Food Composition of the Harvest Mouse (Micromys minutus) in a Western Suburb of Tokyo, Japan, with Reference to Frugivory and Insectivory

Abstract

The harvest mouse (Micromys minutus) is a unique rodent that lives in grass communities and constructs spherical breeding nests from grass or sedge leaves. In Japan, the harvest mouse frequently inhabits communities of tall grasses. These grasses are very tall (>2 m), and the harvest mouse constructs spherical breeding nests as high as approximately 1 m from the ground (Kuroe et al. 2007; Hata 2011), which is much higher than the nests of European harvest mouse which constructs nests at 15–65 cm above the ground (Dickman 1986). Since the harvest mouse is very small (less than 10 g), it should require nutritious food sources (Kleiber 1961; Fancy and White 1985). Animal materials are generally rich in protein while plant leaves contain large quantities of cellulose and little protein and are less digestible for mammals (Robbins 1983). Fruits contain less fiber than leaves, and are therefore more nutritious, but contain less protein than animal materials (Robbins 1983). These facts at least partially explain why small mammals that require more energy per unit body weight than larger mammals are more likely to be insectivorous or granivorous (Pearson 1948). The tall grass communities provide few nutritious plant foods except for some herbaceous plant seeds or insects. Confirmation that the harvest mouse feeds on fruits/seeds and insects would contribute to a more general subject how small mammals that require more energy per unit weight than larger mammals select nutritious foods in food-poor habitats. Surprisingly, however, few studies have been done on the food habits of the harvest mouse. To our knowledge, only Dickman (1986) reported on the omnivorous food habits of the harvest mouse in England, but no information is available in Japan, though Ishiwaka and Masuda (2008) reported evidence that the harvest mouse controls the armyworm (Mythimna separata, Lepidoptera), which suggests that the harvest mouse feeds on insects. Therefore, we analyzed the food habits of Japanese harvest mice living in the tall grass community using fecal analyses. The objective is to quantitatively show the food habits of the harvest mouse with reference to frugivory and insectivory. The term frugivory (fruit feeding) is distinguished from granivory (seed feeding), but in the present study “frugivory” includes both frugivory and granivory because distinguishing fruit and seeds were difficult in many cases.