More than eight hundred fish species are known to hoot, moan, grunt, groan, thump, bark, or otherwise vocalize. Illustration by Kyle T. Webster

In 1909, a French doctor named Étienne Lombard discovered something that most people intuitively know: humans raise their voices in noisy environments. Lombard first observed the effect—which came to be named for him—at the Hôpital Lariboisière, in Paris, where he noted that his patients spoke more loudly when he filled their ears with the hiss or crackle of a “deaf-making apparatus.” The patients seemed to adjust the volume of their speech reflexively, and Lombard suggested that the phenomenon could be used to identify malingerers—those who were faking their hearing loss in order to collect workers’ compensation.

Lombard wrote an account of his study in 1911, for a French journal called Annales des Maladies de l’Oreille, du Larynx, du Nez, et du Pharynx. Since then, other researchers have expanded on his findings. They’ve discovered that, in noisy conditions, we do more than just amplify our voices—we also raise our pitch and elongate our vowels, changes that make our speech more intelligible. And the Lombard effect isn’t limited to humans. Animals use acoustic signalling for many purposes—to attract and court mates, to claim territory and frighten enemies, to find prey and warn others that a predator is near. But nature is noisy. Rain and wind, or a sudden cicada plague, can drown out a call, and there may be a survival advantage for animals that can make themselves heard above the racket. A wide range of creatures, from killer whales to nightingales, demonstrate the Lombard effect—and, according to a recent paper in Behavioral Ecology, some fish do, too.

We may think of them as silent, but fish make many sounds that are rarely appreciated by the human ear. Clownfish chirp and pop by gnashing their teeth together. Oyster toadfish hum and blare like foghorns by quickly contracting muscles attached to their swim bladders. Croaking gourami make their signature noise by snapping the tendons of their pectoral fins. Altogether, more than eight hundred fish species are known to hoot, moan, grunt, groan, thump, bark, or otherwise vocalize. Carol Johnston, an ecologist at Auburn University, is partial to the sounds made by lollipop darters, small fish native to Alabama and Tennessee. “They sound like whales,” she told me.

Johnston has spent more than a decade studying sound production and sensory perception in freshwater fish. In collaboration with one of her doctoral students, Daniel Holt, Johnston recently began investigating how fish that communicate acoustically might cope with anthropogenic (human-caused) noise. It’s an increasingly common question among ecologists. As the global population booms, our planet is becoming louder. According to the United States Department of Transportation, American air and road traffic has roughly tripled since the nineteen-seventies and eighties. Lawnmowers, leaf blowers, and snowmobiles add to the cacophony on land, and the sounds of cargo ships, fishing vessels, military sonar, drilling rigs, and offshore wind farms echo through the oceans. “As the world gets noisier, it becomes more and more relevant to think about how and which animals will have the capacity to adapt,” Sue Anne Zollinger, a research scientist at the Max Planck Institute for Ornithology, in Germany, told me.

Some species are already beginning to alter their behavior. Numerous studies have found that urban birds sing louder and at higher pitches than rural ones, perhaps to overcome the low-frequency rumble of traffic. The endangered North Atlantic right whale, which frequents regions that are busy with shipping traffic, produces louder calls when swimming in noisy seas. Freshwater environments, such as those Johnston studies, are also plagued by disturbances, especially from passing vehicles. “The noise from roads propagates really far,” she told me. “It can mask the signals of fishes at certain distances, and it’s really hard to get away from it.”

In order to test how noise affects fish, Johnston and Holt captured blacktail shiners, a common type of minnow, from tributaries of the Chattahoochee River in Alabama. Male blacktail shiners make growling sounds when they’re courting a mate and knocking sounds when they’re being aggressive. Johnston and Holt transported the fish back to their lab, then placed two males and one or two females at a time into a tank outfitted with audio equipment. They played white noise through a speaker, alternating noisy periods—lasting between seventeen minutes and two and a half hours—with quiet ones. Then they analyzed audio and video recordings of the trials to see how the fish responded to the white noise. The researchers thought that the shiners might move closer together in order to hear one another better, but those results were inconsistent. “The other thing we thought they might do is shout—raise their voices,” Johnston said. “And that’s what they did.” During the noisy periods, the fish produced louder knocks and growls.

In some ways, the knowledge that blacktail shiners and other animals can shout over us is heartening: it’s a reminder that these are dynamic, adaptable creatures, not passive objects in a human-dominated landscape. Their behavioral flexibility may improve their odds of survival as we reshape the world’s wild spaces. But that doesn’t absolve us of responsibility; the Lombard effect depends on specific anatomical and cognitive machinery that not all species possess. “It requires a feedback system,” Zollinger said. “You need to be able to hear your own voice and judge how it sounds in relation to the background noise, and you also need to be able to produce it louder.” For instance, scientists have found no evidence of the Lombard effect in frogs, which vocalize by pushing air from their lungs into their air sacs, a process that requires considerable energy. This high metabolic cost, combined with the frogs’ limited air capacity, may make it impossible for them to croak any louder than they already do.