In the colder months, the dining habits of common tree squirrels, such as the eastern gray squirrel and the American red squirrel, shift dramatically due to scarce resources. Unlike true hibernators, these active rodents do not enter a deep sleep, meaning they must find sustenance throughout the winter. Survival depends on a combination of previously stored provisions and newly foraged items. Limited food availability dictates a metabolic focus on calorie-dense foods to maintain body temperature and energy levels. Understanding their winter diet provides insight into the strategies these small mammals use to persist when the landscape is frozen.
Relying on Cached Stores
The foundation of a squirrel’s winter diet is the collection of food items stored during the fall, a behavior known as caching. Gray squirrels primarily use scatter hoarding, hiding individual food items in thousands of separate, shallow caches across their territory. These underground stores typically contain calorie-rich mast crops like hickory nuts, acorns, and walnuts, which provide the concentrated energy needed for survival.
American red squirrels, in contrast, often practice larder hoarding, amassing a single, large stockpile of food, known as a midden, usually composed of conifer cones and their seeds. Finding these buried treasures under snow depends on a combination of memory and scent. Research suggests squirrels rely heavily on spatial memory cues, like nearby landmarks, to remember the general location of their caches, using scent only for the final retrieval.
Gray squirrels are successful, retrieving anywhere from 40% to 80% of their buried items. When caching acorns prone to rapid germination, squirrels may bite out the embryo tip to prevent the seed from sprouting, preserving the food source for later use. Red squirrels may also cache fungal fruiting bodies in trees to dry them out, creating a less perishable food source for the winter.
Opportunistic Winter Foraging
While cached food is their primary reserve, squirrels must also engage in active foraging to supplement their diet, especially when snow cover makes finding buried nuts difficult or stores deplete. This secondary diet consists of items available directly on trees and shrubs. Tree buds, particularly those from maple and oak trees, become a significant food source.
Squirrels scrape away the outer bark of trees to access the cambium layer, which is the soft, nutrient-rich inner layer that lies just beneath the surface. Red squirrels, which often inhabit coniferous forests, rely on conifer buds and shoots as a regular part of their winter foraging. On occasion, squirrels may consume lichens found on tree trunks, search for any available fungi, or find insect larvae hidden within bark crevices.
In urban environments, opportunistic foraging expands to include anthropogenic food sources. Gray squirrels are observed consuming discarded food waste from trash bins, particularly when natural resources are low. Because active searching requires a significant energy outlay, squirrels tend to remain in their nests during the harshest weather, only venturing out when the need for food becomes pressing.
Water and Energy Requirements
The entire winter diet is driven by the physiological need for high-calorie intake to counteract the effects of cold and maintain essential body functions. Squirrels are warm-blooded, and their small size means they lose heat quickly, requiring a steady supply of energy-dense foods to fuel metabolism and produce heat. The nuts and seeds they rely on are naturally high in fat and protein, making them an ideal fuel source for survival.
Hydration is also a challenge when liquid water sources are frozen. Squirrels meet their water needs primarily by extracting moisture from the foods they consume. They also have a reduced metabolic demand for water during the colder months. When necessary, however, they will actively consume snow or ice to supplement their fluid intake.