Farmers and invasive species experts are hoping looming El Niño conditions will finally provide an opportunity to control a rabbit population that has surged across Australia during recent wet years.
Key points:
- Rabbit numbers have increased due to wet conditions and increased vegetation
- A shift to drier conditions will hopefully provide landholders with an opportunity to finally tackle numbers
- Landholders are urged to follow the guidelines for releasing biocontrol agents to kill rabbits
Despite parts of the country receiving record-breaking rainfall in recent weeks, Australia's overall outlook will be dry.
The Bureau of Meteorology (BOM) has predicted El Niño will continue into 2024 with the potential for higher-than-average temperatures and lower-than-average rainfall in some areas.
The La Niñas of previous years meant an explosion in rabbit populations with an increase in vegetation.
The situation was further exacerbated by a lack of opportunity to release biocontrols, allowing rabbits to continuously breed.
Centre for Invasive Species Solutions chief executive Andreas Glanznig said the change in weather patterns provided a chance to bring rabbit numbers back.
"Rabbit numbers are up due to La Niña and good times, and also just because a lot of land managers haven't been able to use rabbit biocontrol agents like K5," Mr Glanznig said.
"[Those] agents can generally only be released when there's no young rabbits around."
He said rabbits under 10 weeks of age generally were not killed by calicivirus — the most effective rabbit biocontrol agent.
"If rabbits are continually breeding throughout the year it makes it very difficult to find a slot to successfully release a rabbit biocontrol agent so it can kill the old rabbits and not inadvertently immunise young rabbits," he said.
Mr Glanznig said rabbits could breed 12 times a year and caused about $217 million in damage annually to pastures and crops, as well as native wildlife and ecosystems.
"Even though that's a staggering cost, it's still only 10 per cent of what the cost would be if myxomatosis and calicivirus had never been released," he said.
Controlling rabbits
Lesley Loxton has been struggling to control increasing rabbit populations on her property at Compton in South Australia's south-east.
"I've always had some rabbits, but I think they get worse every year and it's unmanageable now because they're just so destructive," Ms Loxton said.
"Even with the myxomatosis that came through and wiped out some, they came back stronger than ever."
She said the rabbits were burrowing under her house and sheds, ringbarking her fruit trees and digging holes that made it dangerous for her to walk around her property.
"They come up in the hay and eat the hay, and the ground in the hay shed's not level anymore," she said.
"I need a hip replacement and a knee replacement so I have to be very careful walking in my yard because of all the rabbit diggings that occur there.
"The brickwork in the carport — that's all caving in … because they've burrowed under the house."
Timing key
Mr Glanznig urged landholders wanting to control rabbits to follow the guidelines, with early autumn providing better conditions for baiting.
"A national survey undertaken a couple of years ago came up with a staggering result — that three-quarters of land managers didn't follow the release guidelines for rabbit calicivirus," Mr Glanznig said.
"There were numerous instances where land managers were releasing K5 during the peak rabbit breeding season.
"What you're then doing is shooting yourself in the foot because you're killing the older rabbits but immunising the young rabbits. You're taking one step forward, two steps back.
"The El Niño phase provides some gaps where there aren't young rabbits in the landscape and that's the ideal time to release a rabbit biocontrol agent."
Mr Glanznig said the agents were suppressing rabbit numbers by about 90 per cent, but their impact did wane over time.
"Rabbit biocontrol agents aren't silver bullets. They need to be used as part of an integrated approach which includes chemical control, warren ripping, and so on if you're going to have a sustained impact and control of rabbits over time," he said.