Ears Map Sounds

a gray and white speckled owl with yellow eyes and a yellow beak looks off camera against a dark background

Biological Strategy

Owl

AskNature Team

Image: NickyPe / Pixabay / Free non-commercial use

Sense Sound and Other Vibrations From the Environment

For living systems, sensing sound and other vibrations is important for communicating and detecting conditions within their environment. Living systems must locate a signal’s source so that they can move toward it (such as when it is food or a potential mate) or away from it (such as when it is a predator). To prompt an appropriate response, living systems must sense these signals, recognize their amplitude or volume (which is sometimes very low), and determine their direction. Living systems must be attuned to signals relevant to them and able to distinguish these from irrelevant sounds to avoid expending unnecessary energy. For example, owls’ ears are asymmetrically placed. This enables them to detect sounds more accurately, which helps them locate small prey at night and avoid wasting energy chasing down irrelevant sounds.

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Transduce/Convert Signals

Sometimes a signal, such as sound or vibration, reaches a living system and needs to be converted into a different, usable form. This requires converting from one type of energy form to another. For example, organisms with eyes have photoreceptors at the back of the eyes that convert light into electrical pulses. These pulses travel to the brain and allows it to register color, shape, and detail.

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Birds

Class Aves (“bird”): Eagles, hawks, sparrows, parrots

Birds are evolutionary engineering marvels. They are descended from dinosaurs, but are far from our idea of heavy, scaly reptiles. Of the specific adaptions that set them apart, most notable is flight—although some mammals can fly, birds take the prize for abundance in the skies. Many birds have hollow, lightweight skeletons and specially-designed wings to help them stay aloft. They also have feathers made of keratin that help them stay warm, attract mates, and improve navigation and aerodynamics in flight. In contrast to their dinosaur ancestors, they lack true teeth and have replaced them with specialized beaks and bills.

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The ears of the owls can map sounds three-dimensionally because of their asymmetric placement.

Image: Mindaugas Urbonas from Lithuanian wikipedia (Profil / Wikimedia Commons /

Image: BS Thurner Hof / Wikimedia Commons /

Image: photo taken by Artur Miko?ajewski / Wikimedia Commons /

Image: Dominic Schulz -> [email protected] / Wikimedia Commons /

Owl focusing on something, head turned about 180degrees

Image: John Gould / Wikimedia Commons /

Long Eared Owl - Strix Otus (Linn.) Otus vulgaris (Flem.), (aka ''<a href=http://commons.wikimedia.org/wiki/Asio_otus title=Asio otus>Asio otus</a>'') - lithograph with hand coloring - 37.9 x 30.9 cm (image); 54.2 x 35 cm (sheet)

Image: Matt Khoth /

“The ‘ears’ of this long-eared owl are not ears at all, but merely decorative feathers. The owl relies mainly on its hearing when hunting. Its ears are placed asymmetrically on either side of its head, and the sounds received by them are interpreted to give a very accurate three-dimensional sound map of its surroundings.” (Foy and Oxford Scientific Films 1982:165)

“Barn owls are better at tracking sounds that move horizontally than
those that move vertically, researchers have found…The work, published
in PLoS ONE1, relies on a phenomenon noted by Ivan Pavlov, of salivating
dog fame, in the 1920s. Pavlov saw that animals respond to stimuli such
as sudden movements or novel noises with a set of automatic responses,
including muscle tensing and pupil dilation.

“Avinash Bala, a neurologist
at the University of Oregon in Eugene, and his colleagues have used
this response to monitor when barn owls (Tyto alba) recognize a new
sound.

“The researchers played the owls sounds whose positions differed
either horizontally or vertically, and measured the birds’ pupil
dilation using a beam of infrared light bounced off the cornea.

“Owls
were about twice as sensitive to horizontal shifts compared with
vertical changes. The birds could detect a change in location as small
as 3º when the source was moved horizontally, compared with 7.5º when
the source was moved vertically…The researchers also mapped which neurons in the auditory centre
of the owls’ brains fired in response to the sounds.

“The activity
pattern of the neurons matched the location of the sound, the team
found. Sounds from above, for example, cause neurons towards the top of
the auditory centre to fire, whereas sounds from lower down trigger
neurons towards the bottom. ‘The owls basically have a topographic map
of space in their brain,’ says Bala.” (Ledford 2007)