Is there anything left to discover about an animal that has lived with humans for thousands of years? Of course, writes an international group of biologists this month Current Biology. The discovery is about the special sound that horses make when they…
neigh
: then they whistle with their larynx and at the same time use their vocal chords as people do when they sing. The result is a combination sound with a low and a high component. With a fundamental tone of 200 and 1,000 hertz respectively, it is a growl and a beep at the same time.
It was previously unclear how horses could produce that beep. But the researchers quickly uncovered the secret when they subjected six larynxes of deceased horses to breath tests in a series. They first let air flow through it and then helium gas. That immediately increased the frequency of the sound, convincing evidence that it had to be a whistle.
High-pitched neighing occurs in Przewalski’s horses, but is absent in zebras and donkeys, the researchers note. They think neighing evolved to convey different messages at the same time. The low growl communicates messages to nearby conspecifics (and people), while the beep carries further.
