UPDATED (2-Oct 2015) See below.
The world is full of strange sounds.
Back in August 2014, I linked to a news blip in the Strange Remains, about residents near a zoo in the UK who petitioned the Paignton zoo to soundproof the giraffe area. They complained about a humming or droning noise that kept them awake at night. One local, Mr. Thorne said, “I am very tired. The noise is still there. I am being disturbed in the night and am being kept awake by this. It is a humming or droning noise that at times it can be quite loud. It has been going on since October/November since last year.”
At the time, they thought it was the oil burner in the giraffe area making the noise. The zoo officials denied the sound was coming from there since the boiler had been turned off. The zoo tried to work with the residents but could not locate or determine the source of the sound.
Well, sometimes reports of anomalies lead to very strange findings. It wasn’t the boiler, it was the GIRAFFES.
Giraffes snort and grunt sometimes. It was also thought (but not confirmed) that they communicate in infrasound, at frequencies too low for us to hear. But there was not much known about giraffe auditory capability or communication. They have a larynx but it was not clear how it was used since the neck is so long. To study sounds (not from an identified subject), it takes systematic and careful recording setups, not easy to do. This is what makes it so difficult to pin down a sound that people report hearing, especially if it’s a one-off sound.
Animals with strong social bonds must communicate. And, other Artiodactyla animals are vocal (cattle, pigs, camels, goats, sheep, hippos, deer, antelope). Zookeepers found it highly unusual that mother giraffes made no sound toward their young. There was reason to suspect giraffes might make some noise so it was speculated that it was infrasound frequency. While giraffes have excellent vision from a nice high perch, at night, they lose the visuals.
Researchers (Anton Baotic, Florian Sicks and Angela S. Stoeger) from the University of Vienna and the Berlin Tierpark zoo collected over 947 hours of audio from three European zoos (Berlin Tierpark in Germany, Copenhagen Zoo in Denmark and Vienna Zoo, Austria) and analyzed the data.
They found the usual burst, snorts and grunts sounds but also found “harmonic, sustained and frequency-modulated “humming” vocalizations during night recordings.
None of the recorded vocalizations were within the infrasonic range.” That’s a surprise! They could be HEARD by people.
The suggestion is that the giraffe “hum” may function as a contact call to re-establish contact with herd mates. When they played these noises back to the zookeepers, they’d never heard them! Take a listen:
It sounds like an animal sound or someone snoring in the distance. We can imagine how it might be disconcerting to people who don’t know what it might be. Plus, we aren’t clear how FAR it travels. So, people not living all that close to zoos may perceive it at night.
The sounds were described as follows:
Hums were rich in harmonic structure, having a deep and sustained sound with an average fundamental frequency of 92.01 ± 25.78 Hz. Minimum frequencies went down to 35.01 Hz and hums ranged from a minimum length of 0.41 s to a maximum of 4.17 s. This call type was recorded only during the nocturnal recording sessions.
Download sound file: Giraffe night sounds
The researchers still did not confirm that the animals communicate in infrasound (remember they LOOKED at the signal patterns of the sound recordings and did not find any infrasound frequencies). But it was confirmed that it was indeed giraffes making these low frequency hums. Note that this is in a zoo environment. It’s not clear how giraffes communicate in the wild.
Having to VISUALLY inspect sound wave patterns from over 900 hours of recordings, obviously, the researchers report that the work was “time consuming, tedious and very challenging”.(1) But it DID produce important results. Many top news outlets covered the story. I wonder if the folks at near the Paignton Zoo know about this?
Full text is here:
Recent research reveals that giraffes (Giraffa camelopardalis sp.) exhibit a socially structured, fission–fusion system. In other species possessing this kind of society, information exchange is important and vocal communication is usually well developed. But is this true for giraffes? Giraffes are known to produce sounds, but there is no evidence that they use vocalizations for communication. Reports on giraffe vocalizations are mainly anecdotal and the missing acoustic descriptions make it difficult to establish a call nomenclature. Despite inconclusive evidence to date, it is widely assumed that giraffes produce infrasonic vocalizations similar to elephants. In order to initiate a more detailed investigation of the vocal communication in giraffes, we collected data of captive individuals during day and night. We particularly focussed on detecting tonal, infrasonic or sustained vocalizations.
With regards to the variety of strange sounds reported all over the world, we can now add “giraffes”!
1. Like ghost hunters listening to all their “EVP” recordings. But in this case, there was actually something sustained and physical to find. Recording random noises and pointing out anomalies is NOT doing science. Notice how much more difficult the scientific-based giraffe work was! The researcher had to be sure to isolate the variable. That is, they had to work to insure that it really WAS the giraffes making the noise and nothing else.
Thanks to tip from B Jessee!
UPDATE: The Torquay Herald Express took my advice and followed up on their story about the Paignton Zoo. But, the zoo officials say it’s a nonstarter idea:
[…] we can see no link between this research and reports of a sound effecting a neighbour last year.
“We are aware that elements of the media are linking the two in a fairly light-hearted fashion, but we need to be clear that there is no such link.
In over 900 hours of recordings, none of which was made at Paignton Zoo, the scientists found just 65 giraffe hums.
Well, granted, we are not given the whole story in the media about the Paignton incident so it could be totally different but the report on giraffes making such noises is not spurious. They were captive giraffes at 3 zoos. It’s not unreasonable to extrapolate that all zoo giraffes do this. Also, I do not see that they found an alternative answer to the mysterious noise. So, we are left with nothing.