Australia mouse plague: What caused the rodent outbreak?

‘It’s like trying to count the stars ... they’re uncountable’

Chantal da Silva
Monday 31 May 2021 12:46
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Mice ‘rain from sky’ in Australia as rodent plague continue

Farmers in Australia are struggling to cope with a major “mouse plague” that has left crops destroyed and homes infested with hundreds of rodents running amok.

In New South Wales, the most heavily hit area, rodents have found their way into schools, hospitals, supermarkets and countless family homes, causing widespread upset.

Mice are literally everywhere – in people’s houses, in their living rooms, in their clothes, in their cupboards, in their beds,” Steve Henry, a researcher at CSIRO, Australia's national science agency, told The Independent.

The outbreak, he said, is having a significant “social ... and psychological impact” on families across the country, with Queensland, Victoria and other areas also impacted by infestations.

Trying to quantify the problem, Mr Henry said, “is like trying to count the stars...they’re uncountable”.

Meanwhile, he said the overall economic impact of the crisis still has yet to be seen as families try to grapple with the immediate costs of having to destroy resources to rid their farms of the mice.

“I know one farmer in central New South Wales who just set fire to 3,000 bales of hay because they’d been so badly contaminated with mice,” he said.

What caused the ‘mouse plague’?

As families across Australia contend with what has been branded a “mouse plague”, many will be wondering what prompted the sweeping infestations.

Major mouse infestations like the one seen in Australia “often happen at the end of a run of dry years”, Mr Henry told The Independent.

This is not the first mouse plague Australia has endured and the current episode came after rains last year left farms abundant with grain, making for a perfect food source for mice.

“New South Wales had four really dry years in a row and then conditions got favourable for mice to breed and there was lots of food there because farmers were growing lots of crops,” Mr Henry said.

Then, he said, the country had a “very mild wet summer”, allowing mice to continue to breed.

“So, they continued to breed right thorough the summer into autumn,” he said.

The worst may be yet to come

Now, as Australia faces the winter months, Mr Henry said the situation could get better – or it could get worse, with CSIRO warning that the outbreak may not have yet reached its peak.

“There are two trajectories for mouse plagues,” Mr Henry explained. “They go really really high and then crash away in one year or they go high and plateau through the winter and then they go again next spring.

“Now, we're going into winter with a pretty good crop, so that will mean there’s a lot of food and mice in the spring if they survive through the winter.”

Ultimately, Mr Henry said, “it’s very difficult to predict the end of an outbreak because they happen cyclically”.

Change could be coming

As rodents run riot on Australian streets, however, researchers are working on one solution Mr Henry said could see mice across the country eradicated.

“Farmers only have one tool available to them and that’s wheat grain coated with a zinc phosphate toxin,” he said.

However, despite the product being used on farms for around two decades now, Mr Henry said farmers have been complaining that the coated wheat grain has not been effective.

After looking deeper into the issue, researchers found that it was the strength of the bait that was proving ineffective, “not because mice were becoming tolerant [to the coated grains]”, he said.

A strengthened product that will see “every wheat grain” provide “a lethal dose” has now been developed, with the grains having just received regulatory approval.

“We're hopeful that will make a significant impact,” Mr Henry said.

Until then, the expert has said that farmers should keep monitoring the situation over the winter and be prepared to tackle the issue in the spring.

“[The mice] are continuing to breed at the moment, so we’re quite concerned about the level of over-winter survival,” Henry said. 

It is likely to be a difficult winter for many home owners, as they continue to struggle with dozens, if not hundreds of mice, invading their homes.

The expert said he had sympathy for families affected by the outbreak, particularly as they face so much uncertainty in the months ahead.

“The people are just sick and tired of dealing with them,” he said.

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