Horse

Horse Communication and infrasound

Excerpts from "Infrasound from Equus Caballus" presented at the Spring conference of the Acoustical Society of America North Carolina Regional Chapter. Authors: E. von Muggenthaler, Philip Hale, Ralph R. Conti

For centuries, the domestic horse (Equus Caballus) has been an integral part of human life. Although some research on the behavior of the wild and domesticated horse exists, there has been limited understanding of the role of communication in their social structure. The authors are not aware of any prior horse vocalization research.

Common horse vocalizations include squeals of aggression and whinnies for facilitating social contact over distance. In donkeys (Equus asinus) there are mouth movements called jawing, yawing, or clapping. This is the opening or closing of the mouth which make a characteristic sound that is audible to humans, (Mcdonnell, 1998). Horses have a unique physiological structure called the auditory tube diverticulum or guttural pouch whose true purpose, remains unknown. The guttural pouches are a pair of pouches located dorso-posteriously to the posterior pharynx. These structures are only found in Equid family and they are dilations of the Eustachian tubes, thin membranous channels that connect the nasopharynx with each middle ear. The capacity of the guttural pouch in adult horses is 472 cm3, and 145 cm2 in foals (Manglai et al., 2000). Guttural pouches perform a role of air exchange between the auditory tube diverticulum, and middle ear (Baptiste, 1997). In 1911 it was proposed that the guttural pouches serve to aid in normal swallowing, equalizing of pressure on either side of the tympanic membrane. Several recent theories about the guttural pouch have indicated that it may be used to cool the blood circulating in the brain during heavy exercise, (Baptiste, 1998), however it is generally accepted that air enters and leaves the pouches during expiration, so the function of the guttural pouches remains open to debate (Hodgson, 1998).

• In February 2003, Ocala Florida and North Carolina 11 horses were recorded.

• In Ocala two horse stalls were treated with sound suppression panels, by AVL Systems.

Results

• Horses produce infrasound.

• Soundproofing for bio-acoustics research is suggested when possible.

• Order Perrisodactlya including Equidae and Rhinocerotidae produce infrasound. Order Artiodactyla includes Hippopotamidae and Giraffidae whom also produce infrasound.

• It is suggested that the guttural pouches are responsible for the generation of low frequency sound, and also may play a role in the reception of infrasound.

A bit may hinder both breathing and vocalizations

• The use of infrasound may be why horses are known to "spook" when human observers detect nothing.

• Horse stables should be better soundproofed

• Horses are herd animals and may rely on infrasound to keep the herd together, or communicate over distance like elephants.