Squirrel Hunters is a fun tune, but deceptive. The first chord is A, so you may be tempted to think it is in the key of A, and maybe it is. However, the other chords are G, and D. That would lead us to think it's in the Key of D. It's all about perspective. We could still say it's in A, and the G chord is a flat 7. But for our purposes we are saying it's in D, because that is the scale you should go to first when soloing or using backup on this tune. This type of ambiguity in the chord structure is called modal. Which means different modes, or keys can be used. The scale degrees, especially the 3rds, and 7ths, are not always defined clearly.