London ? For 350 years, six coal-black ravens have wandered freely around the Tower of London’s inner courtyard as cawing barometers of the monarchy’s vitality. If the ravens ever die or leave the tower, the legend goes, the tower and the kingdom will fall.

Now the fear of bird flu has done what Nazi Luftwaffe bombings, winter blizzards, assassinations and abdications could not, forcing the ravens to be moved inside in isolation for their own safety and to hedge Britain’s bets on the future of the crown.

The lethal H5N1 strain has been found in birds in seven European nations, including France, which is just 21 miles across the Channel, as the infected swan flies, and alarm is spreading in Britain. The government has announced that plans are being prepared to put millions of free-range chickens indoors if the disease reaches British shores. But the country’s most famous birds were moved into custom-made aviaries last Wednesday, a move announced by a spokesman for the Historic Royal Palaces on Monday.