unkindness
A group of ravens is called an "unkindness" or "conspiracy," which seems fitting, since ravens are traditionally considered creepy; in fact, seeing many of them in one place can induce Hitchcockian "The Birds"-like flashbacks in even the least ornithophobic (those people with a fear of birds).8 Feb 2011
Serves me right for feeding the raven.
How many left in the Tower of London.