Raven with message at Winterfell
Ravens are a species of large, black-feathered birds native to Westeros. They are uncommonly intelligent animals and can be trained to serve as messengers. They can fly great distances at speed, and are used by the maesters of Westeros to pass messages between the castles and cities of the Seven Kingdoms. Through complex training methods, the maesters are able to send messages from almost any castle in Westeros to any other.
Pycelle presents a white raven to the Small Council
Although most messages brought by ravens are standard and innocuous, they are also linked to ominous tidings, giving rise to the phrase "Dark wings, dark words".
There is also a cleverer but much rarer species of white raven, which the Conclave of the maesters dispatch from their headquarters at the Citadel in Oldtown only when they agree that the season has turned.[1]
In the books
In the A Song of Ice and Fire novels, ravens are depicted as being identical in appearance but somewhat smarter than "real" ravens. They are used essentially the way carrier pigeons were in real-life. The ravens of Westeros can replicate simple human speech in the manner of parrots. Most ravens can only be trained to fly back to a specific castle when they are released. They usually have to be transported back to their point of origin by land. A small handful can learn to travel between two different castles, and these birds are greatly prized. Only very rarely do ravens occur who are so intelligent that they can be trained to fly to the locations of four or even five castles; ravens this intelligent occur only once a century.
The white ravens used by the maesters of the Citadel are not albinos, but a separate sub-species bred and maintained by the Citadel. This is evidenced by the fact that their eyes are black, not red as in albino animals. White ravens are larger and generally more intelligent than normal ravens, thus why are they are bred and used for only the most important messages, particularly notification that the erratic years-long seasons are changing.
See also
References
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