Why is there a mouse problem?

Mice are typically present in crops in most years, however certain conditions result in rapid population growth, which can lead to mouse plagues. Although mice can reproduce at any time of the year if food is available, the normal breeding season is from spring to mid-autumn. The most important driver of mice populations is food availability. Spilt grain from the previous years harvest is a high value food source for mice within paddocks. There was a large amount of grain left in many paddocks last season due to the delayed harvest and decreases in harvest efficiency because of the wet conditions. Spring and summer rainfall also impact mice ecology directly by ensuring the survival and growth of summer weeds and an earlier onset of winter weeds. These provide an important food source for mice. 

The availability of shelter is also a key requirement for mice survival. Favourable burrowing conditions are cracking or light soil types, and factors such as minimum tillage, stubble retention and reduced grazing, which provide extra cover and habitat for mice. Haystacks, farm sheds and piles of timber and firewood also provide ideal conditions for mice survival. 

Mice have caused problems in grain growing regions of Australia – on and off – for more than 100 years. Serious problems occur on average every 4-10 years, can last up to 2 years, and most commonly follow good cropping seasons. The current situation can be traced back 12-18 months, when numbers first began to rise. The main causes of collapses in mice populations are cessation of breeding, lack of food resources and the spread of disease. Cold weather and frosts will slow or stop breeding, however this alone will not result in mouse plagues ending completely.