Messenger hawk

The messenger hawk is a moderately-sized raptor. Domestically, they are used to transport message scrolls carried in canisters tied to their backs. These hawks are used to deliver important messages throughout the Fire Nation, its colonies, and Earth Kingdom. Messages bear different colored ribbons depending on their importance and intended receiver.

For instance, dragon hawks that carry messages tied with black ribbons are intended to be of great importance. Messenger hawks seem to be the main tool in regular communication in the Fire Nation and can be bought at post offices, such as the one located in Fire Fountain City, which likewise have large roosting towers for the birds.

History
Commander Zhao received a messenger hawk when residing at Pohuai Stronghold carrying the message that he had been promoted to admiral.

Aang and Momo, when playing in the water at the secluded hot springs the team was positioned at, were seen by two Fire Nation guards, who at the time had believed the Avatar was alive. The guards subsequently sent a black-ribboned message on a hawk to the Fire Lord to notify the latter of the former's discovery. The hawk was later captured by the bird of Combustion Man.

Sokka purchased a messenger hawk, which he subsequently named Hawky, after he, Toph, and Aang won a large amount of money scamming rigged betting games. Hawky was used to send a message to Toph's mom and dad.

After the Hundred Year War, the usage of the messenger hawk spread to the other nations. Yee-Li, an Earth Kingdom resident, sent a hawk to contact the members of the Official Avatar Aang Fan Club in Yu Dao.

Anatomy
Messenger hawks are moderately sized birds of prey. Their feathers are primarily buff-colored on the belly and underside of the wings and tail, but a darker reddish-brown on its back and top.

Its wings are relatively broad, and about twice the length of its body. The flight-feathers are a shade of brown in between those of the body. The tail is broad and fan-shaped.

Its head is reddish-brown with two sets of ear-tufts: the bottom is the prevailing color of the head, and sticks out with a number of angular plumes, while the top is lighter and creates and appearance of horns. Its beak is brown, triangular and hooked, and notable for the mustache-like plumes that descend from it.

Behavior
Tamed messenger hawks have a calm temperament, and, if properly trained, able to deliver messages to almost anywhere. They are known to be loyal to their owners. They also seem to know that they have important jobs, and are regarded as more intelligent than other birds in the Fire Nation. They are used by both the Fire Nation government and ordinary civilians for their message-carrying ability.

Connection
Messenger hawks can be connected to homing pigeons, particularly carrier pigeons. Prior to the invention of the telegraph and radio, carrier pigeons were frequently used in battlefields as a means of mobile communication.

These birds are capable of delivering messages to one single location, or their "home". However, unlike the pigeons, messenger hawks appear to have the ability to locate their message's intended destination even if they have never been there before (as evidenced by Katara and Toph's dispatch of Hawky with a letter to Toph's parents).

Trivia

 * Zuko originally had a messenger hawk as a pet which was supposed to have a rivalry with Momo.
 * A wild messenger hawk was flying while Team Avatar traveled near a scorched forest.