Sound of rewilding
Somerset Wildlands has been working with experts at the University of Sussex to conduct innovative new eco-acoustic monitoring at our sites, investigating not only species, but background acoustic richness. While things are largely in the ‘baselining’ phase, there are some interesting results which show the impact that early stage rewilding is having. This blog was written by Harriet Trueman and Dr. Christopher Sandom at the University of Sussex.
Every chirp, rustle and song is becoming an insight into the biodiversity secrets of our natural environments. The scientific worlds of eco- and bio-acoustics are beginning to reveal a way of measuring the soundscape of our landscapes and further our understanding of the language of nature. Somerset Wildlands’ commitment to a nature-led approach to nature recovery has led them to take this approach as a baseline assessment of the biodiversity of their four rewilding sites.
Bioacoustics is a scientific tool that refers to identifying species based on their vocalisations. Passive Acoustic Monitoring devices (think camera trap but for sound) are able to capture the sounds of a landscape, with the recorded files then analysed to identify the vocal species, e.g. birds or bats. This can now be done automatically, using machine learning tools such as BirdNET. While these tools aren’t perfect they can offer useful insights into the presence of different species.
Chris Sandom installing an audio moth at the Athelney site in May 2023.
Eco-acoustics on the other hand, is a scientific tool that investigates the soundscape more generally - including the sounds from wildlife known as the biophony, to the sounds of the weather (e.g. rain) and the environment (e.g. running water) known as the geophony and even encompassing human-made noises such as traffic or construction known as anthrophony or technophony. The main focus of ecoacoustics relates to gaining an understanding of what we can infer about biodiversity from the collective noises in ecosystems. Sound conveys information, think of the mating and alarm calls different species make, and allows information to pass from one individual to others.
Species even compete for real estate in the soundscape, there is evidence that species have evolved to sing at different frequencies or times of day to reduce competition with each other. Where this is the case, a more diverse soundscape should be indicative of higher biodiversity, at least amongst the vocal species.
Across Somerset Wildland’s four sites, Athelney, Godney Marshes Waste Drove and East Waste, and Whites Drove, 15 Audiomoths were stationed for two weeks in Spring 2023 and set to record sounds audible to humans. The surveying was done to take a baseline assessment of Athelney and East Waste, and to record the current conditions at Waste Drove and Whites Drove that have been rewilding for a few years. (Note: A second set of recordings was taken at frequencies used by bats, and an additional report will follow. Preliminary results however show a significant difference between the sites depending on how long they have been rewilding).
Over all the recordings made, BirdNET, after some quality control, registered 44,775 identifications of 55 different bird species. The Eurasian Wren was the most commonly recorded with the species call being identified 9,598 times across the recording period. The Eurasian Skylark was the third most commonly recorded species across all sites. At the newer site of East Waste in Godney, one Audiomoth captured Eurasian Skylark calls over 4,000 times. The more established rewilding site called Waste Drove also recorded a high number of Skylarks, but also recorded a variety of other species regularly as well, including Eurasian Wren, European Goldfinch, Greater Whitethroat, and Reed Bunting. These species have a greater variety of foraging habits, suggesting the rewilding in Godney is increasing the variety of food resources for birds.
To make sense of the complexity of sounds, Acoustic Diversity Indices were calculated to assess the ecoacoustics of the sites. These indicated the four sites are quite similar in their acoustic complexity, all showing greater diversity during the dawn chorus compared to the rest of the day. There was some indication that there were more sounds of technology at Athelney, perhaps from a busier road nearby.
The rewilding at all the sites are still in an early phase and it will be exciting to repeat these surveys in years to come to monitor how they develop.