Mutants of London

Found this info online today.  I've heard of the saying, "If the Tower of London ravens are lost or fly away, the Crown will fall and Britain with it.", but never knew this part of the story.
http://ultrafactsblog.com/post/116593278579/the-ravens-of-the-tower-of-london-are-a-group-of

The ravens of the Tower of London are a group of captive common ravens which live in the Tower of London. The group of ravens at the Tower comprises at least seven individuals (six required, with a seventh in reserve). The presence of the ravens is traditionally believed to protect the Crown and the Tower; a superstition holds that "If the Tower of London ravens are lost or fly away, the Crown will fall and Britain with it."

I've never been a fan of the Mutants in Avalon sourcebook because of the Arthur angle it took, this look much more interesting.  You could use this as the background for a specific Tower Raven (Purebreed) animal species that would start with special perks.