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New Study: Giraffes Hum... but Only at Night

November 10, 2015

Story at-a-glance

  • Researchers reviewing sound recordings from three European zoos picked up a low-frequency humming sound from the giraffes
  • Made only at night, the humming noises registered at about 92 hertz, which is just high enough for humans to hear unaided
  • A rich combination of notes and varying durations of humming were recorded
  • The humming could be a passively produced sound, like snoring, but it might also be a method of giraffe communication used primarily at night when visibility is limited

By Dr. Becker

Most schoolchildren can quickly call out the sounds made by a horse, monkey, or lion… but what about a giraffe? Even adults are left stumped by the question, "What does a giraffe sound like?"

If you've ever been within earshot of a giraffe, you may have heard an occasional snort, but other than that, these gentle giants appear exceptionally quiet. Yet, it's known they are social animals, which means they're communicating with each other – whether we can hear it or not.

What Types of Sounds Are Giraffes Capable of Producing?

Researchers have long puzzled over the way in whichgiraffes communicate. It's been suggested that due to their long necks, they might have difficulty producing enough airflow velocity to induce vocal fold vibrations. However, it's known the animals are capable of producing sounds. As reported in BMC Research:1

"Giraffes do not seem to use vocalizations regularly, but they have further been (anecdotally) described to, 'bleat,' 'brrr,' 'burst,' 'cough,' 'growl,' 'grunt,' 'low moan,' 'moo,' 'sneeze,' 'snore,' or 'snort.'

The snort seems to be the most commonly heard vocalization and has been documented in varying contexts such as being alarmed, annoyed, or when approaching each other.

Snorts and bursts are broad-band signals with no harmonic structure (and thus no measurable fundamental frequency); they seem to be produced by a sudden burst of air out of the nostrils."

It's also been suggested that giraffes communicate using infrasonic vocalizations, which are similar to low frequency infrasonic "rumbles" produced by elephants. However, there is no clear evidence that giraffes use such signals to directly communicate with each other. BMC Research continued:2

"Acoustic communication describes the interchange of information between at least two individuals, where an acoustic signal (typically a vocalization) is being directly transmitted from a sender and perceived by a receiver, that alters the behavior of the communicating animals.

Although grunts and snorts are produced in agonistic interactions, from personal observation of a grunting adult female giraffe… it is unclear what role the acoustic signals play compared to the visual, tactile, and olfactory cues."

New Study: Giraffes Hum at Night…

Researchers from the University of Vienna, Austria, reviewed nearly 1,000 hours of sound recordings from three European zoos. While they found no evidence of infrasonic communication, they did pick up a low frequency humming sound from the giraffes at all three zoos.

Made only at night, the humming noises registered at about 92 hertz, which is just high enough for humans to hear unaided. A rich combination of notes and varying durations of humming were recorded.

It's possible the humming could be a passively produced sound, like snoring or talking in your sleep, but it might also be a method of giraffe communication, perhaps used mostly at night when visibility is limited. According to the study:3

"Interestingly, these vocalizations have so far been recorded only at night. Even giraffe keepers and zoo managers stated that they have never heard these vocalizations before. Anatomical investigations indicate that giraffes have excellent vision with potentially long-range visual acuity, which would provide a means of communication between widely separated conspecifics.

Recent social behavior research has shown that giraffes spend a significant portion of their vigilance towards social partners, suggesting that perception and utilization of visual communication cues are highly developed in the giraffe communication system. Giraffes might use vocalizations more often once vision is limited (e.g. at night time).

… 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."

No Two Giraffes Have the Same Pattern – and Other Fascinating Giraffe Facts

Giraffes, the world's tallest mammals, may reach 14 to 19 feet in height and up to 2,800 pounds in weight. Their long necks give them a unique advantage in spotting predators at a great distance as well as allow them to feast on leaves from treetops that other animals can't reach.

Its height can also be an encumbrance, especially when taking a drink. In order to reach a watering hole, giraffes must spread their legs wide and bend down awkwardly, making them vulnerable to predators. Fortunately, these animals drink water only once every several days, relying instead on the water in plants for most of their hydration needs.4

Also intriguing, while giraffes living in the same area have similar spotted coats, no two giraffes have exactly the same pattern. They're also remarkable in the way they give birth – standing up. This means their young fall more than five feet to the ground at birth but are standing up within 30 minutes and running within 10 hours.

As adults, giraffes can gallop at up to 35 miles per hour, which is useful when trying to escape predators. However, they also have a powerful kick – strong enough to kill a lion. Male giraffes may also battle with one another by butting their necks and heads. These displays don't typically result in injury and end when one animal gives up and walks away.5

Aside from predators like lions and crocodiles, giraffes are also threatened by humans. The animals are hunted for their hides and meat, and sometimes only for their tails, which are used as good-luck bracelets, fly whisks, thread, and more. Unfortunately, the animals make easy targets for poachers.

Giraffe habitat is also being threatened by agriculture, settlement expansions, and the construction of roads. As acacia trees, which are giraffes' main food source, are destroyed, wild giraffe habitat and populations in the wild are shrinking.

Organizations like the African Wildlife Foundation are working with local communities to implement sustainable practices for agricultural and settlement growth. They're also working on reforestation projects in West Africa to plant more acacia trees and allow giraffes to expand their habitats.6

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Sources and References

  • 1, 2, 3 BMC Research Notes 2015, 8:425
  • 4, 5 National Geographic, Giraffes
  • 6 African Wildlife Foundation, Giraffes
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