Everyone (on reddit) is familiar with the use of ravens to carry messages across Westeros. In the Harry Potter novels, owls are used quite reliably to carry post. Carrier pigeons were used in the boring Real World even as recently as WWI.

When did this become being commonplace? How reliable were they? What technology/schools of thought were required? How realistic is it to have birds used to carry messages in archaic settings such as in Game of Thrones? Were certain birds more adapt at this task than others?