Birds are losing their voice
Nature sounds, and birdsong in particular, play a key role in building and maintaining our connection with nature.
But with more than half of the world’s population living in cities and about half of the world's habitable land used for agriculture, humans are increasingly distanced from the wild. We know the planet’s biodiversity has declined sharply in the last decades, but what effect does that have on our day-to-day life? How have our bird soundscapes changed?
Until now, answering these questions has proved difficult because of lack of historical recordings, but new research from an international team led by the University of East Anglia found a way to measure the acoustic diversity and intensity of bird soundscapes reliably. The study shows that dawn choruses in spring have become much quieter and less varied over the last 25 years.
The team of researchers combined data from two citizen science databases: one reports sightings of birds every year in locations across Europe and North America, and contains information dating back to 1996; the other contains audio recordings of bird songs from many different species.
Prof Simon Butler, lead author of the study, explained: “We downloaded recordings from each of the species that were counted in the sights database. Then we clipped the recordings to a consistent time length to represent one individual bird, and finally we built up the soundscapes by layering up individuals and species”. For example, if the count said that three skylarks and two crows were spotted in Suffolk in 2007, then three audio recordings from individual skylarks and two crow recordings would be part of the Suffolk 2007 soundscape.
In this way, the scientists constructed soundtracks across the two continents for the past two decades. Then, they developed an acoustic metric based on the pitch, amplitude and time variability of the sounds to quantify both the diversity and the intensity of the soundscape. “A crow makes a rather monotonous, low frequency sound,” says Butler, “whereas skylarks and warblers make melodious songs that jump around frequencies and across time.”
By analysing how this acoustic metric changed over time, the team observed an overall decline in acoustic diversity and intensity of our soundscapes, both in urban and rural areas across Europe and North America. Northwestern Europe has seen the stronger decline in bird soundscape diversity, probably because agriculture has grown faster and become more intense there.
“What we wanted to do with this paper was to really show the direct impact biodiversity loss has on our lives. Hopefully that will raise awareness of the potential damage to our health and wellbeing, and will encourage people to be more supportive of biodiversity conservation”, says Butler, who then adds: “We also hope people will take time to appreciate what they can hear”.
The study was published in Nature Communications and drew heavily from the work of citizen scientists, who are volunteers with no special training that contribute to research by collecting useful data in larger amounts than any professional scientist could by themselves.