Clint Taylor, who works for Bush Heritage Australia at Bon Bon Station — a former sheep property that is almost the size of Sydney — is all too familiar with the destruction rabbits can cause.
In 2019 the organisation and the station, based near Roxby Downs in South Australia's far north, was awarded a $10,000 grant through the local Natural Resource Management Board to undertake rabbit mapping and control.
"We've prioritised about 10,000 hectares to get mapped as part of that project and engaged the local traditional owners to do the mapping," Mr Taylor said.
"They were out on motorbikes with GPSes and they basically rode transect lines across the property … and any rabbit warrens they came across they marked them with GPSes.
"Over that 10,000ha there was roughly about 450 warrens and probably about half of those were active.
"Having about half of those warrens active after the drought of 2018 and 2019 was pretty surprising."
Mr Taylor said about 100 of the warrens had been fumigated.
"The reason it's important to focus on rabbit control is that rabbit populations can support populations of foxes and cats as well," he said.
"History has shown us that rabbit warren ripping is the best method.
"There's implications involved with that with having to get cultural heritage clearances done and then getting the machinery out there.
"If there are areas with a lot of rabbit activity and it's a smaller area, then sending out people with fumigation equipment at the right time of the year can be very effective."
La Niña and the rabbit surge
Centre for Invasive Species Solutions chief executive Andreas Glanznig said Australia was about to see a rabbit "surge".
"Because we're in a La Niña cycle there's more rainfall, therefore more vegetation and therefore more rabbits," Mr Glanznig said.
"So, what you'd be seeing in many landscapes is a surge of rabbit numbers responding to the increased vegetation available."
He said rabbits remained "the most costly feral pest in Australia", financially and environmentally.
"They impact agriculture to the tune of over $216 million per year in lost agricultural productivity," Mr Glanznig said.
"On the environment side … one rabbit per hectare is enough to stop the regrowth of some native species.
"They impact over 321 nationally listed plants and animals and that includes 24 critically endangered and threatened species such as the pygmy possum, the orange-bellied parrot and the ballerina orchard."
Race against time
Mr Glanznig said it was important to always try and be on the front foot.
"The real opportunity is looking at how we can capitalise and maintain the gains made through the continent-wide release of myxomatosis in the '50s and the calicivirus in the '90s," he said.
"Those two biocontrol measures alone have had a result of over $70 billion of agricultural benefits over the last 60 years and now the real challenge is looking at how we can maintain that benefit.
"Otherwise, the worst-case scenario is what we had in the 1920s — somewhere around 10 billion rabbits absolutely decimating Australian landscapes, environments and farmlands."
Battle against genetic resistance
Genetic resistance is not uncommon, but Mr Glanznig says this is "inevitable" among rabbits, which is why the impact of biocontrol agents reduces over time, and new ones are frequently required.
"If you don't put out a new agent every eight to 10 years, inevitably you'll start to see rabbit numbers increase and therefore rabbit impacts increase," he said.
"To deliver that, we've brought together a range of top-notch researchers from the CSIRO and state governments such as NSW and South Australia and also key universities."
In a bid to combat genetic resistance, Mr Glanznig's team has started to look at new genetic biocontrol technologies. But it could be a decade or two before it's available.
"Genedrive is a technology that enables a gene to be integrated into the genetic make-up of, in this case, a rabbit, so that at the end of the day it produces only, say, functional males," he said.
"Then over time, you can then drive a rabbit population to low numbers or even potentially like functional extinction."
Committee member with the Foundation for Rabbit Free Australia Carolyn Ireland said alongside viruses, a coordinated neighbourhood rabbit control approach was being used.
"So that when you do control rabbits on one property, they don't just go next door or are allowed to breed up or come in from adjoining properties," she said.
"That's best done when there are coordinated programs across a region, with all the neighbours working together with a mix of biological and physical controls, which means digging up rabbit warrens and destroying them."ABC