NEW YORK (AP) – Equines vocalize to forge new associations, extend greetings to familiar companions, and mark auspicious junctures such as meal times.
The precise physiological mechanisms by which horses produce their characteristic vocalizations, commonly referred to as neighs, have long remained an enigma for scientific inquiry.
The equine whinny is an unusual amalgamation of both resonant low-frequency tones and sharp high-frequency sounds, akin to a simultaneous blend of a guttural rumble and a piercing squeal.
The generation of the lower-pitched component was not particularly perplexing. This sound originates from the passage of air over the vocal folds within the larynx, which, upon vibration, produce an audible noise. This process bears a resemblance to the vocalizations employed by humans for speech and song.
However, the origin of the high-frequency element presents a greater puzzle. Barring certain exceptions, larger biological organisms typically possess more substantial vocal apparatuses, which consequently produce sounds of a lower pitch. Therefore, how do horses manage to achieve these higher frequencies?
A recent investigation suggests that they achieve this through a form of whistling.
Researchers employed a diminutive endoscopic device inserted through the horses’ nasal passages to visually document the internal laryngeal activity during the production of both whinnies and the softer, more nuanced nicker, another common equine vocalization. Complementary investigations involved detailed imaging techniques and the expulsion of air through the excised larynges of deceased horses.
The study’s findings revealed that the enigmatic high-pitched components of the whinny are produced via a whistling mechanism originating within the equine larynx. As air vibrates the vocal tissues, a specific region superior to these tissues constricts, creating a narrow aperture through which the whistle can be expelled.
This physiological mechanism distinguishes equine whistling from the oral whistling performed by humans.
“I had not previously conceived of a whistling component being involved; it is genuinely fascinating, and I can now perceive it,” remarked Jenifer Nadeau, an equine specialist at the University of Connecticut, who was not a participant in the research published Monday in the journal Current Biology.
While a limited number of small mammals, such as rats and mice, exhibit this whistling behavior, horses are recognized as the initial large mammalian species to possess this capability. Furthermore, they are the sole known animals capable of producing a whistle through their larynx concurrently with vocal song.
“The realization that a ‘whinny’ is not a monolithic sound but rather an intricate fusion of two distinct fundamental frequencies generated by separate physiological processes is indeed remarkable,” stated Alisa Herbst of Rutgers University’s Equine Science Center in an email correspondence regarding the study.
A significant outstanding question pertains to the evolutionary trajectory that led to the development of horses’ dual-pitched vocalizations. Certain wild equids, such as Przewalski’s horses, and even elk, exhibit analogous vocal behaviors. However, more distantly related equid species, including donkeys and zebras, are incapable of producing these higher-frequency emissions.
The capacity for producing dual-toned whinnies could potentially enhance horses’ ability to transmit multifaceted messages simultaneously. This nuanced vocal range provided by differently pitched neighs may enable them to articulate a more elaborate spectrum of emotions during social interactions, according to Elodie Mandel-Briefer, the study’s lead author from the University of Copenhagen.
“They possess the ability to convey emotional states across these two distinct dimensions,” Mandel-Briefer elaborated.
