Ever wondered what your horses can hear? When you play a radio in the stables, does it annoy or soothe them?
Have you wondered why horses become so anxious in windy conditions? Are you curious about the effects of humans talking, shouting or singing to horses?
Like most mammals, ears are important sensory organs for horses and send information to the brain, via neural pathways. It is how the brain interprets what is heard which can determine a horse’s reaction. Their auditory capacity is superior to ours, as any rider knows who has experienced the hair-trigger reaction of a horse to a sound they can’t themselves detect.
As flight animals, sound frequency and intensity have kept horses alive in the wild for millennia. Predators, for obvious reasons, make as little noise as possible when stalking their prey. Consequently, horses have become attuned to the distant rustle of grass or snap of twig.
And their acute sense of hearing not only allows them to receive vital information which might stop them becoming breakfast, but their ears also allow them to communicate with other equines (and with humans too, providing we can understand).
Understanding just what and how horses hear can be a valuable tool in our daily equine interactions, riding and training.
Form and function
Horse’s ears come in differing shapes and sizes, and vary in position and length. However, they all have the same conical form, which catches and funnels sound and allows them to hear different sounds concurrently.
Horses, like cats and dogs, hear in mono (one ear at a time) whilst we humans hear in stereo.
They can turn each ear in a separate direction to listen and communicate without having to turn their heads, using the 16 muscles they have in each ear. This means they can optimise their chances of picking up the direction from which the sound came from.
The hairs within the ear provide feedback to the horse about its surroundings whilst also protecting its sensitive internal structures. It is no surprise then that Equestrian Sports NZ has joined the growing list of equestrian organisations which no longer allow the trimming of horses’ inner ear hair, for welfare reasons.
The parts of the ear
The pinnae (external ear) acts like a satellite dish or an old-fashioned gramophone speaker, capturing sound waves and channeling them inwards. Whereas our own ears are small, and noise easily spills out of them, a horse’s large ears are designed to collect and thus amplify the sound.
The external ear channels the sound waves into each ear canal, making them more intense, which is useful when a horse is surviving on the plains, but which can be problematic in modern horsey environments where equines are exposed to a diverse range of acoustics.
When sound hits the middle ear, it causes the ear drum to vibrate; these vibrations travel through three tiny bones called (quite appropriately) the hammer, anvil and stirrup. The bones form a chain that transmits the vibrations to a second membrane, which marks the start of the inner ear.
Like our own ears, the inner part holds the sensory organs used for hearing and balance. The snail-shaped cochlea is the hearing part and the vibrations from the membrane travel through them.
What horses hear
Pitch, or frequency, describes the range in which an animal can hear, measured in Hertz (Hz).
Cats are renown for super-sensitive hearing, with a range of 48 Hz (lowest sound) to 85,000 Hz (highest sound), one of the broadest among mammals. Humans are much more limited, with the lowest sounds a healthy young person can detect around 20 Hz and the highest about 20,000 Hz.
Horses are somewhere in between, superior to humans but inferior to cats (and dogs). Horses cannot detect pitches as low as we can, with a lower range kicking in around 55 Hz, but can hear much higher, up to around 33,500 Hz.
A fascinating fact is that horses can detect low-frequency sounds while grazing, via vibrations transmitted through the ground that they pick up through the teeth and jawbone. Hooves also pick up on these vibrations, thus warning of possible predators. A sure sign a horse has heard something is when the lowered grazing head suddenly stops chewing.
At the high end, horses can hear the ultrasonic sound of a bat, the silent (to us) dog whistle and the noises emitted by rodent-repelling devices.
Horses have amazing auditory acuity, or sense perception, and can pick up a human heartbeat from more than 1m away. In addition, researchers have discovered that horses can synchronise their heart rates with other horses in their herd, or with humans.
In her study, Investigating Horse-Human Interactions: The Effect Of A Nervous Human, Swedish animal welfare professor Dr Linda Keeling tested the relationship between human and horse heart rate with fear as an indicator. The study had 20 participants of varying riding ability walk or ride their horse from one point to another four times, and participants were told that on the fourth pass an umbrella would open. The umbrella was never opened, but the heart rates of both the riders and horses increased in anticipation when the human expected the umbrella to open.
Training and daily routines expose horses to a variety of sounds which they need to be able to interpret. As Janet points out, tiny differences in loudness and pitch are critical to comprehending human speech, emotion, music, environmental noises, and animal vocalisations.
Horses ‘learn’ sounds, so that they can distinguish one tonal variation from another. For example, the clank of feed buckets and the sound of your car, are sounds they can learn to respond to through habitual exposure and positive outcomes. Consequently, horses become accustomed to ‘typical sounds’ as a way of understanding their environment. These include being able to interpret the snorts, whinnies and vocalisations of other members of their herd. They know who owns each noise, and what it means.
Habituation and training
Keeping horses calm and focused in noisy surroundings can be challenging. International dressage rider and trainer, Tristan Tucker, explains that horses have to learn to deal with unexpected movement, touch and sounds as these can all illicit a flight response. He says the natural reaction of flight, if left to operate, grows unless horses learn to relax around unexpected sights, touch and noises.
Unsurprisingly, even though police and military horses are selected for calm temperaments, they still go through a rigorous training process to ensure they can cope with stressful situations.
Captain Lisa Rakes, former lead horse trainer for the Lexington Kentucky Mounted Police, is used to de-sensitising horses to unpredictable situations and sounds. She advises that when training, to should repeat a noise until you see a little bit of relaxation, then stop. “Learning happens when the horse stops, but you can’t hurry the process.
“And don’t force a horse to stand still. If you can put his feet to work, even in a small circle, that will keep his mind on you and less on the distraction.”
Many riders use ear plugs or the very fashionable ear hoods as a way of trying to block out noises, reduce stressors and distraction in a competition environment. However, there is next-to no research available on their effectiveness, and most information remains anecdotal.
The use of such gear might also be helpful on windy days, as these conditions distort sounds and intermingle noises, which causes confusion and leads to anxiety and nervous behaviour.
Talking to horses
Humans connect and bond with their equines vocally: a whisper in the ear, a whistle in the field, ‘clucking’ to add a bit of energy to a ride, or a calming murmur when the vet comes. The use of vocal commands and cues has been a common training method throughout time.
Researchers from the University of Copenhagen found that both domesticated and wild horses can tell the difference between negative and positive sounds from their own species, from similar species and from humans. Researcher Elodie Briefer explains: “Our results show that animals are affected by the emotions we charge our voices with when we speak to or are around them.”
The study demonstrated that horses reacted particularly strongly to a negative voice, and in some situations seemed to mirror the emotion they were exposed to – evidence that using a soothing voice can help when you are faced with the challenge of calming a nervous or hyper-vigilant horse.
Horses also communicate with each other – and with us – using their ears. One of the first things people new to horses learns is that ears flat back are a warning sign of aggression or annoyance.
Ears in the loose, droopy position are indicative of relaxation. Ears held loose with openings facing forwards or outwards also signal relaxed but interested. Ears pointed directly forwards indicate focused interest in what’s ahead, and when they are stiff and accompanied by other body language signals, such as flared nostrils, then this is a sign of anxiety.
Ears angled backwards with openings directed towards the rider demonstrates attentiveness and a horse listening to commands.
Summary
Scientists and writers in the area of horse’s sensory perception all comment on the lack of research on the subject of equine hearing. In the future, hopefully this knowledge gap will be bridged, but until then understanding how horses’ ears are designed, their function and their capabilities might help us in our daily interactions and decisions.
