How Birds Hear Without Ears

First, It should be said: birds do have ears, but not like the "ears" you or I think of when we hear the word. They have an inner ear - a structure inside their little heads that looks a lot like a human's, if you were to remove those awkward fleshy-conical structures that stick off the sides of a person's face.

However, without those outer-ears, it should be near-impossible for birds to tell which direction a sound is coming from.

And yet, "a female blackbird should be able to locate her chosen mate even if the source of the serenade is above her," Hans A. Schnyder, chair of zoology Technische Universität München (TUM), recently explained to CBC News.

So how do they do it?

A study recently published in the journal PLOS One details how Schnyder and a team of fellow researchers set out to explore the hearing mechanisms of common chickens, crows, and ducks.

In a controlled lab setting, they measured the volume and frequency of sounds as they hit the eardrums of these birds. They found that when a sound comes from a specific direction, the closest eardrum would register the sound at a louder and different frequency than the furthest eardrum, allowing the bird to determine which way the sound is coming from despite the fact that the sound struck both ears at nearly the same time.

Additionally, there was a noticeable connection between sight and sound for these birds. Because birds have eyes on the sides of their heads, they have a nearly 360 degree field of vision. When they hear a sound, they tilt their head in the general direction their specialized eardrums indicate, and then let their sharp vision take over, sweeping an area for the source.

"This is how birds identify where exactly a lateral sound is coming from," the study authors concluded, noting that the system is far more accurate than would have imagined.

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