For almost 30 years, CSIRO’s rodent management team leader Dr Peter Brown has worked ‘around the traps’ to better understand mice. For much of that time, the team just included himself and Steve Henry.

Since then, the team has grown to 10 and is looking for more members. Under Dr Brown, and with Mr Henry, other team members are senior research scientists Wendy Ruscoe, mouse ecologist, and Kevin Oh, gene technologist.

With last year’s plague now petering out, Dr Brown says the team is focusing on monitoring and new research projects.

“We want to gather more pieces of the puzzle. We want to better understand mice through modelling, better predict when a plague will end, explore the role of diseases in regulating mouse populations and, through all of that, better inform management decisions.”

He says mouse plagues are an interesting paradox. “In agriculture we get these stellar years that follow bad seasons. And then we get mouse problems. This last one across the eastern states was a particularly big one and came off the back of bushfires and very dry years. We started to get good conditions and that is when mice do really well. People are more aware of that now, but we still have room to understand more.”

Modelling

Across five states and 130 monitoring stations, Dr Brown and partner organisations monitor mice three times a year. Using additional information from CSIRO’s mouse-trapping benchmarking sites, models are run. Developed 20 years ago, these models predict what is likely to occur and when.

Through a variation to this GRDC-invested project, Dr Brown’s team will incorporate other data, such as crop and weather forecasts or soil information, to better inform the model.

“I interpret our data now, so I’m essentially making myself redundant, but it would be beneficial to pull all the data that we collect from various sources together to model where mice will be and in what numbers.”

The model will also move to a spatially explicit one. “At the moment we use a point-based system. So, we now know what is happening at a certain location, a point in the map, but we want to be able to extrapolate that data to include other areas.

“We are hoping that with a spatially explicit model, we can zoom in and out of certain locations to provide real-time information on the risk in a coming season.”

Dr Brown also hopes to better understand when mouse populations will ‘crash’.

“We know they crash at some point, and once the crash has occurred, because mouse numbers are very low, they don’t respond for a few years. It means the chances of a plague happening again soon are very low.”

Predicting the crash could be helped by another new research project that is looking at mouse diseases and parasites and how the population responds to them.

“A lot of work was done about 15 years ago, which said there was no ‘Calicivirus’ for mice.” (Calicivirus was released in the late 1990s to control feral rabbits.) “But with research technology changing, maybe there is something out there for mice.”

CSIRO researcher Kevin Oh, an evolutionary ecologist, is working to better understand how mouse populations are structured across the landscape, how far and from where they move, and the extent to which geography helps or hinders that movement.

“Kevin’s research will improve our understanding,” Dr Brown says. “With a library of samples, we can analyse them and understand disease and what role it plays in population dynamics.”

It could help to predict when a plague will end. “We can predict 12 to 18 months out from when a plague will occur but not when it will end. Historically it is May, June or July, but the missing piece of this puzzle is how disease impacts mice and the social dynamics involved. It’s another component that we need to understand.”

Alternative food

With one of the key management strategies being baiting, the CSIRO team will continue its work on alternative food availability and its effect on baiting.

Last year, CSIRO’s work to reassess the bait zinc phosphide and its efficacy led to the APVMA approving an emergency permit for the production and supply of double dose baits, increasing the amount of zinc phosphide on certain products from 25 grams per kilogram to 50g/kg. This has improved the likelihood of a mouse consuming a lethal dose in a single feed.

This work came about as part of CSIRO’s progressive approach to mouse research, including work on alternative foods, how mice choose food substrates, and field trials comparing the two doses of zinc phosphide. The last part of the work, planned for early 2022, involves testing bait efficacy in the presence of alternative food.

“Hopefully it will help us to provide more advice on harvesting and grain left behind. We don’t want alternative food around at sowing and baiting time. We need to look more into the effects of a light tillage, sheep, rolling and seed destructors.”

Dr Brown says this again ties in with mouse ecology research. “We want to know more about the influence of alternative food and farming systems on mouse populations and dynamics.

“Farming systems have changed in the past 15 years as more growers have moved to minimum till. Mice have changed their behaviour too. They are now in paddocks all the time and not just on the fencelines or paddock edges. They have resident warrens in the crop. By better understanding all the links, we can better inform management decisions and find out what works.”

Fodder

In 2021, the team also undertook a pilot study into the effects of mouse plagues on fodder, finding that mice caused a 30 to 40 per cent loss in its value.

Other than weather, Dr Brown says, mice are the only factor that affects the long-term sustainability of fodder storage. In response to the fodder damage that resulted from the plague, many growers fed sheep and cattle at twice the rate they normally would, reducing the amount of fodder stored for dry periods.

“Mice damaged strings and the structure of bales, making transport impractical and leading to destruction of some stacks,” he says.

In addition, growers were concerned about contamination and disease transfer to livestock and workers from mice through their urine, faeces and carcasses.

“There are significant gaps in our knowledge on the impacts of mice on fodder storage. We need to research effective mouse control options, determine the economic impact and undertake a disease study. This would help to inform appropriate management strategies.”

Checklist

As growers prepare for the coming winter season, Dr Brown says it is important to continue monitoring mouse numbers, despite reduced numbers.

“Monitoring reveals changes in populations and can help indicate when control is needed. One of the most important times to undertake monitoring is prior to sowing, from March to April.”

More information: Dr Peter Brown, 02 6246 4086, peter.brown@csiro.au

Read also: Mouse Alert and Genetic detective on the mouse trail.