This is another area in which owls differ from diurnal predators - their hearing is incredibly acute. A further part of the experiment mentioned above was to put live mice in with the Barn owl in the totally darkened room, and using its hearing alone it was able to catch the mice every single time. The reason it was able to do so was that the ears, set on either side of the head, are either positioned asymmetrically with the right ear higher in the skull than the left, or the ear openings themselves are of differing shape. This results in sound reaching each ear a split-second apart and in effect gives the owl stereo hearing of such accuracy that it can pinpoint a sound to within 10mm with no aid from its sight whatsoever. The owls hear into ranges well beyond what we can discern, and are able to filter out sounds they have no wish to hear, which is just as well or they'd go stone deaf in short time, with the amount of racket we make.
All owls have flat 'faces' which are formed by the feathers of the facial disc.
These feathers are very fine and are arranged so as to direct sound directly to the ears. The only diurnal bird with a facial disc is the Harrier which also has a very good sense of hearing. As previously stated, owls can operate in almost totally dark conditions using binocular vision. Therefore, anything protruding in front of the eyes will present something of a barrier to their light-gathering abilities and so reduce their effectiveness. It points its beak downwards, out of its line of sight.