“I was fascinated, because these signal have a very interesting sound and have a complex acoustic structure, she says.
The “hum” turned out to be a low frequency sound, of about 92 Hz. That’s not infrasound – we can still just about hear it with our ears. Stöger and her colleagues say the hum varies in duration and contains a rich combination of notes.
Giraffes have a socially structured system, and for a long time scientists have been trying to figure out how they communicate, says Meredith Bashaw at the Franklin & Marshall College in Lancaster, Pennsylvania. “This new vocalisation could add a piece to that puzzle,” she says.
Bashaw says she can imagine a few potential roles for this humming. “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. Alternatively, it could be a way for giraffes to communicate with each other in the dark, when vision is limited, to say, “hey, I’m here”, she adds.
Unfortunately, Stöger says she and her colleagues were not able to actually observe the giraffes mid-hum, so we don’t know about the behaviours associated with the sounds. But vocalisations in other species with similar social structure is known to convey information about things like age, gender, sexual arousal, dominance, or reproductive states, she says.