6 ravens have to live in the Tower of London at all times. According to a 17th- century legend, King Charles II was warned that removing ravens from the grounds would cause the monarchy and the Tower itself to fall. He took this seriously, decided there must always be 6 ravens within the Tower walls, hired Ravenmasters to care for the birds, and a Ravenmaster is still on staff to this day. Source Source 2 Source 3