They don't oink, moo or roar. But new research suggests perhaps giraffes do have a distinct sound: They hum. It was previously believed that giraffes may make sounds that are impossible for humans to hear, similar to elephants, but the new research suggests otherwise.

Are giraffes vocal?

Giraffes do have a larynx (voice box), but perhaps they couldn't produce sufficient airflow through their 13-foot long (4 meter) trachea to vibrate their vocal folds and make noises. The researchers suspected the reason no one heard giraffe communication was because the sound frequency was too low for humans to hear.

Do giraffes hum?

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.