Giraffes hum to each other, but only at night, study reveals

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RIGHT: The alpha male giraffe (middle) keeps watch over his female and her calf.
RIGHT: The alpha male giraffe (middle) keeps watch over his female and her calf.

A lion roars, a dog barks, and an elephant trumpets. But what noise does a giraffe make?

While many people may be perplexed at this question, because they’ve never heard a giraffe make a distinguishable vocal noise from its long neck, a research paper revealed that giraffes do in fact make sounds to each other at night.

And, the scientists who studied the communication of these graceful African mammals, believe the sounds they make, may “have the potential to function as communicative signals to convey information about the physical and motivational attributes of the caller”.

The study, by scientists at the University of Vienna, cautioned however that this requires further investigations in future studies.

“We detected harmonic, sustained and frequency-modulated ‘humming’ vocalisations during night recordings.”
Research by the University of Vienna

The study said giraffes are known to produce sounds, but there is no evidence that they use vocalizations for communication.

It is widely assumed that giraffes can produce sounds inaudible to humans, similar to elephants. The team collected almost 1000 hours of recordings of giraffe at three European zoos, and on analysing it, they found something besides the “known burst, snorts and grunts”.

“We detected harmonic, sustained and frequency-modulated ‘humming’ vocalisations during night recordings.

 “Important vocalisation types include long-distance contact calls that convey individual identity as well as vocalisations to confirm and strengthen social bonding when reunited after temporary separation.

“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.

“Notwithstanding, giraffes are, in principle, capable of producing sounds. On YouTube there is a video of a newborn calf at a zoo emitting loud bellows while being restrained by keepers to examine its health state. Giraffes do not seem to use vocalizations regularly, but they have further been (anecdotally) described to, ‘bleat’, ‘brrr’, ‘burst, ‘cough, ‘growl’, ‘grunt’, ‘low’ ‘moan’, ‘moo, ‘sneeze’, ‘snore’ or ‘snort’,” said the scientists in a report on the study.

But the study had its challenges.

“As expected, exploring giraffe vocal communication turned out to be time consuming, tedious and very challenging.”

But they present data indicating that giraffes do produce “structurally interesting humming vocalisations apart from the short broadband snorts, bursts and grunting sounds. These hums, however, are apparently mainly produced at night.” And, they say, these humming vocalisations might be of communicative relevance.

The scientists recorded 65 humming vocalisations: 34 hums at Berlin Tierpark, 9 hums at Vienna Zoo, and 22 hums at Copenhagen Zoo.

“Interestingly, these vocalisations have so far been recorded only at night. Even giraffe keepers and zoo managers stated that they have never heard these vocalisations before.”
- Study by the University of Vienna

They described the hums as being “rich in harmonic structure, having a deep and sustained sound” and of varying duration.

“Although we could not identify the calling individuals, the giraffes definitely produced the recorded sounds because we documented similar vocalizations in three different institutions without any additional co-housing species.

“At Copenhagen Zoo, hums occurred approximately within two hours before sunrise, while at the other two zoos, hums occurred mainly in the middle of the night. These patterns might provide suggestive hints that in giraffe communication the ‘hum’ might function as a contact call, for example, to re-establish contact with herd mates.

“Nonetheless, the rich harmonic structure and the frequency modulation indicate that this type of vocalization has the potential to convey relevant information to receivers.

“Interestingly, these vocalisations have so far been recorded only at night. Even giraffe keepers and zoo managers stated that they have never heard these vocalisations before.”

They said anatomical investigations indicate that giraffes have excellent vision with potentially long-range visual acuity, which would provide a means of communication between widely separated giraffe.

“Recent social behaviour research has shown that giraffes spend a significant portion of their vigilance towards social partners, suggesting that perception and utilisation of visual communication cues are highly developed in the giraffe communication system. Giraffes might use vocalisations more often once vision is limited (e.g. at night time). Future studies should test in a well-established experimental setting whether giraffes are more vocal when visual communication cues are absent.”

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