The silent flight of owls has long fascinated ornithologists. No other birds fly with such stealth... First, the leading edge, or primary feathers, on the owls' wings are serrated like a comb. Second, the trailing feathers on the back end of the wing are tattered like the fringe of a scarf. And third, the rest of the owls' wings and legs are covered in velvety down feathers... owls' tattered fringe feathers help to break up the sound waves that are generated as air flows over the top of their wings and forms downstream wakes...Credit, via.
...the silence allows owls to more efficiently use their ears, which are positioned asymmetrically in their skulls: One ear is higher and more forward than the other, and each is shaped slightly different... owls, because of their ears' asymmetry, hear sounds slightly differently through each ear. This allows the raptors to more accurately determine where a sound is coming from.