Superlative

I’ll never forget that scream.

I’d been on a crowded plane that morning and an even more crowded bus that afternoon. Then it was the rusty bed of an old pickup truck. And then it was the bristly back of what seemed to be an even older donkey. As the sun set over the lowland forests of Ecuador’s Esmeraldas Province that night, I rolled out my one-person tent and slid into my sleeping bag.

And then it happened.

The guttural, gravelly roar of the Ecuadorian mantled howler is truly something to behold. It rises above all of the other noises of the forest and carries for miles. But I wasn’t miles away. I was right under it.

Despite that experience, I never really wondered what makes howlers so loud. I suppose I just figured that something had to be the loudest thing in the jungle, and howlers were it.

But Leslie Knapp sees the world in a different way. And thank goodness she does, because her search for answers as to what makes howlers so aurally extraordinary resulted in one of the most charmingly amusing research findings in the history of biology.

Knapp is a biological anthropologist whose main area of study is the major histocompatibility complex, the same part of the immune system that permits a cheetah to take a skin graft from virtually any other cheetah. Her focus, though, isn’t on cats but primates. Knapp studies how histocompatibility genes vary in monkeys, apes, and other simians, and how the diversity of those genes is generated and maintained.

Like me, Knapp had learned about the howler’s awe-inspiringly ear-splitting roar during her travels through Central and South America. But she noticed something I didn’t.

All of the howlers were loud. Really loud. The loudest land mammals in the world, by some estimates. But some species seemed even louder than others—and that didn’t seem to correlate to species size. Knapp wanted to find out why.

Her investigation quickly zeroed in on the howler’s hyoid bone, which works a bit like a megaphone to amplify its screech. The golden mantled howler, Alouatta palliata, has a hyoid that is just under one-half a cubic inch in volume; its call is among the quietest of its noisy brethren. The South American black howler, A. caraya, has a slightly bigger hyoid and thus a deeper, more booming call. The brown howler and Yucatan black howler, A. guariba and A. pigra, respectively, have even larger hyoids and louder calls. And, at nearly four cubic inches in volume, the hyoid of the Venezuelan red howler, A. seniculus, is the biggest of the bunch. It gives the red howler an exceptionally low, loud, and resonant roar, which it uses to show off, call out to potential mates, and try to scare away competitors.

There appears to be a rather substantial trade-off for a large hyoid, though: The red has really small testicles.

Now, because I know you’re probably asking: Yes, there is an established method to measure animal testes. It starts by using digital calipers to determine the length and width of each testicle. After that, it’s a simple matter of using the common formula to calculate the volume of a prolate sphere.¹ Then, to account for variability that exists between the left and right testes, both numbers are added together to get “total testicular volume.”

When Knapp plotted call volume against ball volume, she found the loudest monkey had the smallest testicles, at less than a quarter of a cubic inch in volume. The quietest had the biggest, at a hefty 1.4 cubic inches in volume. The rest fell right onto an inversely proportional plotline.

The loudest monkeys, it appeared, were compensating for something.

Monkeys with smaller testes produce less sperm. For that reason, Knapp figures, they have to work harder to pass along their genes—by getting the attention of more mates.

This was more than a clever, carnal finding. Knapp’s howler study was the first time scientists had seen an evolutionary trade-off between sexual physiology and vocal characteristics, and it has given other researchers another framework with which to understand the ways in which the making and processing of sounds—like the calls of the tiny bumblebee bats in Southeast Asia—can drive speciation. That’s informed additional studies on the evolution of mice, deer, dragon lizards, and frogs.

Knapp figures it might teach us something about us, too. Howlers and humans are evolutionarily close cousins, after all. When the study was released in 2015, Knapp said the research “helps us understand primate behavior, and that way, we can learn more about ourselves.”²

Take, for instance, our love for fast—and loud—cars.

There hasn’t been a lot of scientific research on “compensation cars.” But the year before the “calls and balls” study was published, a British car leasing company reported that it had asked more than 500 luxury and sports car owners—and their partners—some rather personal questions. The results were not flattering.³

To be fair, the survey’s sponsors don’t appear to have had a control group of men who drive quieter, less ostentatious vehicles. And more formal scientific inquiry on the subject tends to show that men are often quite generous in their self-assessments, likely regardless of what sort of car they drive. Even anonymous studies that rely on self-reported measurements, for instance, offer averages that are substantially bigger than those in which researchers get a little more hands-on.⁴ Alas, what we project is often different than what we offer. What the calls-and-balls study tells us, though, is that our inclination toward compensation might not just be the result of human culture. There might, in fact, be something deeper at work.

And that’s just the start of a cacophony of research related to how creatures that exist at—and well beyond—the limits of human hearing use the aural spectrum not only to communicate, but also to navigate, pursue prey, and evade capture.

HOW THE SIMPLE ACT OF LISTENING LED TO A ZOOLOGICAL REVOLUTION

As is the case with a lot of other superlatives, there’s no clear consensus on what creatures are the loudest in the world, because sound is created, transmitted, and perceived in many different ways. What we recognize as “loudness” is a combination of frequency, intensity, and duration. Howler monkeys often get record-holding billing because their cries fit nicely within humans’ range of perception for all three of those parameters. They roar at frequencies we can hear, with an intensity that makes our eardrums rumble, and for a long time. A very long time, as I came to learn the first night I camped in the Ecuadorian forest.

