Birds rely on their keen sense of hearing to detect prey and identify other birds on the basis of their songs. In fact, birds have better hearing resolution than humans, so they hear with much more detail. However, birds lack the external ear anatomy that humans rely on. So how do birds hear?
Birds have ears, but their ears are not structured the same as human ears. Birds and humans both have an inner ear and a middle ear. However, birds differ from humans in that they lack an external ear structure. Where humans have an outer ear organ, birds have a funnel-shaped opening that functions as their outer ear, located on each side of their head. These openings are usually positioned behind and slightly below a bird’s eyes. They are protected by soft barbless feathers called auriculars.
The position of a bird’s head also plays a role in its hearing abilities. Scientists have determined that noises register at different frequencies on each side of the bird’s head. Depending on the angle from which the noise originates, it registers with a certain frequency in the left eardrum but with a different frequency in the right eardrum. This difference in frequencies between the eardrums allows the bird to locate a sound’s origin.
For example, owls are known for their extremely acute hearing, which helps them locate prey at night. This hearing ability is due in part to the asymmetrical arrangement of the ear openings, with one opening being lower than the other. Sounds register in these openings at slightly different times. Owls can use this time difference, which is sometimes only 30 millionths of a second, to determine whether the sounds are coming from their left or their right. Other birds of prey have flaps in front of their ears that help them determine whether sounds are coming from above them or below them. Some owls do appear to have ears on the top of their head, but those are actually tufts of feathers controlled by small muscles under the skin that do not affect their hearing at all.