Two thumbnails of a scene taken from the same distance with the same lens on D810 vs D500 to illustrate what the crop advantage provides vs a much higher resolution camera:
And when you are looking at 100% view to both pictures you get this:
Screenshot of a picture taken with D810 and nikkor 200-500 AF-S VR @ 500mm and viewed at 100% in Nikon view NX-i:
BTW, this picture with D810 was taken at iso 1100
Screenshot of a picture taken with D500 and nikkor 200-500 AF-S VR @ 500mm and viewed at 100% in Nikon view NX-i:
this picture with D500 was taken at iso 5000 (iso five thousand)
If you add the speed, buffer and revolutionary improved IQ over former DX from the Nikon D500, this camera seems the right choice for wildlife to me.