On a stump shooting trip with the dog I looked for a large yellow birch with smooth bark, which I found. I then scored the bark and peeled it off in one complete piece. Birch bark grows around the tree not up and down, so it was relatively easy to take one strip from around it. I made sure to take only a thin layer so as not to damage the tree. I then thinned it down by peeling of the deepest layer. I applied it with titebond and wrapped it with strips of cloth, just like you do with snake skins.
Since birch bark is made from so many layers of paper thin bark only the layer directly next to the back is attached. With the stress of shooting the bark may seperate from itself and come off. But until it does that I think it looks real cool. I had backed the bow with drywall paper tape and the exposed pieces I attacked with brown and black sharpies to contrast and still camoflage the exposed bits.