For generations, the giraffe has been widely perceived as a silent giant of the African savanna. This misconception stems from the fact that they are not frequently or loudly vocal like many other large mammals. Systematic research has revealed that these towering animals possess a range of vocalizations, most of which are subtle or used only in specific circumstances, leading to their reputation for quietness.
The Known Auditory Signals
Giraffes produce several distinct, high-frequency sounds associated with immediate behavioral responses. The most commonly heard vocalizations are the snort and the hiss, both sharp expulsions of air through the nostrils. The snort is a broadband pulsed call, lasting approximately 0.28 seconds, and is frequently used as an alarm signal to alert the herd to danger. The hiss is a short, sharp noise sometimes used as a defensive mechanism when a giraffe is confronted or when an adult is annoyed.
Young calves also contribute to the repertoire with varied sounds, including occasional bleats and weak moans. These sounds are very soft and are heard in close-range interactions, such as when a calf is separated from its mother or expressing mild distress. Adult giraffes may also produce soft grunts or grumbles, which are subtle expressions of discomfort or irritation.
The Nocturnal Hum
The most intriguing and least understood giraffe vocalization is a low-frequency, sustained sound known as the nocturnal hum. This deep bellow was discovered after a study analyzed over 940 hours of audio recordings collected from giraffes in three European zoos. Researchers detected this harmonic and frequency-modulated sound almost exclusively during overnight hours.
The average frequency of this hum is approximately 92 Hertz, which is within the range of human hearing, though it sits on the very low end of that spectrum. The sustained nature of the hum, which can last for several seconds, suggests it is an intentional vocalization rather than a passive noise. While scientists have debated whether this sound is a form of communication, its complex acoustic structure suggests it may convey information about the caller’s physical or emotional state.
The nocturnal timing of this sound has led to theories that it functions as a contact call when visual communication is hindered by darkness. Giraffes rely heavily on their excellent vision for communication during the day, so an auditory signal is helpful for herd coordination at night. The hum is a deep, resonant sound, which is acoustically suited to travel across distances in the dark environment.
Context and Purpose
The various sounds giraffes make are closely tied to specific behavioral contexts within their social structure. The sharp snort is primarily a warning, serving to communicate immediate danger to nearby individuals. This signal is used when the animal senses a predator or is agitated by an unfamiliar presence, quickly transitioning the herd into a state of vigilance.
In the context of the mother-calf bond, audible sounds are used for location and reassurance. Mother giraffes will sometimes emit a loud, low bellow when actively searching for a calf that has strayed. These audible calls help the pair maintain contact, especially when the calf is still young and dependent.
The low-frequency nocturnal hum appears to serve a different, more subtle function, likely maintaining group cohesion. As a contact call, the hum may allow individual giraffes to confirm their location to others in the group while they are resting or moving in low visibility. Whether for alarm, maternal care, or nightly coordination, these vocalizations demonstrate that giraffes use sound purposefully to navigate their environment and social dynamics.