Bird flu killed 13,000 seal pups on a subantarctic island. H5 also reached mainland Australia for the first time

A new study by the Australian Antarctic Program has confirmed that highly pathogenic avian influenza H5 killed roughly 13,000 of 17,000 southern elephant seal pups — the world's largest seal species — from the most recent breeding season on the remote, subantarctic Heard Island in the Indian Ocean. On average, nearly three-quarters of newborn pups died, and in one colony as many as 97 percent. Australian Antarctic Program ↗

The deaths themselves are not new. They occurred between October 2025 and January 2026, and scientists had already recorded the first hundreds of dead animals during October surveys. What is new is the now-published quantification of the scale and the laboratory confirmation that the H5 strain is responsible. And by coincidence, in the very days the study was published, the virus reached mainland Australia for the first time — until then the last inhabited mainland in the world without a confirmed occurrence of this strain. CNN ↗

What the drones showed

The research has not yet undergone peer review; it is a so-called preprint published on the bioRxiv server. Scientists led by biologist Julie McInnes and Jarrod Hodgson mapped the island's coastline using drones and supplemented this with field sampling. "Drones were essential for us to be able to accurately quantify the mortality in the elephant seal breeding colonies," Hodgson explained. Phys.org ↗

Six species tested positive for H5, including the southern elephant seal, king penguin, gentoo penguin, Antarctic fur seal, and other seabirds. Genetic analysis suggests the virus arrived on the island around August 2025 via migrating wildlife from the French Crozet Islands, about 1,800 kilometers away. According to McInnes, H5 on Heard Island repeated a pattern seen on other subantarctic islands, such as South Georgia, where elephant seals were likewise among the hardest-hit species. Australian Antarctic Program ↗

On neighboring McDonald Island, drones captured the same picture of mass pup mortality. However, due to strict protection of this territory, scientists did not collect samples there, so laboratory confirmation is still lacking. Phys.org ↗

H5 also reaches mainland Australia

On June 20, the Australian scientific agency CSIRO confirmed the very first case of H5 on the mainland, in a brown skua found in Western Australia near the town of Esperance, about 600 kilometers southeast of Perth. The virus was also suspected in a dead giant petrel from the same area. Department of Agriculture (DAFF) ↗

Prime Minister Anthony Albanese called the finding "concerning" and pledged that the government would do everything possible to limit its spread. Agriculture Minister Julie Collins clarified that there is so far no evidence of mass die-offs or of the virus entering poultry farms. The Guardian ↗

For Australia, this is a symbolic turning point. The H5N1 strain, which has been circulating across almost the entire world since 2021 and cutting down wildlife from South American fur seals to Antarctic penguins, had long spared only mainland Australia. The subantarctic tragedy on Heard Island together with the first mainland case show that H5 has now penetrated even this long-spared corner of the planet. The scale of the subantarctic die-off has so far not been covered in depth by either Slovak or Czech media.

What hotinfo is following

• Whether H5, following the detection near Esperance, will spread across mainland Australia and reach poultry farms or other species.
• Whether the preprint, once peer-reviewed, will confirm the estimate of roughly 13,000 dead pups and the 97 percent rate in the hardest-hit colony.
• How the virus will affect other subantarctic seal and penguin colonies in the upcoming breeding season.