Vocal cords, also known as vocal folds, are specialized tissues located within the larynx, or voice box. These folds of tissue vibrate as air passes through them, producing the sounds that enable vocal communication in most mammals. Most mammalian species rely on these structures for sound production. While sound production is widespread among mammals, one notable exception exists regarding the typical use of vocal cords for communication.
The Mammal Without Vocal Cords
The giraffe is the mammal widely recognized for lacking true vocal cords that function conventionally. For a long time, giraffes were believed to be almost entirely silent creatures, earning them the nickname “silent giants.” This perception stemmed from rare audible sounds in their natural habitat. Despite this historical belief, recent research indicates that giraffes do produce sounds, though these are not generated by the vibration of vocal folds in the conventional manner.
The unique anatomical structure of a giraffe’s larynx contributes to its distinct sound production. While giraffes possess a larynx, the extraordinary length of their trachea, which connects the lungs to the larynx, presents biomechanical challenges for typical vocalization. This extended distance reduces the velocity and pressure of airflow, limiting the range and volume of sounds that could be produced through vibrating vocal folds. Therefore, while some anatomical components resembling vocal folds might be present, they do not facilitate sound production through conventional vibration.
Communication Without Vocal Cords
Their vocalizations, which are often subtle, include snorts, hisses, grunts, moans, and bellows. These sounds are thought to be produced by air moving through their respiratory system, potentially involving their nasal passages, trachea, or changes in air pressure, rather than vocal fold vibration. For instance, snorts are forceful expulsions of air through the nostrils, often used as warning signals.
A significant form of communication for giraffes is infrasound, consisting of low-frequency sounds below human hearing. This adaptation allows giraffes to communicate over long distances, as low-frequency sounds travel farther through air and earth, useful in vast savanna environments or during low-light conditions. Researchers have also recorded giraffes producing a low-frequency humming sound, especially at night, which might serve as a contact call to maintain group cohesion when visibility is limited. These diverse forms of communication serve various purposes, such as alerting others to danger, expressing distress, attracting mates, or facilitating mother-calf bonding.