Why the Dawn Chorus Is Getting Quieter and Less Diverse

The mornings are getting quieter and less acoustically diverse.

The natural sounds of spring—particularly the dawn chorus of birds singing—are changing, a new study finds. Researchers used citizen scientist data and recordings of birds in the wild to reconstruct the soundscapes of more than 200,000 sites over the last 25 years.

Their findings suggest that soundscapes are becoming quieter and less varied due to changes in the makeup of bird populations. In areas where bird populations have decreased or the species have become less diverse, the dawn choruses reflect those changes.

And because people most often hear birds, rather than see them, changes in the soundscape are one of the main ways humans can sense a change in bird populations, the researchers say.

The results were published in the journal Nature Communications. Lead author Simon Butler, of the University of East Anglia School of Biological Sciences in the United Kingdom, spoke to Treehugger about the findings.

Treehugger: What was the impetus for your research?

Simon Butler: There is growing recognition of the value and benefits of spending time in nature for human health and well-being. At the same time, we’re living through a global environmental crisis, with ongoing and widespread declines in biodiversity. This means that the quality of our interactions with nature is likely to be declining, reducing its potential benefits, but this has not previously been examined. Whilst all senses contribute to the nature contact experience, sound is particularly important, so we wanted to explore how the acoustic properties of natural soundscapes are changing.

Why are natural sounds, and birdsong especially, key to establishing human relationships with nature? 

Birds are a major contributor to natural soundscapes and bird song diversity plays an important role in defining our perceptions of soundscape quality. Indeed, from inspiration for classical music compositions, such as Messiaen’s “Catalogue d’Oiseaux” or Vaughan Williams’ “The Lark Ascending,” to Rachel Carson’s stark warnings about the environmental impacts of pesticides in “Silent Spring,” bird song has always been a defining component of our relationship with nature. 

How did you reconstruct historical soundscapes for your study and why was that key to your research?

We wanted to explore widespread and long-term changes in soundscape characteristics but don’t have recordings of soundscapes from lots of sites over repeat years, so we needed a develop a way to reconstruct historical soundscapes. To do this, we made use of the annual bird monitoring data collected as part of the Pan-European Common Bird Monitoring Scheme and North American Breeding Bird Survey from over 200,000 sites across Europe and North America. These surveys, undertaken by a dedicated network of volunteer ornithologists, generate lists of which species, and how many individuals, were counted in each site in each year it was surveyed. 

To translate these data into soundscapes, we combined them with sound recordings for individual species downloaded from Xeno Canto, an online database of bird calls and songs. First we clipped all the downloaded sound files to 25 seconds and then, starting with an empty 5-minute sound file, we inserted the same number of sound files for a species as there were individuals counted—that is, if there were five individuals of a given species counted, we inserted five 25-second sound files of that species. By layering the appropriate number of sound files for each species we were able to build composite soundscapes for each site that represented what it would have sounded like standing next to the observer as they completed their annual bird count.

Having built soundscapes for each site in each year, we then needed to quantify their acoustic characteristics so we could measure how they were changing over time. To do this, we used four different acoustic indices that quantify the distribution of acoustic energy across frequencies and time within each 5-minute soundscape and allow us to measure acoustic diversity and intensity. 

What were your key findings about how soundscapes have changed?

Our results reveal a chronic decline in acoustic diversity and intensity across Europe and North America over the past 25 years, suggesting that natural soundscapes are becoming quieter and less varied. In general, we found that sites that have experienced greater declines in either total abundance and/or species richness also show greater declines in acoustic diversity and intensity. However, initial community structure and how the call and song characteristics of species complement each other, also play important roles in determining how soundscapes change.  

For example, the loss of species such as skylark or nightingale, which sing rich and intricate songs, is likely to have a greater impact on the complexity of the soundscape than the loss of a raucous corvid or gull species. Critically however, this will also depend on how many occurred on the site, and which other species are present.

Were any of the results surprising to you? 

Sadly not! We know from previous studies that many bird species across North America and Europe are in decline so it’s not surprising this has had an impact on our natural soundscapes. However, on a more positive note, we did identify some sites where soundscape quality has improved over the same time period. The next step is to explore what’s special about these sites to understand why they are bucking the broader trends. 

Why are these findings important? What are the takeaways for conservationists and environmentalists?

Our results suggest that one of the key pathways through which humans engage with, and draw benefits from, nature is in chronic decline. It’s also important to emphasise that we only explore the changing contribution of birds to natural soundscapes here. We know other groups that contribute to natural soundscapes, such as insects and amphibians, are also declining, whilst road traffic and other sources of “human” noise are increasing, which suggests reductions in natural soundscape quality are likely to be even greater than those we show.

As we collectively become less aware of our natural surroundings, we also start to notice or care less about their deterioration. The deterioration of our natural soundscapes is a consequence of widespread declines in bird populations and shifts in species’ distributions in response to climate change. By translating the hard facts on biodiversity loss into something more tangible and relatable, we hope this study can help heighten awareness of these losses and encourage support for conservation through actions to protect and restore high-quality natural soundscape, particularly in areas where people can access, enjoy, and benefit from them most.