What a solid looking eagle, with deep wings. I like the subtle colors displayed. Perhaps a little noise creeping into the darker areas.
My guess would be that +1/3 wasn't enough compensation for this dark bird against the sky, and you had to bring up the exposure on the bird in post, perhaps causing the noise. For Nikon shooters using matrix metering, I usually recommend about +1 compensation as a starting point for birds straight overhead. (Capt. James got me started on using that setting ) The Canons may meter a bit different in that situation, but still probably need more than 1/3 +
What a wonderful capture -- clean, sharp, great detail! Perhaps some NR just in the shadows would work well. The inevitable loss of detail by NR is usually not as significant there.
This really is a good capture and quite unique. With a little bit of work you can bring it up another notch. I would do a little more NR on the underwings.