Or, for that matter, the current bird at Marshside RSPB in Merseyside, which has all the hallmarks of a genuine vagrant? I for one will be including it in my IOC world year list but would not be able to include it within a BOU British year list.
What hallmarks are they? My understanding is that it is hanging around with Mallards and avoiding other geese. Is that inaccurate? There are a lot of escaped Ross's in Britain, even turning up with Pink-feet in no guarantee; a pair of known escapes migrated back and forth between Britain and Iceland in the '70's with Pinkies.
