We know that Sokka's bird, Hawky, went off on a trip to deliver the letter to Toph's parents and never came back.
What happened to Hawky?
The Wikia states:
Hawky never returned to the group after delivering Toph's letter, and it is assumed that he found a new home at the Beifong Estate
But they are citing the Nickelodeon official site as a source, and the site has since been updated removing any information about this.