They are found only on Prison Island. Balgas are similar in appearance to Ories. Like Ories, they resemble bulls or yaks. Balgas may be the dominant male (Ories) in this game. Only two types of Balgas exist.
Xenoblade Chronicles 2
Despite all of the Ardun forms leading up to Relentless Arduran, it has the model of a Balgas and looks like Amman Balgas. This may imply that Balgas are the same species as Armus and Arduns, and probably a dominant male (Ardun) in this game.