Nocturnal “humming” vocalizations: adding a piece to the puzzle of giraffe vocal communication

Giraffes hum at night. These are sustained, low sounds, quite different from the brief snorts that people sometimes hear. For an animal often treated as nearly silent, that opens an intriguing possibility: its voice may have escaped notice partly because people were listening at the wrong time.

Anton Baotic, Florian Sicks and Angela S. Stoeger examined more than 947 hours of recordings from giraffes in zoos in Berlin, Copenhagen and Vienna. Most recordings were made overnight inside the giraffe houses; daytime recordings came from outdoor enclosures. The equipment could capture sounds below human hearing, allowing the team to investigate the suggestion that giraffes communicate through extremely low-frequency calls.

They identified sixty-five hums, all in the night recordings, lasting from less than half a second to just over four seconds. The sounds contained multiple related frequencies and averaged about 92 hertz, above the range classed as infrasound. Without night-time video, the researchers could not identify each caller or determine whether another giraffe responded. Humming might help animals keep contact, but that remains an explanation to test. What the recordings establish is simpler and still striking: giraffes have a sustained nocturnal voice.