The Eastern Gray Squirrel (Sciurus carolinensis) is a familiar resident of North American forests and urban parks. As a diurnal species, the gray squirrel is active exclusively during daylight hours, meaning it requires a secure, sheltered location for sleeping at night. Unlike many other small mammals, this species does not truly hibernate, necessitating reliable shelter year-round to survive cold temperatures and poor weather conditions. This constant need for refuge leads the gray squirrel to construct or acquire two distinct types of sleeping structures to manage daily rest and seasonal extremes.
The Temporary Shelter: Leaf Nests (Dreys)
The most visible form of shelter used by the gray squirrel is the leaf nest, scientifically known as a drey. Dreys are constructed in the crotch or fork of a large tree branch, typically 20 to 40 feet above the ground. Construction begins with a framework of small, gnawed-off twigs woven together to create a sturdy, spherical shell roughly one to two feet in diameter. The squirrel then lines the interior cavity with softer, insulating materials such as dried grass, moss, shredded bark, and pine needles.
This inner lining provides a cozy space for nightly rest, especially during the warmer months. Dreys serve as convenient, temporary homes and emergency shelters, often used when a permanent den is unavailable. Squirrels often maintain several dreys within their home range, using them interchangeably for daily sleep. The temporary nature of the drey means it offers less protection from predators and severe weather, but it is quickly built and easily abandoned.
The Permanent Home: Tree Cavities and Dens
For maximum security and protection, the gray squirrel seeks out a permanent structure called a den, which is most often a natural tree cavity. These dens are typically found within the hollow trunks or large, thick limbs of mature trees. They may form naturally through decay, or they can be abandoned cavities originally excavated by woodpeckers or other animals. The thick wooden walls of a tree cavity provide significantly superior insulation against cold, wind, and rain compared to an exposed leaf drey.
This protective structure also offers a higher degree of defense against climbing predators. To maximize warmth, squirrels line the interior of the cavity with a dense layer of finely shredded bark, moss, and leaves, creating a snug microclimate. These permanent dens are particularly important for reproductive success, as litters raised within the insulated confines of a cavity have a survival rate up to two and a half times higher than those raised in dreys. Gray squirrels will often claim multiple permanent dens within their territory, rotating between them as needed.
Seasonal Use and Activity Patterns
The choice between a drey and a den is heavily influenced by the season and the ambient temperature. The gray squirrel retreats to one of these shelters to sleep for the entire night, from just after sunset until just before sunrise. In the warmer months of spring and summer, squirrels frequently use the less insulated dreys for nightly rest and may change locations every few days. The seasonal shift to winter triggers a change in behavior, with squirrels relying almost exclusively on the insulation of tree cavities.
While they do not hibernate, they do employ physiological tactics to reduce their daily activity to conserve energy. During the coldest periods, their activity shifts from a bimodal pattern of morning and evening peaks to a unimodal pattern, where they only emerge briefly around the warmest part of midday to forage. During extreme cold, multiple squirrels may gather together to sleep in a single den or drey, a behavior known as communal nesting that helps them conserve body heat. This shared shelter is a temporary measure to survive severe weather.