MARY LOUISE KELLY, HOST:
OK, here's a sound.
(SOUNDBITE OF HORSE WHINNYING)
KELLY: You probably recognized it right away. You probably recognized which animal is responsible for it. But there is more to that sound than meets the ear. Here's science reporter Ari Daniel.
ARI DANIEL: Elodie Briefer grew up in the countryside near Geneva, and horses have long been a part of her world.
ELODIE BRIEFER: I was riding horses when I was young. And I did few competitions but would prefer to go for a walk with the horse.
DANIEL: So Briefer's heard a lot of whinnying over the years. She never noticed anything out of the ordinary until she became an animal behavioral scientist and began comparing how different animals, including horses, express themselves vocally.
BRIEFER: The first time I really listened to a horse whinny that I had recorded, I was confused 'cause I thought there were two horses, as if there is two voices at the same time.
DANIEL: Briefer inspected the sound file more closely, and that's when she saw it - two frequencies produced at the same time, one high and one low.
BRIEFER: So they have basically two tones.
DANIEL: Here's one of the whinnies that Briefer recorded.
(SOUNDBITE OF HORSE WHINNYING)
DANIEL: Let me slow it down for you. Listen at the very beginning.
(SOUNDBITE OF SLOWED-DOWN HORSE WHINNYING)
DANIEL: A couple things stood out to Briefer. First, larger animals tend to produce lower frequencies, not higher ones. Second, a fair number of birds can produce two simultaneous frequencies like this, but among mammals...
BRIEFER: It's quite uncommon, at least when it appears all the time in one type of sound.
DANIEL: So Briefer decided to investigate how horses do it. She first went to a Swiss stud farm and threaded a small camera down the noses of 10 breeding stallions until it was just above their larynxes, a procedure the animals are familiar with as part of their regular physical checkups. She then played female whinnies or paraded a mare in front of them.
BRIEFER: And they started whinnying, so we could actually see what's going on.
DANIEL: The vocal folds of the larynx vibrated, just like when we speak, to produce the low part of the whinny. In addition, just above the larynx, horses have this strong cartilage, and the video showed that cartilage constricting.
BRIEFER: Which makes only a small opening.
DANIEL: Likely producing a whistle, the high-frequency part of the whinny. Next, Briefer's colleagues connected with a butcher in France, a country where they eat horses.
BRIEFER: I know it's not the same in every country, but there it's quite common.
DANIEL: The butcher provided half a dozen horse larynxes, which the team blew air through and CT scanned, confirming the results from the stud farm. Finally, the team tracked down several stallions with a rare disease that tends to paralyze one of the vocal folds and recorded their whinnies. The low tone was partially absent, but the high pitch was unaffected. Here's an example.
(SOUNDBITE OF HORSE WHINNYING)
DANIEL: Taken together, Briefer, who's now at the University of Copenhagen, concludes that a whinny is a unique blending of vocal fold vibration that generates the low pitch and a whistling above the larynx that produces the high pitch. The results appear in the journal Current Biology.
JACOB DUNN: It's a really interesting and exciting development in our understanding of animal communication.
DANIEL: Jacob Dunn is an evolutionary biologist at Anglia Ruskin University who didn't participate in the research.
DUNN: So we know how they do it. The next question would be, why do they do it?
DANIEL: Answer might lie in previous work of Elodie Briefer which suggested the two tones of a whinny appear to encode different pieces of emotional information.
BRIEFER: The highest one indicates whether the emotion is pleasant or unpleasant, and then the other one indicates whether the emotion is intense or not.
DANIEL: Offering insights straight from the horse's vocal tract. For NPR News, I'm Ari Daniel.
(SOUNDBITE OF GITKIN'S "CHICHA NOLA") Transcript provided by NPR, Copyright NPR.
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