Directional Hearing in Owls….Robert M. Traynor, Ed.D.

Bird watching is quite a popular sporting event in some circles around the world.  Viewing nature’s creatures in their own habitat is a thrilling experience and quite a passion for those that are intrigued with their habits. If a “bird watcher” focuses on watching Owls, it is referred to as Owl Watching.  It cannot be referred to as  Owling—  a new craze among the  social media crowd and a new phenomenon from Facebook that is catching on with younger groups and appears to be related to the “planking craze”of the early 1990s.

Owl Watchers  have long enjoyed spotting the Great Horned Owl, a species that flourishes in the forests from the North Country of Canada all the way to Latin America.  The Great Horned Owl is a fierce and highly successful predator, thanks to its extremely sensitive ears with their unique design. This bird is generally regarded as sedentary except in the north of its range. Studies in Canada (Saskatchewan) show that 17 of 35 recovered birds moved more than 150 miles, with young birds more prone to travel than adults. By comparison, the southern populations move very little.

Great Horned Owls have the  potential for a very long life. Their maximum recorded longevity is more than 28 years, and when undisturbed they live a relatively long time. However, multiple studies show that the species’ actual mortality rate is very high, especially in the first 2 years of life. Their natural enemies are parasites, disease, and starvation. Unfortunately, the most common causes of death are related to man, with 52% – 86% of deaths in some banding studies caused by shooting and 19% by trapping. Other studies show 21% shooting deaths, 15% trapped, 20% hit by cars, and 7% electrocuted. Road kills, pesticides, illegal shootings, and electrocution are their major causes of death in North America.

To Audiologists, the fascinating thing about Gret Horned Owls is their hearing.  They possess a unique type of directional hearing that allows them to focus on their prey with precision. The owl’s ears are placed on the top sides of its head, and provide acute hearing.  Their hearing, like that of other owls, picks up even the faintest of sounds, which enables them  to take prey in complete darkness. Great horned owls are one of several owl species that have ear tufts.

So what purpose do these “horns” or “ears” serve?  Click Here

Gleason (2012) describes the structure of the Great Horned’s ears as neither horns (a bony outgrowth of the skull of some mammals), nor are they ears in any way associated with hearing.  Scientists disagree as to their function. Some suggest that the ear tufts serve as camouflage by breaking the contour of the owl’s head. Others suggest that they play some role in communication or recognition, enabling the owls to convey some kind of signals to one another. Experts agree, though, that the ear tufts play no role in hearing. A bird’s ears are on the side of the head, not on the top where these feather tufts are located.   Arbour (2005)  states that the Great horned Owl and other Owl ears the shape of the ear opening or aperture varies from round and small to an oblong slit, depending on the species.  Some species have a valve called an operculum covering the ear opening.

Some of the more strictly nocturnal species have asymmetrically set ear openings (i.e., one ear is located higher than the other).  These same species use their pronounced facial discs like radar dishes to guide sounds into their ears.  When an owl hears a sound, it can tell its direction because of the minute time difference between when the sound is perceived in the left and right ears.  Turning its head so that the sound arrives at both ears simultaneously gets it looking in the exact direction from which the sound is coming.  Owls can detect a left/right time difference of about 0.00003 seconds (30 millionths of a second)!  Using its asymmetrical ear openings, it lines up on the sound on the vertical plane.  All these signals combine instantly in the owl’s brain, creating a mental image of the space where the sound source is located.

So accurate are these senses that an owl can capture prey in total darkness without the aid of its eyes and can even capture prey under snow.  Lewis (2007) offers that an Owl’s range of audible sounds is not unlike that of humans (200-12,000 Hz), but an Owl’s hearing is much more acute at certain frequencies enabling it to hear even the slightest movement of their prey in leaves or undergrowth.  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.

Once the Owl has determined the direction of its next victim, it will fly toward it, keeping its head in line with the direction of the last sound the prey made. If the prey moves, the Owl can make corrections mid-flight. When about 60 cm (24″) from the prey, the Owl will extend its feet forward and spread its talons in an oval pattern. Then, just before striking, the bird will thrust its legs out in front of its face and often close its eyes before the kill.  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.

Watch this Fabulous Example of how a Great Horned Owl uses Directional Hearing to its Advantage!

About Robert Traynor

Robert M. Traynor, Ed.D., MBA is the CEO and practicing audiologist at Audiology Associates, Inc., in Greeley, Colorado with particular emphasis in amplification and operative monitoring, offering all general audiological services to patients of all ages. Dr. Traynor holds degrees from the University of Northern Colorado (BA, 1972, MA 1973, Ed.D., 1975), the University of Phoenix (MBA, 2006) as well as Post Doctoral Study at Northwestern University (1984). He taught Audiology at the University of Northern Colorado (1973-1982), University of Arkansas for Medical Sciences (1976-77) and Colorado State University (1982-1993). Dr. Traynor is a retired Lt. Colonel from the US Army Reserve Medical Service Corps and currently serves as an Adjunct Professor of Audiology at the University of Florida, the University of Colorado, and the University of Northern Colorado. For 17 years he was Senior International Audiology Consultant to a major hearing instrument manufacturer traveling all over the world providing academic audiological and product orientation for distributors and staff. A clinician and practice manager for over 35 years, Dr. Traynor has lectured on most aspects of the field of Audiology in over 40 countries. Dr. Traynor is the current President of the Colorado Academy of Audiology and co-author of Strategic Practice Management a text used in most universities to train audiologists in practice management, now being updated to a 2nd edition.