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.
Well, we do never see Hawky again, so a few different options lie ahead.
He could have been killed
This is a grisly, yet very plausible, option. We don't know the dangers of the Avatar world. He could have been attacked, or shot down, who knows? Or the Beifongs could have killed him in anger.
He could have taken his time
Team Avatar moves around quite a bit, so Hawky might have had trouble locating the team in their journey through the four nations.
He could have gotten sidetracked. Hawky is an animal, and at that point in time, it looked spring-summer, which is most animal's breeding seasons. Hawky could have found himself a lady, and forgotten his mission. Not likely, since he's trained, but possible.
He could have found a home Or, Nickelodeon could be right, and he found home sweet home at the Beifong estate.
