Horses have large, funnel shaped ears that are operated by 16 muscles. Their shape allows them to channel sound towards the horses eardrum. Again, being a prey animal requires good senses!
The external ear ‘funnel’ is called the pinnae, and is just a small part of the complex hearing system. A horse can pinpoint sounds, and focus solely on a single one, or analyse almost all sounds concurrently, all while going about his daily business!
A horse’s sense of hearing is much keener than humans. They require this acute sensitivity, because predators don’t announce that they are stalking their prey and every leaf rustling, every cracking twig could be a predator ready to pounce.
Horses have a frequency range of 14 Hz to 25 kHz, much larger than humans 20 Hz to 20 kHz. Even so, most humans can’t even hear 20kHz, in fact, adults can usually hear no higher than 15-16kHz!
Horses are also very sensitive to emotional tones: high, shrill screeches cause fearful reactions, while speaking soothingly, and softly helps calm and reassure them. When handling horses it is vital to understand that the voice is a powerful aid.
But, how does the ear really work?
The large pinnae, made of cartilage, controlled by 16 muscles and able to rotate 180 degrees, catch the sound, funnelling it into the ear. The sound travels through the auditory canal into the middle ear where the eardrum, a thin membrane, is located. The eardrum begins to vibrate, depending on the intensity of the sound, and sends the vibrations through the ossicles, small bones known as the malleus, incus, and stapes (or hammer, anvil and stirrup). These names come about due to their resemblance to the aforementioned items. The stapes, or stirrup is the smallest bone in the body.
From the ossicles, the vibrations are transferred to the inner ear, where the cochlea, the snail shaped auditory canal is found. This is lined with extremely sensitive hairs which generate electrical impulses, which are sent to the brain to be interpreted.
While it is the muscles that keep the horse standing upright, and allow it to be balanced, the inner ear plays a role in telling the brain which way the horse is leaning, and how to correct it. The cochlea is full of fluid, and as the horse moves, so does the fluid. The hairs pick this information up, and inform he brain about the horses position.