Flying Bison
From Four Nations
Flying Bison or Sky Bison are the animal companions of the Air Nomads. It appears that young monks (like Aang) are taken to the Eastern Air Temple where they choose a bison to be their soul companion by offering them an apple. Flying bison have the ability to control air currents using their long flat tails which allow them to fly, according to Aang, the only way to reach an Air Temple was on a Flying Bison (although this theory was proven wrong as Fire Nation soldiers were able to invade the temples using other techniques.) Appa is the only remaining Flying Bison as shown in the series so far.
Appearance
Flying bison have large fuzzy white fur that cover their ten tonne bodies and six legs, they also have a grey fur which travels from their tail to their forehead and ends with an arrow head (possibly the origin for Airbenders tatoo's.
Commands
Flying Bison normally react to the commands of their soul partners, for example, the command to make a bison (or in Appa's case) fly is 'YIP YIP'. This is the only command that has been issued by Aang to Appa.
Sports
The Air Nomads seem to play a sport with the bison at the Northern Air Temple called Flying Bison Polo.