How Birds Pinpoint Sound Without External Ears

Birds don't have external ears, so how do they manage to navigate and identify sources of sound without them? That's the question that scientists tackled and now, they've found out how birds are able to localize sounds without external ears.

Hearing is important for birds. They use song in order to compete for mates and establish territories. This means that identifying the source of a sound is important.

"Because birds have no external ears, it has long been believed that they are unable to differentiate between sounds coming from different elevations," said Hans Schnyder, one of the researchers, in a news release. "But a female blackbird should be able to locate her chosen mate even if the source of the serenade is above her."

Mammals can identify sources of sound by using their external ears, which absorb, reflect or diffract the sound waves due to their special structure. In order to find out how birds manage to do the same, the scientists examined three avian species-a crow, a duck and a chicken.

"We measured the volume of sounds coming from different angles of elevation at the birds' eardrums," said Schnyder.

So what did they find? It turns out that it all depends on the shape of the bird's head. Depending on where the sounds waves hit the head, they're reflected, absorbed or diffracted. In fact, the head completely screens sound coming from certain directions. Other sound waves pass through the head and trigger a response in the opposite ear. The avian brain determines whether a sound is coming from above or below depending on the different sound volumes in both ears.

The findings reveal a bit more about how birds manage to pinpoint the source of sound. This, in turn, reveals a bit more about the various adaptations of different species.

The findings are published in the journal PLOS One.

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