The Northern Flicker is a medium sized Woodpecker, one of 6 woodpeckers that we list as a resident or visitor to Peachtree Park. The others are Red-Bellied, Red-headed, Downy and Pileated Woodpeckers and the Yellow-bellied Sapsucker. It is native to most of North America, parts of Central America, Cuba, and the Cayman Islands, and is one of the few woodpecker species that migrate. 
There are over 100 common names for the Northern Flicker! One of these is the Yellowhammer, its name as the state bird of Alabama (not to be confused with the Eurasian Yellowhammer). Other local names include Flicker, Yellow-shafted Flicker, Southern Flicker, Common Flicker, Gaffer Woodpecker and Gawker Bird.  
These are striking birds. Adults are brown with black bars on the back and wings. A necklace-like black patch occupies the upper breast, while the lower breast and belly are beige with black spots. Males can be identified by a black or red moustache stripe at the base of the beak. The tail is dark on top, transitioning to a white rump which is conspicuous in flight. 
According to the Audubon guide, “flickers are the only woodpeckers that frequently feed on the ground”, probing with their beak, also sometimes catching insects in flight. Although they eat fruits, berries, seeds and nuts, their primary food is insects. Ants alone can make up 45% of their diet. 
Like other woodpeckers, Northern Flickers are cavity nesters who typically nest in trees, but they will also use posts and birdhouses if sized and situated appropriately. They prefer to excavate their own home although they will reuse and repair damaged or abandoned nests. 
During mating season, two males may face off in what has been described as a ‘fencing duel’. The two birds are close and wave their beaks in a figure eight pattern making distinctive wika calls all the while. Somewhere close by a prospective female mate is watching.  We were lucky enough to observe a fencing session in the River Birch trees in our back yard and captured the video below.
References and Additional Information
 Wikipedia: Northern Flicker
 The Sibley Guide to Birds, second edition – David Allen Sibley
 Cornell – All About Birds: Northern Flicker
 Cornell – All About Birds: Northern Flicker – sound
 The Breeding Bird Atlas of Georgia – UGA Press: Schneider, Beaton, Keyes and Klaus, Eds.
 Alabama Department of Archives and History: State Bird of Alabama
 Cornell – All About Birds: Northern Flicker – life history