The newest Ig Nobel Prize of acoustics discovery
The Ig Nobel Prize may be a humorous imitation of the Nobel Prize, but its winners certainly produce groundbreaking and valuable scientific discoveries. Similar to the annual Nobel Prize—an award for academic, cultural, or scientific advances established by Swedish chemist Alfred Nobel (7)—Harvard University rewards weird, amusing, and often gruesome scientific discoveries with the Ig Nobel Prize (1). The university typically holds the live satiric award ceremony in Sanders Theatre, but due to the current coronavirus pandemic, the ceremony was pre-recorded (1). Winners received a budget cardboard trophy and a defunct 10 trillion Zimbabwe note along with the Ig Nobel Prize winner title (1). This year, an international team of scientists won the prize in the acoustics category for getting an “alligator to sound strange when inhaling a party balloon,” as described by Stephan Reber, one of the scientists (1).
From Austria, Sweden, Japan, the U.S, and Switzerland—Stephan Reber, Takeshi Nishimura, Judith Janisch, Mark Robertson, and Tecumseh Fitch conducted a study titled, “A Chinese alligator in heliox: formant frequencies in a crocodilian” to understand how crocodiles communicate (2). This group of scientists wondered why crocodilians were so loud (4) and if they can communicate similarly to humans using vocal tract resonances (2).
Year-round, crocodilians make loud noises, also known as bellows, to communicate with each other (4). These bellows are more common during the mating season and are made by both males and females (4). Since female crocodilians only mate with males larger than themselves, scientists hypothesized that crocodilians used these roaring bellows to inform each other about sex and body size (4). Vocal tract resonances are long intense sounds produced by acoustical vibration, (6) and formants are the sound frequencies of these vibrations (3). If crocodilians have vocal tract resonances, then scientists would have evidence for their hypothesis because formants are often related to the caller’s vocal tract length and thus the overall size of the animal (5).
One may remember the old party trick of inhaling helium from a balloon and talking with one’s voice super high pitched. This trick demonstrates how resonances change because as sound travels faster in helium, a gas lighter than air, the air passages seem shorter and make our resonances higher, or frequency shift upwards (2). The international group of scientists decided to use this party trick on a female Chinese alligator (5); however, instead of the alligator inhaling helium from a balloon, it inhaled heliox, 88% helium and 12% oxygen, from an airtight chamber (4). Although Chinese alligators are small, scientists chose this species within the crocodilian family because they are very vocal (5). In June of 2013, the scientists experimented at St. Augustine Alligator Farm Zoological Park in Florida after receiving approval from the St. Augustine Alligator Farm research committee (5). This experiment did not harm the alligator subject in any way because helium, a noble gas, is chemically inert and completely non-toxic (5).
During the experiment, the alligator was recorded while in a sealed tub with water raised to the maximum bellowing height of 63 centimeters (5). For five minutes, the experimenters induced the alligator to bellow by recordings of other bellowing alligators (5). Then, heliox was added into the tub (5). The alligator was left in the tub for five minutes to allow for the full replacement of respiratory gasses by heliox before being stimulated to bellow for another five minutes (5). After the alligator vocalized in the heliox environment, the scientists raised the water level of the tank to fully eject all of the heliox gas (5). The water was then drained to the maximum bellowing level and the alligator was induced to bellow for the third time in ambient air (5). This procedure was repeated three days later (5).
The scientists used the Pratt acoustic analysis program to create spectrograms of the alligator’s bellows (5). A spectrogram is a visible record of any kind of sound with a vertical frequency scale, showing the frequency components at each moment in time (3). As shown in the spectrogram, there was a consistent shift of high energy frequency bands between the two atmospheres (5). The scientists determined that the frequency bands represented formants (5). The first formant was on average 425.7 Hz in ambient air and 825.1 Hz in heliox (5). For the second, the average frequencies were 1618.4 in ambient air and 3155.2 in heliox (5). Because frequencies in heliox were higher than the frequencies in ambient air, the scientists could conclude that crocodilians communicate with resonances in their vocalizations, similar to how mammals and birds do (5). Furthermore, the scientists still believe that a crocodilian’s bellows may be to inform others of their size, but more research needs to be done (5).
Although the Ig Nobel Prize may be comedic, the work these scientists have done is significant. It is great to see scientists work valued and shared, even if it may be to make others laugh. Their discovery that crocodilians communicate with vocal tract resonances will be important in helping other scientists understand the purpose of a crocodile’s bellow, especially during the mating season. Additionally, their research suggests that resonance frequencies may have played a role in dinosaur vocalizations because birds and crocodilians share a common ancestor with all extinct dinosaurs (5). This discovery in alligator acoustics paves the way for many more important scientific discoveries in the future.
– Allison Wu
References
- Daily Mail. (September 18, 2020). Knife made of frozen poo and an alligator that breathes in helium are among winners of the spoof ‘Ig Nobel’ awards. Retrieved from https://www.dailymail.co.uk/sciencetech/article-8747199/Frozen-poo-knife-highlights-spoof-Nobel-awards.html
- Daily Mail. (September 19, 2020). Ig Nobel Prize: Listen at an alligator inhaling helium in the name of science [Video]. Youtube. Retrieved from https://youtu.be/dXm7DIBXscY
- Encyclopædia Britannica. (2020). Phonetics. Retrieved from https://academic.eb.com/levels/collegiate/article/phonetics/108587#69030.toc
- IFL Science!. (n.d). Alligator Made To Inhale Helium, For Science!. Retrieved from https://www.iflscience.com/plants-and-animals/alligator-made-inhale-helium-science/
- Journal of Experimental Biology. (n.d.) A Chinese alligator in heliox: formant frequencies in a crocodilian. Retrieved from https://jeb.biologists.org/content/218/15/2442.full
- Science In Context. (July 19, 2019). Resonance Retrieved from https://link.gale.com/apps/doc/CV2644031904/SCIC?u=mlin_m_bucking&sid=SCIC&xid=797056f8.
- The Nobel Prize (n.d.) Nobel Prize facts. Retrieved from https://www.nobelprize.org/prizes/facts/nobel-prize-facts/
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