"Like the sad-presaging raven that tolls the sick man's passport in her hollow beak. And in the shadow of the silent night Doth shake contagion from her sable wing."
-- Christopher Marlow, "The Jew of Malta"
Crows, ravens, magpies and other birds of the Corvidae family have played a significant role in the folklore, superstition, and mythology of humankind. Native American cultures believed in Raven the Great Trickster; a mischievious being that was said to have created people and aided their survival. In Europe, the birds had a darker association, seen as malevolent harbingers of impending doom or messagers of Satan.
It is believed that among the early Celtic people, ravens, crows, and magpies were seen as ominous creatures that foretold things to come. Crow (or magpie) augury was and is still practiced in the UK. According to the number of birds seen, they predicted everything from a new birth, prosperity, or death. In Scotland, a raven circling a house foretold a death in the family. In Wales, however, a raven perched on a house brought prosperty to those living within. The prophetic abilities of the raven were believed in Arab countries as well where the dark bird is called Abu Zajir or "Father of Omens".
In Norse mythology, the god Odin kept two ravens, Hugnin (Thought) and Munin (Memory). The ravens would fly throughout the world and return to Odin informing him of everything that happened.
In North American, the native people of the Pacific Northwest credited the Raven with the creation of humankind; and said that Raven brought them fire and created salmon for them to eat. Raven the Great Trickster was a mischievious entity and was associated with humor and the love of life.
In Celtic mythology, the goddess(es), Morrigan, would take the form of a raven during battle and lead those on her side to a savage victory. When the fighting finished she would descend to feed upon the dead.
Superstition of Corvids:
There are a number of superstitions involving ravens, crows, and magpies. Among the many sayings that associate corvids with evil, Satan, and general ill luck is a superstition that is practiced even to this day in England. It is tradition to keep ravens at the Tower of London for it is said that if the ravens ever leave, the tower will crumble and England with it. In fact, the flight feathers of the ravens have been clipped to prevent them from flying away and testing the truthfulnes of the legend.
For some excellent web resources on Corvids and their supernatural associations, take a look at:
The Raven's Aviary and Crows