Factors affecting the numbers of house mice (Mus musculus) in hard beech (Nothofagus truncata) forest

Nothofagus produces heavy crops of seed infrequently, and then house mouse (Mus musculus) populations increase greatly. In the Orongorongo Valley, near Wellington, seedfall of hard beech (Nothofagus truncata) and the numbers of house mice were measured for 22 years. Four heavy seedings were recorded and the numbers of mice were significantly correlated with the beech seedfall. Most mouse stomachs contained remains of arthropods, especially caterpillars and spiders, as well as plant material. Moths emerging from the litter of the forest floor in summer were sampled for seven years; the numbers of Tingena epimylia (Oecophoridae), whose larvae are litter-feeders, were strongly correlated with beech seedfall. The correlation between the numbers of moths and mice was slightly stronger than that between the numbers of beech seed and mice. Because the numbers of T. epimylia varied so greatly, components of the litterfall were also measured for three years. In a seeding year spent male flowers were a substantial part of the litterfall and might be responsible for the higher numbers of moths. These results indicate that factors other than quantity of seed may be important in the beech seed - mouse relationship and need to be explored further.