Noisy neighbours: Listening in to nature in cities and towns

Humans are noisy. In cities and towns, our cars, trains, planes, footsteps and voices all add up to a constant hum of noise and activity.

But beneath this human-made soundtrack lies the croaks, chirps and calls of the natural world. Insects call to each other, frogs and toads make resonant sounds to find a mate and birds broadcast messages. Stripping back the human sounds in urban areas can reveal this hidden soundscape underneath.

Researchers at the Museum are now working out how to use recordings from urban gardens, trees, soil and even ponds to monitor the biodiversity that lives in our towns and cities. At the same time, a community science project run by the Museum is using people power to record roadside sounds all over the UK to monitor biodiversity in these spaces.

Recording nature

Normally, biological surveys rely on people being there to see and identify the huge range animals that live in a certain place. But this method can bias the survey towards those species that are conspicuous and easy to find.

This is where sound recordings come in. They are a great way to discover the less obvious wildlife that lives in, or passes through, an area. By recording continuously in the one place, sound can tell us a lot about the goings on of the natural world.

Called acoustic monitoring, this technique is commonly used in areas of high biodiversity to monitor what animals live somewhere, and how their behaviour and numbers might change over time.

In a town or a city, listening in to wildlife becomes much harder. The noise of cars, trains, trucks and humans can cover up the sounds of birds, frogs or other wildlife. Finding a way to digitally recognise these natural sounds amongst the urban humdrum will help us identify what animals live around us.

A collection of animal sounds at the Museum

Digitally recognising sounds is an important step in developing a tool that can show how biodiversity is changing in our backyards.

While the song of a bird might be obvious, other animals from earwigs to earthworms also make distinctive sounds as they go about their daily business.

The first step to using machine learning to identify sounds in a recording is to train the computer algorithms. To do this, researchers are using a unique sound collection of the calls of birds and insects held at the Museum.

Starting in the 1970's, curators at the Museum have been collecting animal sounds, with these early sound pioneers taking microphones into the field to eavesdrop on the natural world. Some of these recordings now lie in the Museum collection with titles such as 'Excited chortles, aggressive spitting and churring of two foraging banded mongoose, including a squabble over giant millipede'.

In addition to the field recordings, the Museum once had a tiny state-of-the-art recording studio on site to record insects and other small animals. From this little studio, scientists recorded some of the world's clearest and most crisp insect sound recordings.

But these historic recordings don't just make for excellent listening. They are now being used to help scientists to train computers to digitally listen for wildlife calls in urban sound recordings.

Recording biodiversity in the Museum's gardens

Adding to this archive, as part of the Urban Nature Project gardens, Acoustic Biology Researcher at the Museum, Ed Baker, plans to install a grid of small sound recorders throughout the new gardens. These sound recorders will collect sound data as the gardens grow and mature.

These recorders will be plugged into the mains power so they will always be recording the garden sounds day and night. One part of the project will be to find out how close these recorders need to be to their subject to listen in to different habitats in the garden.

Ed says, 'The data we record will form an essential tool in unlocking new solutions to the decline in insect populations and further science-informed nature recovery in the UK. Focusing on acoustic data is a key way to monitor biodiversity and make our cities and towns better for nature.'

'Although decoding audio recordings is difficult, the more we have the easier it becomes.'

The quiet animals

It's not only the loud animals that interest Ed. As part of the project, Ed hopes to find and record the quieter soundscapes of these places. He will be attempting to listen to what is going on inside trees, ponds and even the soil.

He will try to find out what sound signatures beetles, worms and ants make as they forage through the leaflitter and crawl through the underground. Ed also plans to record the ultrasound frequency of bats as they whirl and swoop above the garden in their hunt for insects.

If you're interested in what bats sounds like, you can take a listen to them chatting to each other in Oxfordshire, UK, below.

Listening in to nature as a way to monitor biodiversity change

Ed hopes that these recordings will help the Museum create a tool that can be used to measure biodiversity change in urban areas.

The tool might help someone understand if planting gardens with a particular tree has increased the amounts of birds using the garden, or if making a pond has increased the biodiversity of a garden or park.