Squirrels, members of the family Sciuridae, are recognized globally as highly adaptable rodents. Their image is often tied to the familiar habit of burying acorns and other hard-shelled seeds for later consumption. While nuts and seeds are a concentrated source of fats and proteins, the survival of these energetic mammals depends on a far wider, more varied diet. This dietary flexibility allows squirrels to thrive in diverse environments, constantly adjusting their foraging to meet their nutritional needs regardless of the season or habitat. Their daily menu goes well beyond the standard nut, incorporating a range of plant matter and animal protein sources.
Vegetation, Fruits, and Fungi
The plant-based diet of a squirrel shifts dramatically throughout the year, providing necessary vitamins, fiber, and hydration when calorie-dense nuts are unavailable. In the early spring, before leaves fully emerge, squirrels rely heavily on tree buds and flowers, such as those from maple and elm trees. They will also consume young, soft leaves and plant shoots as they emerge, which are easier to digest than mature foliage.
Summer and early autumn bring an abundance of fruits and berries, which provide sugar and moisture for energy. Wild berries, including blackberries, raspberries, and mulberries, are frequently consumed, along with cultivated garden items like apples and grapes. These items are eaten immediately rather than stored, reflecting their high water content and short shelf life.
Fungi are another significant part of the diet, especially for species living in forested habitats. Squirrels forage for both above-ground mushrooms and subterranean fungi, commonly known as truffles. Consuming fungi helps provide essential micronutrients, such as nitrogen and minerals. For nocturnal species like flying squirrels, the fungi can be a natural source of Vitamin D.
Essential Protein Sources
Squirrels are true omnivores and actively seek out high-protein animal sources that are necessary for physiological functions like growth and reproduction. In the warmer months, insects form a substantial part of this protein intake, including beetles, caterpillars, larvae, and grubs. This boost of animal protein is particularly important for nursing mothers and juveniles undergoing rapid development.
The consumption of bird eggs and nestlings is a well-documented behavior. Squirrels are opportunistic nest raiders, taking advantage of unattended nests to acquire a source of concentrated protein and fats. This behavior is driven by nutritional necessity, especially when other food sources are scarce.
Some squirrel species have been observed hunting and consuming small vertebrates. Observations have documented California ground squirrels actively hunting and eating voles. This predatory behavior highlights the squirrels’ adaptability, allowing them to capitalize on temporary booms in prey populations to acquire necessary nutrients.
Survival Tactics and Opportunistic Foods
When the natural bounty of the growing season is exhausted and buried caches are depleted, squirrels turn to less palatable, but life-sustaining, resources. During late winter and early spring, they often resort to stripping the outer bark from trees to access the inner layer, known as the cambium. The cambium is the soft, living tissue beneath the bark that transports water and nutrients, and is eaten for its sugar content and fiber.
Squirrels will also tap trees to consume the flowing sap, which is a rich source of sugars and minerals, including calcium and sodium. This behavior, which can damage the tree if excessive, is a response to the scarcity of other food options before spring greenery arrives. They utilize this sweet, mineral-rich liquid as a survival mechanism during the leanest period of the year.
Closer to human habitation, squirrels exhibit opportunism by taking advantage of readily available resources in gardens and refuse. They are known to dig up and consume:
- Flower bulbs
- Vegetable patches for corn and tomatoes
- Fruits like strawberries
- Spilled bird seed
- Discarded human food scraps
- Left-out pet food
This showcases their ability to adapt their diet to a human-altered landscape.