How whales evolved to sing

The sound of whalesong can be a source of great relaxation for many, but the way that these giants of the deep produced such alien noises has long been a mystery. Until now.

Will - In 1970, a sound very similar to this one was recorded by Katie and Roger Payne for the first time. < Whale Song > The revelation that whales create such diverse and beautiful calls proved that these giants were not just hunks of meat to kill and eat, but intelligent and complex beings. But these calls aren't the only kind of calls whales can make. A lot of whale calls sound more like this < Deep, low rumbling > and a large vocal range is pretty essential to whale survival. As the University of Southern Denmark's Coen Elemens explains.

Coen - Communication by sound is really important for actually all whales. And that is because if you're imagining being out in the open ocean and you would drop into the water, there is no way you can communicate with vision and sound is the only means where you can communicate over very large distances. And if they can't find each other, they can't mate. So it's really important they're able to find each other and they do this by using sound.

Will - And despite anyone that's ever listened to a self help CD being aware of whale song, up until now we simply didn't know how they did it. It's very hard to study an organism that when it dies, either sinks to the bottom of the sea or explodes on a beach. Us humans, we rely on our larynx and vocal cords to wobble air in the way we want to create noise. But about 50 million years ago, the whale's ancestor transitioned from land to water, and that brings with it a couple of challenges.

Coen - They had a huge problem because they now had to breathe in and out, huge volumes of air very rapidly. When you have vocal folds sitting in the way, then basically this really impedes the ability to breathe when they go to the surface. So what we found instead is that these animals have a big U-shaped cartilage sitting in their larynx, and that keeps their larynx basically open when they exhale and inhale these huge amounts of air within seconds.

Will - So that allowed them to breathe. But anyone that's ever tried to shout underwater with a traditional larynx will tell you the sound doesn't really carry across the hundreds of miles that whales need to keep in touch with one another.

Coen - What we see now is that these animals have evolved a structure that sits on the inside of the larynx and we best described as sort of a cushion. It's like a big chunk of fat with a muscle attached to it. And when they rotate this u-shaped cartilage against this cushion, then they're able to vibrate this cushion again with air. And that couples really well into the water. And it's these very low frequency sounds that are audible at large distances,

Will - A fascinating set of solutions. But they do come with limitations, which have been exposed by factors that millions of years of evolution really couldn't have foreseen.

Coen - This new mechanism we found is probably used by all the baleen whales and they're made for very low frequency calls. Using our experiments and combining this with computer simulations, we could estimate the range of frequencies these animals can make, but also what's the range of depth at which they can make these sounds? You can imagine if you take a balloon down on the water, it shrinks really rapidly because the air is compressing. And the same is happening with the air in the whale lungs. If you go deeper than let's say a hundred metres, there's just not enough air for these animals to make sound. And the other limit is the frequency range. So these animals can use this mechanism probably from like 20 or 10 Hz to about 300 Hz. And this frequency range and also the depth range from surface to hundred metres is where humans make most boating noise. So that means that the overlap of this noise greatly reduces the distance at which these animals can talk to each other.

Will - Marine noise from shipping and drilling and mining, once again rears its ugly head. The frequency of man-made noise drowns out whale conversation at the surface and the pressure at greater depth is too great for whales to produce strong enough sound. But now that we know the mechanism, is there anything we can do to keep the whales chatting?

Coen - I think we actually can do something about this. So people are aware of the noises we make in the ocean and there are laws being made to mitigate basically the sounds we make. And I hope what we now can contribute is to really say this is frequency ranges and depth ranges where these animals just cannot escape our noise. So we have to either find a way to make noise in other frequency bands or time it differently or maybe you can drive some innovations to change the sounds that boats make. This is very well possible. So I think now we have a good physiological line of evidence to show that these animals are not just able to sing higher because this will take evolutionary timescales and not human timescales.