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The Rabbs’ fringe limbed treefrog with its barklike mating call was extinct in 2016.Brian Gratwike/Wikipedia Commons
This story was originally published in Yale E360 and is reproduced here as part of the Climate Desk collaboration.
Sound is what makes the world go roundInsubstantial tremors in air is one of the most fleeting things on Earth. But sound is also a great connector, revealer, and facilitator. Because sound waves can travel through and around obstacles, they connect living beings to sonic information networks. Some of these networks are communicative—songs, music, and speech—and some amount to eavesdropping—predators and competitors listening to one another as they breathe, move, and eat. Listening can reveal the unrevealed dynamics of the natural world. Listening can be a powerful way to understand and connect in times of crisis or rapid change.
We hear a lot of sonic loss. This loss can be partially caused by species extinction. The song of the Kauaʻi ʻōʻō, a honeyeater bird from Hawaii, or the Rabbs’ fringe-limbed treefrog from central Panama will never again ring through forests. Another form of habitat loss is the decreased sonic diversity. This includes a decrease in the variety and richness of sounds, the range and tempo of different tempos, as well as the temporal variability and sonic expression through daily, seasonal, and annual cycles.
Tree plantations or row crops can sound bland and dull compared with the lush sonic diversity and vigor of a forest rich in diverse life. The loss of sonic diversity can also be caused by excessive engine and industrial noises. They smother other sounds and fragment the acoustic connections that once linked communities and populations. Then there is the loss that comes from our inattention. The richness of our sensory experience, which is essential for right action, is lost when we stop listening.
Each habitat has its own unique sonic signature. This is due to the thousands of voices that are present at each location. It took a long time before this sonic diversity emerged. Predation likely kept sonic communication from developing for hundreds of thousands of years. Low frequencies were what the first animals on land and in the oceans could hear. To cry or sing was to invite the death. Vocal creatures are those that can quickly escape from danger or defend themselves. Birds, crickets, and frogs owe their songs to their jumping legs and wings.
Once communication sound evolved, beginning with ocean fishes and crustaceans, and then moving on to cricket-like insects and insects on land, the creative forces behind evolution quickly diversified sound. They began with simple cries, but built the complexity and nuance that we now hear. These creative evolutionary processes worked over many time scales, and so sound reveals the many layers of life’s generative powers. Sonic loss can erode the legacy of these times and reduce evolutionary creativity and the possibility for the future.
The vastly different soundscapes that we hear around the globe are caused by plate tectonics at the continental level and ancient movements of animal species from one continent to the next. The bird communities of the Americas, for example, sound very different from those of Australia because only a few of Australia’s diverse assemblage of ancient songbirds left the continent of their origin and dispersed to other places. These emigrants then spread their sound to other lands, each following its own acoustic path. Each continent and ocean has its own species, each one adapting to different social and physical conditions. This diversifies sound. Songs of forest species are more difficult to transmit through dense foliage, and are therefore slower and less complex than songs of open-country species. Sexual selection has added layers to the exaggeration and excess of mating songs. This has led to new vocal extremes in mating songs.
Social learning of sounds has led to cultural evolution in a few mammals as well as birds. This has resulted in the development of highly localized dialects, vocal fashions, and other forms of cultural evolution. These dialects can be found in some species, such as the white-crowned sparrows living along the California coast. They are fine-grained and change on a scale of kilometers. This is a result of the short dispersal distances between the young. The dialects are more common in sparrow species, whose young disperse further, and mark large swathes of North American continent. Sonic communication was a key factor in cultural evolution and sexual selection. It was a social signal that accelerated local adaptation and species divergence.
All these levels are characterized by loss. On a global scale, distinctiveness has been lost. We’ve lost millions of singing whales and billions of vocalizing fish. For example, in the North Atlantic, the collapse in cod populations has reduced the number of thrumming and grunting sounds that this species makes during its mating season. In the 20th Century, humans killed at most 2.9 million whales. They also removed the sounds of sperm and fin, minke, humpback and other species. This transformed the oceans into a sonic desert, with their song and calls.
Every marine mammal and fish that has been lost occupied a particular habitat. Their demise creates an aquatic geography of sound, which is replaced by the crackling of seismic air guns and the drone of ship engines searching for buried oil. On land, homogenization of species caused by recent introductions of non-native species—such as European starlings and common mynas—and eradications of indigenous species leads to the convergence of soundscapes on different continents, especially in urban and agricultural areas.
A female humpback with her calf.
Media Drum World via ZUMA Press
However, there is still a lot of sonic diversity. To celebrate and hear distinctiveness, we can help reverse and stem the loss. The “100 Soundscapes of Japan,” launched by that nation’s Ministry of the Environment in 1996, does just this, honoring both natural and cultural sounds such as bird song, wind in reed beds, or the ringing of bells. Can we imagine such a program being offered in every corner of the globe, as a way for people to share sensory experiences and create a culture of listening?
Loss of sonic diversity can also be seen in ecosystems at smaller scales. It is a sign of loss of species and changes to the rhythms of life. Some of these changes are accessible to human ears—the early arrivals of migrating birds or the loss of familiar insects or frogs—but others are more readily discernible with the help of recording and sound analysis technologies. For example, the daily cycle of primate, bird, and bird calls in Kalimantan’s logged forests, Indonesia, was different from that in unlogged forests. This pattern was revealed by remote recording devices and statistical analysis over many weeks. We can use sound to assess biodiversity in one place and time. However, the ebbs and flows of sound reveal hidden dynamics within ecosystems.
At the individual level, the sonic crises manifests as too much or too little sound. The regent honeyeater, for example, is now so rare in New South Wales that the cross-generational sonic connections that sustain the bird’s song have been frayed. Many of these honeyeaters encounter so few singing elders of their own species that they have no chance to learn their species’ song. They sing distorted songs or borrow lyrics from other species. This is bad news for future breeding success.
Urban areas and the oceans have high levels of human-caused noise. Vocal species from many different species must sing louder to be heard above the noise. The most severe cases in the oceans are when sound from military sonar or seismic exploration is loud enough that it can directly harm animals. Even at lower sound levels the social networks of noise singers are partially blocked, disrupting social dynamics.
Humans are also affected by the noise stress. The first urban noise complaints were recorded on Babylonian clay tablet records. Over half of the world’s population lives in cities. There, we are often exposed to uncontrollable or alarming sound. These burdens do not come at the same time. Low-income and minority communities have suffered the most from racist and classist urban planning. Urban noise is more than an inconvenience. It disrupts learning, disrupts sleep, and causes physiological harm like increased rates of cardiovascular disease.
The sonic crises extends from the global scales of ocean basins and continents to the individual scales of singing birds and city dwellers. We are in a crisis because we are not paying attention at all scales. “Not listening” is a form of sonic loss. The crises in which we live are not just “environmental,” of the environs, but perceptual. Calamity is certain to follow if the most powerful species of the Earth stop listening to others’ voices.
Our lives are embedded in systems that aim to divert our attention from the sounds of the Earth and instead focus on the human. It is well-known that digital platforms and algorithms can do this in many ways, and it is often criticized. Subtler is a practice of not hearing in education and policy-making. We teach within walls that block all sounds from non-humans. Our lesson plans and curricula are tightly controlled. There is no room for the call to a raven, wind in pine needles, or cricket song to redirect the pedagogical flow. This is also true for many corporations, governments, as well as environmental organizations. Even when we discuss the fates of living rivers or forests we sequester ourselves, thereby preventing any sensory connection and preventing us from learning from the living beings whose fates are being discussed.
The vitality and health of the world is dependent on how we listen to the Earth, what we hear, and then what we do.