It wasn’t until quite recently that we paid much attention to animal-generated frequencies outside the human range of hearing, which begins at roughly 20 hertz and extends through about 20,000 hertz.⁵ That anthropocentric bias kept us from some rather basic revelations about our animal brethren, and for far longer than it should have.

Even those who had spent most of their lives with elephants, for instance, didn’t seem to realize the very narrow range of sounds we could hear weren’t the only ones the animals could make. And when that discovery did come, it came from someone who had only just begun listening to elephants.

For decades, biologist Katherine Payne had been working to record and analyze the sounds of humpback whales, resulting in the landmark discovery that whales “sing” to one another using complex refrains, evolving melodies, and even repeated patterns that resemble human rhymes.⁶ In the mid-1980s, a colleague from what was then known as the Washington Park Zoo asked Payne to come to Oregon to compare notes on megafauna. She could tell the zoo’s staff what she knew about humpbacks; they’d reciprocate with information about elephants. Intrigued, Payne was on a flight to Portland within a week.

Payne wasn’t content to just talk about elephants. She wanted to hear them, too. So she asked the zookeepers to give her some time to be in the presence of their largest charges. The keepers obliged, though not before offering a somber warning: Don’t get too close. “You’ll be noodles if they drag you through the bars,” one of the men warned.⁷

As soon as the keepers left, though, Payne found herself surrounded by thick, gray, wrinkled trunks, sniffing her clothes, feeling her shoulders, and meeting her eye to eye. To Payne, it seemed as though the elephants were trying to make it clear that she was welcome in their presence.

Payne left Oregon a week later, knowing she’d had an experience most folks could only dream about. But she didn’t think she’d seen or heard anything of scientific importance.

It wasn’t until she was midair, on the plane flight home, that it hit her. She’d had a nostalgic feeling, being in the presence of the elephants; it had been hauntingly reminiscent of her teenage years, when she sang in a Catholic choir while standing next to the pipes of the chapel organ. It was something deep and resonant, and by the time she had landed, she knew she needed to get back to Portland.

When she did, she came equipped with an infrasonic tape recorder. And when she sped up the recordings to make them audible to the human ear, the whole world changed.

These enormous animals, creatures we’d known for millennia—or thought we’d known, at least—were so much more complex than we had ever imagined. All along, we’d assumed the only sounds they were emitting were the ones we could hear. As a result, we figured they were mostly quiet beasts—trumpeting when alarmed, grunting a bit here and there when in the midst of something strenuous, but not particularly prone to chattiness. We now know the truth: Elephants are some of the world’s great talkers.

Payne’s further research in Africa confirmed elephants were communicating with one another all the time, at up to 90 decibels (that’s like standing next to an espresso maker when it’s churning out a chai latte)—but at frequencies humans can’t hear.⁸ And owing to the fact that very low frequencies can travel a lot farther than higher ones, they were communicating across great distances, chatting up fellow travelers across long stretches of savannah.

Once we knew how talkative elephants actually were, the floodgates burst open. We realized bull elephants announce they are in musth.⁹ We began to see the different roles that short- and long-distance communication play in the lives of these animals.¹⁰ We began to reassess the ways in which elephants had evolved.¹¹

The torrent of research that stemmed from Payne’s remarkable realization didn’t stop with elephants. It inspired other scientists to look for animal vocalizations that were outside the range of human hearing. That led to discoveries about whales,¹² cows,¹³ and rodents,¹⁴ which in turn led to research that has informed the ways in which we protect dolphins,¹⁵ care for farm animals,¹⁶ and model human depression, respectively.¹⁷

That latter work is particularly important for those with mental health challenges. The overwhelming majority of clinical medical research, including a lot of research aimed at better understanding the way our minds are impacted by our lives, is conducted with animal models. But for a long time, we weren’t even listening to all of the different frequencies lab animals use to communicate. Payne’s work prompted additional research into animal sounds that are outside human hearing, and that gave psychological researchers additional ways to understand the animals in their labs. That has led to a significantly improved capacity to understand mental health in lab rodents, which is vital for our understanding of human mental health.

The frustrating thing about all of this is that we really could have gotten to it sooner. At the point Payne began to suspect there was more to elephant communication than what we could hear, it had been more than 100 years since Francis Galton had proven, through the invention of something we now call a dog whistle, that animals can hear ultrasonic sounds.¹⁸ And it had been nearly a half century since a Harvard undergraduate named Donald Griffin brought a cage full of bats into the office of a professor who had developed a machine capable of detecting ultrasonic frequencies, revealing bats could not only hear but also speak in such tones.¹⁹ If very small animals can communicate above the level of human hearing, after all, it should have stood to reason large ones might be able to communicate below our range of perception. But once we’ve pigeonholed something, even something as big and loud as an elephant, it’s hard to break out of our assumptions.

Today we know elephants aren’t alone in their use of very low frequencies to communicate. In Africa, they share the infrasonic airwaves with hippos, rhinos, and giraffes. Out on the savannah, the sounds we can’t hear may actually be louder than those we can.

