Finally, the theory that giraffes are silent giants can be overturned. Scientists have discovered that they communicate by more than just body language- they also hum.
A study recently published in BMC Research Notes details the new insights about giraffe vocal communication. A team of researchers from Austria and Germany collected over 1000 hours of audio from giraffes held in captivity at three different European zoos.
Although they recorded several instances of mothers calling to their young calves, hardly any other noise was detected.
“Although giraffes do have a well-developed larynx and laryngeal nerves, it was long suggested that due to the long neck, giraffes might have problems to produce an air-flow of sufficient velocity to induce self-sustained vocal fold vibrations,” said study co-author Angela Stoeger of the University of Vienna.
The team was about to call it quits when the realized something peculiar. As the sun began to set and the stars began to shine, the giraffes began to hum.
“Interestingly, these vocalizations have so far been recorded only at night,” said Stoeger. “Even giraffe keepers and zoo managers stated that they have never heard these vocalizations before.”
The team has not yet determined the purpose of the humming. Perhaps it is to reassure one another that they are still nearby when it is dark out? Or perhaps it is a more joyful expression.
“The image of our giraffes humming happily to themselves all night is a delightful one,” said Stoeger.
A long-held explanation for giraffe silence is that it occurs on especially low frequency or infrasound. But this was not the case. Humans can hear the humming, just with great difficulty. The humming occurred at approximately 92 Hz, a very low decibel.
That is not to say no one has ever heard this humming before. Residents living near the Paignton Zoo in England have frequently complained of a low frequency noise coming from the giraffe house at night.
“It is a humming or droning noise that at times it can be quite loud,” said one resident, Peter Thorne, “I am very tired. I am being disturbed in the night and am being kept awake by this.”