More than 13,000 southern elephant seal pups have died on Australia's remote Heard Island, as testing confirms the spread of the deadly H5N1 bird flu virus among penguins, seals, and petrels in the subantarctic region.
Mass Mortality Event
Government scientists conducting drone and ground surveys in October 2025 and January 2026 observed the mass deaths on Heard Island, located about 4,000 km southwest of Perth and 1,700 km north of Antarctica. Death rates averaged 76% across the island, reaching up to 97% in one location. High mortality was also recorded at nearby McDonald Island.
Dr. Jarrod Hodgson, a senior research scientist and co-lead author of a preprint paper on the findings, stated that the figures may be an underestimate, as mortality was still ongoing when the team departed. In a typical year, pup mortality is generally below 5%.
Species Affected
Six out of nine species on Heard Island have tested positive for H5N1, including southern elephant seals, king penguins, gentoo penguins, Antarctic fur seals, and South Georgia diving petrels. Several hundred dead adult king penguins were also observed.
The subantarctic islands are home to more than a million breeding seals and seabirds, many of which are nationally and internationally listed. Wildlife veterinarian Dr. Tristan Burgess noted that the significant impacts on elephant seals are consistent with other outbreaks in the southern hemisphere.
Origin and Spread
Genetic analysis suggests the virus was likely introduced via wildlife from the French Crozet Islands, about 1,800 km away, with an estimated arrival in August 2025. This marks the first detection of H5 bird flu in an Australian external territory and shows the continued eastward movement of the virus around the subantarctic.
The Australian Antarctic Program continues to monitor for signs of bird flu in the Australian Antarctic Territory and on Macquarie Island, where no suspected cases have been reported.
Government Response
On Thursday, the federal government announced an additional $11.2 million in the 2026-27 budget to prepare for potential impacts of H5N1 on at-risk native species on the Australian mainland. Environment Minister Murray Watt stated that while Australia is currently free from the serious and contagious H5 bird flu, the country must be realistic about the likelihood of an incursion and plan accordingly.
Dr. Michelle Wille, an avian influenza expert at the University of Melbourne, described the survey results as “really devastating” but consistent with impacts elsewhere in the subantarctic. She emphasized the importance of public reporting, urging people to report sick or dead birds or marine mammals via the emergency animal disease hotline (1800 675 888).
