H5 bird flu is yet to reach the Macquarie Marshes, but landholders fear the region's feral pig problem could make an outbreak harder to contain.
The internationally recognised wetlands, near Warren in central north-west NSW, provide habitat for tens of thousands of waterbirds, including many threatened species.
David Duncan from the Macquarie Wetlands Association manages Burrima, a conservation property bordering the nature reserve.
He said an outbreak of the H5 strain of bird flu in the marshes could be particularly damaging, given the number and diversity of waterbirds that gathered in the wetlands.
Mr Duncan said bird flu would add to an existing biosecurity problem in the marshes, with feral pigs, foxes and cats already taking a significant toll on native wildlife.
Introduced predators are estimated to kill millions of native animals across Australia each day, while Mr Duncan said pig numbers around the marshes had surged after several favourable seasons since the 2017–2020 drought.
"The feral pigs and cats and foxes are already creating massive damage, and they are a threat as a potential vector to spread bird flu."
Mr Duncan said controlling pigs required a coordinated approach because they could travel long distances between properties, and the responsibility should not fall solely on individual landholders.
"They move big distances. They might be on your farm one day, but they can be three or four farms away the next night," he said.
"You can't do something on your own. You've got to do something at least at a district level to try and control them. It needs to be vigilant and constant."
He said greater attention needed to be paid to biosecurity threats already present in the environment, rather than focusing on only emerging threats.
"Biosecurity is far more than preparing for or reporting the next exotic disease or pest to arrive," he said.
"It must control or eradicate the introduced species and pests that are already here, killing out native wildlife."
'They're going to take a big hit'
University of NSW conservation biologist Richard Kingsford said waterbirds were particularly vulnerable because they congregated in large numbers at wetlands, allowing the virus to spread through contact, faeces and scavenging birds.
Widespread wetland habitat across western NSW and the Murray-Darling Basin has helped keep birds dispersed, but Professor Kingsford said the risk could increase as conditions become drier.
"This influenza can kill sometimes half of a population. So that's how devastating it can be for wildlife," Professor Kingsford said.
Controlling an outbreak across large and remote wetlands would also be difficult, although Professor Kingsford said some populations could bounce back.
"Over time there's a potential for some of these populations to recover, but they're going to take a big hit," he said.
Professor Kingsford will undertake his annual aerial waterbird survey across eastern Australia in October and November, covering up to 2,000 wetlands.
But authorities cannot monitor every wetland, meaning landholders, birdwatchers and citizen scientists could play an important role in detecting an outbreak.
"It's essentially the citizen science that is going to tell us what's going on," he said.
Questions over how to respond
On Monday, the NSW government confirmed new H5 bird flu cases in Woy Woy on the Central Coast and Bulli in the Illawarra region, bringing the total number of cases in the state to 32.
There have been no cases detected in inland NSW.
Landholders near the marshes are being advised to avoid grazing livestock in areas heavily populated by waterbirds where possible, particularly if sick or dead birds are present.
A NSW Government spokesperson said H5 bird flu infection or disease had not been reported in beef cattle herds globally.
"Although transmission to livestock is considered low risk, there is a need for vigilance and grazing on or near wetlands like Macquarie Marshes may increase the risk," the spokesperson said.
But Macquarie River landholder and RiverSmart Australia chair, Kate Milner, said that could be difficult to implement.
"That sounds great on a piece of paper, but not in practice," she said.
"Cattle need water, and they will graze in the marshes and along the river, which is where birds congregate."
The NSW government has also urged landholders to maintain strong farm biosecurity and keep working and pet dogs away from wild birds and carcasses.
But Ms Milner said landholders still had questions about the potential impacts of an outbreak, including what it could mean for backyard poultry, water supplies and access to the marshes.
"There's quite a lot of talk flying around, but nobody really knows," she said.
A community information session will be held in Warren on Thursday to give landholders more information about preparing for and responding to an outbreak.
People who find sick or dead birds are being urged not to touch them and to report them to authorities.