We also now know bats aren’t the only small mammals who use ultrasonic communication. Rodents of many species are chirping away at frequencies too high for our ears. Rats, for instance, produce a 22,000-hertz alarm call in dangerous situations, and also have a 50,000-hertz call they use in friendly encounters with other creatures²⁰—so high it’s even outside the range of hearing of most dogs.²¹

Those revelations have bolstered another assumption we long held about animal calls at the highest and lowest ends of the spectrum, but hadn’t tested: that an animal’s calling frequency generally correlated to its body size.

That’s what Kobe Martin thought. And the graduate researcher at Australia’s University of New South Wales told me she would have been perfectly happy to simply continue to accept the bigger-means-lower assumption as a scientific fact, if only there had been some bit of science to cite when she mentioned it in her research. But when she went to find a reference for that widely held principle, she came up empty.

“No one had sat down and looked at it in great detail,” she said. “There was this widely accepted concept that large mammals have low-pitched voices and small mammals have high-pitched voices. People had thought about it. But no one had thought to quantify it.”

That lack of research wasn’t just impacting our ability to understand the calls of other mammals. One of the things that distinguishes us as a species is the way we communicate. Understanding how our abilities to communicate evolved requires an understanding of how other mammals evolved to communicate. A lack of serious study, Martin said, left us unable to understand our place in the hertz-emitting hierarchy, and unable to so much as approach the question of why we speak and listen in the frequencies we can make and hear.

“When something is as big and widely assumed as this idea,” Martin said, “someone usually comes around and says, ‘Maybe we should test this.’”

And since no one had, she did. Martin and her team scoured the scientific literature for the minimum and maximum frequencies of every mammalian species they could find—nearly 200 of them in all. Then they plotted the frequencies of the animals’ calls against their body masses, just like the folks from EcoNetLab had done to arrive at their conclusions about how size impacts speed.

At first, everything was looking as expected. There were some outliers—“cheaters,” Martin calls them, like the howler monkey, which had evolved specialized equipment for making sounds deeper than their body size would typically allow.²² By and large, though, the trend was clear: The bigger the animal, the lower its calls.

Then Martin’s team got to the aquatic mammals. And that’s when the data went haywire.

The researchers knew, of course, that marine mammals like dolphins often have high-pitched calls. Martin said she expected, though, to see a parallel trend in which those calls got progressively lower as the animals got bigger, in line with what was happening with terrestrial mammals. And that would make a lot of sense in the vast ocean, she said, since bigger animals need more space, and low frequencies travel longer distances in the water.

That’s not what was happening, though. Some of the biggest animals, like the mighty baleen whales, were among the highest pitched. Some of the smallest, like the adorable eared seals, were among the lowest pitched.²³

It’s important to remember that aquatic mammals all evolved from animals that once lived on land. At one time in their evolutionary history, it can be assumed, all of these creatures were subject to the as-it-gets-bigger-its-voice-gets-deeper principle. But “it’s as if the ocean environment released these animals from that rule,” Martin said.

So, when it comes to sound, size matters. But environment matters even more. Size may be, as John Bonner suggested in Why Size Matters, the greatest driving force for all of biology, but it’s not always the force that drives every change.

Martin’s work demonstrated specific traits are often the result of an evolutionary game of roshambo.²⁴ Perhaps more importantly, though, her findings showed us, once again, that superlative outliers can do a great deal of damage to widely held assumptions about how the living world works. And if there’s one thing that really sparks great science, it’s the destruction of widely held assumptions.

WHY YOU CAN’T CALL EVERY NOISY CREATURE A LOUDMOUTH

We’ve known about the Micronecta scholtzi’s special talent for decades, but it has sort of been hidden in the research.

Back in 1989, a University of Helsinki zoologist named Antti Janssen published a report about the insect’s novel noisemaking. “The sound production of Micronecta,” Janssen wrote, “involves the rubbing of a ridged area of the basal processus of the right paramere (pars stridens) against one or two ridges (plectrum) located near the median edge inside the pocket formed by the left lobe of the eighth segment.”²⁵

OK then. Still awake?

I don’t begrudge scientists for writing like scientists. But science doesn’t have to be stodgy. It can be fun. It can be irreverent. It can be gross. And when you tell people that the rapid, noisy series of chirps they would hear if they were standing next to just about any pond in Europe are, in fact, the result of an insect that is rubbing its penis²⁶ against its ribbed belly . . . well, they tend to pay attention.

M. scholtzi’s booming wang has been recorded at about 99 decibels—as loud as a helicopter flying just 100 feet overhead.²⁷ Relative to its .07-inch length, this species of lesser water boatman is the loudest-known animal in the world.²⁸

This is more than just a funny superlative fact. It’s an avenue for opening eyes (and ears) to the different ways sound is created and utilized in our world. Because when we think about what creatures are the loudest, we typically think about which ones create the most decibels with their lungs, throats, tongues, and mouths. But across the living world, animals have evolved very different methods of creating sound-producing pressure waves, and they have very different purposes for doing so as well.

