A group of ravens is referred to as a congress or an unkindness. The most famous unkindness of six ravens at the Tower of London are employees, kept on staff at the expense of the British government. There are claims that the ravens were decreed to be kept by King Charles II to prevent disaster, or that they had been placed near the Tower in order to dramatize execution proceedings. These days they're kept around for tourists, and they are fed well (for ravens) on a diet consisting of raw meat, bird formula biscuits soaked in blood, whole rabbit, eggs once a week, and occasional pieces of fried bread.
Ravens are fairly vicious by nature, so the Tower's Ravenmaster must bond with them over a period of six weeks when they are fledglings. These birds are so vital to the Tower's image that several fledglings are kept as understudies for the six working birds as they die, even though the average raven lifespan is twenty-five years. The current raven roster at the Tower consists of Gwylum, Thor, Hugin, Munin, Branwen, Bran, Gundulf, Baldrick, Fleur, and Colin.