It's still not completely polished, but this is what I meant by re-texturing and re-shading and whatnot. My earlier example is only intended to show the "flow" of the animation. (I didn't want to change the original palette, but I just had to...) I added back in the touches that the original had, too (the little pixel shifting, the flurry of feathers left behind on each flap, etc. to more closely resemble the original)
Just for the sake of it. a bird's wings aren't a flat surface as most of the examples here have shown. my advice is to animate using a silhouettes as it removes the distractions of contour lines and helps to capture the volume of an object in motion.