Using soundscapes to monitor urban diversity by Shade Walker
Daily sounds of local traffic, the coffee machine pouring, conversations over breakfast, and morning birdsong, are all familiar to us, signaling the start of a new day. As sound waves pulse through the air, they encounter physical structures in the environment, and it is through this interaction that unique landscapes of sound are born which become integral characteristics of each ecosystem. These whispers of nature and other features are considered the soundscape, where biological sounds (animals), geophysical sounds (wind, water, etc.), and anthropogenic sounds (traffic, coffee machines, etc) are interwoven1.
Soundscape Dynamics
How do soundscapes help us understand urban ecosystems and the biodiversity that is within them? First, the structural components of the environment influence how sound waves travel through the area. Features in motion (rivers, waterfalls, ocean waves etc.) produce sound waves, while stationary features (mountains, trees, etc.) absorb or amplify sound waves. Within the walls of an urban centre, skyscrapers and roadways dominate, in contrast to the dense vegetation and water features of a natural landscape. Hard, impervious structures reflect sound waves, amplifying the sounds that pepper the inner workings of the city, such as construction, industrial projects, and transportation networks2. When these sounds are amplified, it elevates background noise levels, contributing to noise pollution in the environment. The dense vegetation and soft substrates of natural landscapes allow excess noise to be absorbed contributing to quieter ambient levels2. This is why in cities the prevalence of noise often urges us to seek out green spaces and nature reserves as an acoustic refuge of sorts. Studies have shown that being exposed to ‘natural’ sounds (sounds that indicate you are in nature – i.e. rivers, birdsong etc.) for 20 minutes or more improves cognitive function and reduces stress in humans1.
How Urban Sounds Affect Wildlife
It is not only humans who respond to the noisy atmosphere of cities – wildlife do as well. In urban areas, species have been shown to modify their acoustic behaviour to compensate for excess anthropogenic noise. Birds, for example, increase the frequency of their songs and decrease the song’s overall complexity3. These changes help birds send and receive acoustic signals with less disruption from anthropogenic noise. In amphibians the change is similar, where calls are altered in pitch, rate, and frequency to enhance communication between members of their species amidst noisy environments. In some frog species, males have exhibited lower mating success because calling in this way requires a higher energy investment to maintain4. In the case of mammals, a study done on the micro-bat species Pipistrellus pipistrellus (the common pipistrelle) showed modified call structure related to foraging activities5. As it turns out the layout of cities influence the distribution of the common pipistrelle’s prey (flying insects), and these resource patterns have resulted in increased competitive behaviour among urban bats communities. Altering their call structure is believed to establish dominance within feeding groups, assisting top members in claiming food and territory.
Soundscape Monitoring
It is through intricate changes in the proportion of each sound type (biological, geophysical, anthropogenic) and the acoustic activity of species that enable soundscape monitoring to be effective in investigating biodiversity patterns and habitat quality in urban spaces. Soundscape monitoring is an emerging method of understanding ecosystem dynamics in a way that is cost effective and less time consuming than manual methods of ecological surveying. It is also non-invasive, since recordings are taken via remote recording units which can be deployed over an extended period. Passive Acoustic Monitoring (PAM) is an example of non-invasive species monitoring that is used along with acoustic indices to analyse ecosystem dynamics6. Through acoustic indices, data is extracted that corresponds to various biodiversity metrics. Data that can be extracted using these indices include: the variety of vocalizations present (Acoustic Diversity Index – ADI), the abundance of vocalizing species (Bioacoustic Index – BIO), and the proportion of anthropogenic sounds relative to biological sounds (Normalized Difference Soundscape Index – NDSI)7. A study conducted on bird diversity in urban parks used acoustic indices to understand how birds utilise their environment during winter and how active they are during a daily cycle8. They also assessed the impacts of anthropogenic activities on bird diversity and how vegetation structure can mitigate the negative effects of anthropogenic noise. This is one example of how acoustic indices are being incorporated in current biodiversity research.
Limitations and Benefits of Soundscape Monitoring
How soundscapes can be used to map ecosystem dynamics and services (Wang et al. 2024)
At present, there are still some limitations to overcome within this field, data biases during interpretation being one of them. In urban areas, human conversation is often categorized as biological sound when analysing recordings using the current technology. While not technically inaccurate as humans are animals, this categorization creates a bias for the proportion of “natural” biodiversity present in the study site. Another limitation is the complexity of urban environments across geographic regions, making it difficult to standardize acoustic indices globally, which limits the scope of their application and interpretation6.
Despite these limitations, soundscape monitoring still offers valuable benefits to both humans and wildlife in urban areas. Biodiversity hotspots can be identified through soundscape mapping, which uses the variation in intensity of acoustic activity across an environment to determine ecosystem functions. Therefore, these aspects of assessing urban green space quality and locating biodiversity hotspots will facilitate future urban planning that conserves biodiversity1.
Soundscape monitoring and analysis is a new field of ecological research that shows promise for the long-term assessment of urban biodiversity diversity. With this in mind, we should tune in to the dynamics of our local soundscape and perceive the new opportunities on the horizon for soundscape application. Perhaps in a few decades, we will understand a bit more about the benefits the hidden world of sound offers.
References
1. Wang et al. 2024 – Soundscapes for urban ecological security evaluation
2. Proulx et al. 2019 – Anthropogenic landscape changes and their impacts on terrestrial and freshwater soundscapes
3. Hao et al. 2024 – Anthropogenic noise and habitat structure shape dominant frequency of bird sounds along urban gradients
4. Mudke & Aravind 2025 – A global synthesis of the impacts of urbanisation on Amphibians
5. Starik & Göttert 2022 – Bats adjust echolocation and social call design as a response to urban environments
6. Azberger et al. 2025 – The potential of soundscapes as an ecosystem monitoring tool for urban diversity
7. Botero-Cañola et al. 2024 – Acoustic indices track local vertebrate biodiversity in a subtropical landscape
8. Song et al. 2025 – Assessing the drivers of bird diversity in urban parks during winter: Insights from acoustic indices
I am interested in urban ecology and evolution. Urbanization can have drastic impacts on local ecosystems, both negative and positive, and creates a new environment for organisms to experience. To understand the impacts that urbanization plays on organisms, I look through the lense of population genetics and molecular evolution.
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