Fantastic tune. If you want to hear a ton of versions, check out pretty much any Philly show. For some reason, they love(d) to play it here. Probably b/c we love to hear it. But when you play it, do you use a true E7? I usually play it acoustic in just plain ol' E.
But I think the epitome of cowboy psych rock is Loser (or Deal.... or Me and My Uncle) -- more card playin', drinkin', and gamblin'. I guess Birdsong was written in that 74-75 period, so it could slip right in.