Bird Flu Killed 13,000 Seal Pups on Remote Antarctic Islands
A deadly strain of bird flu has killed an estimated 13,000 seal pups on two of the most remote islands on Earth.
Researchers now believe they know exactly how it got there.
What the Drone Surveys Found
Heard and McDonald Islands sit roughly 2,485 miles southwest of mainland Australia, an isolated sanctuary that has long sheltered breeding seabirds and marine mammals.
Wildlife biologists from the Australian Antarctic Program conducted drone surveys and field work there in October 2025 and January 2026, specifically checking for signs of the H5N1 strain.
What they found was, in the words of senior research scientist Jarrod Hodgson, "sobering."
Drone imagery revealed seal pup carcasses littering the grayish volcanic shores of both islands.
The southern elephant seal pup mortality rate was estimated at 76% across a population of 17,000 pups born on the islands this breeding season — with one concentrated area showing a death rate of 97%.
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How the Virus Likely Reached Such a Remote Place
The islands' extreme isolation made the outbreak's origin a genuine scientific puzzle.
Genetic analysis of the virus samples suggests the answer: the H5 strain was likely introduced through wildlife traveling from the French sub-Antarctic Crozet Islands, located roughly 1,800 kilometers away.
Researchers estimate the virus likely arrived around August 2025, carried not by humans or shipping but by migratory birds or seals moving between the two island groups.
As of February, neither the Australian mainland nor New Zealand had recorded any H5N1 cases, underscoring how the disease moved through a wildlife corridor entirely separate from the populated landmasses nearby.
Lead researcher McInnes noted the pattern is consistent with what scientists have already observed elsewhere.
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A Pattern That's Now Repeating Across the Sub-Antarctic
"Our results show a similar pattern to other sub-Antarctic islands, such as South Georgia, where elephant seals have been hardest hit," McInnes said, according to CNN.
That comparison matters because South Georgia's elephant seal colonies experienced a similarly devastating bird flu event in recent years, suggesting H5N1 has found a consistent and lethal pathway into pinniped populations across the wider Antarctic region.
Penguins and seabirds on Heard and McDonald Islands were also affected by the outbreak, though the survey's primary mortality data focuses on the elephant seal pup population, where the impact was most measurable and severe.
The findings have been published on the preprint server BioRxiv but have not yet undergone formal peer review — a detail the research team has been transparent about while still releasing the data given the scale of the die-off.
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The Question the Survey Couldn't Answer
What the drone surveys captured is mortality among pups — animals born this season, with no prior immune exposure and limited mobility to escape a contaminated colony.
What they did not capture is the toll on the breeding adult population.
"The thing we don't know from our surveys so far is what the impact was on the breeding adult population of southern elephant seals," Hodgson said.
That distinction matters enormously for the colony's long-term survival. A population can recover from a single catastrophic pup season if breeding adults remain largely intact. It cannot recover the same way if adults were also dying in significant numbers, since they are the only source of future pups.
Until further field surveys assess adult mortality directly, the long-term population trajectory for Heard and McDonald Islands' elephant seals remains the open and consequential question this outbreak has left behind.
Key Takeaways
- An estimated 13,000 seal pups, along with penguins and seabirds, died from H5N1 bird flu on Heard and McDonald Islands in the sub-Antarctic.
- Drone surveys by the Australian Antarctic Program in October 2025 and January 2026 documented the die-off; senior scientist Jarrod Hodgson called the images "sobering."
- Southern elephant seal pup mortality was estimated at 76% across 17,000 pups born, with one area reaching a 97% death rate.
- Genetic analysis suggests the virus arrived via wildlife from the French Crozet Islands, roughly 1,800 km away, around August 2025.
- The pattern mirrors a similar outbreak at South Georgia, where elephant seals were also hit hard.
- Researchers say the impact on breeding adult seals remains unknown — a critical gap for assessing the colony's long-term recovery.
