More than 13,000 seal pups die on remote Australian island amid bird flu outbreak

Testing confirms spread of deadly H5N1 virus on the subantarctic Heard Island, about 4,000km south-west of Perth

More than 13,000 seal pups have died on an Australian territory, as testing confirmed the spread of deadly H5N1 bird flu among penguins, seals and petrels on subantarctic islands.

The mass mortality of southern elephant seal pups on Heard Island, about 4,000km south-west of Perth and 1,700km north of Antarctica, was observed by government scientists conducting drone and ground surveys in October 2025 and January 2026.

Death rates were extremely high, averaging 76% across the island, and up to 97% in one location. The results, which have been submitted as a preprint research paper, also included evidence of high seal pup mortality at McDonald Island.

Dr Jarrod Hodgson, a senior research scientist and co-lead author of the paper, who was aboard the icebreaker RSV Nuyina on voyages to Heard and McDonald islands, said the figures may be an underestimate. “When we departed the island, mortality was still ongoing.

“The mass mortality was very sobering, but it’s something that we had prepared for.”

In comparison, pup mortality in a typical year would generally be below 5%, he said.

Six out of nine species on Heard Island have now tested positive for the H5N1 strain, including southern elephant seals, king penguins, gentoo penguins , Antarctic fur seals and South Georgia diving petrels.