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Fall 2012

Urban Jungle

The changing natural world at our doorsteps | Illustration and text by Patterson Clark      

December 11, 2012

Squirrel nests: A night in a drey

Now that most leaves have dropped, eastern gray squirrel nests, or dreys, are easier to see, usually about 30 feet off the ground, where two limbs meet, often in an oak providing acorns for the rodents.

Built in the summer or early fall, the drey begins as a collection of small, gnawed-off branches bearing green leaves. Even though they are brown in the winter, the leaves surrounding the drey continue to cling tightly to their branches because they were harvested well before the tree began the process of shutting down and shedding its leaves.

The drey's branches are loosely woven into a foot-wide hollow sphere, the inner surface of which is lined with a variety of materials, including grass, moss, leaves, shredded bark and pine needles. The outer layer of leaves helps shed water while the lining insulates against cold. A single entrance hole faces the tree trunk.

Some dreys appear flat or incomplete. Those may be either what's left of a hot-weather sleeping platform or the best efforts of young squirrels that were born in June.

Adult squirrels usually build a couple of dreys, giving themselves another shelter option should one nest be disturbed by a predator or overrun with fleas and lice. Sometimes two squirrels occupy a drey, cozying up to share long nights, frigid days — and body heat. In the morning, if it's not too cold, they leave the nest to eat, play or mate.

Squirrels give birth to broods of about three in June and January. June broods are sometimes born in dreys, but January broods are most often born and raised in tree cavities, which are much safer. Drey broods are 40 percent less likely to survive than squirrels born in tree cavities, which offer more stable, concealed and protected shelter, provided the entrance hole is no wider than three or four inches. A larger hole invites predators, namely raccoons.

Sources: Journal of Ecological Research, Journal of Mammology, University of Michigan Museum of Zoology, North Carolina State University, Cornell University

Eastern gray squirrel nest, or drey