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WASHINGTON (CBSDC) — They say late at night you can hear the mournful call of the giraffes.

Once the sun sets, the long-necked creatures hum an eerie tune, that is described as like the sound of a creaking ship.

Scientists made this discovery by recording the sounds 22 different giraffes made at three European zoos.

In the audio, the animals produced “a low-frequency vocalization with a rich harmonic structure and of varying duration,” according to a new study.

“The acoustic structure is interesting, and might indicate that it is a communicative signal,” senior author Angela Stoeger, the head of the mammal communication lab at the University of Vienna, told LiveScience. “But future research will have to verify this idea.”

Biologists really don’t know much about how giraffes use sound to communicate.

The animals are often heard snorting or grunting, but it’s not clear whether the giraffes are trying to say something or just making noise.

“There have been suggestions that the giraffe’s long neck makes vocalization physically impossible, due to the difficulty of sustaining the required airflow from lungs to mouth over such a distance,” Stoeger explained.

The researchers say more work is needed to find out what the giraffes may be saying to each other.

No word on when we might know what the fox says.

The study was published in the journal BMC Research Notes