Crow and Raven
In animal symbolism, crows and ravens are often interchangeable—if one is associated with a characteristic, the other often adopts the same characteristic. However, in some aspects, they differ. For example, crows represent those who like to be around other people, while ravens prefer solitude. Both share the characteristic of vision and prediction, meaning prescience and precognition. They are also intuitive and clever, going hand in hand with foresight.
The Romans certainly believed they had these powers, since birds were vital to the practice of augury (divining the future from the flight patterns of birds). An augur (a type of priest) would be told the flight patterns, and from that he would divine the message.
There is a lot of mythology surrounding crows and ravens. For instance in Greek mythology, Apollo instructed a crow to watch over his pregnant lover. In this myth, crows were white. But when the crow brings Apollo bad tidings about his lover, he turns the crow’s feathers black. Good or bad, crows and ravens are represented as guards or sentinels. Ravens are said to keep guard over the Tower of London in England. As the legend goes, should the ravens ever leave the grounds, the Tower will fall. Ravens still inhabit the Tower to this day. This brings in an element of magic to these corvids, and magic is something ravens are strongly associated with.
Information from Ted Andrews's Animal-Speak, Jessica Dawn Palmer's Animal Wisdom, and Steven D. Farmer's Power Animals.