Horses have the ability to produce a distinct and repeatable call.
Equines vary frequency during vocalization, giving them the potential for expression. Of the sounds that horses make, whinnies have the greatest potential for long range communication. The challenge is to build up a large equine vocalization data base to determine if a particular acoustic spectrum might be associated with a particular situation.
An analysis of previously recorded whinnies indicates that, in general, there are two principal components: a tonal or constant frequency component; and a frequency dependent component, typically characterized by a rapid increase in frequency followed by a more gradual decrease. The latter produces the sound we usually associate with a whinny and we refer to as the "call".
The objective of this research conducted at the University of Connecticut was to find a situation where a number of whinnies were collected under constant, known condition.
A total of 100 sonograms form four separated mare/foal pairs were collected. The acoustic structure of the whinnies were very consistent. There was a tonal structure, which tends to be slightly different for each mare's "voice", comprising of a basic frequency and its harmonics. Imbedded in this, however, was a distinct persistent call with a characteristic frequency structure: a sharp rise to about 2,000 Hertz and then a gradual decline. The call was consistent throughout the whinnies of an individual mare and was very similar when comparing different mares.
Based on this initial research, it appears that horses have the ability to produce a distinct and repeatable call as part of a whinny. The spectra of the call in the whinnies recorded were similar to a softer call made by a mare looking for her foal while being relocated to the barn. What is not known at this time is whether this particular call might apply to other situations too. As a horse is primarily visually oriented, most whinnies occur when vision is.
The next step is to determine if whinnies can contain distinctly different calls under different circumstances as a tool for communicating information, stress, or feelings to other horses or people.