian influenza on these islands “are the first detections in an Australian overseas territory and show the virus’s eastward movement” in the subantarctic region.
Genetic analyses suggest that the virus arrived on Heard Island in August 2025, originating from a cluster of small islands in the southern Indian Ocean known as the Crozet Islands, about 1,800 kilometres away.