Take, for instance, the tiger pistol shrimp. When it snaps at something with its claw, a plunger-like tooth on the claw’s moveable finger, also known as the dactyl, forces water into a socket on the immobile propus, causing a rapid jet of water to shoot out that can incapacitate prey or intimidate other shrimp.²⁹

While it was long assumed the loud sound emanating from the action was the result of the claw snapping together, in 2000 a team from the University of Twente in the Netherlands demonstrated through high-speed video recording that the pop actually occurs when the vapor cavity at the end of the water jet collapses.³⁰ The result is an up-to-210-decibels sound that has been giving sonar-using underwater explorers and warfighters trouble for more than 100 years.³¹ The calculations the Twente team made in its analysis of the shrimp’s snap, though, is now being used to help scientists who use air guns and hydrophones to map the ocean floor.³²

It’s not just underwater creatures that have figured out how to use their various appendages to cause a racket, of course. Most folks know crickets make their sounds by drawing the “scraper” on one wing, along the “file” on another. The intervals between the resulting sounds have been shown to be a remarkably good predictor of outdoor air temperature, a phenomenon called Dolbear’s Law.³³

You might think the loudest of these crickets would be hard to lose track of, but that’s what happened to the Colombian bush cricket, Arachnoscelis arachnoides. The spider-like katydid was first described in 1891. After that, entomologists figured the insect had either gone extinct or been mistakenly identified as a separate species in the first place. It wasn’t rediscovered until 2012. With a song exceeding 110 decibels, how did it managed to hide so long? Part of the reason is that most of its calls are ultrasonic—we simply couldn’t hear them.³⁴

Just as herpetologist Christopher Austin proved in the forests of New Guinea when he discovered the world’s smallest frog, sounds can lead us to incredible new discoveries. What else might we discover if we begin to pay better attention to the world that exists outside our range of hearing?

It’s time to listen up. After all, our very existence—and the existence of every living thing on this planet—started with a sound: a tiny pop that changed everything.

Today, oxygen comprises 21 percent of the volume of the air in our atmosphere, and it’s been like that for a long time. But it wasn’t always like that. There was, at first, no free oxygen.

The first “free O” in our world arrived by way of cyanobacteria, which released it as a waste product when it split water to get hydrogen. That process, the first instance of photosynthesis in our known universe, began about two and a half billion years ago, give or take a few hundred million years.

At first it happened a little. And then it started to happen a lot. Light from the sun would be absorbed by a chlorophyll molecule and, in a nanosecond, the molecule would lose an electron and become positively charged. “The result,” Paul Falkowski writes in Life’s Engines, “is that for a billionth of a second there is a positively charged molecule and a negatively charged molecule inside a protein scaffold, and they are separated by only a billionth of a meter.”³⁵

That’s a situation that can’t last, because positive charges attract negative charges. And when that happens, the protein scaffold collapses, creating a pressure wave—a tiny popping sound that may have been the first noise ever made by any life-form.³⁶ Pop by pop by pop, tiny cyanobacteria pumped dioxygen into the atmosphere in what has come to be known as the Great Oxygenation Event, creating the conditions that have permitted life as we know it to exist on this planet.

Long before any creature had evolved to have anything resembling a mouth or throat or lungs, life was already a noisy affair.

And it just got noisier from there. Just not always in the ways we imagine.

WHAT DO CROCODILE SOUNDS TELL US ABOUT DINO DADDIES AND MOMMIES?

I really do hate to damage people’s reverence for the mighty Tyrannosaurus rex. The indubitable badassness of that dinosaur, after all, has led a whole lot of young people to investigate the world of paleontology, a veritable gateway drug for other biological sciences.

But when I ask students to tell me what the loudest creature ever to walk the face of the planet was, T. rex is almost always one of the first guesses. And, well, there’s a tiny problem with that.

OK, actually, there’s a really big problem with that.

T. rex, you see, was an archosaur, like today’s avians and crocodilians. Birds chirp, sing, squawk, and honk. Crocs gurgle and grumble. But neither of those groups of animals roar the way many of us have come to believe these big, hungry, prehistoric carnivores did.

Loud and resonant roars, like those of lions and tigers, don’t appear to have evolved in any species outside of large mammals—which didn’t come along until long after the dinos were gone.³⁷ Such sound-making is the product of vocal cords that are flat and square-shaped, which stabilizes the cords and allows them to better respond to air being forced out of the lungs.³⁸ Dinosaurs, though, don’t appear to have had vocal cords at all. What’s more, the biological tools that modern archosaurs use to make the sounds they do make—a syrinx for birds and a larynx for crocs—evolved well after dinos went extinct. So forget roaring; dinosaurs might not have been able to vocalize at all. Indeed, T. rex might have been the strong silent type.

If dinos did make noise, research suggests, the sounds they made were likely “closed-mouth vocalizations,” low-pitched gurgles similar to those made by larger birds like ostriches and cassowaries, and by all of the crocodilians, including alligators and gharials.³⁹

So dinosaurs may not have been big, scary roarers. However, research from an international team of scientists studying archosaur vocalizations suggests they might have been pretty good parents.

First, the researchers recorded the calls of three kinds of crocodile, plus the American alligator and the spectacled caiman of Central and South America, noting how the calls shifted in frequency and pitch as the animals aged and grew. When the calls of small juveniles—those up to about 14 inches long—were played back to these crocodilians, the mama reptiles moved toward the source of the sound. Meanwhile, the calls from large juveniles—those up to about three feet in length—“hardly elicited an approach.” When the baby crocs’ calls were electronically manipulated to play back at an even higher pitch, the mamas exhibited an even greater tendency to move toward the calls.⁴⁰ That excited the research team, because mother birds have been known to respond in similar ways to baby bird calls.

