Tamworth mouse problem: Why we have so many mice, and why they're 'absolute breeding machines'

A CSIRO researcher says the high numbers of the rodents result from a really good season and if the conditions continue, they will "keep breeding through the summer".

Steve Henry confirmed during the past four months the national science agency had been receiving reports of high numbers of mice from southern and western Queensland, "right down through the central western cropping zone and into areas of South Australia".

Tamworth hardware store owners have seen a huge increase in the sales of mouse traps and baits, with one store even reporting a 200-300 per cent sales boost in traps.

They're being put through their paces trying to keep up with the demand.

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"Typically after a number of tough seasons which you guys have had up there, and then you get good rainfall, the mice then seize that as an opportunity," Mr Henry said.

"Once you get rainfall you start to get a whole range of food and shelter in the system and that means they can start breeding early [in the spring] and then continue to breed through the spring and probably into the following autumn.

"Certainly if conditions remain favourable, and we've had really quite a nice mild summer... and a really good harvest ... it means they'll be using that grain and the food available and the shelter and with ongoing moist conditions it means that will enable them to keep breeding through the summer."

Mice start to breed when they're about six weeks old, and then they can have a litter every 19 to 21 days after that, Mr Henry says.

"The really tricky thing about them is they give birth to a litter, and then they can fall pregnant straight away again," he said.

"And so there's no waiting time in terms of the next litter, so by the time they're weaning the first litter, they're giving birth to the second litter.

"They're an absolute breeding machine."

Science says there are six to 10 mice per litter.

"They say a single pair of mice can give rise to 500 offspring in a season, basically," Mr Henry says.

"For rural communities we sort of say over 800 mice per hectare equates to a plague," Mr Henry said.

"If you've got one burrow per 100 square metres, that's 100 burrows per hectare, and if there's two mice in every burrow, that's 200 mice per hectare.

"So you're up around 400, 500 burrows per hectare to get to that sort of plague level.

"So that's a lot of mice.

"But it sounds like, after a number of really good years, and mice in the town, it sounds like we're starting to get to the point where there's really high numbers of mice across the board.

"You'll notice I'm reluctant to say the 'p' word.

"What I say to farmers is if they're seeing quite a few mice around, they've probably got a problem, regardless of whether it's a plague or not, and they should be looking to do something about it before they sow their next crop."

Mr Henry, whose work focuses on mice in crops and is funded by the Grains Research and Development Corporation (GRDC), said for farmers, it was important to try to reduce the residual food left in the paddock, including spraying out germinations after rain.

He did not recommend farmers bait right now.

"Hold fire, don't rush out and bait mice now when there's lot of other residual food out there," Mr Henry said.

"Wait until that residual food has been depleted by germination or by grazing, if farmers have sheep that they use in their system, they graze the stubble, the sheep eat a lot of the spilt grain that's on the ground, and when that food's been depleted, then apply your bait, because it gives it a much better chance of being discovered and being effective."

The CSIRO researcher said he was not an expert about the pests in towns, but "the trick to stopping mice coming into houses" was to block up all the tiny cracks and crevices in the house.

"So where pipes come in through walls and places like that and under doors and those sorts of things are places where mice can get into houses," Mr Henry said.

"Particularly old houses that have got lots of cracks and crevices mice can get into, and they can get through way smaller spaces than you would expect.

"Actually cramming steel wool into those little cracks is the way to prevent them getting in."

Tidying up in the yard could also make a difference.

"Clean up around sheds, so anywhere where there's harbour for mice, where mice can hide outside, so piles of wood and those sorts of things, clean up around the house, mow long grass, reduce the amount of shelter there is for mice," Mr Henry said.

"Chicken runs are famous as great place for mice to live, and bird aviaries, because there's lot of spilled grain and food on the ground, and so they provide the source population.

"So clean-up around outside, block up all the cracks and then I think trapping's the best way to do it, because you reduce the risk of secondary poisoning to pets and other animals."

In 2014, the CSIRO launched the MouseAlert website and app to allow farmers to report mouse sightings.

Mr Henry said it was aimed at farmers initially and was a really good tool for people to add data to, and have a look at what was going on in their region.

"I'm prepared to say people in town could use it, because mice in towns are indicative of mice in the rural sector, the chances of you having significant problems with mice in towns and there not being a problem in the surrounding countryside is very low," he said.