Distinguishing between the White Geese in Flocks

One of the birding experiences I was most looking forward to was seeing large flocks of geese, particularly seeing Snow and Ross's Geese and trying to distinguish the two.  Surprisingly, it can be quite difficult to distinguish between them when they are in a flock on the ground because they keep their heads tucked quite often.  Besides, the birds are often skittish because of hunters, so they don't give you great looks that often.  I got a decent chance to look at some white geese today.  Here are some of the (less than stellar) photos:

 The left bird demonstrates the larger size of the Snow Goose and the larger bill of this species.  The size can often be difficult to tell, but here you can see that the right bird is noticeably smaller with a small bill (Ross's Goose).

 This shot shows the difference in bill size.  The left bird (Ross's) has a very small bill while the right bird (Snow) has a much larger bill.

 Another shot of the previous birds (Ross's on left and Snow on the right).

 The two left birds (Ross's) demonstrate shorter necks; rounder heads; and small, stubby bills.  The right  bird (Snow) presents with a longer neck; a flatter head profile; and a longer, more robust bill.

The bird on the left (Ross's) shows a smaller head and bill while the bird on the right (Snow) shows a larger head and bill.