See how often they participate in the script: HERE.
Character Story: Link can summon a hawk by blowing into Hawk Grass. The hawk can assist link in order to solve certain puzzles or quests. It can be used to attack faraway enemies or retrieve certain objects.
Race Story: Animals appear all throughout Hyrule and are often often helpful in their own ways, either directly or through subtle advice. Link can talk to them when he is in his wolf form.