The production of sound is a fundamental biological process for nearly all mammals, relying on a specialized organ known as the larynx, or voice box. Within this structure reside the vocal folds, often referred to as vocal cords, which vibrate as air is expelled from the lungs, generating the acoustic energy necessary for communication. This mechanism is deeply ingrained in the mammalian class, serving as the standard for social structure, mating, and survival. Therefore, the existence of a mammal that seemingly defies this physiological expectation presents a biological puzzle.
The Mammal That Defies Expectation
The giraffe, the world’s tallest land animal, is the mammal associated with having no vocal cords. For centuries, this creature was considered to be almost entirely silent, leading to the assumption that it was essentially mute. Early observers believed that the giraffe simply could not produce sound because of its unique anatomy, despite anecdotal reports of occasional moans, snorts, or grunts. Recent scientific investigation, however, has revealed that the giraffe is not silent, but rather employs a communication strategy that is difficult for human ears to detect.
The Giraffe’s Vocal Anatomy
Although the giraffe possesses a larynx, its structure prevents the powerful, sustained vocalizations common to most other mammals. The giraffe’s version lacks the well-developed, elastic true vocal folds that are necessary to vibrate efficiently and produce loud, self-sustained sounds. This absence of functional vocal folds is the reason for its perceived silence.
The giraffe’s extremely long neck also introduces a mechanical constraint on sound production. The trachea, or windpipe, measures between 2 and 2.4 meters (6.6 to 7.9 feet) in length, creating an exceptionally long column of air. To produce a loud sound, the animal would need to generate an enormous rate of airflow from the lungs to overcome the resistance of this lengthy tube and cause the vestigial vocal folds to oscillate. This challenge, combined with the lack of robust vocal folds, explains the giraffe’s inability to produce audible roars or calls. Despite functional limitations, the giraffe’s larynx and associated laryngeal nerves are structurally well-developed.
How Giraffes Communicate
While they lack the ability to produce loud calls, giraffes utilize distinct acoustic signals and non-vocal cues to maintain social cohesion. They use a nocturnal hum, a low-frequency sound observed predominantly at night in both captive and wild populations. These sustained, harmonic hums typically register at an average frequency of around 92 hertz, which is within the range of human hearing but often subtle enough to be missed in the environment.
Beyond this audible hum, scientists also hypothesize that giraffes use infrasound, which are sounds below the lower limit of human hearing. This very low-frequency communication may allow giraffes to coordinate over long distances on the open savanna, as low-frequency sounds travel farther than high-frequency ones. Some studies suggest these infrasonic vocalizations are produced using a mechanism known as Helmholtz resonance, similar to blowing air across the neck of a bottle. Additionally, giraffes communicate through non-vocal means, such as snorting, which may signal alarm, or a specific coughing sound made by males during courtship.
Other Specialized Vocal Systems
Several other species have evolved solutions to vocalization that deviate from the standard vocal fold mechanism. For instance, many marine mammals, such as dolphins and porpoises, do not use their larynx to generate high-frequency clicks and whistles. Instead, these sounds are produced in the nasal passages using specialized structures called phonic lips or nasal plugs.
Elephants also employ a sophisticated system, using low-frequency infrasound rumbles that travel for miles across the ground and through the air. These calls are produced through their larynx, similar to human speech, but the extreme low frequency allows them to communicate socially over great distances in the dense environment of the savanna.