HI Nigel et al.:
Behavior is a big clue. If the crow is beachcombing it's a Northwestern.
If it's dumbster diving, its an American. If it does both, it's a hybrid.

sincerely
--

Ian Paulsen
Bainbridge Island, WA, USA
Visit my BIRDBOOKER REPORT blog here:
http://birdbookerreport.blogspot.com/