The harvest mouse (Micromys minutus) is a tiny, specialized rodent that navigates the dense, vertical stalks of tall grasses, reeds, and cereal crops. This small mammal utilizes its prehensile tail to move through its elevated, arboreal habitat. The diet of the harvest mouse is not static but changes significantly throughout the year, driven by the availability of resources in its environment.
Year-Round Primary Food Sources
The harvest mouse is omnivorous, balancing high-calorie plant matter with protein-rich invertebrates to sustain its high metabolism. Seeds and grains form the caloric backbone of its diet, providing the necessary energy for continuous activity since this species does not hibernate. These granivorous preferences include a wide variety of grass seeds, such as those from reeds and sedges, along with cultivated cereal grains like wheat and oats.
Invertebrates serve as a crucial source of protein, especially during the breeding season. The mouse consumes a range of small arthropods, including insects, caterpillars, and spiders. They frequently descend from the stalks to forage on the ground for species like pill bugs and carrion beetles, despite their reputation as high-level climbers. Supplemental, high-energy foods are also gathered directly from plants, often including nectar and pollen from flowers.
Seasonal Variations in Consumption
The harvest mouse diet shifts across the seasons as local vegetation cycles change. During the peak abundance of summer and early autumn, the diet is most diverse, featuring a significant intake of animal protein to support breeding and growth. Invertebrates can constitute up to 30% of the total diet during this time, coinciding with the highest availability of insects. They also consume fresh seeds, berries, and fruits like rosehips and blackberries, which provide sugar and fat for the coming colder months.
As late autumn transitions into winter, the mice must pivot to a graminivorous diet due to the scarcity of fresh food and insects. The proportion of invertebrates drops significantly, while consumption of seeds and leaves increases substantially. During the harshest periods, when the stalk zone of grasses has died back and fallen, the mice rely on less palatable items. These include moss, roots, fungi, and the inner bark or stems of certain plants, which sustain life until spring.
Foraging Habits and Hydration
The harvest mouse is an agile forager, utilizing its slender body and specialized limbs to access food unreachable by most other small rodents. Its prehensile tail acts as a fifth limb, coiling around grass stalks to provide a secure anchor while the forepaws manipulate food items. This allows the mouse to climb high on vertical stems to reach seed heads, where it husks and consumes the grain.
While primarily nocturnal, harvest mice can be active throughout the day, especially in winter when they must forage during milder temperatures to maintain their body heat. To prepare for periods of scarcity, they engage in food caching, storing seeds and other durable items in or near their nests for later consumption.
The mice require an external source of hydration and do not rely on metabolic water alone. They obtain this water by drinking dew drops directly from the leaves and stalks of plants. This intake is supplemented by the high moisture content of the fresh plant material they consume.