We all know that dolphins use echolocation to hunt down fish for dinner - just like bats do to chase insects in the dark - but how they make those trademark clicks and squeaks has largely been a mystery.
Now, thanks to a newly created speech model, researchers might have finally figured out how they do it, and it all comes down to one thing: snot.
Previous research has shown that dolphins produce their clicky sounds inside their nasal passages, which lie right beneath their blowholes. Inside these passages, lumps of tissue called dorsal bursae smack together and vibrate to create the sounds, but that still doesn't explain how they achieve such high, odd-sounding pitches.
Since it’s difficult to examine this process in real-time - the lumps can bump together up to 1,000 times per second - biologist Aaron Thode from the Scripps Institution of Oceanography in San Diego set out to create a new model, basically a computer program, to see if he could simulate these strange sounds in the lab.
To create the simulation, Thode and his team - which consisted primarily of his father, Lester Thode, a retired researcher who previously worked at the Los Alamos National Laboratory - went about adapting a human vocal cord model to accurately reproduce the sounds a dolphin makes.
This process involved analysing the frequencies of dolphin clicks to see what needed to change inside the human model to produce them. In other words, since a human model already existed, Thode had to rework the entire thing to make it less human and way more dolphin.
Before we go any further, we need to first understand that there are two parts to a dolphin’s click: the bump and the ring. Basically, when a dolphin clicks, it creates a strange sounding tap followed by a longer, high-frequency ring (check out the video below to hear it in action). These two parts go hand-in-hand, and occur right after each other to various degrees - sometimes a long squeak with a slight bump, or vice versa.
According to Helen Thompson from Science News, the team went into the experiment with the assumption that the bump, which sounds a lot like a person clicking their tongue, was caused by the lumps of tissue smacking together. The ring, which is extremely high-pitched, was produced by these tissues pulling apart.
But during their study, the team couldn’t achieve the same high frequencies found in the dolphin clicks without coating the nasal passages in sticky mucus (read: snot). This suggests that, without snot, a dolphin wouldn’t be able to use echolocation nearly as effectively.
The findings have yet to be peer-reviewed, so until then, we have to treat them as preliminery. But if confirmed, this discovery would fill in a gap of knowledge that's been keeping researchers from understanding this mode of echolocation and communication for decades.
"It's harder than you might think to make loud, high frequency sounds," said Thode. "Wet, sticky surfaces could serve a purpose in this."
This hypothesis was backed up by the fact that team was able to produce off-sounding clicks when using small amounts of snot. These miss-clicks are often heard in nature, too, meaning that they are likely produced when dolphins are running low on nasal mucus. They were also able to reproduce the well-known whistle noise dolphins are known for with mucus, adding even more weight to the discovery.
Despite the success of the newly created model, Thode cautions that it's still a work in progress and needs further study to verify the results. The team plans on collecting more data from actual dolphins to make sure their model accurately predicts the sounds created naturally - specifically, if the model can create the sounds at the same rate of speed real dolphins do.
Hopefully, as the research continues, the findings will offer a new way for scientists to analyse how whales communicate so we can finally figure out if they’re bad-mouthing us or not.
The team’s findings were presented this week at the annual meeting of the Acoustical Society of America in Utah.