Biologists have recently discovered that giraffes hum.
The prevailing theory about giraffe vocalization had been that they are not capable of generating substantial sounds because of the physical difficulty of them producing sufficient air flow through their long necks. However, some had suggested that giraffes employ low-frequency “infrasonic” sounds below the level of human perception, similar to elephants and other large animals who use it for long-range communication.
After extensive research in three European zoos, Angela Stöger at the University of Vienna, Austria, found no evidence of infrasonic communication, but she did pick up an intriguing humming noise coming from the giraffe enclosures at night—in all three zoos. “I was fascinated,” Stöger was quoted as saying in New Scientist, “because these signals have a very interesting sound and have a complex acoustic structure.” That hum turned out to be a low-frequency sound, of about 92 Hz. That’s not infrasound; the human ear can detect it, but just barely. Stöger and her colleagues say the hum varies in duration and contains a rich combination of notes.
Giraffes have a structured social system, but scientists don’t know much about how they communicate, according to Meredith Bashaw at the Franklin & Marshall College in Lancaster, Pennsylvania. “This new vocalization could add a piece to that puzzle. ... It could be passively produced—like snoring—or produced during a dream-like state—like humans talking or dogs barking in their sleep,” she says. But she indicated that it could also be a method of low-granularity information for giraffes to use in the dark, when vision is limited, as if to say, “Hey, I’m here.” There’s still information to be collected about the behaviors accompanying the humming. But it wouldn’t be too unexpected if the humming is used to transmit information about age, gender, sexual arousal, dominance, or reproductive states, Bashaw said.
John Doherty at Queen’s University Belfast, who studies giraffes in Samburu Reserve in northern Kenya, has come across similar vocalizations, “in a captive giraffe. ... But, in this case, [the giraffe] was clearly disturbed by a husbandry procedure being carried out on its calf in a separate but visible enclosure.”
Interestingly, last year residents of Paignton in southwest England complained of a humming or droning noise coming from the giraffe house at night: “I am very tired. The noise is still there,” said one resident. “I am being disturbed in the night and am being kept awake by this.” For her part, Stöger doubts that the complainants were actually hearing giraffes: “The giraffe signals are not so intensive. I personally doubt that neighbors would hear that,” she said.
After the jump, giraffe humming!
