Scientists so far used to think that giraffes, unlike other animals, are largely silent beasts, without any oink, moo or roar. But a recent study has suggested that perhaps giraffes do have a different sound: they hum.

Previously it was believed that giraffes probably make sounds that are impossible for humans to hear, alike elephants, but the latest study has suggested otherwise.

During the study, published in the journal BioMed Central, researchers recorded more than 940 hours of sounds from giraffes at three zoos over a course of eight-years. Beyond the rare snort or grunt, the researchers also recorded humming sounds that the giraffes made only during night. Wired reported that the humming was 92Hz in frequency, which human beings can hear but is pretty low.

The researchers concluded, “These results show that giraffes do produce vocalizations, which, based on their acoustic structure, might have the potential to function as communicative signals to convey information about the physical and motivational attributes of the caller”.

The researchers couldn't prove that the sound is used for communication, but they have discovered ‘suggestive hints’ that the hum could serve as a ‘contact call’, for instance to re-establish contact with herd mates. They have speculated that the hums probably occurred at night because giraffes' typically keen vision is less effective at that time.

Still a further study is needed to know if it’s possible that the giraffes used these noises to communicate with one another. The study should test in a well established experimental setting whether giraffes are more vocal in the absence of visual communication cues or not.