Humans are not alone in being able to switch vocal registers, shifting from a deep, mellow voice to a high-pitched falsetto. Many animals can do this too, new research shows. These registers serve different communicative purposes and are an evolutionary adaptation used to signal everything from strength to social status, the researchers say.
Until recently, scientists assumed that vocal registers were a uniquely human trait – closely linked to our ability to speak and sing.
People have three vocal registers. We speak in the ordinary register. Then there is a deeper register many people use when speaking in a serious tone. And finally, there is the falsetto register – the very high-pitched tones singers use when aiming for a birdlike trill.
These low and high tones are not part of a smooth continuum – they rely on distinct ways of using the vocal cords. Yodelling is an extreme and audible example of a register switch – from the ordinary register to falsetto and back again – and illustrates precisely the kind of vocal shifts that researchers have now observed in animals too.
“Yodeleiiiii yodeleiiiii!”
Even so, surprisingly little research has focused on how these three vocal registers are produced – or whether humans are even the only species capable of using them to form vowel-like sounds.
Now, for the first time, a new study published in Philosophical Transactions of the Royal Society B shows that many animals – far more than previously believed – have three distinct vocal registers, which they use in complex, context-dependent ways, just like humans do.
“There are very strong opinions about how vowels in these registers are formed and whether other animals are capable of using vocal registers,” explains a researcher behind the study, Coen Elemans, Associate Professor, University of Southern Denmark, Odense.
“In earlier work, we showed that toothed whales such as dolphins use three distinct registers – both for social communication and for highly precise echolocation. This functional use of register shifts is comparable to human speech and song. In this new study, we showed that vocal registers are far more widespread in the animal kingdom than we ever imagined.”
Many animals also change registers
Coen Elemans and human voice scientist Christian Herbst reviewed existing scientific literature to track down evidence of vocal register use across the animal kingdom.
Their review uncovered signs of register use in monkeys, dogs, songbirds, pigeons and even certain frog species – suggesting that the ability to shift vocal registers may be a common evolutionary strategy.
The evidence is stronger for some animals than for others.
Like humans, animals appear to use vocal registers to extend the range of frequencies they can produce.
“The only way to reach truly high frequencies is by switching registers. If you can shift register, you automatically expand your frequency range. We already know this is true for humans – but no one had really looked for it in animals before. And it turns out to be much more common than we thought,” says Coen Elemans.
Multiple registers give animals access to a broader emotional and signalling repertoire – from the high-pitched calls of babies to the deep, low sounds used to signal threat, strength or dominance.
“Pitch plays a big role in communication between, say, a mother and her offspring. It is particularly important for things like crying. On the other hand, deepening your voice signals strength and social rank. We know this from humans when we want to be taken seriously – and animals use the same strategy,” Coen Elemans explains.
How to examine vocal cords in animals
According to Coen Elemans, the transition between registers is fascinating in itself – not least because it involves more than just hitting higher notes.
This is not simply a matter of pitch. Each register relies on a fundamentally different way of using the vocal cords. For example, the technique people use for speaking will not produce falsetto tones.
This is why register shifts are often audibly marked: a clear jump in tone when moving from the speaking register to falsetto.
“Yodeleiiiii yodeleiiiii!”
However, trained singers can switch registers so smoothly that the shift cannot be heard at all. That is part of what makes them good singers.
“And it also means you cannot just listen to an animal’s voice and tell whether it is using multiple registers,” says Coen Elemans.
To prove that an animal is changing registers, researchers used high-speed video recordings to capture the movement of the vocal cords – often with sub-millimetre precision and in real time – while the animal was producing sound.
“It all happens in a matter of milliseconds,” notes Coen Elemans.
He adds that the study brings researchers a step closer to understanding how animals – and humans – communicate with sound and how these sounds are physically produced.
“The fascinating aspect is that both humans and animals use the same kind of register shift to create more complex sounds and more advanced communication,” he says.
The findings suggest that the foundation for sophisticated sound production – and perhaps even for language-like communication – may be more deeply rooted in nature than previously realised.
