(noun) A concave, relatively flat, forward-facing arrangement of feathers on a bird's face that helps direct sound to the bird's ears for more acute hearing. Facial discs are most prominent on owls, and the shape, size and coloration of the disc, as well as markings within it, can be vital for proper species identification. Harriers such as the northern harrier and black harrier also have facial discs, though less well defined than the facial discs of owls.
Birds with facial discs can control the orientation of the feathers on the edge of the disc to focus sound, especially in flight. This allows hunting birds to fine-tune their flight to successfully capture prey by following the tiny, nearly imperceptible sounds of mice, voles or insects under the snow or deep in grass.
Photo – Barn Owl © U.S. Army Corps of Engineers Europe District