When you see something that birds do, you know what birds do. When you see something that crocs do, you know what crocs do. When you see something that both birds and crocs do, though, you might just be seeing what dinosaurs did, because what we see in both our reptilian and feathered friends, the researchers wrote, is more likely to have been “rooted deeply in the archosaurian evolutionary tree,” the branches of which began to separate about 220 million years ago.

An ever-improving fossil record is helping us understand dinosaur physiology. But deriving dino behavior from the fossil record is a much greater challenge, to say the least. The more similarities we can find in birds and crocs, the better idea we’ll have about not just what dinosaurs looked like, but what they were like in other ways, too—like how they might have sounded. And once we’ve got a good guess as to what dinosaurs sounded like in general, there’s a chance we can make some quality suppositions as to what they sounded like in specific situations—like when they were feeling relaxed or excited.

Will we ever know for certain what dinosaurs sounded like, how they used their vocalizations, and for what purposes? Perhaps not. But the closer we get to understanding more about them—including and perhaps especially how they communicated—the more we’ll understand how our own behaviors fit into a much grander evolutionary picture.

WHY THE WORLD’S LOUDEST FROG CHANGED ITS ACCENT

Long before we arrived on this planet, and long before the dinosaurs ruled the Earth, the masters of our world were amphibians. Big ones. Scary ones. Just plain weird ones.

A 200-pound salamander called eogyrinus. A giant-headed river prowler named megalocephalus. A two-foot-long “snake amphibian” called ophiderpeton.

This was during the Carboniferous period, a 60-million-year stretch that began about 360 million years ago and that brought forth upon this planet a multitude of swamp forests, new plant life, and a whole lot of noise.

We’ll never be sure what dinosaurs sounded like, because there aren’t any dinosaurs left. But we can make some very educated guesses about the Carboniferous soundscape and its choir of ancient amphibians, because our world is still crawling (and swimming) with frogs, toads, newts, and salamanders.

And they are loud. Incessantly and often ear-splittingly so.

Take, for instance, the coqui frog, Eleutherodactylus coqui, which is often called the loudest amphibian in the world. The call for which it was named—“koh-kee . . . koh-kee”—has been measured at greater than 90 decibels. And the little frog, which seldom grows bigger than two inches in length, sings and sings and sings some more.

So loud and so unremitting is the coqui that, shortly after it landed in Hawai’i from its native Puerto Rico, likely in a shipment of nursery plants in the late 1980s, it was declared a dangerous invader. The Hawai’i Invasive Species Council decried its “annoying call from dusk to dawn.”⁴¹ It was the first and only time I know of that a government institution went to war with a species primarily because of the noise it creates.⁴²

Like so many so-called invaders in so many other places across the globe, though, the coqui has proven adept at thwarting those who believed they could stop its conquest. Hawai’i has spent millions of dollars on dozens of schemes to kill off the frog—including weekly volunteer hunting parties set up neighborhood-watch style and one short-lived effort to caffeinate the little amphibian to death.⁴³ Yet the coqui abides. In some areas, according to the state of Hawai’i, there are more than 10,000 of them per acre.⁴⁴

When she began studying coquis in Hawai’i a few years ago, ecologist Karen Beard was interested in investigating a common concern—that the frogs would compete for food with native birds, reducing populations of endemic species. She suspected they would. But after scouring the Big Island, where the coquis are rampant, meticulously counting both amphibians and avians, and comparing the numbers to historic data, Beard and her team learned the native population hadn’t suffered at all. The biggest difference was that the nonnative bird population had increased.

“It looks like the coquis were a good food source for them,” Beard told me.

Sydney Ross Singer, whose family maintains a 60-acre refuge for the cacophonous frogs on the Big Island, has argued the “Frog War” is nothing more than a witch hunt, pointing out that more than a quarter of the creatures that make up Hawai’i’s current population of arthropods aren’t native either—and just as nonnative birds eat a lot of coquis, the coquis eat a lot of other nonnative species.

“I’m disturbed by what we’re teaching our children,” Singer told me. “For a while the school system had a coqui bounty campaign in which children could kill frogs and bring them to school for prizes. We’re teaching them it’s OK to kill something just because you don’t like the sound of it.”⁴⁵

The stop-it-at-all-costs approach also ignores the benefits potential organisms like the coqui frog might offer, particularly as it pertains to seeing—and hearing—evolution in action.

Owing in no small part to its decibel level, there are few animals in the world whose calls have been so intricately studied as the coqui. For a half century, starting in Puerto Rico, researchers have been trying to understand not just how the frog manages to be so loud, but why it needs to be, and attempting to ascertain how the coqui uses its piercing call within its ecological niche. One interesting finding is that the two parts of the frog’s call seem to have distinct purposes. By recording both parts of the call and watching the responses of various frogs as the calls were played as recorded (“koh-kee”), separated (“koh” and “kee”), and reversed (“kee-koh”), neurophysiologist Peter Narins has demonstrated the first note serves to establish territory, while the second note is used to attract mates. Essentially, “koh” translates into “stay off my lawn” and “kee” means “well, hello there.”⁴⁶

That, at least, is what the calls mean in Puerto Rico. But as the coqui has added more stamps to its passport, we’ve been getting an opportunity to understand how animal calls can be affected when a creature goes global.

