IN THE rainforest, thousands of species sing and call, forming acoustic layers so rich that the human mind can be overwhelmed. Drop a hydrophone into an ocean and you will hear similar richness, but made of sonic timbres alien to our air-adapted ears. Shrimp fizzle like cooking bacon fat, fish thrum and bleat and dolphins ping and chitter.
Hundreds of thousands of other vocal wonders ring out across the world. Every vocal species has a distinctive sound. Every place on the globe has a singular acoustic character.
This magnificence is of relatively recent origin. Compared with visual and chemical signals, the diversity of sounds flourished late on Earth. The keen ears of predators probably held back sonic evolution for hundreds of millions of years. But 300 million years ago, a few cricket-like insects and the ancestors of sturgeon and other fish started to sing. Sonic diversity has flourished ever since, spurred by the great advantages offered by vocal communication.
We live in a world of sonic wonder, yet this richness is being eroded worldwide. In oceans, forests and cities alike, sonic diversity is under assault.
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In some places, sonic loss is caused by the destruction of habitats, from felled forests to overfished oceans. Elsewhere, noise is the problem. Machines pump so much sound into water and air that other species can’t hear one another.
The problem of noise is most acute in the oceans, where seismic exploration, shipping and sonar create a cacophony so dire that it is uninhabitable, or nearly so, for many species.
In habitats such as dense rainforests or turbid oceans, sound is the only way for most animals to communicate even over short distances. This communication – mating songs, cooperative signals about food, cries that indicate social status and alarm calls – allows complex animal life to thrive.
In noisy or silenced ecosystems, the viability of species and communities is threatened. Sound connects animals to their mates, offspring and compatriots, and so noise can degrade the social and ecological networks of vocal species.
Sound and its diminishment also matter for practical reasons. As sound travels through dense vegetation or murky water, it gives us information about unseen or hard-to-measure trends in biodiversity. Land managers use the diversity of sounds in rainforests to rapidly assess the vitality and diversity of ecosystems. It would take decades to catch and identify every species, yet sound recordings capture some of the essence of biodiversity within hours.
Humans are also affected by environmental noise, with complaints about noise pollution dating to the very first cities, recorded on clay tablets from Babylonia. This noise is no mere inconvenience: its stresses create physiological burdens that sicken and kill. The European Environment Agency estimates that environmental noise in Europe causes 12,000 premature deaths and 48,000 new cases of ischaemic heart disease per year.
Sound gives us a tool to directly measure the environment. Documenting noise pollution means we can assess environmental harm and take steps to remediate environmental injustice.
What can be done to address these problems? Perhaps amid the scientific studies of trends in sonic loss, activism to advocate for justice and policy-making to reduce noise pollution and habitat destruction, we might also find space to listen. Just as we go out with friends to hear a concert, might we do the same for the birds in a city park? In this simple act, we might find inspiration – and a direct connection to our more-than-human neighbours.
David George Haskell is a biologist and author of Sounds Wild and Broken
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