Very neat photo and yes quite a catchy title. Hate to nit-pic but I think this is not quite a Butt shot. A "true" Butt shot would have the Eagle's legs and underside of the tail in view. This is more like a "low angle back view".
Excellent eye and feather detail. What lens did you use?
I used a cheap Quantaray 70-300 super macro zoom. Probably somewhere around 200mm zoom. believe it or not this cheap and broken lens gives me some of the sharpest images I have ever taken. I use it a lot and even sold my Sigma 50-500mm because it wasn't even close to the fast glass of this ameteur lens.
