Effects of contrasting habitats on population parameters and diet of Apodemus sylvaticus (Rodentia) in south-western Iceland

Population parameters, body mass and diet of Apodemus sylvaticus were compared in two nearby study sites in southwestern Iceland: open grassland and mixed woodland. Live trapping was conducted at approximately 5 week intervals from September 2004 to October 2005. In addition, mice were caught in snap-traps every month to estimate food composition from stomach contents. Estimated population density was up to 10 times higher in the woodland than in grassland but seasonal dynamics were the same, with peak density in autumn and low density in spring. Apparent monthly survival varied greatly throughout the winter in the grassland, ranging from 39% to 78%, but was stable at around 60% in the woodland. Mice fed predominantly on seeds in all seasons, with an exception during the spring when arthropod larvae were the most common food type. Food varied more by seasons than by habitats, but evidently mice from the woodland were less likely to feed on green material and showed more seasonal fluctuations in seed consumption. During mid-winter, woodland mice of both sexes were heavier than mice in the grassland. To some extent, the observed differences in density, survival, weight and diet could be reflecting differences in habitat quality in the two contrasting habitat types.