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A deadly strain of bird flu, known as H5 bird flu, has arrived on the Australian mainland.

The federal agriculture minister, Julie Collins, this weekend confirmed that a brown skua – that had been found sick in Western Australia – had died from the H5N1 virus. The skua is a wild migratory bird.

A second bird, a sick giant petrel found nearby, was also likely infected.

Australia’s run as the only continent free of the virus has now ended. H5 bird flu has killed millions of birds and thousands of marine mammals since it began spreading across the globe in 2021.

What is H5 bird flu and why are authorities concerned?

The H5 bird flu is a “highly pathogenic” virus, which means it is highly contagious and causes serious illness, including animal deaths.

Dr Ariful Islam, a veterinary epidemiologist at Charles Sturt University who researches avian influenza viruses, says the virus is a “panzootic”, meaning it has spread across multiple continents and affected many species. 

The disease has already infected millions of wild birds, including threatened species, and has had a devastating impact on agricultural industries, particularly poultry, Islam says.

According to Wildlife Health Australia, more than 560 wild bird species and more than 100 different types of mammals have been affected by the virus.

Where did it start?

The deadly bird flu strain (H5N1 clade 2.3.4.4b) started in Asia, but has been spreading globally across Europe and the Americas since 2021, arriving in Antarctica during the 2023-24 summer.

Australian researchers estimate the virus arrived on Heard Island, an Australian territory located about 4,000km south-west of Perth, in August 2025. It has spread among penguins, seals and petrels, killing more than 13,000 southern elephant seal pups and hundreds of king penguins.

How did it arrive on the Australian mainland?

The brown skua, a subantarctic species, was found sick at Cape Le Grand national park near Espearance on Sunday 14 June and subsequently died. An initial positive test for H5 bird flu in WA was later confirmed by the CSIRO’s Australian Centre for Disease Preparedness. 

A second bird, a giant petrel found in the same area, has tested positive for the disease at a WA government laboratory.  That result is being confirmed by further testing at the CSIRO lab.

Islam says further environmental sampling and monitoring are needed to determine the extent of the outbreak. “We need to know the full spectrum of the disease ecology, and the transmission dynamics and pattern in that area of Western Australia,” he says.

The two birds most likely migrated to Australia from the subantarctic, according to BirdLife Australia.

It is not yet known if the virus has spread further. Collins says there is no evidence to date of mass mortality or of infection in poultry. She says a nationally coordinated response will initially focus on determining whether the disease has spread to other wildlife.

It will likely be known within days whether the disease has affected local wildlife populations.

What does it mean for Australian agriculture?

The virus differs from the H7 bird flu, which caused outbreaks in poultry farms across several Australian states in 2024 and 2025, and led to the euthanising of hundreds of thousands of chickens. 

Dr Michelle Wille, an expert in avian influenza viruses at the University of Melbourne, says H5 has had significant impacts on the poultry industry in other parts of the world.

“For example, since the arrival of the virus in the US, more than 200m chickens have been culled, which, of course, is bad for birds, bad for farmers and bad for consumers.”

Wille says the virus has led to human infections, generally among people who work with infected poultry.

What are the risks for human health?

Bird flu infections in people are rare, often mild, but potentially dangerous. 

The Australian Centre for Disease Control says bird flu in people is rare and often mild but can cause severe disease or death.

People can be infected by breathing in contaminated dust or air, or by touching an infected animal. Symptoms can include fever, cough, sore throat, conjunctivitis and muscle aches and pains.

Dr Matt Mason, from the University of the Sunshine Coast’s school of health, says the risk to the general public remains low, and there is limited evidence of human-to-human transmission.

“Almost all human cases recorded globally have resulted from exposure to infected poultry or, in the US, dairy cattle.”

Australia’s first reported human case in 2024 was travel-associated, in a child who likely acquired the infection overseas and later recovered. 

From 2003 to early 2026, there were 997 reported cases of human H5 infection from 25 countries. Of these, 478 were fatal, the World Health Organization reports. In the US, there have been two deaths out of 71 cases, according to the US Centers for Disease Control and Prevention.

What are the risks to native wildlife?

Dr Fiona Fraser, Australia’s threatened species commissioner, says if H5 bird flu becomes established in wildlife, there is little that can be done to stop its spread.

Governments have analysed which of Australia’s birds and mammals could be most at risk, which include, for example, the Tasmanian devil, the critically endangered orange-bellied parrot and the Australian fur seal.

Authorities have developed more than 100 response plans for at-risk animals and important natural sites such as Ramsar wetlands and islands.

“We’ve taken into account whether they’re already threatened with extinction, but also other natural traits, such as whether they’re water birds, whether they’re marine species, whether they congregate, to understand which species are most susceptible,” Fraser says. 

Jack Gough, the chief executive at the Invasive Species Council, says the risk is “no longer theoretical” and if the virus begins circulating among native birds, it could lead to massive declines in some species and push others closer to extinction.

“There is a very good chance that the impact on Australia’s native wildlife will be even worse than it is in the northern hemisphere,” he says. “This is a genuine wildlife emergency, and it must be treated as such with emergency funding to increase efforts to protect wildlife populations.”

The council says Australia could help protect native species by boosting wildlife resilience, and wants the federal government to invest $200m over two years to tackle invasive species, restore habitat and reduce predators. 

The Australian Marine Conservation Society fears the mainland arrival of H5 bird flu could pose a “real extinction risk” for the endangered Australian sea lion, with only 12,000 remaining along the coasts of South Australia and WA. 

“Bird flu poses a real risk to the future of the Australian sea lion, found nowhere else in the world, potentially pushing it to extinction,” the campaign director Alexia Wellbelove says.

“The experience worldwide demonstrates the potential for this virus to be catastrophic for Australia’s unique wildlife and threatened species.

“Investing in boosting the resilience of our threatened species by protecting and restoring their habitat, and reducing pressures on their populations, is now essential to ensure their future.”

What to do if you see sick birds or marine mammals?

Members of the public are urged to avoid contact with any dead or sick birds or animals showing signs of bird flu. Report sightings to the emergency animal disease hotline 1800 675 888 or birdflu.gov.au.