That's one well composed tune. I don't have my guitar with me but I'd have to say that could be played in a C major pentatonic (the A minor pent) to start... or whichever key it's in. He adds some grace notes in there for flavor, like the chicken picking type sounds, and does those 3rd intervals moving up the scale like.

|-----------8-----------10--------------12---
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|--8 / 9--------9 / 10--------11 / 12----------
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