A male koala letting out a deep roar, as if he were huge. Or a chirping cheetah, which sounds like a harmless bird instead of a dangerous feline. The sound repertoire of animals is much larger than we usually think. This is partly because bioacoustics, the field that studies animal sounds, is in full development: new measuring instruments and research methods are still being developed. But there is another reason, emphasizes the Austrian animal behavior biologist Angela Stöger (1976), who specializes in bioacoustics. “We are simply not used to really listening to nature. We often think of animal sounds as background music rather than a form of communication. Especially when it concerns sounds that we are not familiar with.”
In her recently published book About singing mice and squeaking elephants Stöger reports on two decades of animal sound fieldwork, with matching sound fragments. If you want to hear the high-pitched squeaky guinea pig-like sounds elephants make, or the ngwèh-ngwèh cries of newly hatched Nile crocodiles, you can scan the QR codes scattered next to the text.
That koala roar in your book sounds imposing. Why does such an animal do that?
“Koala males don’t roar all year round, only when they’re ready to mate. Then they let out a call around 30 hertz, if you are standing in a eucalyptus forest that sounds very impressive. The low tone ensures that they can be heard over a long distance, but there is also a competitive element to it. Often male animals with a low voice also have more testosterone. The deeper the roar, the greater the attraction for females.
“A koala’s vocal cords are much too small to produce that deep sound. But two British biologists have unraveled the secret: the folds of the soft palate, near the throat, are exceptionally large. When you inhale, the skin folds tighten, so that they can vibrate as if they were also vocal cords.”
In 2005 I accidentally discovered that an African elephant in the zoo also squeaked
You do a lot of research on elephants. What sound do they make?
“They cover a very wide repertoire, from a barely audible rumble around 20 hertz to high guinea pig-like squeaks. They make those lowest tones with the help of their trunk. It is infrasound, felt rather than heard, like the tremors of an earthquake. This allows them to communicate with each other over miles away.
“The high-pitched beeps let elephants hear when they are excited about something, for better or for worse. That squeak can be around 2,000 hertz, which is impossible for their 15-centimeter-long vocal cords. They do it by vibrating their lips, like trumpet players.
“Initially, that high-pitched sound was mainly known from Asian elephants, but in 2005 I accidentally discovered that an African elephant in the zoo also squeaked. He turned out to mimic that behavior of two Asian female elephants with whom he lived for years. And the Asian elephants among themselves often seem to learn the squeak from family members. Elephants, like humans, are therefore capable of learning a vocal repertoire.”
Some bird species adapt their song to the background noise, for example by singing higher
Is animal language similar to human language?
“The linguist Noam Chomsky defined language as the biological characteristic of living beings. Just like us, animals produce sounds to communicate with each other, with or without their vocal cords. Human language is unique in the way we developed and use it, but you can say the same about many animal languages. Different species have different skills. We are good at combining sounds and giving them meaning. But we cannot, like elephants, communicate with relatives miles away without technological aids. Or catch mosquitoes with our voice, like bats do.”
Read about language in cows: ‘What this cow wants to ask me now is in fact: Who are you?’
What don’t we know about animal noise?
“Wow, so much. We do not yet know the vocal repertoire of many species at all. And take that chirping cheetah. We have no idea why it sounds like a bird. Perhaps it is a form of acoustic mimicry, imitating another species on purpose to protect itself from enemy lions. But more research is really needed.
“We also know little about sounds made by insects or amphibians. And perhaps some sounds are simply not yet audible with the current measuring equipment.”
What would the ideal sound recorder look like?
“A combination of GPS, sound and video would be the best, so you can see who is making what sound and when. But at least as important is the development of good algorithms to analyze the sound. You could also use noise monitoring as an early warning system to prevent conflicts between people and wild animals. If you hear that a herd of elephants is approaching, villagers may be able to get to safety in time.”
I wanted to investigate how noise pollution affects marine mammals
Do animals suffer from noise pollution?
“Absolute. First of all, they have to communicate louder to make themselves audible, and that takes energy. Some bird species adjust their song to the background noise, for example by singing higher or at a different time. Or they leave for another area. It is also known that mammals adjust their activities to the amount of noise. But not all animal groups are so flexible.
“And the worst thing is: noise is everywhere. From oceans to safari parks, there’s no escaping it. There is still far too little attention to noise pollution. Underwater, animals can be thrown off course by low noise from container ships. And it is already known from northern countries that wolves and reindeer move away when windmills are erected. Animals don’t have noise-canceling headphones with which they can simply shut out sound.”
Which animal sound is still on your wish list?
“That of manatees! They are closely related to elephants. As a child I was fascinated by marine mammals. I grew up with the TV documentaries of marine biologist Hans Hass, a kind of Austrian Jacques Cousteau, and by the age of ten I knew all the names of whales by heart. It was in the 1980s, scientists had just discovered that whales could sing. Fascinating.
“During my studies I chose all marine biology subjects, even though I live in a country that is four hours away from the nearest sea. I wanted to investigate how noise pollution affects marine mammals. But then a professor came along and asked if I wanted to do research into the bioacoustics of elephants. At first I thought they were big, gray and boring, but soon I closed them in my heart.”