Anyone who has ever heard a friend’s accent and vocabulary shift when they move to a new place knows how fast humans can adopt the tones and lexicon of a different part of the world.⁴⁷ Lexiconic adoption makes some sense for humans; it signals familiarity with, understanding of, and even acquiescence to the established culture on the part of newcomers. But what would happen to your accent if you moved somewhere where there weren’t any fellow humans?

That’s essentially what happened when the coqui landed in Hawai’i. Since there weren’t native frogs of any species there already, and no animals as loud as it is, E. coqui entered an “empty” auditory niche. Theoretically, the lack of competition should have meant the coqui’s call didn’t need to change. But it did. And fast.

Already, researchers have seen a significant, and quintessentially Hawai’ian, impact. In the Aloha State, the frog’s “well, hello there” call is as loud and proud as ever, while its “stay off my lawn” call is now significantly quieter. Researchers believe this correlates to population density: In some areas the coqui population is as much as three times denser in Hawai’i than in Puerto Rico.⁴⁸

What this tells us is that animal calls can be quite sensitive to environmental change—an observation backed by recordings Narins took of coquis he found along an eight-mile stretch of Puerto Rico Highway 191 in the Caribbean National Forest, first in 1986 and then again nearly a quarter-century later. During the intervening years, Narins learned, the frogs’ calls increased in pitch and shortened in duration—a change that correlated to a significant increase in temperature.⁴⁹

While most of our attention was focused on eradicating it from places it “doesn’t belong,” the world’s loudest frog was calling out to warn us of the impact of climate change.

In our defense, it’s not always easy to hear such warnings. We’re not moths, after all.

HOW BATS AND MOTHS ARE FIGHTING AN EVOLUTIONARY WAR

Want to take a guess as to what was not in Hayward Spangler’s obituary? (If you said “whatever superlative thing he discovered,” you’re right.)

But it’s not just the folks who wrote the University of Arizona entomologist’s obit who missed his contribution to our knowledge of Galleria mellonella, the greater wax moth—it was also fellow scientists who study it.

In the early 1980s, Spangler collected moth larvae from an infested honeybee comb in Tucson and raised the moth babies in a small room in his lab at the Carl Hayden Bee Research Center. Once they reached adulthood, he blasted the moths with a quick burst of ultrasonic noise he made with a transducer he purchased at RadioShack. Using a laser vibrometer, which allows researchers to measure vibrations without touching a vibrating surface, he found that a pair of tympanic hearing organs on the abdomen of G. mellonella were sensitive to sounds at up to 320 kilohertz, or 320,000 vibrations per second.⁵⁰ When the moths were flying, Spangler later noted, they would respond to the ultrasonic noises by folding back their wings like a peregrine falcon and diving to the floor, or by looping and landing on the nearest surface—mirroring behaviors observed in moths when bats approach in the wild.⁵¹

Spangler published his findings in the Annals of the Entomological Society of America and the Journal of the Kansas Entomological Society. Both were upstanding peer-reviewed publications, but neither was exactly required reading in the wider world of biological sciences. Even today, with the advent of academic search engines with seemingly endless libraries, Spangler’s early work on moths can be hard to track down. Compounding this problem, Spangler recorded his observations but didn’t put them into context—he didn’t ever say, “I have discovered a moth than can hear frequencies higher than any other known animal.”

In 2013, a report from researchers from the University of Strathclyde in the United Kingdom did just that. The study, which was published in the much-more-well-known journal Biology Letters, was praised by one fellow scientist for offering a “shocking increase in the frequency sensitivity of moths’ ears” that would “require researchers to rethink” the rules of auditory systems.⁵²

What did this “shocking” study show? Pretty much what Spangler had already shown: that a pair of tympanic hearing organs on the abdomen of G. mellonella were sensitive to sounds at 300 kilohertz.

There was one difference: The new study included the words “the highest frequency sensitivity of any animal.”⁵³

Framing is everything. Among the media organizations that jumped on the superlative story—without noting Spangler had made a similar discovery thirty years earlier—were the New York Times, the BBC, and National Geographic.

Spangler is hardly the first scientist to have his or her discoveries overlooked by other scientists and the wider world. Today just about everyone knows Gregor Mendel as the father of modern genetics. His work demonstrating heredity, though, was roundly ignored during his lifetime and not “rediscovered” until three other scientists, Hugo de Vries, Karl Correns, and Erich von Tschermark, reached similar conclusions. That didn’t happen until nearly a half century after Mendel’s now-famous experiments with smooth and wrinkled peas, and some sixteen years after his death.

Setting aside the notion of who first recognized greater wax moths could hear at supremely ultrasonic frequencies, however, we can focus on a fascinating mystery: How did G. mellonella even come to own this aural niche in the first place?

Not much in nature happens at 300 kilohertz. Not that we know of, anyway. G. mellonella’s chief predators are bats, whose highest known echolocation calls taper out around 200 kilohertz. So why does the greater wax moth need to be able to be able to pick up more than 100,000 extra vibrations per second?

