A house mouse (Mus musculus) population eruption in response to rimu (Dacrydium cupressinum) seedfall in southern New Zealand

We document an increase in house mouse (Mus musculus) abundance in a year (2002) when there was light beech (Nothofagus species) seedfall but very heavy rimu (Dacrydium cupressinum) seedfall in Waitutu Forest, southern New Zealand. On our nine study grids, mouse numbers in November were highly correlated with rimu seedfall. Feeding trials with wild-caught captive mice showed that mice typically opened the rimu nut and ate the seed (endosperm and embryo) leaving the husk. Chemical analysis showed that the nutritional content and calorific value of rimu seed was more than sufficient to sustain growth and reproduction in house mice. We conclude that the heavy rimu seedfall drove the house mouse population eruption in Waitutu Forest. Although large increases in house mouse populations in beech forest systems are well documented, this is the first description of a mouse population increase as a result of a podocarp seeding event in New Zealand. We highlight the potential risk these dynamics pose to threatened native birds living in mixed forest systems.