Trapping successive generations in disease hotspots
In the windswept solitude of Heard Island, four thousand kilometres from the Australian mainland, a pathogen has rewritten the future of a species. H5 bird flu — the same virus reshaping wildlife populations across the globe — has claimed more than 13,000 southern elephant seal pups in a single breeding season, erasing three-quarters of a generation in a place so remote it once seemed beyond reach. The discovery marks the first detection of highly pathogenic avian influenza in an Australian external territory, and it arrives as a warning: distance is no longer a shield, and the Southern Ocean's most vulnerable communities now live in the shadow of a moving threat.
- A virus that has devastated wildlife on multiple continents has now breached Australian territory, killing 13,359 seal pups — up to 97% of offspring in some harems — in a single season on Heard Island.
- The southern elephant seal, already classified as vulnerable to extinction, is uniquely exposed: its instinct to return faithfully to the same breeding grounds year after year may trap successive generations in permanent disease hotspots.
- H5 has spread across six species on the islands — penguins, fur seals, seabirds — signalling that the outbreak is not contained to one population but is threading itself through an entire ecosystem.
- Scientists are watching Macquarie Island with particular dread, where dense colonies of already-fragile species could allow the virus to transmit at catastrophic speed if it arrives.
- Australia has committed $113 million to preparedness and remains the only continent free of H5, but researchers and government officials alike acknowledge that the virus is closing the distance.
Four thousand kilometres south-west of Australia, on the remote and windswept Heard Island, researchers made a discovery last October that had never been recorded in an Australian external territory: H5 bird flu, the highly pathogenic avian influenza reshaping wildlife populations worldwide. What initially appeared to be hundreds of dead seal pups scattered across the island's breeding colonies would, on closer analysis, reveal a catastrophe of far greater scale.
When a second research team returned in January and processed their data, the toll came into focus: an estimated 13,359 southern elephant seal pups had died from the virus — more than three-quarters of all pups born on the island that season. In some harems, mortality reached 97 per cent. The outbreak was still unfolding when observations ended, meaning the final figure may be higher still.
The virus likely arrived in August 2025, carried by infected wildlife from the Crozet Islands roughly 1,700 kilometres away. Once established, it moved through the dense breeding colonies with devastating efficiency, eventually being detected across six species including king and gentoo penguins, Antarctic fur seals, a brown skua, and a South Georgia diving petrel. But the southern elephant seals — recently classified as vulnerable to extinction — bore the heaviest losses. Their deep fidelity to traditional breeding grounds, a trait that has defined the species for millennia, now works against them: they are unlikely to abandon infected sites, potentially exposing generation after generation to the same disease.
To survey terrain too remote and rugged for ground teams, researchers deployed drones across 120 flights covering 1,600 kilometres of airspace, gathering data later combined with viral genome analysis to reconstruct the outbreak's spread. The findings, published in BioRxiv and awaiting peer review, carry implications well beyond Heard Island.
Scientists warn that if H5 reaches Macquarie Island — within Australian territory and home to vast, dense aggregations of penguins, albatrosses, and seals — the consequences could be catastrophic. The pattern is already visible elsewhere: in Argentina in 2022, H5 killed 96 per cent of southern elephant seal pups, and a year later only a third of the population returned to breed. In South Georgia, breeding females fell by 47 per cent between 2022 and 2024.
Australia remains the only continent free of H5 bird flu. The federal government has committed $113 million to preparedness, with an additional $11.2 million directed toward at-risk species and population resilience. But officials and scientists share the same quiet understanding: the virus is moving, and the Southern Ocean's remoteness is no longer the protection it once was.
Four thousand kilometres south-west of Australia, in the churning waters of the Southern Ocean, lies Heard Island and McDonald Islands—a remote territory where seals breed in vast colonies and seabirds wheel overhead in the wind. Last October, researchers arriving on a voyage discovered something that had never been found in an Australian external territory before: H5 bird flu, the highly pathogenic avian influenza that has devastated wildlife populations across the globe.
At first, the scale seemed manageable. Scientists from the Australian Antarctic Program reported finding hundreds of dead southern elephant seal pups scattered across Heard Island. But when a second research team returned in January and analysed the data they had gathered, the picture became far grimmer. The researchers now estimate that 13,359 seal pups died from the virus—more than three-quarters of the 17,364 pups that had been born on the island that season. In some seal harems, the mortality rate reached 97 per cent. The figure may yet prove conservative; the outbreak was still unfolding when the researchers completed their observations.
