An initial surprise upon hearing the elk's bugle is how high-pitched the sound is for such a big beast.
"Larger animals tend to have deeper resonances and lower voices," lead author David Reby from the University of Sussex explained in a press release.
The paradox has puzzled scientists for decades, so when Reby's colleague Megan Wyman returned from a trip recording deer bellows in New Zealand, Reby knew that they might have a chance to finally solve the mystery.
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While studying these and other recordings of the animals, another stroke of good luck happened - at least for the researchers.
A member of the research team, Yann Locatelli, learned that a male elk in the herd at France's Muséum National d'Histoire Naturelle had died. The natural death gave the scientists a chance to study the elk's anatomy underlying calls.
All of the analysis allowed the team to determine that elks whistle while simultaneously roaring through their vocal chords. The call includes an unnatural sounding, high-pitched shriek that reaches frequencies up to 4000 Hz.
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The high and low pitched sounds can shift independently. For example, sometimes the high-pitched wail rises and falls while the tone of the lower-pitched roar remains constant. The vocal folds vibrate and produce a call that matches the animal's size, while the bull simultaneously produces a high-pitched, high-volume, wraith-like cry by whistling.
Physicist Joel Gilbert, also on the research team, calculated how the air released by the bull might vibrate in the animal's oral cavity. He realized that the jet of air could hit the elk's soft palate (known as the velum) in much the same way that air in a flute vibrates.
Like a wind instrument musician, the process requires the elk to make some skillful mouth and other facial movements, too.
Reby and his team wrote, "The mouth is kept open during the vocalization, whereas the upper lips are curled upwards and the nostrils are moved backwards."
As for why the male elks go to such trouble to produce the sound, the authors speculate that these impressive animals have evolved such a dual-noise call "to advertise body size at close range while simultaneously advertising their presence over greater distances using the very high-amplitude whistle component."