The gray squirrel of North America often sleeps alone, unless the temperature drops very low. In this case, two squirrels may nest together. The only exceptions to this is a mother caring for her litter, which generally ranges in size from one to six babies.
Squirrels build leaf nests and also use hollowed out tree dens as shelter. Most squirrels have more than one den in their home territory. Tree dens are normally used in winter months, while leaf nests are used primarily during the summer. Male and female squirrels of all ages take part in nest building. Squirrel nests are woven together with small branches and lined with moss, grass and pine needles.