Language of sound: What the hoot of an owl or the croak of a frog can reveal – if only we listen

In the stillness of the night the hoot of an owl, the howl of a wolf, a frog’s croak or an insect’s tweet have both a thrill and an eeriness to it. Many humans associate these broadcasts with the landscape of ghosts and ghouls, some believe that even the dead communicate through sounds.

In living organisms, sounds serve to communicate and gain information about their surrounding environment. Sounds are produced to mark territory, announce resource availability, for reproduction, to communicate with the young and warn about lurking dangers. For years now, scientists have used the sounds of organisms to learn more about the organisms. In several groups of insects, for example, sounds are the ultimate key to differentiate and identify closely related species.

In 1998, Bernie Krause, a professional musician, sound engineer and naturalist from California, classified all sounds into three categories. The variety of sounds that living organisms make using their own body parts are called “biophonic sounds”. The whistling wind, gurgling waters, rumbling thunder or crashing boulders are “geophonic sounds” of natural elements. The ringtones of the mobiles, vehicular sounds, clanging bells from temples and churches, the deafening amplifiers, groaning machineries and such diverse sounds created in the environment by humans are the “anthrophonic sounds”. Together they make up the soundscape of the modern world. This landscape of sounds – cacophony to a lay person – is the emerging field of study in ecology termed “soundscape ecology”.

One of the earliest uses of the term soundscape was in the 1960s by a city planner, Michael Southworth, to understand the effects of sounds from built areas of urban landscapes. He wanted to know the perceptions people held towards spaces and explore its relationship with the activities they participated in. Inspired by this term, Canadian composer and naturalist Murray Schaffer, exploring natural sounds to use in his music, set up the famous World Soundscape Project. A decade later, he referred to the blend of sounds as “the acoustical characteristics of an area that reflect natural processes”.

Listen to the biophony and geophony in a garden or wilderness area, especially at night when anthrophony are minimal and you will instantly understand what Murray meant.

Messages hidden in sound

Is it possible that the vocal responses from living organisms to anthrophony or geophony are information that may help in conservation practices, in ways we are yet to discover? Studies have shown that the sounds produced by living organisms change in response to persistent noise from the environment since it interferes with their communication. The sound of water flowing in a stream is a major source of background noise for frogs living nearby. They will have to call loudly to be heard; but this would mean spending precious energy needed for other activities. So frogs change the pitch of their calls in order to be heard over the sound of water. Fang Zhang and his colleagues from China studying the concave-eared frog Odorrana tormota, found that these frogs have evolved calls that fall in the ultrasonic range and have also developed a specialised ear structure to receive them. This is evolution in action in response to a changing environment.

When noise increases, the area (of the sound spectrum) available for animals to hear each other decreases, that is, the area in which their calls can be audible is reduced, due to the loudness of the surrounding sounds. This is called “communication masking”. A joint study undertaken by institutions from the United States and Canada found that noise arising from vessels operating near a marine national sanctuary reduced the sound space available for baleen whales to communicate. The Gulf of Maine is a prime fishing area where whale watching is a thriving tourism activity in summer and autumn. The study found that sounds from each vessel operating here reduced the communicating space by 30%. Whales are stressed if they cannot communicate. The phenomenon of whale-stress has been increasing over the years, according to researchers.

The winter soundscape in south-central Alaska is no different. Although geophony was the predominant sound, the anthrophony was found to have significant negative effects on wildlife and wilderness quality.

A soundscape study by researchers from the Okinawa Institute of Science and Technology Graduate University revealed the effects of land-use on two bird species, the Okinawa rail and ruddy kingfisher. As the researchers moved from urban to rural areas, they recorded an increase in species, especially forest species sensitive to disturbances. Small patches of forests that were near roads or urban lands appeared to be a refuge for bird species in general, and the ruddy kingfisher and the endemic and endangered Okinawa rail in particular. Despite urbanisation, the forests served as an important site for biodiversity, specially for the endemic species. They suggest that longterm monitoring of soundscape along with other methods can provide a wholistic picture of biodiversity. Several studies in different habitats have documented a decline in the diversity, density and reproductive success of bird species, due to noise.

