Close your eyes in a forest, a city park or a desert at night and you hear a soundscape – the combination of every sound in a place. Soundscape ecology is the science that studies these combined sounds as a living part of the environment, and uses them to monitor ecosystems.
Three sources of sound
The field, shaped by researchers such as Bernie Krause and Bryan Pijanowski, divides a soundscape into three components:
- Biophony – sounds made by living organisms: birdsong, frog choruses, insect stridulation, whale calls.
- Geophony – non-biological natural sounds: wind, rain, thunder, flowing water, waves, ice.
- Anthrophony – sounds made by humans and our machines: traffic, aircraft, voices, music, industry.
Listening to the balance between them tells you a lot about a place. A healthy tropical forest at dawn is dominated by biophony; a city street by anthrophony; a storm by geophony.
The acoustic niche hypothesis
Krause noticed that in undisturbed habitats, animal sounds seem to fit together like an orchestra: species use different frequency bands and different times of day, so that each can be heard. This is the acoustic niche hypothesis. On a spectrogram of a rich habitat, insects may occupy a high band, frogs a middle band and birds the gaps between – while in damaged or noisy habitats the structure breaks down.
Measuring soundscapes
Because sound is cheap to record continuously, ecologists deploy automatic recorders for weeks or months and compute acoustic indices – numerical summaries such as acoustic complexity, diversity or the ratio of biophony to anthrophony. These help track biodiversity, the timing of breeding seasons and the impact of disturbance across large areas.
How noise affects wildlife
Human noise is not just an annoyance. Studies have shown that birds in noisy cities sing higher, louder or at different times to be heard over low-frequency traffic; that road noise can reduce bird breeding success; and that ship noise interferes with whale communication. Protecting natural quiet – as the US National Park Service does with its soundscape programme – is increasingly recognised as part of conservation. Listen to the parks' recordings in nature sounds.
Listen for yourself
Try a simple exercise on a walk: stop for two minutes and count the sounds you hear, sorting them into biophony, geophony and anthrophony. Then explore soundscapes from around the world – birdsong and dawn chorus, frogs and insects, rain or city streets – and compare how they look in a spectrogram.
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