According to a news release from Cell Press, researchers have discovered the secret behind koalas’ low-pitched voice. Researchers note that the pitch of male koalas’ mating calls is approximately 20 times lower than it should be, given the marsupial’s somewhat diminutive stature. The study’s findings are described in greater detail in the journal Current Biology.

According to researchers, the reason behind koalas’ low-pitched voice is a specialized sound-generating organ that has never before been observed in any other land-residing mammal. The key component of this organ is its position outside the voice box, what researchers refer to as the larynx.

“We have discovered that koalas possess an extra pair of vocal folds that are located outside the larynx, where the oral and nasal cavities connect,” noted Benjamin Charlton of the University of Sussex in a statement. “We also demonstrated that koalas use these additional vocal folds to produce their extremely low-pitched mating calls.”

The koala’s low-pitched calls are generated as unending series of sounds on inhalation and exhalation, just like a donkey’s braying. On breathing in, koala calls produce noise like snoring. As the animals breath out, the calls produce noise like burping. “They are actually quite load,” Charlton posited.

“Because koalas produce the low [rate of vibration] sections of bellows on inhalation, we reproduced natural sound production in three male koala cadavers by sucking air through the pharynx and the larynx via the trachea, mimicking inhalation of air using the lungs,” wrote the researchers in the study’s abstract. “This allowed us to investigate whether an ingressive flow of air can induce self-sustained oscillation of the velar vocal folds and produce low frequency sounds.”

“An endoscopic video camera was attached to a tube leading from the suction pump and placed inside the trachea using a ring-tie to make the seal airtight. This in situ placement of the video camera just below the larynx allowed us to visualize the velar vocal folds through the space between the arytenoid cartilages (to which the laryngeal vocal folds are attached) and visually document their role in sound production, whilst ruling out the involvement of the laryngeal vocal folds,” the researchers added.

According to the researchers, koalas’ low-pitched voice is more normal for an animal the size of an elephant. Size is linked to pitch in that the dimensions of the laryngeal vocal folds typically determine the lowest frequency that an animal can produce. Thus, tinier animals will usually produce calls with higher frequencies than bigger animals.

Koalas have gotten around that limit by placing those vocal folds in a new location. According to the researchers, the folds are two long, fleshy lips in the soft palette, located above the larynx at the connection between the oral and nasal cavities. They may not appear all that dissimilar from the laryngeal vocal folds of other mammals, but their placement is very unique.

“To our knowledge, the only other example of a specialized sound-producing organ in mammals that is independent of the larynx are the phonic lips that toothed whales use to generate echolocation clicks,” Charlton posited.

The mix of morphological, video, and acoustic data in the new research represents the first proof in a land mammal of an organ other than the larynx that is set aside specifically for sound generation.

The researchers plan on examining other mammals more in depth to determine whether this vocal development is really exclusive to koalas.

According to National Geographic, a koala is a pouched mammal, meaning that a female koala carries her baby in her pouch for approximately six months after giving birth. When the baby comes out of its mother’s pouch, it clings to her back or belly until it is approximately a year old. Koalas reside in eastern Australia, where they feed on eucalyptus trees and sleep for up to 18 hours per day.

National Geographic adds that koalas get most of their water from eucalyptus leaves. Koalas consume a lot for their size — approximately 2.5 pounds of leaves a day. A special digestive system allows the marsupials to eat the tough eucalyptus leaves and stay unaffected by their poison.

Unfortunately, these pouched mammals were widely hunted during the 1920s and 1930s, and their populations dropped significantly. However, conservation efforts have allowed these special creatures to regain some of their former numbers. The primary issue when it comes to conserving the koala population is finding enough space for the mammal. Each animal needs approximately 100 trees.

According to a report by the Species Survival Commission, rising atmospheric carbon dioxide levels will lower the nutritional quality of eucalyptus leaves, leading to nutrient shortages in the species that feed on them, like koalas. Thus, koalas may no longer be able to meet their nutritional requirements, leading to malnutrition and starvation.

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