Fumigation program under way as rabbit population exceeds acceptable density

Tablets which turn into phosphine gas have been placed inside networks of underground burrows in parks including Mt Painter, as rabbit numbers increase beyond acceptable densities in some areas.

Populations at Mt Ainslie, Mt Majura, Jerrabomberra Wetlands, O'Connor Ridge, Percival Hill and Jerrabomberra Grasslands have all exceeded control limits, as La Nina provides ample grass for the invasive species to thrive.

In addition to fumigating warrens, ACT rangers use bait, bulldozers, guns and biochemical weapons to keep the pests at bay.

Invasive animals project manager Mark Sweaney said ACT Parks use spotlight monitoring to gauge when populations are exceeding an environment's threshold.

He said big populations sometimes required a more labour intensive response than fumigation, whereby the rabbits are poisoned.

"We're really careful about secondary poisoning where a native animal might either eat the bait or eat the poisoned rabbit," he said.

Mr Sweaney said they use cages too small for kangaroos to fit inside and use rabbit specific bait.

"Actually, they do really like carrot," he said.

The feed goes out in the early evening which is when rabbits like to eat and any leftovers are removed the next morning, Mr Sweaney said.

"And then we'll have people out searching the whole area for carcasses and removing those," he said.

While bunnies are breeding too quickly in some areas, research shows numbers are still well below the population peak which occurred prior to the introduction of biochemical control.

Australia first released the myxoma virus in 1950, drastically reducing rabbit numbers and reportedly increasing wool and meat production profits by $68 million in two years.

After the pests developed immunity to myxomatosis, the calicivirus was released in 1996 and then a second strain was used in 2017.

The CSIRO played a crucial part in the development and implementation of both programs.

Scientist Dr Tanya Strive said the exotic incursion of another calicivirus around 2014 or 2015 has also helped keep populations down.

The "rabbit pandemic" has spread across multiple continents since reaching Australia's shores by unknown means, she said.

Dr Strive said a major study released in 2013 found the economic benefit of biochemical controls to Australia's farming industry was $70 billion over 60 years.

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She said in addition to the damage they do to the land and livestock having to compete for grass, rabbits also sustain populations of invasive predators like feral cats and foxes.

"Apart from them being such a prolific species and breeding, like rabbits if you like, they have both bottom down and top up trophic effects on the ecosystem," Dr Strive said.

She said myoxa and calicivirus were still spreading in Australia and still killing significant numbers of rabbits.

"We're keeping track of which virus is where and when, and how they interact," she said.

"We're also looking at whether there's possible ways to use what's already here in a way that will give us a better outcome."

Dr Strive said while it may be a pipe dream, absolute eradication had to be the inspirational goal.

She said genetic modification technology, which would alter DNA to skew the sex ratio of a population, could be a future solution.

"It's not something that is likely to be ready in five years, it may never be ready, but the concept in itself is so powerful that it's really too good to theoretically consider," Dr Strive said.

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