Nature
PUBLISHED
How do horses make their signature high pitched whinny? It's a question that’s puzzled researchers and seems to go against what would be typical for such a big animal. However, new research has revealed that they are actually making two sounds at the same time – and moreover, the horses are even whistling.
The rest of this article is behind a paywall. Please sign in or subscribe to access the full content.A general rule exists that the larger the animal, the lower the frequency of the sounds they produce. This is known as “acoustic allometry”. However, as with all the best rules, exceptions exist in that some larger species can produce very high pitched noises, such as wapiti (Cervus canadensis).
To look more closely at how both low- and high-frequency noises are made in horses, researchers inserted endoscopic cameras into the noses of 10 Franches-Montagnes stallions and recorded what was happening inside their throats when the whinny was made. By recording the larynx and the vocal cords, they revealed that the lower part of the whinny was created using vocal fold vibrations in much the same way that humans talk or sing. However, the higher part of the sound was where things started to get interesting.
The team used a range of methods, including passing helium through the larynxes of dead horses to work out how the high-frequency sound was being made. The high-pitched noise got even higher with the helium, confirming it's actually a whistle. The team found that the high-frequency part of a horse whinny was generated not by the vocal folds, but by an “aerodynamic whistle mechanism within the larynx,” they explain in the paper.
The authors further confirmed this by looking at recordings from horses with a condition called recurrent laryngeal neuropathy, which affects their vocal folds. As now expected, the low-pitched sound was clearly affected but not the high-pitched whistle, showing that that part of the sound is created differently.
“Knowing that a ‘whinny’ is not just a ‘whinny’ but that it is actually composed of two different fundamental frequencies that are created by two different mechanisms is exciting,” Alisa Herbst, a researcher from Rutgers University’s Equine Science Center who was not directly involved in the study, told the Guardian.
The ability to produce both the high- and low-frequency sounds together is a phenomenon known as biphonation. This is found in the sounds of dolphins who squeak and click simultaneously, and also in rodents. The discovery of this new mechanism reveals just how much we still don't know about animals, even those as familiar as horses.
The study is published in Current Biology.
