Landcare Scientists Measure the Mouse Menace

Forest and Bird, Issue 314, 1 November 2004, Page 9

Landcare Scientists Measure the Mouse Menace

— Source:

Landcare Research.

DIANA LEUFKENS,

Scientists researching the threat mice pose to beech forests have found the damage may be less to the beech than to other native plants. ‘The results raise critical questions about the impacts mice may have through consumption of other native plants, insects and fungi, according to Landcare Research scientists Dr David Choquenot and Dr Wendy Ruscoe. "By consuming these species as secondary food items, mice may be having a more insidious effect on forest biodiversity than their consumption of beech seeds alone may suggest. ‘The regular irruption of mice in high-seedfall years also has important flow-on effects on the numbers of "mouse predators"

— notably stoats — and the prey they subsequently consume, notably our forest birds. More than 70 percent of New Zealand’s native forest is either dominated by or otherwise contains beech trees. These trees may be particularly susceptible to seed consumption by mice due to their cycle of ‘masting, the production of large quantities of seed on an irregular basis every two to four years. Many believe that beech trees use masting to swamp the capacity of seedeaters to eat all seeds before germination can occur, but our beech trees evolved in the absence of mice. Dr Ruscoe says that regardless of whether alternative food sources are available to mice, they continue to search for and

consume beech seeds until there are none left. ‘This means they are theoretically able to eliminate seed reserves in beech forests, whether or not alternative food such as native moth larvae is available, she says. The scientists monitored how many seeds mice could find and eat, and the rates of increase and decrease in ‘mouse abundance’ as seed availability rose and fell. When combined and built into a specially developed mathematical model, these factors indicate that mice would rarely be able to consume all the beech seed produced during moderate to heavy ‘masting’ years. "Therefore, mice are not a likely threat to the continuous

presence of beech trees, Dr Ruscoe says. ‘However, seed availability appears to be important to mouse dynamics. ‘Our research provides a more reliable basis for predicting when mouse abundance is likely to irrupt, and will help refine our ideas on how to target control measures for them. The research also highlighted a lack of understanding of the role mice play in forest ecosystems. ‘Given the pervasive nature of mice in beech forests, and difficulties associated with their control, there will be further research on understanding and managing their effects.