World-first recordings finally reveal the sound made by the world's largest and most reclusive chorister: the Antarctic blue whale. Pop on some headphones to experience sounds that 'you feel as much as you hear'.
The Antarctic blue whale was almost hunted to extinction.
Over 30 years of surveys starting in the 1970s, the International Whaling Commission only spotted around 300 individuals.
The world's largest animals were targeted because of their size, but whalers probably didn't realise that even as they were chasing and killing these immense beasts, the animals would have been singing.
That's because the song of the Antarctic blue whale is mostly infrasonic; you may not be able to hear the first, untreated recording even on headphones.
'They're closer to the type of seismic sounds that come from earthquakes than they are to sounds that humans are good at hearing,' says Dr Brian Miller. Miller is an acoustician with the Australian Antarctic Division, and he recorded these sounds in the Southern Ocean around Antarctica.
'You feel it as much as you hear it.'
This particular call's highest pitch point is 86Hz, and it then stretches well below where any of us might be able to sense it, at least with our ears.
These whale songs can be heard over hundreds?if not thousands?of kilometres under water. If we raise that same sample of whale song up 10 semitones, you start to get an idea of its power:
Physiologically speaking, scientists are stumped as to how these sounds are produced.
'We don't really know with a lot of certainty how any of the baleen whales produce their vocalisations,' says Miller.
'Getting evidence for how whales produce their sound has proven quite tricky. Most scientists believe that these sounds are produced by whales shifting air around within their bodies. But it's not clear whether or not they're using structures that are anatomically similar to vocal chords, or some other mechanism.'
It makes sense that Antarctic blue whales would produce some of the lowest sounds emitted by any animal on earth, because, of all the blue whales, they're the biggest.
Let's raise that same whale song another ten semitones. Now, at about two octaves above its original pitch, you start to get a feel for the immense vibrations and pulses that these whales push out through the water.
Miller says that when a whale starts a song call, it will hum the same tune for a long period of time.
'We're not entirely sure how long an individual whale will sing that song for, but what we have discovered is that Antarctic blue whales tend to aggregate into denser clusters of whales that are all inhabiting a particular area. In these aggregations of whales, the songs seem to be produced continually.'
Early in 2015, on the Australia-New Zealand Antarctic Ecosystem Voyage, Miller used a specially developed sonobuoy?a floating microphone array?to listen for the sounds of Antarctic blue whales.
From the distant calls he recorded, Miller could work out where the whales were. The course of the ship could then be altered so that behavioural, identification and DNA studies could be undertaken.
Using this new technique, Miller and his team were able to guide the NZ research vessel Tangaroa towards a group of over 80 whales.
If whales can be said to sing, the sound of a group is something like a leviathan symphony:
These vocal aggregations might be spread out over a hundred or more square kilometres, but that's a relatively small space for these immense animals, which measure over 30 meters in length.
'Sometimes, we couldn't see the base of the blow because it was actually beyond the horizon,' says Dr Mike Double from the Australian Antarctic Division.
The whales occasionally come together into even more dense groupings within the wider aggregation, visible to spotters on the ship's open decks.
'It was like hitting the jackpot,' says whale geneticist and spotter Natalie Schmitt, who saw them feeding and even breaching.
'When you get close to a blue whale and it blows next to you, because it's feeding down there, the blow smells like fish. Whenever I go into a fish market or I smell fish I'm brought back to that moment when I'm on the bow of the ship and a blue whale has just blown next to me,' says Schmitt.
'It's such a sight to behold and such a rare privilege.'