Squirrel existence is fundamentally tied to the presence of trees, which provide both high-energy sustenance and secure habitat. Squirrel preferences are an ecological calculation based on the caloric payoff and structural utility a tree provides. Understanding these preferences involves looking beyond a single food source to the full suite of resources trees offer for metabolism, shelter, and reproduction.
Trees That Provide Primary Food Sources
The most sought-after trees for squirrels are those that produce hard mast, which are the energy-dense nuts and acorns crucial for surviving the winter. Species like Oaks, Hickories, Walnuts, and Pecans are highly favored because their fruit is rich in fats, proteins, and carbohydrates. The high fat and oil content makes them an efficient food source for building the fat reserves necessary for year-round activity.
Oaks (genus Quercus) are a particularly significant resource, and squirrels demonstrate a preference between the two main groups. White Oak acorns are often consumed immediately because they contain less bitter tannin and are generally sweeter. Red Oak acorns, while more bitter, mature over two seasons and tend to be more reliable producers annually, making them a consistent, storable food source that lasts well into the winter.
Hickories (Carya spp.) and Walnuts (Juglans spp.) are prized for their high caloric value and hard shells, which protect the kernel for long-term caching. Squirrels bury these hard mast items, a behavior known as scatter-hoarding, to secure a food supply that sustains them through periods of scarcity. A single gray squirrel can bury thousands of nuts each autumn.
Trees That Offer Critical Shelter and Nesting
Beyond food production, trees must also offer specific structural features that meet the squirrel’s needs for shelter, protection from predators, and raising young. These needs are met through the use of natural tree cavities and the construction of leaf nests, known as dreys. The safest and most preferred shelters are den cavities, which are hollows formed by decay or created by woodpeckers in the trunk or large limbs of older trees.
These den trees provide superior insulation and protection during severe weather and are often used for overwintering and as maternity dens, where survival rates for young are significantly higher. When cavities are unavailable, squirrels construct dreys, which are bulky, spherical nests made of leaves, twigs, and bark, typically positioned high in the forks of sturdy branches. Deciduous trees with strong, wide-spreading branches, such as mature Oaks and Maples, are ideal for supporting the weight and structure of these dreys.
Seasonal and Secondary Tree Resources
When the primary hard mast supply is exhausted, squirrels adapt their diet to a range of secondary tree resources. In late winter and early spring, the diet shifts to include tree buds, which are a valuable source of stored energy and calcium before the leaves unfurl. Squirrels will forage on the buds of various species, including Maple, Elm, and Oak, to meet their nutritional requirements during this lean time.
The seeds of coniferous trees, such as Pines and Spruces, also become a significant secondary food source, with squirrels skillfully dismantling the cones to extract the tiny, winged seeds. Furthermore, the sap and inner cambium layer of certain trees, particularly Maples, can be accessed in the spring by stripping the bark, providing a sugary liquid that offers a quick energy boost. In periods of extreme food shortage, squirrels may consume tree bark to acquire trace minerals or wear down their constantly growing incisors.