Floods across eastern Australia have reduced mouse numbers but the recent plague left some properties exposed to inundation
Last modified on Fri 17 Dec 2021 04.50 EST
As flood waters move through New South Wales, farmers are finding their levees have been compromised by holes and burrows left by mice at the height of the mouse plague.
Richard Heath, the executive director of the Australian Farm Institute, said the tunnels and nests created by mice are particularly problematic during wet weather.

“If you’ve got levee banks breaking or earthworks formed to channel water in a particular way and they fail, then you can have really severe or damaging intense flooding because you’re basically channelling water where it’s not meant to go,” Heath said.
Major rainfall events over the last few weeks across Australia’s east have caused multiple flood peaks, which continue to move through the Condamine-Balonne and border rivers in Queensland, and the Lachlan, Namoi and Barwon rivers in NSW.
As flood waters approached Bedgerabong from the burst banks of the Lachlan River, wheat and canola farmer Scott Darcy was checking his boundary levee every day, ready to fill the holes left by mice.
Darcy says he was lucky because the flood was so slow moving he was able to “get on top” of plugging the holes.
He said the mice were “everywhere” when the levee bank was freshly pushed up in June.
“Every orifice, every piece of machinery – around them or under them – you’d see 30 to 40.”
The problem is often amplified by foxes following the mice, creating even bigger holes in the levee, Heath said. If landholders only discover the holes after flood waters have arrived, it can be too late.
“To repair a levee bank properly you have to knock it down and rebuild it, so you have to wait until the water’s gone to be able to rebuild it,” Heath said.
Heath said another legacy left by the mice is significant damage to farm machinery from wiring that has been chewed.
“If it’s machinery only used occasionally, you only notice when you get it out.”
Many farmers have also been plagued by mouse faces, with their grain rejected because of contamination.
“You can drive a truck all the way from the inland paddocks down to the port and not realise you’re about to be rejected,” Xavier Martin, the vice-president of NSW Farmers, said in November.
“There’s a big cost just for the transported grain to be returned back to the farm.”
He said many mice survived through to September but “the torrential rain has given them a lot of swimming lessons”.
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Martin said prior to the wet weather there had been reports of mice getting stuck in harvesting equipment, but the October and November rain had caused a “massive” decline in numbers.
Despite the damage to the flood levees, Heath said “overwhelmingly farmers would be looking at the positive aspect of flooding on mice – that it drowns them”.
Steve Henry, a CSIRO researcher specialising in the impact of mice on the grain industry, said reports about mice emerged in spring last year but that after the harvest “things really kicked off”.
Henry does not expect the plague will return this year as the flooding would have suppressed numbers. He said while adults would have been able to escape the water, any babies would have drowned.
But Martin said the heavy rain and the inability of headers to cope with the mud meant there was a lot of food left behind for the mice.
“Farmers are still going to have to monitor mice levels post harvest, otherwise populations could potentially explode into autumn again,” said Martin.
Henry said farmers harvesting as much of the crop as the can will reduce the amount of food available for mice. “That in itself reduces their capacity to go on breeding throughout the summer.”
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