Below is the info I just got from Wild bird Magazine but posted in the Long Island Birds site. Not knowing exactly how that big ol' tail works was killing me...I even put off eating to find this out. Very unlike fatty me.

- To maintain their grip on tree trunks woodpeckers have two toes pointing forward and two pointing backward. The “backward-pointing outer toe, can rotate laterally or forward when tree climbing.”

- The woodpecker tail acts almost like another foot when it comes to bracing the bird on the tree; it functions as a brace. “The enlarged tail bones…accommodate large tail muscles. Then climbing vertically, a woodpecker uses these muscles to push its tail against the tree surface to counteract the force that it applies with its feet.” The stiff shafts of the tail withstand this applied force, affording the brace effect of the tail.