The following article was published in Scottish Wildlife Magazine June 2019, issue 98, pp32-33 and is reposted with permission of Scottish Wildlife Trust.
When was the last time you stopped what you were doing and just listened? The sounds we hear can tell us much about our environment. On a spring day we might hear hungry chicks calling to be fed, children playing in the local park, a telephone ringing in a nearby house. All these sounds form a ‘soundscape’ unique to the location that you are in.
The term soundscape was coined by analogy with landscape to capture the idea that the sounds we perceive form a rich and nuanced acoustic environment. We can broadly categorise sound according to their origins. Sound created by birds, mammals, insects and other animals is termed ‘biophony’, while the sounds created by human activity is termed ‘anthropophony’. Soundscape ecology studies the relationships between these types of sound and how different organisms interact acoustically with their environment.
Many animals use sound to communicate within social groups: to attract a mate, to announce the arrival of a predator, for navigation and for territory holding. There is a rich tradition of scientists making field recordings of animal sounds across the globe, resulting in extensive audio libraries of environmental recordings covering many species – many now available online. With sound recording equipment improving all the time, it’s now possible to collect acoustic data around the clock, yielding rich information such as the presence and daily activity of certain species in a specific area. The technology has to date been used to monitor bats, birds, frogs, crickets, marine mammals, elephants and even some fish.
As well as studying specific species, researchers have tried to account for the way in which soundscapes are structured. For example, the ‘acoustic niche hypothesis’ proposes that animals such as birds and insects will tend to make their vocalisations stand out by pitching them at a frequency different to that used by other species that typically live alongside them. That is, the available frequency ranges somehow become shared out between species so that there is minimal overlapping.
It’s not surprising that there is evidence to suggest that the increasing noise that humans create, for example from road traffic and industrial activity, can have a negative effect on biodiversity. In the case of birds, anthropophony can block out sounds which signal danger and can also interfere with the messages that males use to defend their territory and to attract mates. Some species have learnt to compensate for this, with urban bird populations having different behaviours from their forest counterparts. One strategy exploits the so-called ‘Lombard effect’ – like humans at a cocktail party, birds will raise the volume of their sounds to overcome the background noise level. Other responses are to shift the time of singing activity to avoid urban rush hour, or to raise the pitch of songs to avoid them being drowned out by low-frequency traffic rumbles.
Reducing ambient noise is good for both humans and wildlife, yet mitigating the acoustic effects of road traffic – for example, by erecting noise barriers or making road surfaces more porous – is expensive and often not feasible in city centres. As well as reducing noise pollution in general, planners are recognising the importance of preserving and enhancing existing ‘quiet areas’, including parks and private gardens. From a wildlife conservation perspective, more research is required on the noise sensitivity of different animals and whether, for example, targeting noise reduction measures during the breeding season can achieve significant benefits.
In the CitySounds project, we set ourselves the goal of capturing a comprehensive ‘picture’ of an urban soundscape, using recording equipment located in trees. Initially, our focus was on the sounds that can be detected in the Meadows, a much-used city-centre greenspace in Edinburgh. Our follow-on project, ParkLife, has expanded the scope to embrace three other parks within the city and to also integrate information from social media about human use of the greenspaces. As well as looking for acoustic indicators of biodiversity, we are interested in the variety of sounds produced by human activities beyond background traffic: for example street music, festivals, recreational games, emergency sirens, and so on.
We are still in the process of collecting this unique and substantial soundscape dataset and although we have not carried out significant analysis of the data, we can begin to observe patterns. The image above spans six hours from midnight to 6am on 13 June 2018. Towards the right-hand side of the image, an increase in spectral activity is noticeable. This correlates to what we would expect around 4am on the morning in question — dawn was 3:56am in Edinburgh that day.
Longer term, we hope to be able to use artificial intelligence to detect and recognise different categories of events within a noisy city soundscape. This will give us more precise tools for understanding soundscape ecology, which in turn will help us be smarter and more effective in reducing our acoustic impact on the natural world.