Declining Bird Song At Dawn
Alarming signs that birdsong is in decline were announced recently. A major new study from the University of East Anglia reveals that the sounds of spring across North America and Europe are becoming quieter and less varied. Iacopo Russo reports...
Iacopo - If you wake up in the morning, somewhere in the Suffolk countryside and you open the window, this is the beautiful bird soundscape you're going to hear. Yes, you might get lucky, but do you have any idea of what those dawn choruses might have sounded like 20 years ago? Thanks to new research published this week, I can now give you a glimpse of that. Professor Simon Butler explains how our Birdsong soundscape has changed in the last decades.
Simon Butler - There were broad scale declines and acoustic diversity in our natural soundscapes, which means they're getting quieter and less varied, and that's occurring in a similar pattern across both North America and Europe. Declines have been stronger in Northwest Europe perhaps linked through to faster rates of agricultural intensification, and that potentially has quite big impacts on our potential to derive benefit from that. So we know that soundscapes can contribute to our health and wellbeing and as the quality of those soundscapes decline driven by biodiversity loss, the likely benefits that we can draw from those, are also likely to decline.
Iacopo - Why didn't we know this already? What problem did you manage to solve?
Simon Butler - There's widespread information and data now showing that there are declines in bird populations across North America and across Europe, but we don't know what the impact might have been for our soundscapes and we don't have historical recordings of what natural soundscapes used to sound like, so it's quite challenging to explore the impact of biodiversity loss. So we had to come up with a way of reconstructing historical soundscapes. We turn to the underlying data that demonstrate declines across the two continents, which are small scale annual monitoring schemes that are systematically undertaken across both continents, and use those as the building blocks for reconstructing our soundscapes.
Iacopo - So how did you recreate the soundtracks & soundscapes then?
Simon Butler - The approach was to combine these monitoring data with recordings of individual species. There's the citizen science data that we have for bird monitoring. We have a fantastic database collected by citizen scientists of recordings of individual species. We downloaded recordings for each of the species that would have been counted on the sites, we clipped all of those recordings down to 25 seconds. The assumption behind this is that a 25 second sound file represents one individual of a given species. And so we combine those two data sets together, for example if we had a site where five skylights were recorded, we inserted 5 25 second sound files for skydive into our soundscape. And then we layered up individuals and then we layered up species to build a composite soundscape that broadly represents what it might've sounded like standing next to the surveyor as they were doing the counter that site in that year.
Iacopo - You have sort of recreated the virtual soundscape by combining survey data on how many birds and what kinds of birds are there and individual recordings of bird species. How did you go about measuring the intensity and the diversity of this soundscape?
Simon Butler - That's absolutely right. We've got these reconstructed soundscapes and to quantify those, there are some acoustic metrics that we use acoustic indices that describe the distribution of acoustic energy between frequencies. So whether they're low pitch or high pitch sounds, and across time. Whether the sound is more variable and syncopated or whether it's sort of a continuous monotonous sound. These different metrics measure different dimensions of the, what we would call 'the acoustic space' and how that acoustic energy is distributed. We want to see a diverse range of frequencies occupied by the calls of different species within the community and lots of variation in how those sounds are delivered across time.
Iacopo - Are there birds that contribute more to the diversity of the soundscape? Is a crow less nice to hear than a Skylark? Is there a way to quantify that?
Simon Butler - Absolutely. So you can drill that down to individual species and things like corvids and crows, for example, have quite a low frequency sound. There's not a lot of variation in their delivery. It's quite consistent and stable in terms of the pattern of delivery, whereas skylarks and some of the warblers, for example, have a really varied and rich melodious sound that jumps around across frequencies and it gives a real richness and breadth to the soundscapes. If we're losing those kinds of species, those songbirds, warblers, skylarks, those kinds of species we're going to get big gaps in our caustic space that are no longer being occupied by those species. And so the diversity and the intensity of the sound that we hear will be declining.
Iacopo - Is there a way we can invert this trend? What do you think we should do?
Simon Butler - Conserving and restoring natural soundscapes will be driven by underlying biodiversity conservation. But what we hope to do with this paper is really demonstrate the direct impact of biodiversity loss. And by raising awareness of the day-to-day impacts that biodiversity loss might be having for us as we spend time out in nature and what the implications of that might be for our health and wellbeing. Hopefully that will encourage people to be more supportive of actions for biodiversity conservation, and also take time to appreciate what they can hear. I think that's really important.
Chris - Sobering stuff that was Simon Butler. He's at the University of East Anglia. And that research was just out in Nature Communications.