A suitable embankment mowing strategy for habitat conservation of the harvest mouse

The harvest mouse Micromys minutus (Pallas 1771), a small rodent, builds its nests on tall grasses such as Amur silvergrass Miscanthus sacchariflorus (Maxim.) Benth. This mouse species is endangered by grassland habitat loss worldwide. Although embankments are one of the mouse’s nest sites in Japan, these habitats are not stable because of regular mowing. To investigate ways of increasing the habitat suitability of embankments, research was carried out over a 2-year period in western Japan on an embankment where Amur silvergrass was dominant. Two to three divisions of the embankment were mowed at intervals in spring and autumn, and seasonal changes in nesting and vegetation were examined. Nest sites were evaluated using Manly’s index. In each year, the nesting period was extended and more nests were built compared to past years when phased mowing was not performed. The density of nests in each division increased in order of mowing in spring, but was low in autumn. Amur silvergrass was the preferred nesting plant and other perennial grasses were avoided. Annual grasses were preferred over Amur silvergrass in 2005. Nesting restarted when Amur silvergrass recovered to heights of >100 cm in all divisions, regardless of the mowing month. Each year, 120–160-cm-tall Amur silvergrass was preferred, while plants <80 cm high were avoided. Phased mowing, which allows annual grasses and Amur silvergrass sufficient time to recover, is clearly an effective method of maintaining stable nesting habitat for the harvest mouse on an embankment.