Planting native evergreens such as oaks, wax mytles, evergreen sumacs and pines can provide this much needed cover. If they pose no hazard, dead trees can be left standing to provide safe cavities for wildlife, including pileated woodpeckers and flying squirrels. You can also install winter roosting boxes. Plans for roosting boxes are available from many books and can be purchased from your local bird shop. Putting out new birdhouses in the winter assures that they will be weathered and available for early nesting birds.
Winter is also a great time to create a brush pile.
By collecting yard debris like branches, twigs, and fallen leaves, you can create cover for birds and small mammals like rabbits, and at the same time offer a hibernation place for some species of turtles, salamanders and insects. The mourning cloak butterfly, for example, overwinters as an adult in woody debris and may use your brush pile. Many butterfly species and other insects will lay their eggs or overwinter as pupae in brush piles. Fallen leaves can also be used as mulch to protect plant roots from freezing temperatures, or composted and used as organic fertilizer next summer. Water can be scarce for wildlife in winter when natural sources are frozen.