A drey is where a tree squirrel or flying squirrel lives. Tree squirrels, in this case, refer to squirrels that live in trees, and the flying squirrels are also tree-dwellers, though they have a special flap of skin which enables them to glide hence the derivative name of flying. The drey is a nest made of dry materials including twigs, grass, and leaves on top of the trees where the squirrel dwells most of the time. These structures are also called drey nests to distinguish them from the dens that other species of squirrels live. Squirrels prefer forks in trees around 30 to 45 ft from the ground. They also sometimes build their dreys at high points on human structures including attics or outer walls of buildings. This, however, poses a risk for human beings since such outer walls and attics are usually near electrical cables which squirrels sometimes chew through creating a fire hazard.
The process of the construction of dreys begins with the collection of leaves and twigs after identifying the location. The materials used are varied depending on the location and the species of squirrel, these materials range from barks and leaves of evergreen trees by the Eastern gray squirrel. The Southern flying squirrel has been observed to use fungal plants in addition to parts of deciduous trees and other twigs. In some cases, the same species of squirrel such as the Northern flying squirrel utilizes different building materials depending on its location. In North America, it will use shredded bark while in the Pacific North West it uses lichen as the main material.
The twigs and branches form the exterior of the drey while the inside is made of grass, shredded bark, and other finer materials. A complete drey resembles a hollow foot-wide orb, having one or sometimes two entrance holes arched in a way that keeps the rain out. The second hole is primarily an escape route from predators. However, in some cases, squirrels take over dreys that were built by other squirrels but are presently abandoned. The drey practically ensures the survival of the squirrels by keeping out predators and adverse climate. Therefore, they require constant maintenance after construction to keep them in good shape to be able to withstand the elements. The average drey is used for a year or two, but others have been used for decades by several generations who continually add fresh twigs and other materials.
Males and females may live in one drey during the breeding season, but this is only for a short period. This is because pregnant females stay alone in dreys until their young are born, which is typically three of them and twice in a year that is in January and in June. The ones born in January are raised in tree cavities while those born in June stay in dreys. Other squirrels may also huddle up in the same drey when it is cold during winter for warmth.