Hi Sam, note the dark fringe along the edge of wing, which make the underwing look somehow paler when compared with Hobby. You also get less buffish colours on the belly and underwing in Amur, usually quite well defined B&W rather then brownish appearance of Hobby. Structurally, I feel Amur are slimmer in comparison with Hobby. In close inspections, the red talons and beak should be quite apparent. Here are some photos I took the other day of a few Amurs.
http://matthewkwanbirding.blogsp ... falcon-at-last.html
