Bird flu killed thousands of seal pups on Heard Island

Bird flu appears to have ripped through one of the planet’s most remote wildlife refuges, killing an estimated 13,000 southern elephant seal pups on Heard Island and showing how fast H5N1 can destabilize a protected sub-Antarctic ecosystem. New findings from the Australian Antarctic Program found the virus in multiple species and extended the outbreak to McDonald Islands, a warning sign for remote oceans already under mounting environmental stress.

Scientists released the findings on June 18, 2026 and said they had been submitted to a scientific journal. Samples from nine vertebrate species were tested at CSIRO’s Australian Centre for Disease Preparedness, and six species tested positive for Influenza A H5N1 clade 2.3.4.4b. The positive detections included southern elephant seal, king penguin, gentoo penguin, Antarctic fur seal and South Georgia diving petrel.

The most severe damage was to southern elephant seals. Drone surveys carried out during voyages in October 2025 and January 2026 estimated average pup mortality at 76%, with mortality reaching 97% in one area. Researchers estimated that Heard Island produced about 17,000 pups and that about 13,000 died island-wide. By January 2026, dead pups were being found in all surveyed breeding areas, and there was evidence of mortality on McDonald Island as well. Because the sites are remote and protected, no on-ground sampling was done on McDonald Island, so laboratory confirmation there was not possible.

The virus was first suspected on Heard Island in October 2025, after scientists aboard the RSV Nuyina saw unusual elephant seal mortality. That made the outbreak the first detection of H5 bird flu in an Australian external territory and a sign that the virus had continued its eastward movement through the sub-Antarctic. The pattern closely resembled what had been seen at South Georgia, where elephant seals have been hardest hit.

The outbreak did not spare all wildlife. Researchers reported several hundred dead adult king penguins and elevated mortality in king and gentoo penguins, but no unusual mortality in albatross or in the Heard Island shag and black-faced sheathbill, two endemic species. Heard Island and McDonald Islands sit about 4,000 kilometers southwest of mainland Australia and are described as among the world’s least anthropogenically disturbed places. Southern elephant seals are already listed as vulnerable on the IUCN Red List, and the scale of the losses shows how quickly even remote, fragile breeding systems can be upended.