Surround sound

An understanding of how horses hear can help us keep them happy, as Peter Green MRCVS explains

- Peter Green

A LARGE proportion of the equine athletes competing at the Tokyo Olympics this summer were wearing ear bonnets. As well as keeping insects out of the ears, these muffle the sounds of the arena and therefore improve a horse’s concentration.

But what exactly do horses hear? Research into the topic is revealing some fascinating facts.

Across most mammals, size is related to range of hearing. Larger animals tend to be able to hear lower frequency sounds better and usually cannot hear high-frequency sounds. Humans are somewhere in the middle, with a hearing range from about 20Hz at the low end to 20KHz at the upper end.

Horses are much bigger than us, so we would expect them to be able to hear lower frequency sounds better than we can and not the very high-pitched ones. But horses are an exception to the rule; their hearing range is higher, starting at about 50Hz and going way above ours to 33KHz. They are most sensitive to sounds in the range of 1–16Khz, a much broader extent than most mammals.

The design of equine ears and the ability to turn them in the direction from which the sound is coming also means that a horse can amplify sounds better than us. They can hear ultrasonic sounds (those with a soundwave frequency above human aural capacity), and also very quiet sounds that for us are completely inaudible.

This may have been an evolutionary adaptation to hearing the quiet rustling of a stealthy approaching predator. It does mean that we must be careful about the use of ultrasonic devices around them; ultrasonic rodent deterrent units, for example, are not a good idea in stables, as horses will find them as unpleasant as mice do.