Unlike mammals, birds have no external ears. The outer ears of mammals play an important function in that they help the animal identify sounds coming from different elevations. But birds are also able to perceive whether the source of a sound is above them, below them, or at the same level. Now a research team from Technische Universität München (TUM) has discovered how birds are able to localize these sounds, namely by utilizing their entire head. Their findings were published recently in the PLOS ONE journal.
Unlike mammals, birds have no external ears. The outer ears of mammals play an important function in that they help the animal identify sounds coming from different elevations. But birds are also able to perceive whether the source of a sound is above them, below them, or at the same level. Now a research team from Technische Universität München (TUM) has discovered how birds are able to localize these sounds, namely by utilizing their entire head. Their findings were published recently in the PLOS ONE journal.
It is springtime, and two blackbirds are having a sing-off. They are both competing for the attentions of a female. But to pick a successful suitor, the female must first be able to find him.
“Because birds have no external ears, it has long been believed that they are unable to differentiate between sounds coming from different elevations,” explains Hans A. Schnyder from the TUM Chair of Zoology. “But a female blackbird should be able to locate her chosen mate even if the source of the serenade is above her.”
Mammals identify sound sources in the vertical plane using their external ears, which absorb, reflect or diffract the sound waves because of their special structure. Their sense of hearing uses this information to determine the elevation of the sound source. But how do birds perceive these differences?
The head does the work of external ears
By studying three avian species – crow, duck and chicken – Schnyder discovered that birds are also able to identify sounds from different elevation angles. It seems that their slightly oval-shaped head transforms sound waves in a similar way to external ears.
“We measured the volume of sounds coming from different angles of elevation at the birds’ eardrums,” relates Schnyder. All sounds originating from the same side as the ear were similarly loud, regardless of their elevation. The ear on the opposite side of the head registered different elevations much more accurately – in the form of different volume levels.
Different volume levels reveal sound sources
It all comes down to the shape of the avian head. Depending on where the sound waves hit the head, they are reflected, absorbed or diffracted. What the scientists discovered was that the head completely screens the sound coming from certain directions. Other sound waves pass through the head and trigger a response in the opposite ear.
Continue reading at the Technische Universität München.
Blackbird image via Shutterstock.
