Can't tell t'other corvid from which?

Jays and magpies I know, treepies and nutcrackers are new to me but crows, ravens, rooks, jackdaws and choughs are all black.  How to tell them apart? Andrew Graham tells us there's one of them we can't mistake and why there are so many around in Tisbury at the moment..  Go to MoreNews for the full story.