The virus likely arrived in August of the previous year, carried by infected wildlife from the Crozet Islands, roughly 1,700 kilometres away. Once it took hold on Heard Island, it spread through the dense breeding colonies with devastating efficiency. The researchers detected H5 in six species across the islands—king penguins, gentoo penguins, Antarctic fur seals, a brown skua, and a South Georgia diving petrel—but the southern elephant seals bore the brunt. These seals, recently classified as vulnerable to extinction, return faithfully to the same breeding grounds year after year, creating ideal conditions for the virus to establish itself and persist. Unlike other species that might abandon an infected site, elephant seals are unlikely to desert their traditional colonies, potentially trapping successive generations in disease hotspots.
The findings, published in the scientific journal BioRxiv but not yet peer-reviewed, carry implications that extend far beyond Heard Island. If H5 spreads to other sub-Antarctic regions—particularly Macquarie Island, which lies within Australian territory—scientists warn of potentially catastrophic consequences. The Southern Ocean and sub-Antarctic environments host large, dense aggregations of already vulnerable species: albatrosses, penguins, elephant seals, fur seals. These conditions are precisely what the virus needs to transmit rapidly and establish itself across vast populations.
To reach their conclusions, researchers deployed modern technology in ways that would have been impossible a decade ago. They completed 120 drone flights totalling 54 hours of airtime and covering 1,600 kilometres, allowing them to survey remote and inaccessible terrain without disturbing the animals. Ground searches, by contrast, could cover only 8.8 kilometres. The drones gathered data that researchers then combined with viral genome analysis to build a comprehensive picture of the outbreak.
This is not the first time H5 has ravaged seal populations in the Southern Hemisphere. In Argentina in 2022, an outbreak killed 96 per cent of southern elephant seal pups. A year later, only one-third of the seals returned to breed. In South Georgia, the number of breeding females fell by 47 per cent between 2022 and 2024. The global southern elephant seal population is concentrated in just four geographically separated regions, which means that outbreaks in any one location carry disproportionate weight for the species as a whole.
Australia remains the only continent without H5 bird flu. The federal government has invested $113 million in preparedness, with Environment Minister Murray Watt acknowledging that while the country is currently free of the virus, the global spread makes an incursion increasingly likely. The government has allocated an additional $11.2 million in this year's budget toward supporting at-risk species and building population resilience. For now, Australian wildlife remains protected by distance and vigilance. But the virus is moving, and the Southern Ocean's remoteness is no longer a guarantee of safety.
Citações Notáveis
The emergence of HPAI poses a severe and potentially catastrophic threat to the wildlife of the Southern Ocean and sub-Antarctic environments, where large, dense breeding and moulting aggregations of already vulnerable species create ideal conditions for rapid viral transmission.— Research report published in BioRxiv
For now we're free from the serious and contagious H5 bird flu, but as it continues to spread globally, we must be realistic about the likelihood of an incursion here, and plan accordingly.— Federal Environment Minister Murray Watt
A Conversa do Hearth Outra perspectiva sobre a história
Why did the virus hit the seals so much harder than the other species on the island?
Seals breed in enormous, tightly packed colonies and return to the same spots year after year. They don't flee when disease arrives. Penguins and other birds can move to new breeding grounds, but seals are locked into their traditional sites. Once the virus establishes itself, it becomes a trap.
How did researchers even know how many seals died? The island is remote and harsh.
Drones. They flew 120 missions, covering ground that would have taken months to walk. The drones could see into valleys and coves where people couldn't go without disturbing the animals. That technology made the scale of the die-off visible.
Is this the first time bird flu has hit seal populations?
No. Argentina saw 96 per cent of seal pups die in 2022. South Georgia lost nearly half its breeding females between 2022 and 2024. What's new is that it's reached an Australian territory. The worry now is whether it spreads to Macquarie Island, where the conditions are just as ideal for transmission.
What makes the Southern Ocean so vulnerable?
The animals there breed in massive, dense aggregations—thousands of seals and penguins packed together. They're already stressed by climate change and other threats. The virus doesn't need much to spread in those conditions. It's a perfect storm.
Can anything be done to stop it?
Not really, once it's there. The focus now is monitoring—watching Macquarie Island and the Antarctic territory closely—and building healthier populations elsewhere so the species doesn't collapse entirely. Prevention is the only real tool left.