Species: Japanese harvest mouse

Status: Classed as “vulnerable” in Japan’s “Red List” Measuring just 6 cm, with a tail of around 12 cm, and weighing about 10 grams, the tiny kayanezumi (Japanese harvest mouse; Micromys minutus japonicus) lives in tall grasses found along riverbanks, in temporarily uncultivated fields and in seminatural meadows. The mice build nests about the size and shape of a grapefruit high above the ground amid the stalks of grass, and they eat the grains of these grasses along with crickets and other small insects.

Japanese harvest mice once found abundant habitat in the fields of susuki (Japanese pampas grass; Miscanthus sinensis) that farmers maintained to supply material for thatched roofs, “green manure” for fields and as feed for farm animals. These fields were usually cut and then burned once every few years, but with their function as a source of building and farming materials gone, most have either been developed or have grown over with shrubs and trees. Consequently, the Japanese harvest mouse must now find habitat in abandoned rice fields or river banks, and it has become increasingly rare in recent years.

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