Anything that's not an abnormal bird must either be a normal bird or a whirlybird. Tweety is a bird, but not a normal bird. Tweety has her wings clipped. Tweety has two parents. They are normal birds.
Every normal bird can fly.
An ostrich is a bird, and not a normal bird. A whirlybird is not a normal bird. A whirlybird is not a bird. Every object that is not a bird that is not normal is either a normal bird or a whirlybird. Tweety is a bird.