Symbolism, Imagery, Allegory
You know what's better than dragons? Crows. And don't even get us started on how awesome ravens are. Okay, so maybe crows and ravens aren't as powerful as dragons, but they do hold a lot of symbolic value in A Game of Thrones.
What do these birds do? First, they can fly, which means they can see the big picture. This is exactly what happens with one of Bran's crow dreams, where he sees the whole world. In fact, it's a wise three-eyed crow that tells him to fly in his coma-dream (18 Bran 3). Crows and ravens are also important in this book for their role as messengers. And finally, "crows" is another term that some people use to describe the Night's Watch (61 Jon 8.87), since they dress all in black.
So what does this all mean? Well, notice that crows and ravens are associated with three things: (1) Bran's mystical abilities (for instance, in a dream, Bran has a crow lead him into the crypt to find his dead father, and that's before he knows that his father is really dead); (2) communication (all the messages get flown around by raven, which is cooler but messier than e-mail); and (3) the Night's Watch.
Communication… supernatural… Night's Watch. Aha! Perhaps these birds represent the importance of communicating with something supernatural that's north of the wall. Is that a stretch? What do you think?