Bird flu killed an estimated 13,000 seal pups on a sub-Antarctic island
A new study estimates that the H5N1 strain of bird flu killed about 13,000 of roughly 17,000 seal pups — more than 75% — on remote Heard Island since last August, the BBC reported on June 18 . Southern elephant seal pups were hit hardest, with mortality in some breeding “harems” as high as 97%. Researchers also recorded higher-than-expected deaths among penguins.
The findings come from a research expedition that reached the Heard and McDonald Islands — Australian territory some 4,000 km southwest of the mainland, home to more than a million breeding seabirds and seals — in October 2025 and found the shoreline littered with carcasses. The team used drone surveys and ground sampling across nine species. The work was posted to the preprint server bioRxiv and has not yet been peer reviewed.
The scale of mortality adds to evidence that H5N1, which has spread among birds worldwide and increasingly into mammals, is now reaching some of the planet’s most isolated wildlife colonies. Australia remains the only continent with no detected cases of this strain, making the outbreak on its sub-Antarctic territory a closely watched marker of how far the virus is advancing toward the mainland and Antarctica.