Messenger hawk

Messenger Hawks are moderately sized birds of prey with dark red or brown feathers all over their bodies and two long plumes falling from their tails. The leg feathers are white. In domestic use, they have canisters on their backs for transporting message scrolls. These hawks are used to deliver important messages throughout the Fire Nation and Earth Kingdom Colonies. For example: When someone needs to send a message to the Fire Lord, they tie a Black Ribbon to the hawk, indicating that it carries a message for Fire Lord Ozai.

Messenger Hawks seem to be the main tool in regular communication in the Fire Nation. Messenger Hawks can be bought at post offices, such as the one located in Fire Fountain City. Sokka recently bought a Messenger Hawk, Hawky.

These birds seem to have a calm temperament and seem to be obedient, able to deliver messages to almost anywhere. They seem to be very tame and loyal to their owners. They also seem to know that they have important jobs, and seem to be better than other birds in the Fire Nation.

The Messenger Hawk was first seen in the episode, "Winter Solstice Part 1: The Spirit World" flying in the opening sequence.

Connection
The Messenger hawks can be connected to messenger pigeons, especially homing pigeons. Homing pigeons were used to carry important military messages, much like the messenger hawk is in Avatar. Pigeons can only transport messages in a single direction, to one specific location, due to their homing instinct. However, messenger hawks appear to have the ability to locate their messages' intended destination even if they have never been there (as evidenced by Katara and Toph's dispatch of Hawky with a letter to Toph's parents in "The Runaway").

Trivia

 * In the pilot episode of Avatar, Zuko has a Messenger Hawk as a pet.