The main character is surely the big bad owl. There might also be other small animals like little birds, squirrels or rabbits that are affected by the owl's actions.
Well, the big bad owl story is often about an owl that is seen as a bit of a villain in the story world. Maybe it hunts too much or scares the other small animals. But without more details, it's hard to say the exact full story.
Owl's big eyes are to allow them to see clearly in low light conditions. Their eyes are adapted to gather more light, giving them an advantage when it's dark. Also, big eyes aid in spotting prey from a distance.