Looks like woodpeckerin' by a big one like a Northern Flicker maybe.
Upon further review, Flickers nest in tree cavities but would rather foage on the ground.

I'm going to go with the Pileated Woodpecker.
Dangerous for him working that close to the ground.
Bobcat, fox or coyote could grab him pretty easily I would think.

http://share3.esd105.wednet.edu/rsandelin/Fieldguide/Animalpages/Birds/Woodpeckers.htm
They have that "jungle call"....I sometimes hear that in the summer woods.

http://en.wikipedia.org/wiki/Pileated_Woodpecker#Distribution_and_habitat
The excavation in this pic looks a bit like yours, Dave.

Birds are cool creatures and fun to observe.