The deer mouse, a member of the genus Peromyscus, is one of the most widespread and abundant rodents across North America, spanning a vast geographical range from Alaska and Canada down to central Mexico. These mice typically weigh between 10 and 24 grams and measure 119 to 222 millimeters in length. They are characterized by a grayish to reddish-brown coat, large eyes and ears, and distinct white underparts and feet.
The Definitive Answer: Omnivorous Nature
Deer mice are indeed omnivores, consuming a varied mix of both plant and animal matter. This means they do not rely on a single food source, shifting their consumption based on what is locally available and abundant. This flexibility contributes to their ecological success and ability to thrive across diverse habitats. Their ability to digest a wide array of nutritional sources provides an advantage over more specialized feeders.
Specific Components of the Diet
The plant-based portion of the deer mouse diet is highly diverse and includes seeds, nuts, fruits, and flowers. They use their sharp incisors to gnaw through the hard coats of seeds and nuts, making otherwise inaccessible food viable. Fungi also forms a regular part of their consumption, and they may even help disperse the spores of mycorrhizal fungi in forest ecosystems.
The animal component of their diet is primarily composed of invertebrates, such as insects, spiders, and earthworms. Larval and adult insects, including beetles and caterpillars, provide a high-protein source, which is important during warmer months for breeding and growth. They also consume carrion and practice coprophagy, consuming their own feces to recycle nutrients and obtain necessary vitamins produced by gut bacteria.
The balance between plant and animal matter shifts significantly with the seasons and habitat type. In summer, the diet often favors insect prey, providing high protein for reproduction. During the colder months, the focus changes to seeds and grains, which are more readily stored and remain available. For example, deer mice in pinyon juniper habitats have been recorded consuming over 90% arthropods, while those in sagebrush habitats may have a diet composed of up to 69% seeds.
Habitat and Foraging Behavior
Deer mice occupy a wide range of ecological zones, including alpine areas, boreal forests, grasslands, deserts, and agricultural fields. Their diet is highly adaptable to local conditions, meaning a mouse in a forest will eat different items than one in a desert. Their foraging activity is primarily nocturnal, and they search for food under the cover of darkness. During the day, they remain in nests built in burrows, logs, tree cavities, or under rocks.
A primary survival behavior is food caching, where they store food, especially seeds and nuts, for later consumption in secret larders or granaries. These caches can be quite large, sometimes containing over a liter of food, and are essential for surviving the winter when surface foraging is difficult.