Squirrels are widely known for burying nuts and seeds, leading many to assume they are strict herbivores. This perception is incorrect; these adaptable animals are omnivores whose diet naturally includes both plant and animal matter. While nuts, seeds, and fungi form the bulk of their food intake, animal-based items are a necessary inclusion. The typical plant-based diet often lacks sufficient amounts of certain macronutrients and minerals, forcing squirrels to seek out alternative sources of protein and mineral-rich materials.
Invertebrates and Eggs: Common Protein Sources
The most common animal matter squirrels consume is invertebrates, which are easily accessible and provide a concentrated source of protein. Insects like beetles, caterpillars, grasshoppers, and grubs are frequently foraged from the forest floor, tree bark, and leaf litter. This protein is important for growth and maintenance, supplementing their carbohydrate and fat-heavy diet of nuts.
Invertebrate consumption is particularly heightened during the breeding season when energy demands for reproduction and lactation are at their peak. A high-protein diet supports the rapid development of young squirrels. Along with insects, bird and reptile eggs represent another readily available, protein-dense food source. Squirrels opportunistically raid nests, consuming both eggs and, occasionally, vulnerable nestlings.
Opportunistic Predation of Small Vertebrates
Although the consumption of insects and eggs is common, squirrels will sometimes engage in opportunistic predation of small vertebrates. This behavior is often a response to a nutritional requirement or an abundance of easy prey, rather than their primary feeding method. Small mammals such as young mice, voles, or baby rabbits confined to a nest are vulnerable targets.
Recent scientific observations have documented this predatory behavior, such as a study noting California ground squirrels actively hunting and consuming voles. This behavior was most frequent during a temporary, localized boom in the vole population, highlighting the opportunistic nature of the feeding strategy. The protein and fat from a vertebrate meal provides a significant energy boost that is far more nutrient-dense than a typical plant-based food item.
Scavenging for Essential Minerals
Beyond the need for protein, squirrels actively consume non-living animal products to supplement their mineral intake. This is particularly true for calcium and phosphorus, which are often found in low concentrations in their primary diet of nuts and seeds. The behavior of gnawing on bones and antlers is a widespread phenomenon known as osteophagia.
Shed deer antlers, for instance, are composed of a high concentration of minerals, with calcium making up approximately 19% and phosphorus around 10% of their hardened structure. Squirrels chew on these mineral deposits, leaving behind characteristic parallel gnaw marks from their incisors. This practice is most frequently observed in female squirrels during late winter and early spring when they are pregnant or lactating. This high demand for calcium is necessary for bone formation in developing young and for milk production. Occasionally, squirrels also scavenge on carrion or the dried bones of small animals to secure these vital mineral supplements.