Alan, gorgeous! Is that moire in the wing feathers?
There is some Moire in the wing feathers, seen at high magnification but which won't affect the size of prints for my annual album. For birds at medium distance and in flight etc, the lack of AA-filter in the 5DS R gives significantly better results over say the 7DII and the 5DIV. But, occasionally you do get Moire with close-ups and a very sharp lens like the 400mm DO (± 1.4xTC) or even the 100-400mm II, which is the reason I got the 5DIV. Here it is OK, but I once had a kingfisher shot ruined by Moire. I don't know what the bird shooters with the Nikon D500 and 7200, and all the Olympus and Sony cameras find. Perhaps their soft lenses act like AA filters.
I have been looking again at the Moire from the 5DSR (at 560mm) and have compared with a similarly sized shot from the 5DIV (800mm). I must admit I hadn't noticed the Moire until you pointed it out. I now see it's also there to a similarly low extent on the 5DIV. So, in this case the lack of the AA-filter isn't the sole reason for the Moire, which, from my reading, is a bigger problem than I had thought in general in very sharp close ups of birds.
Interesting observation, Alan. I just looked through some pics w the 5DMKIV and don't see Moire in some likely examples. Maybe the frequency in these just didn't line up with the pixel pitch. I haven't used the 5DSR since getting the 5DMKIV, but will look back at some old files. These were at 840 mm.