November 3, 2011
Not all cats roar (which is probably a good thing for those of us who own housecats), but those that do fascinate us with their mysterious and frightening sounds. Research published this week in PLoS ONE gives us new insight into the inner workings of the roars of lions and tigers—the secret is in the cats’ vocal folds.
A group of biologists and speech scientists studied how lions and tigers roar by examining and testing tissue from the larynges of three lions and three tigers from the Henry Doorly Zoo in Omaha that had been euthanized because they were old and sick. The researchers were particularly interested in the vocal fold tissues, soft connective tissues made of collagen, elastin, a lubricant and fat.
Vocal folds are just another name for vocal cords, and they are a bit different in lions and tigers than in other species. In most species, the vocal folds are shaped like triangles where they protrude into the animal’s airway. But in lions and tigers, the protrusions are flat and shaped like a square, courtesy of the fat deep within the vocal fold ligament. This shape allows the tissue to respond more easily to passing air, letting the kitties roar louder with less lung pressure. A lion or tiger can roar as loud as 114 decibels, about 25 times louder than a gas-powered lawn mower.
The cats are also aided by the strength of their vocal folds, which can withstand stretching and shearing as air moves past them and the folds vibrate. The size of the animal or the vocal fold, or the frequency of the sound, didn’t matter. Elk have vocal folds about the same size, but they make high-pitched sounds. And humans speak in a range of sound frequencies similar to those of lions’ and tigers’ roars, but obviously our voices are much softer.
This study “is confirmation that the frequencies of phonation are described by mechanical properties of the vocal folds and not by nerve impulses from the brain,” says study senior author Ingo Titze, executive director of the National Center for Speech and Voice.
But Titze also says that there are some similarities between a lion’s roar and a baby’s cry. Both have “very loose and gel-like” vocal folds that make irregular vibrations that create rough sounds (low-frequency in the cats, high-pitched in the babies) and draw our attention.
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