One possibility: Wax moths are to bats as pronghorns are to cheetahs. That is to say, while the wax moth doesn’t need to be able to hear at 300 kilohertz these days, it might not always have been that way. Fossil records indicate long-extinct bat genera like Icaronycteris and Palaeochiropteryx had inner ear cavities that were very large relative to their skulls, as do all modern echolocating bats.⁵⁴ If any—and certainly if many—of the bats that have crossed evolutionary paths with G. mellonella and its predecessors had higher-frequency calls, it would have put evolutionary pressure on the moths to “hear higher.”

Another possibility is that the greater wax moth’s hearing is the latest procurement in a bat-versus-moth evolutionary arms race of epic aural proportions. This mega-anna-old fight has produced tiger moths, which make ultrasonic noises to “jam” the signals of their predators,⁵⁵ and barbastelle bats, which counterbalance their high-frequency echolocation calls with low-amplitude “whispers” moths can’t hear until it is too late.⁵⁶ By evolving hearing that goes well past its current need, moths not only have the ability to react to lower predatory pitches faster, but also have built in some wiggle room in preparation for the bats’ next evolutionary adaptation—a case, perhaps, of preemptive adaptation.

However it happened, this evolutionary battle could impact not just moths and bats, but us as well. At the University of Strathclyde, where that second study establishing the upper limit of wax moth hearing was conducted, an electrical engineer named James Windmill is taking what he has learned about insect ears and applying it to the creation of ultra-small, simple, and task-flexible acoustic systems. Among his bio-inspired designs are microphones variably sensitive only at selected frequencies, which could give humans better capacity to filter out noises they don’t want to hear and hone in on the ones they do, just as moths must do given their extreme range of frequency perception. The obvious application for such technology is hearing aids, but the technology could also be applied to tiny medical devices capable of detecting very specific signals of stress inside the human body. Similarly, such microphones could be used in industrial systems, offering safety engineers another way to monitor noisy, complex workspaces for signs of trouble that, if addressed quickly, could improve worker safety and stop production delays.

It may have taken three decades after Spangler’s discovery of its extreme range of hearing for G. mellonella to finally be seen as useful to other scientists. But given the wax moth’s history as a pest—it gets its name from the fact that its caterpillars love to munch on beehives and can devastate entire colonies of bees—we might consider ourselves lucky we didn’t figure out a way to eliminate it entirely before we could better understand the lessons it could teach us.

That, after all, is what we very nearly did to another aural wonder of the world.

WHAT SPERM WHALES ARE TELLING US ABOUT LISTENING TO THE WORLD

When the first scientific treatise was written about Physeter macrocephalus, the general consensus was that it was a rather quiet beast.

“The sperm whale is one of the most noiseless of marine animals,” wrote Thomas Beale, who served as the ship’s doctor on two whaling ships, the Kent and the Sarah & Elizabeth, in the early 1800s. “It is well known among the most experienced of whalers that they never produce any nasal or vocal sounds . . . except for a trifling hissing at the time of the expiration of the spout.”⁵⁷

Beale, of course, never observed whales underwater, where they spend the vast majority of their lives. He only saw them when they were either about to be killed or were actually in the process of being killed. Such is the problem with trying to do science as part of a hunting expedition—and this, we would do well to remember, is how much of the natural world came to be described in the eighteenth, nineteenth, and twentieth centuries, as whalers, anglers, trappers, and other killers of animals reported back to scientific bodies their observations about the creatures they encountered, and often destroyed, during their adventures. The starting point for our understanding of thousands upon thousands of species were observations taken while the animals were literally fighting or fleeing for their lives.

But Beale could not have been more wrong in his assertion about the sperm whale’s quiet demeanor. Thus his lament that those who had earlier attempted to describe P. macrocephalus “should rather have left a blank in the page” seems rather ironic.

Beale did make some rather important observations. But he also got a lot wrong, including his estimation that the sperm whale was probably “the largest inhabitant of the globe.” It is indeed a mighty beast, but only about half as long as the blue whale.

The idea that the sperm whale was a “quiet giant” stuck longer than the idea that it was the largest. It wasn’t until the late 1950s that research unconnected to the whaling industry was conducted,⁵⁸ and revealed that sperm whales do, in fact, make noise. Those noises are mostly clicks and buzzes, as opposed to the “songs” many of us associate with whales, but P. macrocephalus was anything but the “noiseless” creature Beale had described.

It would be nearly a half century further down the road before scientists got around to measuring those sounds. When they did, they found the sperm whale’s rapid-fire “clicks” regularly exceeded 200 decibels, and a team of researchers from Denmark’s University of Aarhus recorded one whale at 236. In absolute terms, that was “by far the loudest of sounds recorded from any biological source.”⁵⁹

Why does a sperm whale need to be this loud? Consider the environment in which it hunts, up to 6,000 feet deep in the blackness of the ocean. Its tiny eyes don’t do it a heck of a lot of good down there.

That’s where its huge head comes in. The whale’s noggin, which takes up a third of its body, is full of hundreds of gallons of a waxy substance known as spermaceti. (For some reason, people once thought this stuff was whale semen, hence the creature’s name, but it’s really just a water-insoluble chemical compound of fatty acids and alcohol molecules.) Twisting through the spermaceti are two nasal passages, one of which runs to the whale’s blowhole and the other of which runs to an organ known as the phonic lips, which some scientists call “monkey lips” because that’s what they resemble. When the whale smacks these lips together, the sound reverberates through the spermaceti, a number of air sacs within it, and the animal’s skull. This all happens in a matter of milliseconds.⁶⁰

And that’s when the game of Marco Polo begins.

