Walter
 
You might be aware of this but Richardson's, plus apparent Richardson x Barnacle hybrids have been photographed in flocks of Barnacle Geese wintering in Scotland.  This was written up in Birding World (UK) in 2003.  I don't know whether any educated guesses were made about the provenance of the mixed pairings and hybrid birds. It might be worth double-checking all of your Richardson's to see if any of them had slightly darker breasts or white forehead patches which might indicate a hybrid.  
 
Regards
 
Clive

Walter Ellison <> wrote:
At Great Oak Pond the geese were in for their daily bathe and loaf. Among the 1500 Canada Geese, were 150 Snow Geese (four blue), 7 CACKLING (RICHARDSON'S) GEESE, and, acting as if paired with one of the Richardson's, an adult BARNACLE GOOSE. Such a neatly attired and dainty goose, with its white face, glossy black neck and breast, black mantle and pale whitish gray lower back and wings with black and white barring. The Barnacle Goose had no bands and both hind toes were visible (thus not clipped) as it walked at the east end of the pond. Also present were a female Merlin, a Cooper's Hawk, 18 Killdeer, 2 Dunlin, a Lesser Yellowlegs, 100 Green-winged Teal, and 15 Ruddy Ducks. Yesterday there were still two STILT SANDPIPERS at Great Oak Pd.