The sight of a squirrel is almost universally associated with burying acorns or cracking open a nut. This common image has fostered a widespread belief that these creatures are strictly herbivores, surviving solely on plant matter. However, the diverse and adaptable feeding habits of squirrels classify them as opportunistic omnivores. While nuts and seeds form a significant part of their diet, they actively seek out and consume animal protein to meet specific nutritional needs throughout the year.
The Predominantly Herbivorous Diet
The majority of a squirrel’s daily calorie intake, often 70 to 80 percent, comes from plant-based sources. Their powerful, continuously-growing incisors are adapted for gnawing through the tough shells of tree nuts like walnuts, hickory nuts, and acorns. These seeds provide the concentrated fats and carbohydrates necessary for energy and winter survival.
Beyond nuts, squirrels forage extensively for other plant materials depending on the season and local environment. Their diet includes soft mast, such as berries and fruits, and fibrous components of their habitat. They also consume the tender parts of trees, including young shoots, flower buds, and the nutritious cambium layer found beneath the bark.
Fungi, including various species of mushrooms, also form part of their regular intake, supplementing their diet with vitamins and minerals. While this core diet establishes a baseline of energy, it is insufficient to support all of the animal’s biological functions, particularly during periods of high demand.
Specific Sources of Animal Protein
To supplement their plant-heavy diet, squirrels actively forage for animal matter, which provides a concentrated source of protein and other nutrients. The most frequently consumed animal protein comes from invertebrates, which are readily available throughout the warmer months. These include insects, such as beetles, grasshoppers, and caterpillars, as well as grubs and larvae unearthed from soil or rotting wood.
When the opportunity arises, squirrels, particularly ground squirrel species, engage in opportunistic predation on small vertebrates. Documented prey includes reptiles like lizards and frogs, as well as small rodents such as mice. This behavior is less common in arboreal squirrels but does occur, highlighting their flexibility as foragers.
The raiding of bird nests is another source of meat consumption observed in several squirrel species. They consume unguarded bird eggs and nestlings, providing a compact, nutrient-dense meal. The nocturnal Southern flying squirrel, for example, has a diet notably rich in insects, bird eggs, and nestlings.
Scavenging also contributes to their protein intake, especially when active foraging is unproductive or resources are scarce. Squirrels consume carrion, or the remains of dead animals, including roadkill, to obtain necessary nutrients. This demonstrates an adaptability that allows them to utilize any accessible source of protein and fat.
Nutritional Drivers for Omnivory
The primary reason squirrels seek out animal protein is to satisfy their high demand for nitrogen, a fundamental component required for growth and tissue repair. While plant matter offers fats and carbohydrates, it can be low in readily available protein, especially during late winter or early spring before new growth appears. The consumption of insects and small vertebrates directly addresses this protein deficit.
The need for concentrated nutrients is heightened in female squirrels during reproductive periods. Gestation and the subsequent lactation phase create an intense demand for protein and fat to ensure the healthy development of their litters. Animal protein is an efficient way to meet these elevated energy and nutrient requirements.
Another nutritional driver is the need for certain minerals that are scarce in a purely plant-based diet. Calcium, for example, is necessary for bone health and is particularly important for lactating females. Animal sources, such as eggshells or the bones of scavenged carrion, provide a bioavailable source of this mineral.
Seasonal fluctuations also influence the shift toward omnivory. During dry periods, when plant moisture content is low, ground squirrels may consume arthropods not just for protein, but also to satisfy their water requirements. This opportunistic flexibility ensures they can thrive across varied habitats and changing conditions.