Under Friendly Neighing: Science Unveils Horse Communications 0 13

Horses use neighing to attract the attention of new companions, greet familiar ones, and express positive emotions – for example, during feeding. However, the mechanism behind this characteristic sound has long remained unclear to researchers.

Neighing is an unusual combination of low and high frequencies, a peculiar mix of a hoarse guttural sound and a piercing tone that occur simultaneously. The origin of the low component is relatively clear: it arises when air passes through vibrating folds of tissue in the larynx – much like how human speech and singing are formed. However, the source of the high sound has long raised questions. Typically, large animals have massive vocal systems and produce predominantly low sounds. Therefore, it remained unclear how horses create a high-frequency component.

New research has shown that they actually use a whistling mechanism for this. To understand the sound production mechanism, scientists introduced a miniature camera through the nasal passages of horses and observed what happens inside when the animals neigh or produce another common, quieter, and softer sound. Additionally, specialists performed detailed scanning and passed air through isolated vocal structures of deceased horses.

It turned out that the high-frequency part of the neighing is a type of whistle formed directly in the vocal apparatus. The airflow causes the tissues to vibrate, and the area located just above contracts, creating a narrow opening through which the whistling sound emerges. This mechanism differs from the whistling that humans produce using their lips and oral cavity.

The question of how horses developed the ability to produce two-toned sounds remains open. Similar vocalizations are found in Przewalski's horses as well as in moose. However, more distant relatives of horses – donkeys and zebras – are unable to produce such high-frequency components.

It is likely that the two-toned neighing allows horses to convey multiple signals simultaneously. Differences in pitch may expand the range of emotional nuances that the animals express during communication. According to the study's author, Elodie Mandel-Briefer from the University of Copenhagen, this feature makes horse communication more multifaceted.