Researchers have explained how horses produce a complex whinny that combines a low tone and a much higher tone simultaneously. The low frequency results from vocal‑fold vibration, the same basic mechanism humans use when singing, while the high‑frequency component arises from a laryngeal whistle created by a turbulent airstream inside the larynx.
Small rodents such as rats and mice were already known to make laryngeal whistles, but horses are the first large mammals shown to use this mechanism. They are also the only animals known to produce a laryngeal whistle at the same time as vocal‑fold vibration.
The team tested the idea with excised larynx experiments. They blew air through larynges removed from deceased horses and alternated the gas between air and helium. Because sound travels faster in helium, whistle tones shift to higher frequencies while vocal‑fold vibration does not. As predicted, the high‑frequency part of the whinny rose in pitch with helium while the low frequency stayed the same. William Tecumseh Fitch said the frequency shift was immediately obvious and confirmed that the mystery was solved.
The study suggests biphonation may have evolved so horses can send multiple messages at once. Przewalski’s horses also show biphonation, but more distant relatives such as donkeys and zebras appear to lack the high component, indicating a unique adaptation in horses. Romain Lefèvre noted that solving this biomechanical puzzle required combining approaches from veterinary medicine to acoustic physics.
- Swiss National Science Foundation
- Austrian Science Fund
- Institut Universitaire de France
The study is published in Current Biology. Source: University of Copenhagen.
Difficult words
- biphonation — production of two different tones at once
- laryngeal whistle — a high tone made by airflow in larynxlaryngeal whistles
- excise — to remove surgically or cut outexcised
- turbulent — marked by chaotic, fast irregular airflow
- vocal-fold vibration — sound caused by vibrating tissue in larynxvocal‑fold vibration
- frequency — how often a sound wave repeats per time
Tip: hover, focus or tap highlighted words in the article to see quick definitions while you read or listen.
Discussion questions
- How might biphonation help horses communicate in social groups? Give examples.
- How did using helium and excised larynx experiments help the researchers test their idea?
- Why was combining veterinary medicine and acoustic physics important to solve this biomechanical puzzle?
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