Where Are an Owl’s Ears?
The tufts on the top of some owls’ heads may look like ears, but the real ears lie beneath feathers at the sides of the head. Like other birds, owls don’t have outer ears to help collect sound waves like human ears.
Instead, they have just a small hole on each side of the head that leads to the eardrum. (It’s easy to see the ear openings on vultures and other birds that have naked heads.)
The curved feathers around an owl’s face help guide sound waves into their ears. An owl’s hearing is so keen that it can easily hear a mouse running across the ground.
The shape of the ear opening (known as the aperture) depends on the species of Owl – in some species, the opening has a valve, called an operculum covering it. The opening varies from a small, round aperture to an oblong slit with a large operculum.
All owls of the family Tytonidae have rounded openings with large opercula, while in Strigidae, the shape of the outer ear is more varied.
Some Owl species have asymmetrically set ear openings (i.e. one ear is higher than the other) – in particular the strictly nocturnal species, such as the Barn Owl or the Tengmalm’s (Boreal) Owl.
These species have a very pronounced facial disc, which acts like a “radar dish”, guiding sounds into the ear openings. The shape of the disc can be altered at will, using special facial muscles.
Also, an Owl’s bill is pointed downward, increasing the surface area over which the sound waves are collected by the facial disc. In these four species (Ural, Great Grey, Boreal/Tengmalm’s & Saw-whet), the ear asymmetry is actually in the temporal parts of the skull, giving it a “lop-sided” appearance.
An Owl can also tell if the sound is higher or lower by using the asymmetrical or uneven Ear openings. In a Barn Owl, the left ear left opening is higher than the right – so a sound coming from below the Owl’s line of sight will be louder in the right ear.
The translation of left, right, up and down signals are combined instantly in the Owl’s brain, and create a mental image of the space where the sound source is located.
Studies of Owl brains have revealed that the medulla (the area in the brain associated with hearing) is much more complex than in other birds. A Barn Owl’s medulla is estimated to have at least 95,000 neurons – three times as many as a Crow.