For the tragically uninitiated, Marco Polo is a summertime rite of passage, a swimming pool game of tag in which the player who is “it” closes their eyes while other swimmers flee. When the blind swimmer says “Marco,” the others must say “Polo,” giving the pursuing player a clue as to where they have gone.

That’s how sperm whales catch squid. Except instead of screaming “Marco,” the sperm whale pops those monkey lips together and then waits for the echo to bounce off those tasty cephalopods. And, of course, for the whale—and especially the squid—it’s not a game.

Wanting to get a better look at this, a team of researchers led by biologist Patrick Miller from the University of St. Andrews in the United Kingdom headed to the northern Mediterranean Sea and the Gulf of Mexico, where they tagged twenty-three whales with devices to record the animals’ sound, depth, and orientation. Almost all of the whales’ rapid-fire clicks, also known as “creaks” or “buzzes,” came in the deepest part of their dives—and correlated to times of intense maneuvering.⁶¹

That’s absolutely remarkable, because squid are quite squishy—not exactly the sort of objects one imagines would “bounce sound” all that well. What sperm whales must lock onto are the squids’ parrot-like beaks, which at their largest are just a few inches long, but are usually much smaller.

The US Navy has long studied bats and dolphins, searching for clues about how those animals use echolocation, nature’s tremendously more advanced version of human-made sonar. That research has led to advances in what the military calls “environmentally adaptive target recognition”—the ability to easily and flexibly filter out background noises by using multiple frequencies to “see around” distracting sounds, like those pesky snapping pistol shrimp.⁶² That’s especially important for locating small objects in the water—a life-or-death imperative in a world in which underwater mines are becoming smaller and easier to manufacture.

The sperm whale offers another model for echolocation—one based not only on frequency and amplitude, but also on the rhythm and patterns of its clicks. So far, though, there has been very little research dedicated to better understanding the way sperm whales echolocate, and how we might be able to emulate them. The world’s largest and loudest echolocator—and potentially the best as well—has gone virtually unstudied.

For now, the Navy’s chief interest in sperm whales comes as a result of the controversy surrounding how warfighter-based sonar disturbs, and even kills, marine mammals. It’s no secret that the US military’s environmental record isn’t good, and defense leaders have fought hard against environmentalist lawsuits and court orders seeking to protect animals sensitive to the tremendously loud noises the Navy pumps into the oceanic acoustic environment. If naval leaders realized how much they stand to gain by protecting P. macrocephalus, they might change course. And if the inner workings of a unique echolocation system built by millions of years of evolution isn’t enough, perhaps naval researchers will be drawn to another newly emerging area of research related to sperm whales: The animals also might have a very finely tuned magnetic navigation system.

The way researchers came upon this hypothesis is quite sad. As far back as the Middle Ages, people have been documenting whale beachings, but although we’ve long known whales sometimes strand themselves, and sometimes do so in groups, scientists aren’t sure why. One of the most promising, albeit tragic, opportunities to study this phenomenon presented itself in early 2016, when twenty-nine sperm whales, all of them male, were found on the beaches of Germany, the Netherlands, Great Britain, and France. Autopsies were conducted on twenty-two of the whales, and it appeared that they were all in good health before getting stranded.

Given where they were found, the fact that all of the whales were male was not particularly surprising. Females and young tend to stay at lower latitudes—they typically get no farther north in the Atlantic than the Azores Islands, west of Portugal. But when males reach independence, around the age of ten to fifteen, they form bachelor groups that migrate much farther north.

But young male sperm whales do this every year. So what was different in 2016? Solar storms—coronal mass ejections that play havoc with Earth’s magnetosphere, subtly disrupting the magnetic polarity of our planet. There were two storms around the time of the beachings, and researchers from Germany and Norway, who published their findings in the International Journal of Astrobiology, believe the storms could have caused the whales to become disoriented.⁶³

If that’s true, it means sperm whales don’t just navigate by echolocation, but also with the help of the Earth’s magnetic field, possibly through trace magnetic elements buried inside the whale’s spermaceti. Essentially, this theory goes, the whales navigate for long distances by “listening” to the magnetism of the Earth—perhaps in ways that can inform our own navigational technologies.

We very nearly didn’t learn any of this, though, because sperm whales, like so many of their fellow cetaceans, were almost hunted to extinction. By the time Herman Melville published Moby-Dick in 1851, the widespread whale slaughter was well underway—and was already besieging global whale populations. Melville romanticized, excused, and diminished the scope of the slaughter, writing that the sperm whale was “immortal in his species, however perishable in his individuality.” By the time Melville died in 1891, the estimated global population of about 1.1 million sperm whales had been cut by a third—and that was before the advent of industrialized whaling. By the time the global ban on whaling took effect in 1986, that population was down by two-thirds.⁶⁴

If the ban had not taken effect, there is little doubt we would now live in a world whose loudest creature had fallen completely silent—long before we realized how much we had to gain from the simple act of listening.