But are there more details that the soundscape can reveal about the environment we live in? Ecologist Bryan Pijanowski of Purdue University and his colleagues think it is possible. They believe that sounds carry a lot of information – if we listen.

Indicators of ecosystem health

The most telling effect of soundscape ecology comes from the recordings Bernie Krause made at Lincoln Meadow, Sierra Nevada Mountains, in 1998. As he reveals in his talk, a logging company had convinced the residents that no harm would come to the environment if they were allowed to selectively cut down a few trees. Krause obtained permission to record sounds before and after the selective logging. He recorded the early morning chorus of birds and sounds of the stream flowing before the event. The recordings were proof of the density and diversity of birds at the Meadow.

He returned a year later to record at the same site. Visually, Lincoln Meadow looked just the same. But the dawn chorus he had heard was missing. The call of a woodpecker, not there earlier, could be heard. But gone was the diversity of calls he had recorded. He has since visited the place 15 times in the intervening 25 years to record sounds, but the chorus has still not returned. While visually Lincoln meadow was normal, the story of the sounds speak of the loss of a vast diversity of birds due to selective logging. A loss that could not be restored even after 25 years.

“Natural sound could be the ‘canary in the coal mine’,” said Purdue’s Pijanowski who is one of the scientists involved deeply in the field of soundscape ecology. “Sound could be the first indicator of changes in climate and weather patterns, the presence of pollution or other alterations to a landscape.”

His words bring to mind Rachel Carson’s path-breaking work “The Silent Spring”. She did not hear the bird calls in the spring. This simple observation was investigated, which brought to focus the changed nature of soil and pesticide pollution, leading finally to a ban on DDT.

Recently, acoustic recordings were set up in Puerto Rico by Ben Gottesman from the Centre for Global Soundscapes, Purdue University, before Hurricanes Irma and Maria hit. His recordings gave some insight into the effect the storms had on biodiversity. While fish chorus was heard louder during the event, some species like the snapping shrimps went silent. It took several days before they started calling again. Changes in the natural soundscape can be indicative of disturbances in the ecosystem and biodiversity loss. Scientists feel that it can be a tool to understand the effects of climate change.

The rise of technophony

The soundscape of modern day humans is no longer biophony; it is technophony. Our ancestors could read the change of seasons by listening to the calls in their environment. Today, humans hear, rarely listen. It does not occur to us that the insect calls or their absence signify a change, one that may need to be investigated. Sounds can tell about the health of a landscape. How quickly we hear biophony after a natural disaster or not hear it for a period may be indicative of the recovery process of habitats and a reason to intervene if needed. Soundscape study may help us better understand the nature of recovery of precious ecosystems ravaged by the monsoon in Kerala.

Many humans find biophony irksome, while anthrophony is welcome. Come summer, the cicadas can be heard in large numbers in Provence, a district in south-eastern France. They are happily welcomed by Provencians, for whom the insects are symbols of peace. Not so for the tourists, coming to enjoy their holidays. For them, it is a nuisance. They even lodge complaints with the mayor to have the insects killed, and kill if the chance arises. Pijanowski is keen to heal this disconnect with nature. He wants to bring natural sounds among our daily experiences. He believes that reconnecting with sounds will help us become environmentally conscious humans and overcome what psychologists have termed “Nature Deficient Disorder”.

To quote Krause,“Biophonies and geophonies are the signature voices of the natural world... In a matter of seconds, a soundscape reveals much more information from many perspectives, from quantifiable data to cultural inspiration... while a picture may be worth 1,000 words, a soundscape is worth 1,000 pictures.”

This article first appeared on Mongabay.