Image: Mellisuga helenae Size Comparison.svg on wikipedia
I gotta give it to the bee hummingbird, of course. While there's a good chance you've heard of this one (since it's rather famous for its title of Smallest Bird!) you are less likely to know it's a practitioner of a certain hummingbird courtship technique: males woo females with sound displays! These require flying/diving just right to vibrate/flutter key feathers and produce a specific noise. Pretty fancy for something as long as your finger.
