Robert Rule Graham, a British pilot, aeronautical engineer, and bird lover, identified three features that suppress sound in owl flight. First, he observed an unusual feature known as a comb, a row of fine hairlike bristles that extend forward along the leading edge of the wing (where it meets the oncoming air). He also noted a belt of ragged wispy vane fringes on the wing’s trailing edge (its rear edge) and, finally, a soft layer of velvet coating the whole wing.
