Emerging
Published Jun 19, 2026Updated Jun 191
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H5N1 Bird Flu Linked to Mass Seal Pup Deaths on Australia's Heard Island
Highly pathogenic H5N1 avian influenza has killed an estimated 13,000 southern elephant seal pups on Australia's remote Heard Island, with mortality rates averaging 76 percent and reaching up to 97 percent in some colonies. This marks the first detection of the virus in an Australian external territory, with genetic analysis indicating the virus likely arrived from the Crozet Islands around August 2025.
Quick Facts
- H5N1 bird flu outbreak
- mass seal pup deaths
- drone surveys
- genetic analysis
- Australian Antarctic Program
A new study reveals that the highly pathogenic H5N1 avian influenza virus has caused the deaths of approximately 13,000 southern elephant seal pups on Australia's remote Heard Island, marking the first detection of the virus in an Australian external territory.
Researchers from the Australian Antarctic Program (AAP) conducted drone surveys in October 2025 and January 2026, finding an average mortality rate of 76 percent among seal pups, with some colonies experiencing up to 97 percent loss. The total southern elephant seal pup production was estimated at about 17,000.
The virus, part of the globally circulating H5N1 clade 2.3.4.4b, was detected in six species, including elephant seals, king and gentoo penguins, Antarctic fur seals, and seabirds. While elevated mortality was observed in penguins, the most severe impacts were on seals.
Genetic analysis suggests the virus likely arrived around August 2025 via wildlife movements from the French sub-Antarctic Crozet Islands, about 1,800 kilometers away, indicating a continued eastward spread of the virus across the sub-Antarctic region. Similar mortality patterns have been observed on other sub-Antarctic islands such as South Georgia.
The study, submitted to a scientific journal and released as a preprint, also found drone evidence of seal pup mortality on nearby McDonald Island, though ground confirmation is still pending. Researchers noted that no suspected cases of H5 bird flu have been detected on mainland Australia (including Tasmania), Macquarie Island, or the Australian Antarctic Territory to date.
Lead author and wildlife biologist Julie McInnes emphasized that these observations mark the first detection of H5 bird flu in an Australian external territory. AAP scientists conducted 120 drone flights covering over 1,600 kilometers to assess mortality across the islands, allowing surveys of inaccessible breeding sites with minimal disturbance.
Why This Matters
This outbreak demonstrates the widening geographic reach of H5N1 beyond traditional bird populations, now severely impacting marine mammals in the sub-Antarctic. For global health and wildlife managers, it underscores the need for expanded surveillance across remote island ecosystems and highlights the risk of further spread to Antarctica and other vulnerable wildlife populations.
Timeline & Sources
Aug 1, 2025
WireLikely arrival of H5N1 virus on Heard Island via wildlife from Crozet Islands
Oct 1, 2025
WireFirst drone survey conducted by AAP
Jan 1, 2026
WireSecond drone survey; widespread seal pup deaths recorded across breeding sites
Jun 19, 2026
WireStudy findings announced by AAP