The deer mouse (Peromyscus maniculatus) is one of North America’s most widespread small mammals, inhabiting diverse environments from forests to grasslands across the continent. This small rodent is an opportunistic omnivore, meaning its diet shifts readily based on available food resources. Its ability to consume a broad array of plant and animal matter allows it to maintain robust populations even when facing seasonal scarcities.
Staple Foods and Seed Consumption
The foundation of the deer mouse diet is seeds, classifying them as predominantly granivorous. Seeds, nuts, and grains provide the concentrated, high-energy nutrition needed to fuel their active lifestyle. Deer mice consume a wide variety of dry plant materials, including grass seeds, weed seeds, and conifer seeds.
The consumption of tree seeds, such as those from pine and fir, is a significant part of their foraging and often contributes to the failure of forest regeneration efforts. To access the nutritious kernel, the mouse uses its sharp incisor teeth to gnaw away the hard outer seed coat, a process known as hulling. Studies show that a deer mouse can consume or destroy a volume of seed equivalent to approximately one-third of its own body weight in a single night. This high intake demonstrates their reliance on energy-dense staples for survival.
Seasonal Shifts and Supplementary Nutrition
While seeds are the dietary mainstay, the deer mouse shifts consumption patterns when staple foods become less plentiful, particularly during warmer months and winter. During spring and summer, arthropods and other invertebrates become a prominent part of the diet. The consumption of insects, spiders, and caterpillars provides high-protein nutrition, which is especially important for breeding females and growing young.
This animal matter can compose a significant portion of their summer intake, sometimes reaching a majority of the diet depending on the habitat. To meet moisture and vitamin needs, deer mice supplement their diet with fungi (like mushrooms and truffles), green vegetation, leaves, roots, and various berries and fruits when available.
Foraging Habits and Food Caching
The deer mouse is a nocturnal forager, beginning its search for food after twilight and retreating to its nest or burrow during the day. Its foraging is aided by a highly developed sense of smell, which helps it locate buried seeds, nuts, and invertebrates, even under leaf litter or soil. The mouse’s high metabolic rate necessitates an almost constant effort to acquire food to maintain its energy balance.
A defining behavior is food caching, a survival strategy used especially in preparation for winter. They engage in two primary caching methods: larder hoarding and scatter hoarding. Larder hoarding involves accumulating a large volume of food, sometimes up to three liters of seeds, in a single location near the nest chamber. Conversely, scatter hoarding involves burying small quantities of food in multiple caches spread across their home range. This stored food sustains the mice through periods of cold weather or deep snow cover when active foraging is impossible.
Diet’s Role in Disease Transmission
The foraging and caching habits of the deer mouse create the potential for pathogen transmission, most notably the Sin Nombre hantavirus. This virus causes Hantavirus Pulmonary Syndrome (HPS) in humans. It is carried asymptomatically by the mouse and shed in its urine, droppings, and saliva. When searching for food or nesting sites, deer mice frequently enter human structures like sheds, barns, or cabins, contaminating surfaces and stored materials.
The virus is transmitted to humans primarily through the inhalation of aerosolized particles when dried rodent waste is disturbed, such as by cleaning a contaminated area. The mouse’s dietary need to find and store energy-rich foods like grains and seeds drives it into close proximity with human food stores and sheltered environments.