We all know that hoarse feeling after a night in a noisy bar, but imagine how elk and European red deer stags feel building up to their annual recital?According to Tobias Riede, stags put on a performance of operatic proportions during the mating season, and all with virtually no preparation; we'd rip our vocal folds to shreds if we tried the same. What is more, Rocky Mountain elk stags hit high notes that should be out of their range. Their vocal folds should be much too long to produce such high-pitched calls. Curious to know how the elk's vocal folds perform these extreme feats, Tobias Riede and Ingo Titze, from the National Centre for Voice and Speech in Denver Colorado,decided to take a closer look inside the elk's voice box().
Fortunately for Riede, there is a ready supply of elk vocal folds in Colorado; hunters have to turn in the beasts' necks and heads so that the authorities can track the development of chronic wasting disease. Dissecting the tissue to see if the vocal fold structure accounted for the elk's high pitch and remarkable resilience, Riede soon realised that there were no unusual features that could account for the vocal folds' extreme performance. The elk's vocal folds were composed of a muscle, covered in a flexible epithelium linked by a ligament, much like other animals'.
However, it was clear that the elk vocal folds were a much closer approximation to human vocal folds than other animals. Riede explains that the ligament in dog vocal folds tends to be quite small, but the elks' were relatively thick and long; just like the ligament in human vocal folds. Which makes elk vocal folds a good model for human vocal folds, despite being three times the size.
Having found that the elk's vocal folds look much like ours, Riede decided to test the tissue's material properties to see if they accounted for the animals' high-pitched voices. According to Riede, one of the ways for animals to hit the high notes is to stretch the vocal folds, but elks would have to apply 9 times as much tension as humans for their long vocal folds to hit the same notes. Had elk evolved a stronger ligament and epithelium to allow them to scale the vocal heights? Slowly stretching the vocal fold epithelium and measuring the force applied, it was clear that the tissue was as floppy as other creatures'. And although the ligament was slightly stronger than human vocal fold ligaments, it wasn't 9 times stronger. So neither the vocal fold's structure or its material properties can account for the animal's high pitch.
Riede suspects that there is something else going on, but he's not sure what. He suggests that the vocal folds may not vibrate along their full length, either because a muscle protrusion, part way along the fold,effectively shortens the vibrating tissue's length, or the tissue's flexibility varies, shortening the vibrating section of the vocal fold and allowing elk stags to hit the high notes.
