Video: Owls Have Heads Designed for Hearing

Barn owls are the subject of many studies on auditory neuroscience because of their exquisite ability to localize sound.

The silent flight of owls is pure beauty and grace in motion. In fact, in order to lessen the noise levels of airplanes, aeronautics designers are studying owl feathers for potential applications. But that’s not the only thing that is truly amazing about these birds. Their hearing is exceptional.

In fact, an owl’s whole head is designed for listening. And, as you’re about to see in the video below, they can outperform a kestrel—a keen-sighted, fierce falcon—even in daylight hours and when prey is hidden under snow.

A face fabricated for hearing

An owl has a round, satellite-dish-shaped face that is specifically designed to detect sounds. This form of face on the owl has a similar effect to what happens to you when you cup your hands around your ears and aim them toward a sound in order to hear it better: your cupped hands collect sound more efficiently than open air. However, by turning its face toward the ground, an owl gathers sounds far more efficiently than we can. In fact, at certain frequencies, an owl’s hearing is 10 times more sensitive than ours. And an owl can alter the shape of its face disc by using special muscles to channel sounds at will.

An owl’s ear tufts might look like ears, but in truth they are simply feathers that indicate an owl’s mood. The bird’s real ears are hidden at the sides of its head, behind the eyes.

Although some owls sport ear tufts, they’re not ears at all, but simply display feathers that indicate an owl’s mood, sort of like how a cat swivels its ears to signify how it feels. An owl’s true ears are hidden at the sides of its head, behind the eyes; and they are covered by the feathers of the facial disc.

A facial ruff (a ring of stiff feathers) form a curved wall around an owl’s face that acts like a reflector for sound. The ruff increases the surface area over which sound is collected, increasing sound sensitivity by about 20 decibels. The symmetry or asymmetry of an owl’s ruff is species specific. Diurnal owls (such as burrowing owls) have symmetrical ruffs, while nocturnal owls (such as barred owls) usually have asymmetrical ruffs.

Lopsided ears designed for listening

Asymmetry can also apply to the position of the ears. Some species of owls have one ear opening higher than the other. This unique adaptation allows the owl to determine what height a sound is coming from, as well as the direction. Asymmetrical ears send the sounds to the brain with two slightly different signals that allow owls to pinpoint the source.

Behind its ears, an owl has modified, dense feathers packed tightly together forming a ruff around the face, much like the lip of a cereal bowl.

For example, a barn owl’s 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.

Brains triggered for triangulation

Studies of owl brains have revealed that their medullas (the area in the brain associated with hearing) are much more complex than those in other birds. A barn owl’s medulla, for example, is estimated to have at least 95,000 neurons, or three times as many as a crow’s medulla.

You can think of owls’ medullas as being triangulation calculators. To understand how triangulation works, picture a triangle with one very short side and two very long sides that are unequal in length, one just a little longer than the other. The short side is the base of the triangle, and the two long sides meet in a sharp point.

Some owl species, such as barn owls, have asymmetrically set ear openings (one ear is higher than the other). ©From “How Does an Owl’s Hearing Work?,” BBC Earth

Now imagine a mouse at the sharp point of the triangle. The base of the triangle is the distance between the owls’ two ears. The long sides trace the distance from each ear to the mouse.

To triangulate on a sound, the own turns its head. When the two sides of the triangle are equal in length, the sound is arriving at both ears simultaneously, and the owl is directly facing its prey. Owls can detect a left-right time difference of about 0.00003 seconds (30 millionths of a second). Owls do this triangulation continually, without thinking, and even in rapid sequence while flying.

A beak built for bouncing sounds

Most birds of prey have beaks that extend off their faces, creating a more aerodynamic head and giving them more surface area for breaking the necks of prey and for ripping food.

A hunting owl begins a strike when it is about two feet from a mouse. The hit is hard; success is high.

An owl’s beak, however, is built to maximize sound reception. It is pointed downward, increasing the surface area over which soundwaves can be collected by the facial disc and redirected to the ears.

Once an owl has determined the direction of its prey, it will fly toward it, keeping its head in line with the direction of the last sound the victim made. If the prey moves, the owl is able to make corrections mid-flight. When it is about 24 inches away from its prey, an owl will bring its feet forward and spread its talons in an oval pattern. Just before striking, it will thrust its legs out in front of its face and will often close its eyes before the kill.

Watch the video below from BBC Earth. In it, a barn owl, a mostly nocturnal predator, uses her super hearing to find prey—even though it’s under snow and she is hampered by having to hunt in daylight.