Mice numbers and behaviour in the Southern Mallee

In recent weeks BCG has been monitoring 13 paddocks around Birchip to better understand mice numbers and their behaviour.

The aim was to find answers to questions raised about the level of mouse activity in the area and their feeding preferences. The hypothesis was that the stubble type that had become the habitat of a certain mouse population would influence feeding preferences.

Monitoring:

A number of growers in the Birchip region were approached to provide access to four paddocks with different stubble types (wheat, barley, canola and lentils (or vetch)).

Within each paddock 2 x 100m long transects were set up with canola oil soaked chew cards pinned at 10m intervals. At either end, four plates were placed with 30 grains on each (barley, wheat, canola, lentils) to help determine feeding preferences. Potential mouse holes were counted and talcum powder dusted over them so their activeness could be determined.

Once transects were established, they were monitored for three consecutive days. Each day grain remaining on the plates was counted and photos were taken of all the chew cards, with any completely destroyed being replaced.  

An additional two transects were established in a paddock that was scheduled to be windrow burned. This was monitored prior to and following burning (removal of food source).

Findings:

Mouse numbers via active holes

Across the 13 paddocks, active holes ranged from 0-1000 per hectare, averaging at 300-400. From the small survey carried out, there could be no conclusion made around the number of active holes in relation to stubble type or the level of ground cover.

Table 1: Data collected on some of the monitored paddocks providing a snapshot into the variation observed between the different stubble types, potential and active holes, grazing management and ground cover.

Assessing mouse activity

The number of chewed squares on mouse survey cards was used to assess the activity of mice. Each card is made up of a 100 square grid, each square is equal to 1%. If after monitoring for two nights, 5-10% of the squares were chewed then it can suggest that mice may be an issue.

However, the use of chew cards to determine mouse activity was discovered to be highly variable. Within transects, it was found that one chew card could be completely chewed while the two either side (10m apart) remained untouched.

Feeding preference

Assessment of grain removed from plates placed at the transect ends, showed the mice appeared to select for cereal grains over canola and lentils. However, in most cases, following three days, all grain was removed.

From the monitoring that was done, no conclusion could be drawn as to the impact of grazing on activity or numbers when compared to un-grazed paddocks. Similarly, no conclusion could be drawn as to mouse activity and numbers on different stubble types. Each paddock appeared to behave differently.

Key messages:

• Monitor your paddocks, every paddock appears to be different.
• Dry conditions mean that holes may not be as obvious to spot as mice can be living in cracks.
• There was no clear feeding preference for a particular grain type (they may possibly prefer cereals – good news for cereal based bait products).
• Baiting is really our only option for mouse control – if you think you have mice, bait early particularly with dry sowing where grain may not germinate immediately.
• Chew cards don’t tell the whole story. They give an indication. If using chew cards it is best to put out a number within a paddock.

This research was funded by the GRDC as part of the ‘Maintaining profitable farming systems in the retained stubble – Component 1 project’ (BWD00024).