A drey is the nest of a tree squirrel, flying squirrel or ringtail possum. Dreys are usually built of twigs, dry leaves, and grass, and typically assembled in the forks of a tall tree.Lawniczak, M. (2002). "Sciurus carolinensis", Animal Diversity Web. They are sometimes referred to as "drey nests" to distinguish them from squirrel "cavity nests" (also termed "dens"). In temperate regions, dreys become much more visible in the autumn, when leaf-fall reveals new nests built the previous summer or in early fall.
A favoured site for a drey is a tree crotch about 9–13 m (29–42 ft) above ground level. Squirrels may also nest in or exterior walls of buildings, where a drey may be regarded as a fire hazard, as some squirrels have a habit of gnawing on electrical cables. At other times, squirrels may inhabit a permanent tree den in the hollow of a trunk or large branch.
Drey construction materials and sizes differ according to squirrel species and region. Eastern gray squirrels, for example, tend to use the leaves, bark and twigs of deciduous trees such as beech, elm, and oak. Southern flying squirrels will often employ fungal , deciduous leaves, bark and twigs in their nests, while northern flying squirrels often use shredded cedar bark (among other types of bark), , , leaves and twigs in their dreys. In the Pacific Northwest, the northern flying squirrel employs the common Bryoria lichen as the primary material. A drey is almost always at least above the ground, and flying squirrels build much higher.
Sometimes squirrels build their own dreys and sometimes they occupy a vacant drey that was previously constructed by another tree squirrel, often of a different species. Dreys must protect against the environment, and require constant upkeep to remain water- and predator-resistant. Squirrels often build more than one in a season, as reserve nests, lest the primary drey be disturbed by predators or overrun by fleas or lice. Some dreys have been observed in use for more than a decade by multiple generations of squirrels, although the average drey may be used only a year or two before being abandoned. If used repeatedly, squirrels must constantly maintain their drey, replenishing twigs and leaves as necessary. Remnants of an abandoned nest may be visible for years.
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