There are currently seven ravens in the Tower of London. Tradition says that there should be six, so one is viewed as the 'spare'.
The fact that they've become a tourist attraction in their own right meshes well with the apparent pandering to legends. Rationally minded Beefeaters - military men and women all - can brush away any accusation of superstitious thinking, by stating that visitors expect ravens.
But don't be fooled. It's all about the legend.
One Beefeater - the nickname given to the Tower of London guards - is employed to look after the ravens there. The current Tower Ravenmaster is Chris Skaife, who even Tweets regular messages about the birds in his care.
The Tower of London ravens are kept extremely well. They each enjoy hearty meals - each one getting 500g of meat every day, alongside bird biscuits soaked in blood and regular chopped apples - as well as the best veterinarian care in Britain.
At night, they live in cages, but only because foxes crawl through the sewers and have been known to attack them. First thing in the morning, Skaife does his rounds, letting them out of their aviaries alongside the White Tower and the Wakefield Tower. Then the ravens fly free all day.
To a given value of 'free' that is. All of the ravens in the Tower of London have one wing clipped. This allows them to take to the air, but not very far. Often it's only up to land on a low perch. Some struggle to make it as high as the turrets atop this ancient London landmark.
But why all that effort in care and captivity? That's because of the old saying, 'if the ravens leave the Tower, the kingdom will fall'; yet the warning may not be as venerably ancient as is often assumed. Then again, it might.