The deer mouse, Peromyscus maniculatus, is one of the most widespread and abundant mammals across North America, ranging from Alaska to Mexico and inhabiting nearly every terrestrial habitat type. Understanding what this rodent eats is fundamental to comprehending its role in various ecosystems, where it acts as both a seed disperser and a seed predator. The deer mouse is an opportunistic omnivore, meaning its diet is highly flexible and changes depending on the season, local environment, and availability of food resources. This adaptability allows the species to thrive in diverse settings.
Staple Plant-Based Foods
The foundation of the deer mouse diet is plant matter, primarily seeds, nuts, and grains. These items are rich in carbohydrates and fats, making them an ideal high-calorie food source. The mouse is considered largely granivorous, relying on seeds from grasses and various other plants throughout the year.
Specific seeds consumed vary widely by region, but they often include those from foxtail, wheat, and corn in agricultural areas. In forested habitats, deer mice feed heavily on the seeds of valuable trees, such as pinyon pines and Douglas-fir. Studies have shown that pinyon seeds can make up as much as 77% of the deer mouse diet when available. The mice also consume nuts, which provide concentrated sources of fat important for building up energy reserves before winter. Their sharp incisors are used to gnaw through hard seed coats and shells.
Essential Protein Sources
While plant matter forms the bulk of the deer mouse’s diet, animal matter is a necessary component, supplying the protein and fat crucial for reproduction and growth. Deer mice regularly consume insects and other small invertebrates, collectively known as arthropods, which are a major food group alongside seeds. This protein intake can include beetles, spiders, caterpillars, larvae, and snails.
The reliance on animal prey fluctuates significantly with the season, often peaking during the warmer months when insects are most abundant. Even in winter, animal flesh can still account for a substantial portion of the diet, sometimes ranging from 15% to 55%. In some pinyon-juniper habitats, arthropods have been found to comprise over 90% of the diet, demonstrating an ability to shift to a nearly insectivorous diet. This high-protein feeding is important for breeding females, as it supports the high energy demands of gestation and lactation.
Seasonal Dietary Supplements
Beyond staple seeds and essential invertebrates, the deer mouse diet includes a variety of opportunistic foods that provide supplementary nutrients and moisture. These items are consumed only when readily available and are not considered primary survival foods. Fungi, including mushrooms and truffles, are eaten and may contribute to the dispersal of mycorrhizal fungal spores.
Berries and fleshy fruits are consumed when in season, offering a temporary boost of sugars and water. When primary food sources like seeds and insects are scarce, deer mice may turn to less palatable resources like green vegetation or roots. The consumption of green plant matter is sometimes correlated with periods of low precipitation, suggesting it is a source of moisture as well as calories.
Foraging Habits and Food Storage
The deer mouse is a primarily nocturnal creature, conducting the vast majority of its foraging activity under the cover of darkness. Locating food relies heavily on its sense of olfaction, or smell, which allows it to detect seeds and insects hidden beneath leaf litter or soil. The mouse is also semi-arboreal, meaning it can climb trees to forage for seeds and nuts, although much of its activity remains on the ground.
A defining feature of the deer mouse’s survival strategy, particularly in regions with cold winters, is food caching. During the autumn, the mice diligently collect and store food, especially seeds, in hidden locations known as granaries. These caches are typically placed in protected spots such as:
- Underground burrows
- Hollow logs
- Tree cavities
- Abandoned bird nests
The volume of seeds stored can be considerable, with a single cache sometimes holding up to 0.6 liters, and the total winter store potentially reaching 3 liters. This behavior ensures a reliable food supply for the winter months, when the mouse may enter a state of daily torpor to conserve energy. Stored food is the most important factor in preventing winter starvation.