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The roar of a lion or tiger may sound like it's powered by huge lung power, but new research by the University of Utah shows the shape of feline vocal cords is what enables them to break the decibel meter with little effort.
Scientists had previously suspected the fat in lion vocal folds, or cords, enabled the roars because fat made the folds larger, and it was believed that size translated into acoustical amplitude at lower frequencies.
"It's not the size, it's the mechanical properties," said co-author Tobias Riede, a research assistant professor of biology. "The organ is the size of a fist, a relatively small organ that can produce enormous power. You would think that this lion would have to put a lot of effort into the roar, but it turns out this is not the case. They can do it with very low lung pressures."
The research, published this week in the Public Library of Science's online journal PLoS ONE, was conducted by the U.'s National Center for Voice and Speech, which is also exploring vocalization among other animals, such as elk, dogs and alligators. The senior author is speech scientist Ingo Titze, the voice center's executive director, who holds appointments at both the U. and the University of Iowa.
The study, funded by the National Science Foundation and the National Institutes of Health, used vocal folds recovered from three tigers and three lions euthanized for humanitarian reasons at Omaha's Henry Doorly Zoo. The research can help medical science develop ways to repair voices of human patients that have been compromised by cancer or overuse.
"If you understand how vocal folds are structured and what effects that structure has on vocal production, then it could help doctors make decisions on how to reconstruct damaged vocal fold tissue," Riede said.
Lion and tiger roars can reach 114 decibels in an ear a few feet away — roughly 25 times the volume of a gasoline lawn mower. Think of standing within 10 meters of a jet engine, Riede said.
Titze's team believes the secret behind lions' and tigers' ability to roar loudly at a deep pitch is the flat, square shape of the vocal folds, which can withstand extreme stretching and shearing.
Scientists know that these big cats have not evolved loud voices as a way for males to attract mates because there is little sexual dimorphism, that is, difference between the genders when it comes to vocalizing. Roaring is more likely geared toward frightening intruders, and that requires the kind of racket that commands attention.
"In some ways, the lion is a large replica of a crying baby, loud and noisy, but at very low pitch," Titze said in a press release. "In both cases, we hear loud, grating sounds that grab people's ears. When a baby cries, the sound isn't pretty. The sound is basically rough. The vibration isn't regular."