Adult Downy Woodpeckers are the smallest of North America’s woodpeckers. The Downy is virtually identical in plumage pattern to the larger Hairy Woodpecker, but it can be distinguished from the Hairy by the presence of black spots on its white tail feathers and the length of its bill. The Downy Woodpecker’s bill is shorter than its head, whereas the Hairy Woodpecker’s bill is approximately equal to head length. 
Downy Woodpeckers forage on trees, picking the bark surface in summer and digging deeper in winter. They mainly eat insects, also seeds and berries. In winter, especially, Downy Woodpeckers can often be found in suburban backyards with trees and will feed on suet at bird feeders.  They are good for pest control and eat tent caterpillars, bark beetles and apple borers. 
Adult males vary from the females in hat they have a red patch on the back of their head. Juvenile birds display a red cap. 
These little woodpeckers will catch your eye with their hopping movements, usually upwards on a tree trunk or limb as they look for insects.
Downys don’t sing songs, but they do make noise by drumming on trees and sometimes on metal and they will make a pik sound. 
Downy Woodpeckers nest in a tree cavity excavated by the nesting pair in a dead tree or limb. In the winter, they roost in tree cavities. Their nest cavity is lined with only wood chips. 
References and Additional Information
 Wikipedia: Downy Woodpecker
 The Sibley Guide to Birds, second edition – David Allen Sibley
 Cornell – All About Birds: Downy-Woodpecker
 Cornell – All About Birds: Downy Woodpecker – sound
 The Breeding Bird Atlas of Georgia – UGA Press: Schneider, Beaton, Keyes and Klaus, Eds.