Updated

The ravens at the Tower of London have been moved indoors to protect them from the threat of bird flu, the man in charge of the birds said Monday.

According to legend, if the ravens leave the 11th century fortress on the River Thames, its White Tower will crumble and the Kingdom of England will fall. King Charles II decreed in the 17th century that there must always be six ravens at the Tower.

"Although we don't like having to bring the Tower ravens inside, we believe it is the safest thing to do for their own protection, given the speed that the virus is moving across Europe," said Derrick Coyle, the Yeoman warder who is also the Tower's raven master.

A spokeswoman for the Tower said the six birds were taken inside as a "contingency measure" and will live in custom-built aviaries. The ravens are named Branwen, Hugine, Munin, Gwyllum, Thor and Baldrick.

The spokeswoman said on customary condition of anonymity that Coyle had been monitoring the virus since it first appeared in Asia and had been planning to take the ravens inside as soon as it appeared in Western Europe.

Seven EU nations — Austria, Germany, Greece, Hungary, Italy, France and Slovenia — have reported the disease's lethal H5N1 strain in wild birds.

The H5N1 virus has devastated poultry stocks and killed at least 92 people, mostly in Asia, since 2003, according to the World Health Organization.

Most human cases of the disease have been linked to contact with infected birds. But scientists fear the virus could mutate into a form that is easily transmitted between humans, sparking a pandemic.