You probably didn't expect giraffes to sound like this

It has long been thought that giraffes, in contrast to, say, lions, were silent. But research published this month in the journal BioMed Central, suggests the opposite.

The study, conducted by researchers at the University of Vienna and the Berlin Tierpark and examining zoos across Germany and Denmark, appears to indicate that giraffes create “harmonic, sustained and frequency-modulated ‘humming’ vocalizations during night recordings.”They came to this conclusion after recording over 940 hours of sounds from giraffes at three zoos over an eight-year period, which was then determined to be 92Hz in frequency. This range is quite low, barely able for humans to hear, which may account for why zookeepers were previously unaware of the sounds.

You can listen to examples of the giraffes' vocalizationshere andhere.

The humming – which the scientists describe as a “deep and sustained sound” – is far more varied than previously thought for the giraffe species.

“I was fascinated, because these signals have a very interesting sound and have a complex acoustic structure,” co-author Angela Stoeger told New Scientist.

Giraffes have been known to make some small noises, which the study describes as “bleating,” quiet “mooing,” or even “coughing.”

But these study’s findings indicate that giraffes do, in fact, use sound to communicate with one another, beyond these short bursts recorded by zookeepers. These humming noises both reaffirm social allegiance in the small, solitary groups of which giraffes are frequently a part, and are used to signal changes within that social order.

Of particular interest to the researchers was that the majority of the sounds were frequently produced at night. Due to the isolation of the individual giraffes studied at the three different zoos in the study, the researchers speculated:

“Although we cannot provide behavioral data, we would like to note that at all 3 zoos all giraffes [were] kept under similar housing conditions during night times. 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.”

This social structure is similar to that found in chimpanzees or African buffaloes, who, although they congregate in larger herds than giraffes do, also use complex vocalizations to both affirm and re-establish bonds among their peers.

The researcher’s findings contradict the notion that giraffes, because of their unusual height and build, rely purely on visual cues for communicating with one another and removing themselves from danger. This knowledge could be helpful to conservationists, who might be able to do more for the species in the wild if they are able to understand when, how, and why they give non-visual cues.

The Giraffe Conservation Foundation estimates that there are fewer than 80,000 giraffes left in the wild, across all giraffe subspecies. Current conservation efforts are targeted at informing the public, collecting accurate data, and educating local populations about sustainability.