Very nice bird and a good image. I only find the split colored background a bit distracting, specially the top half. Also did you clone any thing around the edge of the tree trunk?
Bird is sharp and nice head turn, sits in the frame nicely too..... but not so keen on the very different contrasting background colors and the end of the branch looks a bit too PS'd
Great advise above, the split background is the main deal here. Otherwise a great capture, good head angle, detail and the exposure techs are good. Often we take what we get but sometimes we can work a subject and improve the background/foreground or remove distracting elements. Woodpeckers are very territorial see if you can get him again with a better background.
Tell me more about your field techniques, meter mode, tripod and tine of day.