Much like the fox, there’s one sound no one knows: what does a giraffe say? In the many years we’ve been observing these long-necked animals in the wild and in zoos, we almost never hear them piping up.
Apparently, we just haven’t been listening right. Scientists previously speculated that giraffe tracheas (wind pipes) might be too long to force their vocal cords to vibrate, or perhaps the animals made noises too low for humans to hear, similar to the infrasonic “rumbles” elephants produce to communicate over long distances.
But it turns out giraffes do vocalise, just not how we previously thought. A dedicated group of biologists with enormous patience just had to listen to giraffes long enough to find that out.
And? Giraffes hum, actually. But only at night.
This shouldn’t really come as a surprise. The occasional grunt or snort aside, giraffes should – in theory – be able to make sounds beyond blowing air through their nose. After all, within that famously long neck, they have what is needed to produce sound: a sufficiently developed larynx (voice box) and the necessary nerves connecting to it. The hardware is in place.
Thanks to long-term studies, we now also know that giraffes live in the sort of socially complex herds where a good system of vocal communication comes in handy, much like African elephants and chimpanzees. Living in groups based on family connections and sex means individual members often use specific calls to keep in touch after being separated by distance or time.
It’s like calling your mom after a week or telling your buddy, “Hey, it’s me. I’m here. What’s up?” Communication can reaffirm those bonds, which is why we see it in so many social animals.
Knowing all of this, Anton Baotic and his colleagues at the University of Vienna and Berlin Tierpark (a zoo in Germany) wanted to set the record straight about giraffe acoustics.
To do that, they placed advanced recording systems in the giraffe enclosures at three European zoos, tuning in on the animals outdoors during the day and indoors at night. The researchers also filmed the animals during daytime hours to observe interactions and behaviours that might correspond with any sounds the giraffes made (in retrospect, Baotic and his team are probably wishing they'd used night-vision cameras to capture what happened when the lights were out).
After what turned out to be a “time consuming, tedious and very challenging” endeavour, involving listening to more than 900 hours of audio recordings and then visually examining spectrograms of the most promising results, the researchers found the elusive call of the giraffe comes only at night.
At two of the zoos, the giraffes produced a low-frequency humming in the middle of the night, while the other zoo’s giraffes hummed around two hours before sunrise (no other animals were housed with the giraffes during this experiment).
While darkness prevented the team from confirming which giraffes were doing the humming and in what sorts of situations, Baotic did point out that the hums emerged when the animals were away in their stalls for the night, so the humming "might allow a giraffe to keep in touch with [others] acoustically when vision is limited and they cannot see each other".
Giraffes actually have excellent vision, which comes in handy for evading potential predators like lions. But what happens when the sun goes down and the big cats can still see you, but you can't see them? This could be where the night-time humming comes in to help herds stay safely together.
“For years, giraffes have been ... thought to be almost ‘mute’,” says Baotic. “[But] we are confident that they do use vocalizations to communicate with each other.”
Top header image: Marion Wacker, Flickr
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